Brake rotors and methods for making the same

This invention relates to metal and ceramic matrix composite brake rotors comprising an interconnected matrix embedding at least one filler material. In the case of metal matrix composite materials, the at least one filler material comprises at least about 26% by volume of the brake rotor for most applications, and at least about 20% by volume for applications involving passenger cars and trucks. In a preferred embodiment of the present invention, the metal matrix composite brake rotor comprises an interconnected metal matrix containing at least about 28% by volume of a particulate filler material and more preferably at least about 30% by volume. Moreover, the composite rotors of the present invention exhibit a maximum operating temperature of at least about 900.degree. F. and preferably at least about 950.degree. F. and even more preferably at least about 975.degree. F. and higher.

FIELD OF THE INVENTION 
This invention relates to metal and ceramic matrix composite brake rotors 
comprising an interconnected matrix embedding at least one filler 
material. In the case of metal matrix composite materials, the at least 
one filler material comprises at least about 26% by volume of the brake 
rotor for most applications, and at least about 20% by volume for 
applications involving passenger cars and trucks. In a preferred 
embodiment of the present invention, the metal matrix composite brake 
rotor comprises an interconnected metal matrix containing at least about 
28% by volume of a particulate filler material and more preferably at 
least about 30% by volume. Moreover, the composite rotors of the present 
invention exhibit a maximum operating temperature of at least about 
900.degree. F. (482.degree. C.) and preferably at least about 950.degree. 
F. (510.degree. C.) and even more preferably at least about 975.degree. F. 
(524.degree. C.) and higher. 
BACKGROUND OF THE INVENTION 
Recent efforts to improve the fuel economy and emissions levels of air and 
ground vehicles have created a need for new materials which can provide 
weight savings to the vehicle without sacrificing performance levels. The 
immediate desirability of such materials is enhanced when the weight 
savings can be acheived by directly substituting the materials for current 
materials in existing designs. Moreover, the long-term desirability of 
such materials is maximized when the unique properties of the materials 
provide the possibility of improved designs and performance for vehicle 
components. 
Traditionally, automotive brake rotors have been made from cast iron which 
provides good wear resistance and excellent high temperature properties. 
However, cast iron is dense relative to other candidate materials and, 
therefore, a cast iron brake rotor is relatively heavy. A heavy brake 
rotor is considered to be undesirable for at least three reasons. The 
first reason is that a heavy brake rotor contributes to the overall weight 
of the vehicle and thus reduces its fuel efficiency and correspondingly 
increases its emissions levels. The second reason (relevant mainly to 
passenger cars and trucks) is that a brake rotor is part of the "unsprung" 
weight of a vehicle (i.e., the weight of a vehicle that is below the 
springs) and, as such, contributes to the noise, vibration and harshness 
(commonly known in the automobile industry as "NVH") associated with the 
operation of the vehicle. When the unsprung weight of a vehicle is 
reduced, the NVH properties are usually improved. The third reason is that 
a brake rotor is a part of a vehicle that requires rotation during use 
and, accordingly, a heavier brake rotor requires the use of additional 
energy to increase and decrease the rotational speed of the rotor. In 
addition, the ability of a heavier brake rotor to cause undesirable 
vibration during rotation is greater than that associated with a lighter 
brake rotor. 
The search for a material to replace cast iron in brake rotors has 
identified several possible candidates and their advantages and 
limitations. Each of these materials and its relevant advantages and 
limitations is discussed below. 
Steel has been considered as a brake rotor material because of its 
excellent strength to weight properties. Although denser than cast iron, 
the superior strength of steel enables the use of smaller brake rotors 
which could result in weight savings. However, at the present time, the 
weight savings that have been obtained with steel brake rotors have been 
minimal. 
Titanium has also been considered as a brake rotor material. The excellent 
strength to weight properties of titanium, as well as its high temperature 
properties, would enable titanium brake rotors to satisfy all of the 
requirements discussed above for a desirable brake rotor material. 
However, the high cost of titanium has prevented its widespread use as a 
brake rotor material in most non-aerospace applications. 
Various polymeric materials have also been considered as brake rotor 
materials. These materials have the advantage of being relatively 
inexpensive but they have not been able to achieve the high temperature 
strength necessary to perform adequately as a brake rotor material. 
Various ceramic materials have also been considered as brake rotor 
materials. Although many ceramic materials have demonstrated excellent 
wear resistance properties and the ability to withstand extremely high 
temperatures, the brittle nature of most ceramic materials has precluded 
the widespread use of ceramic brake rotors. Although the use of new 
processing techniques and the inclusion of reinforcing materials has 
created a new generation of ceramic and ceramic matrix composite materials 
with increased strength and reduced brittleness that perform well as brake 
rotor materials, the present production cost of such materials relative to 
other available materials has not been able to justify, for most ground 
vehicles, the weight savings that many of these materials can provide 
relative to cast iron. However, some of these new ceramic and ceramic 
matrix composite materials are being tested for use as brake rotor 
materials in heavier ground vehicles and/or in vehicles that demand 
increased performance from their brake rotors. In these situations, the 
higher cost of such materials is justified by their ability to provide 
increased performance. 
Aluminum and magnesium alloys have also been considered as brake rotor 
materials. These metals show excellent strength to weight properties but 
their high temperature properties are not adequate for most brake rotor 
applications. Specifically, brake rotor tests using both magnesium and 
aluminum rotors have demonstrated that unacceptable amounts of surface 
scoring and rotor warpage occur after repeated braking cycles. These 
problems can be partially alleviated by incorporating various alloying 
elements into the magnesium and aluminum metals and/or heat treating the 
final brake rotors before use. However, the use of such additives and/or 
techniques raises the cost of the brake rotors and can cause the rotors to 
display undesirable side effects, such as increased brittleness and high 
temperature instability. Accordingly, the use of alloying additives and 
heat treatment techniques, either alone or in combination, has not been 
able to produce commercially viable brake rotors for most of the current 
brake rotor applications. 
Recent attempts to reduce or eliminate the problems associated with using 
aluminum and magnesium as brake rotor materials have been directed toward 
the production of various types of aluminum and magnesium metal matrix 
composite materials. These materials generally consist of a metal matrix 
having embedded therein one or more reinforcing materials. Several 
techniques for forming metal matrix composites have been developed, some 
of which use pressure or a vacuum to push or draw a molten metal into a 
mass or preform of reinforcing material (hereinafter sometimes referred to 
as "filler material" or "filler"). Other techniques for forming metal 
matrix composite materials do not require the use of pressure or a vacuum 
to enable the molten metal to infiltrate the filler material. Such 
infiltration techniques are sometimes referred to as "spontaneous 
infiltration" techniques. Representative methods for forming metal matrix 
composites and/or casting metals can be found in the following Patents: 
U.S. Pat. No. 5,028,392, which issued on Jul. 2, 1991, in the names of 
Lloyd et al., and entitled "Melt Process For the Production of 
Metal-Matrix Composite Materials With Enhanced Particle/Matrix Wetting"; 
U.S. Pat. No. 5,028,494, which issued on Jul. 2, 1991, in the names of 
Tsujimura et al., and entitled "Brake Disk Material For Railroad Vehicle"; 
U.S. Pat. No. 4,865,806, which issued on Sep. 12, 1989, in the names of 
Skibo et al., and entitled "Process For Preparation of Composite Materials 
Containing Nonmetallic Particles In A Metallic Matrix"; 
U.S. Pat. No. 4,759,995, which issued on Jul. 26, 1988, in the names of 
Skibo et al., and entitled "Process For Production of Metal Matrix 
Composites By Casting and Composite Therefrom"; 
U.S. Pat. No. 4,961,461, which issued on Oct. 9, 1990, in the names of 
Klier et al., and entitled "Method and Apparatus For Continuous Casting of 
Composites"; 
U.S. Pat. No. 4,473,103, which issued on Sep. 25, 1984, in the names of 
Kenney et al., and entitled "Continuous Production of Metal Alloy 
Composites"; 
U.S. Pat. No. 4,404,262, which issued on Sep. 13, 1983, in the name of 
Watmough, and entitled "Composite Metallic and Refractory Article and 
Method of Manufacturing the Article"; 
U.S. Pat. No. 3,970,136, which issued on Jul. 20, 1976, in the names of 
Cannell et al., and entitled "Method of Manufacturing Composite 
Materials"; 
U.S. Pat. No. 3,915,699, which issued on Oct. 28, 1975, in the names of 
Umehara et al., and entitled "Method For Producing Metal Dies or Molds 
Containing Cooling Channels By Sintering Powdered Metals"; 
U.S. Pat. No. 3,718,441, which issued on Feb. 27, 1973, in the name of 
Landingham, and entitled "Method For Forming Metal-Filled Ceramics of Near 
Theoretical Density"; 
U.S. Pat. No. 5,042,561, which issued on Aug. 27, 1991, in the name of 
Chandley and entitled "Apparatus and Process for Countergravity Casting of 
Metal With Air Exclusion"; 
U.S. Pat. No. 4,862,945, which issued on Sep. 5, 1989, in the names of 
Greanias et al. and entitled "Vacuum Countergravity Casting Apparatus and 
Method With Backflow Valve"; 
U.S. Pat. No. 3,547,180, which issued on Dec. 15, 1970, in the name of 
Cochran, and entitled "Production of Reinforced Composites"; and 
U.S. Pat. No. 3,364,976, which issued on Jan. 23, 1968, in the names of 
Reding et al., and entitled "Method of Casting Employing Self-Generated 
Vacuum". 
The entire disclosures of all of the above-listed U.S. Patents are 
expressly incorporated herein by reference. 
An example of a metal matrix composite brake rotor can be found in U.S. 
Pat. No. 5,028,494, which issued on Jul. 2, 1991, in the names of 
Tsujimura et al. (hereinafter referred to as the '494 Patent). In the '494 
Patent, an aluminum composite material is produced as a brake disk 
material for railroad vehicles. In the method of the '494 Patent, 
reinforcement particles of alumina, silicon carbide, mica or the like are 
dispersed and mixed into a molten aluminum alloy. The reinforcement 
particles are 5 to 100 microns in diameter, and are dispersed uniformly in 
the alloy in an amount of 1 to 25% by weight (i.e., about 0.7% to about 
18.4% by volume for alumina reinforcement material; about 0.8% to about 
22.0% by volume for silicon carbide reinforcement material and about 1.0% 
to about 25.7% by volume for mica reinforcement material). It is stated in 
the '494 Patent that the brake disk material produced by the method 
disclosed in the '494 Patent is "light in weight and has high strength, 
good thermal conductivity and high wear resistance." 
Thus, it can be deduced from the above information that metal matrix 
composite materials are currently being examined and tested for use as 
brake rotor materials. Moreover, it should be noted that the metal matrix 
composite brake rotors currently being produced for the railroad vehicle 
industry (as evidenced by the '494 Patent) use an aluminum metal matrix 
with a reinforcement material loading of up to about 26% by volume. 
It has been unexpectedly discovered that brake rotors produced from metal 
matrix composites having reinforcement loadings of at least about 26% by 
volume, and preferably at least about 28% by volume, demonstrate 
unexpectedly enhanced performance in comparison to materials with lower 
reinforcement loadings (i.e., reinforcement loadings lower than about 26% 
by volume). Specifically, many metal matrix composite brake rotors 
produced with less than about 26% by volume of reinforcement material have 
been unable to meet industry performance requirements in certain tests 
known as "fade tests" (discussed in detail later herein) wherein the brake 
rotor is repeatedly tested under cyclical braking conditions (e.g., the 
brake rotor is mounted on a vehicle braking system or a dynamometer and 
used to brake a vehicle from about 60 mph to 0 mph several times and then 
from about 80 mph to 0 mph for a required number of times or until 
failure). Such brake rotors exhibit unacceptable surface scoring 
(i.e.,surface disfigurements, such as scratches or grooves) after the fade 
tests and, in some cases, portions of the brake rotors (e.g., the cooling 
fins and/or the rotor surface which contacts the brake pad) were deformed 
and appeared to have been melted during the tests. 
In contrast, metal matrix composite brake rotors having reinforcement 
loadings greater than about 26% by volume, and preferably greater than 
about 28% by volume, have easily survived the above-described fade tests 
with acceptable levels of surface scoring and no significant deformation. 
Further, it has been determined that the ability of a rotor to withstand 
certain standard industry tests which simulate some of the most severe 
conditions experienced by automotive rotors can be discussed in terms of 
the maximum operating temperature ("MOT", discussed in detail later 
herein) which a rotor can withstand prior to experiencing at least some 
undesirable surface melting. The rotors of the present invention exhibit 
an MOT of at least about 900.degree. F. (482.degree. C.), and preferably 
at least about 950.degree. F. (510.degree. C.) and even more preferably at 
least about 975.degree. F. (524.degree. C.), and, even more preferably, 
about 1000.degree. F. (538.degree. C.) and higher. 
Moreover, it has been discovered that certain ceramic matrix composites can 
also achieve the aforementioned MOT's and higher. Certain preferred 
techniques for forming ceramic matrix composites are discussed herein. 
Accordingly, the increasing demand for higher fuel efficiency and reduced 
emissions has created a need for brake rotors on ground vehicles that are 
capable of satisfying current performance requirements while providing 
weight savings to the overall vehicle with respect to the brake rotors 
currently in use. The present invention provides brake rotors that can 
satisfy these needs. 
DESCRIPTION OF COMMONLY OWNED PATENTS AND PATENT APPLICATIONS 
A novel method of making a metal matrix composite material is disclosed in 
Commonly Owned and Copending U.S. patent application Ser. No. 08/078,146, 
filed Jun. 16, 1993, as a continuation of U.S. patent application Ser. No. 
07/933,609, filed Aug. 21, 1992 (now abandoned), which is a continuation 
of U.S. patent application Ser. No. 07/725,400, filed on Jul. 1, 1991, now 
abandoned, as a continuation of U.S. patent application Ser. No. 
07/504,074, filed on Apr. 3, 1990, now abandoned, as a continuation of 
U.S. patent application Ser. No. 07/269,251, filed on Nov. 9, 1988, now 
abandoned, as a continuation of Commonly Owned U.S. Pat. No. 4,828,008, 
which issued on May 9, 1989, in the names of White et al., and entitled 
"Metal Matrix Composites". According to the method of the White et al. 
invention, a metal matrix composite is produced by infiltrating a 
permeable mass of filler material (e.g., a ceramic or a ceramic-coated 
material) with molten aluminum containing at least about 1 percent by 
weight magnesium, and preferably at least about 3 percent by weight 
magnesium. Infiltration occurs spontaneously without the application of 
external pressure or vacuum. A supply of the molten metal alloy is 
contacted with the mass of filler material at a temperature of at least 
about 675.degree. C. in the presence of a gas comprising from about 10 to 
100 percent, and preferably at least about 50 percent, nitrogen by volume, 
and a remainder of the gas, if any, being a nonoxidizing gas, e.g., argon. 
Under these conditions, the molten aluminum alloy infiltrates the ceramic 
mass under normal atmospheric pressures to form an aluminum (or aluminum 
alloy) matrix composite. When the desired amount of filler material has 
been infiltrated with the molten aluminum alloy, the temperature is 
lowered to solidify the alloy, thereby forming a solid metal matrix 
structure that embeds the reinforcing filler material. Usually, and 
preferably, the supply of molten alloy delivered will be sufficient to 
permit the infiltration to proceed essentially to the boundaries of the 
mass of filler material. The amount of filler material in the aluminum 
matrix composites produced according to the White et al. invention may be 
exceedingly high. In this respect, filler to alloy volumetric ratios of 
greater than 1:1 may be achieved. 
Under the process conditions in the aforesaid White et al. invention, 
aluminum nitride can form as a discontinuous phase dispersed throughout 
the aluminum matrix. The amount of nitride in the aluminum matrix may vary 
depending on such factors as temperature, alloy composition, gas 
composition and filler material. Thus, by controlling one or more such 
factors in the system, it is possible to tailor certain properties of the 
composite. For some end use applications, however, it may be desirable 
that the composite contain little or substantially no aluminum nitride. 
It has been observed that higher temperatures favor infiltration but render 
the process more conducive to nitride formation. The White et al. 
invention allows the choice of a balance between infiltration kinetics and 
nitride formation. 
An example of suitable barrier means for use with metal matrix composite 
formation is described in Commonly Owned and Copending U.S. patent 
application Ser. No. 07/934,823, filed on Aug. 24, 1992, as a continuation 
of Commonly Owned U.S. Pat. No. 5,141,819, entitled "Method of Making 
Metal Matrix Composite with the Use of a Barrier", which issued Aug. 25, 
1992, in the names of Michael K. Aghajanian et al. from U.S. patent 
application Ser. No. 07/415,088, filed on Sep. 29, 1989, now abandoned, 
which was a continuation of Commonly Owned U.S. Pat. No. 4,935,055, which 
issued on Jun. 19, 1990, in the names of Michael K. Aghajanian et al., and 
entitled "Method of Making Metal Matrix Composite with the Use of a 
Barrier". According to the method of this Aghajanian et al. invention, a 
barrier means (e.g., particulate titanium diboride or a graphite material 
such as a flexible graphite tape product sold by Union Carbide under the 
trade name GRAFOIL.RTM.) is disposed on a defined surface boundary of a 
filler material and matrix alloy infiltrates up to the boundary defined by 
the barrier means. The barrier means is used to inhibit, prevent, or 
terminate infiltration of the molten alloy, thereby providing net, or near 
net, shapes in the resultant metal matrix composite. Accordingly, the 
formed metal matrix composite bodies have an outer shape which 
substantially corresponds to the inner shape of the barrier means. 
The method of U.S. Pat. No. 4,828,008, was improved upon by Commonly Owned 
and Copending U.S. patent application Ser. No. 07/994,064, filed on Dec. 
18, 1992, which is a continuation of U.S. patent application Ser. No. 
07/759,745, filed on Sep. 12, 1991, now abandoned, as a continuation of 
U.S. patent application Ser. No. 07/517,541, filed on Apr. 24, 1990, now 
abandoned, which was a continuation of U.S. patent application Ser. No. 
07/168,284, filed Mar. 15, 1988, now abandoned, all in the names of 
Michael K. Aghajanian and Marc S. Newkirk and entitled "Metal Matrix 
Composites and Techniques for Making the Same." In accordance with the 
methods disclosed in this copending U.S. Patent Application, a matrix 
metal alloy is present as a first source of metal and as a reservoir of 
matrix metal alloy which communicates with the first source of molten 
metal due to, for example, gravity flow. Particularly, under the 
conditions described in this patent application, the first source of 
molten matrix alloy begins to infiltrate the mass of filler material under 
normal atmospheric pressures and thus begins the formation of a metal 
matrix composite. The first source of molten matrix metal alloy is 
consumed during its infiltration into the mass of filler material and, if 
desired, can be replenished, preferably by a continuous means, from the 
reservoir of molten matrix metal as the spontaneous infiltration 
continues. When a desired amount of permeable filler has been 
spontaneously infiltrated by the molten matrix alloy, the temperature is 
lowered to solidify the alloy, thereby forming a solid metal matrix 
structure that embeds the reinforcing filler material. It should be 
understood that the use of a reservoir of metal is simply one embodiment 
of the invention described in this patent application and it is not 
necessary to combine the reservoir embodiment with each of the alternate 
embodiments of the invention disclosed therein, some of which could also 
be beneficial to use in combination with the present invention. 
The reservoir of metal can be present in an amount such that it provides 
for a sufficient amount of metal to infiltrate the permeable mass of 
filler material to a predetermined extent. Alternatively, an optional 
barrier means can contact the permeable mass of filler on at least one 
side thereof to define a surface boundary. 
Moreover, while the supply of molten matrix alloy delivered should be at 
least sufficient to permit spontaneous infiltration to proceed essentially 
to the boundaries (e.g., barriers) of the permeable mass of filler 
material, the amount of alloy present in the reservoir could exceed such 
sufficient amount so that not only will there be a sufficient amount of 
alloy for complete infiltration, but excess molten metal alloy could 
remain and be attached to the metal matrix composite body. Thus, when 
excess molten alloy is present, the resulting body will be a complex 
composite body (e.g., a macrocomposite), wherein an infiltrated ceramic 
body having a metal matrix therein will be directly bonded to excess metal 
remaining in the reservoir. 
Further improvements in metal matrix technology can be found in commonly 
owned U.S. Pat. No. 5,249,621, which issued Oct. 5, 1993, in the names of 
Aghajanian et al. and entitled "Method of Forming Metal Matrix Composite 
Bodies by a Spontaneous Infiltration Process and Products Produced 
Therefrom" from U.S. patent application Ser. No. 07/863,894, filed Apr. 6, 
1992, which is a continuation application of U.S. patent application Ser. 
No. 07/521,043, filed May 9, 1990, now abandoned, which is a 
continuation-in-part of U.S. patent application Ser. No. 07/484,753, filed 
Feb. 23, 1990, now abandoned, which was a continuation-in-part of U.S. 
patent application Ser. No. 07/432,661, filed Nov. 7, 1989, now abandoned, 
which was a continuation-in-part of U.S. patent application Ser. No. 
07/416,327, filed Oct. 6, 1989, now abandoned, which was a 
continuation-in-part of U.S. patent application Ser. No. 07/349,590, filed 
May 9, 1989 (now abandoned), which was a continuation-in-part of U.S. 
patent application Ser. No. 07/269,311, filed Nov. 10, 1988, now 
abandoned, in the names of Michael K. Aghajanian et al. and entitled "A 
Method of Forming Metal Matrix Composite Bodies by a Spontaneous 
Infiltration Process, and Products Produced Therefrom". According to this 
Aghajanian et al. invention, spontaneous infiltration of a matrix metal 
into a permeable mass of filler material or preform is achieved by use of 
an infiltration enhancer and/or an infiltration enhancer precursor and/or 
an infiltrating atmosphere which are in communication with the filler 
material or preform, at least at some point during the process, which 
permits molten matrix metal to spontaneously infiltrate the filler 
material or preform. Aghajanian et al. disclose a number of matrix 
metal/infiltration enhancer precursor/infiltrating atmosphere systems 
which exhibit spontaneous infiltration. Specifically, Aghajanian, et al. 
disclose that spontaneous infiltration behavior has been observed in the 
aluminum/magnesium/nitrogen system; the aluminum/strontium/nitrogen 
system; the aluminum/zinc/oxygen system; and the aluminum/calcium/nitrogen 
system. However, it is clear from the disclosure set forth in the 
Aghajanian, et al. applications that the spontaneous infiltration behavior 
should occur in other matrix metal/infiltration enhancer 
precursor/infiltrating atmosphere systems. 
Another related Commonly Owned and Copending U.S. patent application Ser. 
No. 08/083,823, filed on Jun. 28, 1993, which is a continuation of 
Commonly Owned U.S. Pat. No. 5,222,542, which issued Jun. 29, 1993, which 
is a continuation-in-part of U.S. patent application Ser. No. 07/269,308, 
filed Nov. 10, 1988, which issued to U.S. Pat. No. 5,000,247 on Mar. 19, 
1991, and naming as sole inventor John Thomas Burke and entitled "Method 
For Forming Metal Matrix Composite Bodies With A Dispersion Casting 
Technique and Products Produced Thereby". These patent applications and 
patents relate to a novel method for forming metal matrix composite 
bodies. A permeable mass of filler material is spontaneously infiltrated 
by a molten matrix metal. Particularly, an infiltration enhancer and/or an 
infiltration enhancer precursor and/or an infiltrating atmosphere are in 
communication with the filler material, at least at some point during the 
process, which permits molten matrix metal to spontaneously infiltrate the 
filler material. After infiltration has been completed to a desired 
extent, additional matrix metal is added to that matrix metal which has 
spontaneously infiltrated the filler material to result in a suspension of 
filler material and matrix metal having a lower volume fraction of filler 
relative to matrix metal. The matrix metal then can be permitted to cool 
in situ or the mixture of matrix metal and filler material can be poured 
into a second container as a casting process to form a desired shape which 
corresponds to the second container. However, the formed suspension, 
whether cast immediately after being formed or after cooling and 
thereafter heating and casting, can be pour cast into a desired shape 
while retaining beneficial characteristics associated with spontaneously 
infiltrated metal matrix composites. 
A novel method of forming a metal matrix composite by infiltration of a 
permeable mass of filler contained in a ceramic matrix composite mold is 
disclosed in Commonly Owned U.S. Pat. No. 4,998,578, which issued on Mar. 
12, 1991, from U.S. patent application Ser. No. 07/380,977, filed on Jul. 
17, 1989, as a continuation of U.S. Pat. No. 4,871,008, which issued on 
Oct. 3, 1989, from U.S. patent application Ser. No. 07/142,385, filed Jan. 
11, 1988, by Dwivedi et al., both entitled "Method of Making Metal Matrix 
Composites". According to the method disclosed in the Dwivedi et al. 
Patents, a mold is formed by the directed oxidation of a molten precursor 
metal or parent metal with an oxidant to develop or grow a polycrystalline 
oxidation reaction product which embeds at least a portion of a preform 
comprised of a suitable filler (referred to as a "first filler") to form a 
ceramic matrix composite mold. The formed mold of ceramic matrix composite 
is then provided with a second filler and the second filler and mold are 
contacted with molten metal, and the mold contents are hermetically 
sealed, most typically by introducing at least one molten metal into the 
entry or opening which seals the mold. The hermetically sealed bedding may 
contain entrapped air, but the entrapped air and the mold contents are 
isolated or sealed so as to exclude or shut-out the external or ambient 
air. By providing a hermetic environment, effective infiltration of the 
second filler at moderate molten metal temperatures is achieved, and 
therefore obviates or eliminates any necessity for wetting agents, special 
alloying ingredients in the molten matrix metal, applied mechanical 
pressure, applied vacuum, special gas atmospheres or other infiltration 
expedients. 
The above-discussed commonly owned patents describe a method for the 
production of a metal matrix composite body, which may be bonded to a 
ceramic matrix composite body, and the novel bodies which are produced 
therefrom. 
A method of forming macrocomposite bodies by a somewhat related process is 
disclosed in Commonly Owned and Copending U.S. patent application Ser. No. 
07/966,124, filed on Oct. 23, 1992, as a continuation of U.S. patent 
application Ser. No. 07/747,213, filed on Aug. 19, 1991 (now abandoned), 
as a continuation of U.S. patent application Ser. No. 07/269,464, which 
was filed on Nov. 10, 1988, and issued as U.S. Pat. No. 5,040,588 on Aug. 
20, 1991, in the names of Marc S. Newkirk et al., and entitled "Methods 
for Forming Macrocomposite Bodies and Macrocomposite Bodies Produced 
Thereby". A continuation of U.S. Pat. No. 5,040,588, was filed on Aug. 19, 
1991, as U.S. patent application Ser. No. 07/747,213, now abandoned. These 
applications and Patent disclose various methods relating to the formation 
of macrocomposite bodies by spontaneously infiltrating a permeable mass of 
filler material or a preform with molten matrix metal and bonding the 
spontaneously infiltrated material to at least one second material such as 
a ceramic and/or a metal. Particularly, an infiltration enhancer and/or 
infiltration enhancer precursor and/or infiltrating atmosphere are in 
communication with a filler material or a preform, at least at some point 
during the process, which permits molten matrix metal to spontaneously 
infiltrate the filler material or preform. Moreover, prior to 
infiltration, the filler material or preform is placed into contact with 
at least a portion of a second material such that after infiltration of 
the filler material or preform, the infiltrated material is bonded to the 
second material, thereby forming a macrocomposite body. 
A method of forming metal matrix composite bodies by a self-generated 
vacuum process is disclosed in Commonly Owned and Copending U.S. patent 
application Ser. No. 08/085,575, filed on Jul. 1, 1993, as a continuation 
of Commonly Owned U.S. Pat. No. 5,224,533, which issued on Jul. 6, 1993, 
which was filed on May 22, 1992, as U.S. patent application Ser. No. 
07/888,241, as a continuation of U.S. patent application Ser. No. 
07/381,523, filed on Jul. 18, 1989, now abandoned, in the names of Robert 
C. Kantner et al., and entitled "A Method of Forming Metal Matrix 
Composite Bodies by a Self-Generated Vacuum Process, and Products Produced 
Therefrom". These patent applications and patent disclose a method whereby 
a molten matrix metal is contacted with a filler material or a preform in 
the presence of a reactive atmosphere, and, at least at some point during 
the process, the molten matrix metal reacts, either partially or 
substantially completely, with the reactive atmosphere, thereby causing 
the molten matrix metal to infiltrate the filler material or preform due 
to, at least in part, the creation of a self-generated vacuum. Such 
self-generated vacuum infiltration occurs without the application of any 
external pressure or vacuum. 
A method of forming macrocomposite bodies by a somewhat related process is 
disclosed in Commonly Owned and Copending U.S. patent application Ser. No. 
08/021,297, filed on Feb. 22, 1993, as a divisional of Commonly Owned U.S. 
Pat. No. 5,247,986, entitled "A Method of Forming Macrocomposite Bodies by 
Self-Generated Vacuum Techniques, and Products Produced Therefrom" which 
issued Sep. 28, 1993, in the names of Robert C. Kantner et al. from U.S. 
patent application Ser. No. 07/824,686, filed on Jan. 21, 1992, which was 
filed as a continuation of U.S. patent application Ser. No. 07/383,935 
(now abandoned); and U.S. Pat. No. 5,188,164, issued Feb. 23, 1993, in the 
names of Robert C. Kantner et al. and entitled "A Method of Forming 
Macrocomposite Bodies by Self-Generated Vacuum Techniques using a Glassy 
Seal" from U.S. patent application Ser. No. 07/560,746, filed on Jul. 31, 
1990, which was filed as a continuation of U.S. patent application Ser. 
No. 07/383,935 (now abandoned); in the names of Robert C. Kantner et al., 
and entitled "A Method of Forming Macrocomposite Bodies By Self-Generated 
Vacuum Techniques, and Products Produced Therefrom". These patent 
applications and patents disclose a method whereby a molten matrix metal 
is contacted with a filler material or a preform, optionally in contact 
with a second or additional body, in the presence of a reactive 
atmosphere, and, at least at some point during the process, the molten 
matrix metal reacts, either partially or substantially completely, with 
the reactive atmosphere, thereby causing the molten matrix metal to 
infiltrate the filler material or preform due to, at least in part, the 
creation of a self-generated vacuum. The infiltrated material may be 
bonded to the carcass of the matrix metal and/or the second or additional 
body thereby forming a macrocomposite body. Such self-generated vacuum 
infiltration occurs without the application of any external pressure or 
vacuum. 
Methods of forming shaped metal matrix composite bodies by a self-generated 
vacuum process are disclosed in Commonly Owned and Copending U.S. patent 
application Ser. No. 07/803,769, filed on Dec. 5, 1991, which is a 
continuation of U.S. patent application Ser. No. 07/520,915, which was 
filed on May 9, 1990, now abandoned, in the names of Aghajanian et al., 
and entitled "Method of Making Metal Matrix Composite Bodies With Use of A 
Barrier" and commonly owned and copending International Application No. 
PCT/US91/03232, filed on May 9, 1991, claiming priority to U.S. patent 
application Ser. No. 07/520,915, and entitled "Barrier Materials For 
Making Metal Matrix Composites". These applications describe methods for 
making a metal matrix composite produced by spontaneously infiltrating a 
molten matrix metal into a permeable mass of filler material or a preform 
having at least one surface boundary established or defined by a barrier 
means. Specifically, an infiltration enhancer and/or an infiltration 
enhancer precursor and/or an infiltrating atmosphere are in communication 
with the filler material or preform, at least at some point during the 
process, which permits molten matrix metal to spontaneously infiltrate the 
filler material or preform up to the barrier material. A barrier material, 
typically, inhibits the transport of molten matrix metal beyond itself, 
thereby permitting the formation of shaped metal matrix composite bodies. 
The barrier means disclosed in these applications may be any suitable means 
which interferes, inhibits, prevents or terminates the migration, 
movement, or the like, of molten matrix alloy (e.g., an aluminum alloy) 
beyond the defined surface boundary of the filler material. Suitable 
barrier means may be any material, compound, element, composition, or the 
like, which, under the process conditions of this invention, maintains 
some integrity, is not volatile and preferably is permeable to the gas 
used with the process, as well as being capable of locally inhibiting, 
stopping, interfering with, preventing, or the like, continued 
infiltration or any other kind of movement of the molten matrix metal 
beyond the defined surface boundary of the ceramic filler. Barrier means 
may be used during spontaneous infiltration or in any molds or other 
fixtures utilized in connection with thermo-forming of the spontaneously 
infiltrated metal matrix composite, as discussed in greater detail below. 
The barrier materials of these applications may be a physical barrier 
(e.g., colloidal graphite, certain glass-forming materials, etc.), a 
reactive barrier (e.g., calcium carbonate, aluminum phosphate, colloidal 
silica, etc.), or any combination of the two (e.g., Grade A-17 alumina 
having an average particle size of about 3.5 microns obtained from Alcoa 
Industrial Products, Bauxite, Ark.). The barrier material should prevent 
the molten matrix metal from infiltrating beyond the desired boundaries of 
the filler material or preform and, preferably, provide a smooth surface 
finish to the final metal matrix composite body. Further, the barrier 
should not react or dissolve into the molten matrix metal or the filler 
material, unless such behavior is desired, e.g., when a reactive barrier 
is utilized. Any material or combination of materials which satisfy the 
above-described criteria for a particular matrix metal/infiltration 
enhancer and/or infiltration enhancer precursor and/or infiltrating 
atmosphere/filler material system may be utilized as a barrier material in 
that system. 
The subject matter of this application is also related to that of several 
commonly owned ceramic and ceramic composite Patents and commonly owned 
and copending ceramic and ceramic composite Patent Applications. 
Particularly, these Patents and Patent Applications describe novel methods 
for making ceramic and ceramic matrix composite materials (hereinafter 
sometimes referred to as "Commonly Owned Ceramic Matrix Patent 
Applications and Patents"). 
A novel approach to the formation of ceramic materials is disclosed 
generically in Commonly Owned U.S. Pat. No. 4,713,360, which issued on 
Dec. 15, 1987, in the names of Marc S. Newkirk et al. and entitled "Novel 
Ceramic Materials and Methods for Making Same". This Patent discloses a 
method of producing self-supporting ceramic bodies grown as the oxidation 
reaction product of a molten parent precursor metal which is reacted with 
a vapor-phase oxidant to form an oxidation reaction product. Molten metal 
migrates through the formed oxidation reaction product to react with the 
oxidant thereby continuously developing a ceramic polycrystalline body 
which can, if desired, include an interconnected metallic component. The 
process may be enhanced by the use of one or more dopants alloyed with the 
parent metal. For example, in the case of oxidizing aluminum in air, it is 
desirable to alloy magnesium and silicon with the aluminum to produce 
alpha-alumina ceramic structures. This method was improved upon by the 
application of dopant materials to the surface of the parent metal, as 
described in Commonly Owned U.S. Pat. No. 4,853,352, which issued on Aug. 
1, 1989, in the names of Marc S. Newkirk et al., and entitled "Methods of 
Making Self-Supporting Ceramic Materials", a European counterpart to which 
was published in the EPO on Jan. 22, 1986. 
A novel method for producing a self-supporting ceramic composite by growing 
an oxidation reaction product form a parent metal into a permeable mass of 
filler is disclosed in commonly owned and copending U.S. patent 
application Ser. No. 08/017,940, filed Feb. 16, 1993, as a continuation of 
U.S. patent application Ser. No. 07/659,473, filed Feb. 25, 1991, which 
issued as U.S. Pat. No. 5,187,130 on Feb. 16, 1993, which in turn was a 
continuation of U.S. patent application Ser. No. 07/415,180, filed Sep. 
29, 1989 (now abandoned), as a divisional of U.S. patent application Ser. 
No. 07/265,835, filed on Nov. 1, 1989, as a continuation of U.S. patent 
application Ser. No. 07/659,473, which issued as Copending U.S. Pat. No. 
4,916,113, on Apr. 10, 1990, and entitled "Methods of Making Composite 
Articles Having Embedded Filler" which is a continuation of U.S. Pat. No. 
4,851,375, issued Jul. 25, 1989, and entitled "Composite Ceramic Articles 
and Methods of Making the Same" all in the names of Marc S. Newkirk, et 
al. which was a continuation-in-part of U.S. patent application Ser. No. 
06/697,876, which was filed on Feb. 4, 1985 (now abandoned). 
A method for producing ceramic composite bodies having a predetermined 
geometry or shape is disclosed in Commonly Owned and Copending U.S. patent 
application Ser. No. 07/973,808, filed on Nov. 9, 1992, as a continuation 
of U.S. patent application Ser. No. 07/659,481, filed Feb. 25, 1991, which 
issued as Commonly Owned U.S. Pat. No. 5,162,273, on Nov. 10, 1992. 
Moreover, U.S. Pat. No. 5,162,273, issued from a continuation application 
of U.S. patent application Ser. No. 07/368,484, filed Jun. 19, 1989 (now 
abandoned), which is a continuation of U.S. patent application Ser. No. 
06/861,025, filed May 8, 1986 (now abandoned). In accordance with the 
method in these U.S. Patent Applications, the developing oxidation 
reaction product infiltrates a permeable preform of filler material in a 
direction towards a defined surface boundary. It was discovered that high 
fidelity is more readily achieved by providing the preform with a barrier 
means, as disclosed in Commonly Owned U.S. patent application Ser. No. 
07/659,523, filed Feb. 22, 1991 (now abandoned), which is a continuation 
of U.S. patent application Ser. No. 07/295,488 (now abandoned) filed Jan. 
10, 1989, which is a continuation of U.S. Pat. No. 4,923,832, which issued 
May 8, 1990, both in the names of Marc S. Newkirk et al., a European 
counterpart to which was published in the EPO on Nov. 11, 1987. This 
method produces shaped self-supporting ceramic bodies, including shaped 
ceramic composites, by growing the oxidation reaction product of a parent 
metal to a barrier means spaced from the metal for establishing a boundary 
or surface. 
Ceramic composites having a cavity with an interior geometry inversely 
replicating the shape of a positive mold or pattern are disclosed in 
Commonly Owned U.S. Pat. No. 5,051,382, which issued Sep. 24, 1991, from 
U.S. patent application Ser. No. 07/329,794, filed Mar. 28, 1989, which is 
a divisional of U.S. Pat. No. 4,828,785, which issued May 9, 1989, both in 
the names of Marc S. Newkirk, et al., a European counterpart to which was 
published in the EPO on Sep. 2, 1987, and in U.S. Pat. No. 4,859,640, 
which issued on Aug. 22, 1989, a European counterpart to which was 
published in the EPO on Mar. 9, 1988. 
The feeding of additional molten parent metal from a reservoir has been 
successfully utilized to produce thick ceramic matrix composite 
structures. Particularly, as disclosed in Commonly Owned U.S. Pat. No. 
4,918,034, issued Apr. 17, 1990, which is a continuation-in-part of U.S. 
Pat. No. 4,900,699, issued Feb. 13, 1990, both in the names of Marc S. 
Newkirk et al., and entitled "Reservoir Feed Method of Making Ceramic 
Composite Structures and Structures Made Thereby", a European counterpart 
to which was published in the EPO on Mar. 30, 1988, the reservoir feed 
method has been successfully applied to form ceramic matrix composite 
structures. According to the method of this Newkirk et al. invention, the 
ceramic or ceramic composite body which is produced comprises a 
self-supporting ceramic composite structure which includes a ceramic 
matrix obtained by the oxidation reaction of a parent metal with an 
oxidant to form a polycrystalline material. In conducting the process, a 
body of the parent metal and a permeable filler are oriented relative to 
each other so that formation of the oxidation reaction product will occur 
in a direction toward and into the filler. The parent metal is described 
as being present as a first source and as a reservoir, the reservoir of 
metal communicating with the first source due to, for example, gravity 
flow. The first source of molten parent metal reacts with the oxidant to 
begin the formation of the oxidation reaction product. As the first source 
of molten parent metal is consumed, it is replenished, preferably by a 
continuous means, from the reservoir of parent metal as the oxidation 
reaction product continues to be produced and infiltrates the filler. 
Thus, the reservoir assures that ample parent metal will be available to 
continue the process until the oxidation reaction product has grown to a 
desired extent. 
A method for tailoring the constituency of the metallic component of a 
ceramic matrix composite structure is disclosed in Copending and Commonly 
Owned U.S. Pat. No. 5,017,533, which issued on May 21, 1991, from U.S. 
application Ser. No. 07/389,506, filed on Aug. 2, 1989, which in turn is a 
continuation of U.S. patent application Ser. No. 06/908,454, filed Sep. 
17, 1986 (and now abandoned), both of which are in the names of Marc S. 
Newkirk et al., and entitled "Method for In Situ Tailoring the Metallic 
Component of Ceramic Articles and Articles Made Thereby". 
Moreover, U.S. patent application Ser. No. 07/904,739, filed on Jun. 26, 
1992, as a continuation-in-part application of U.S. Ser. No. 07/793,933, 
filed on Nov. 14, 1991, which issued on Feb. 9, 1993, as U.S. Pat. No. 
5,185,303, which was filed on Aug. 16, 1990, as a continuation of U.S. 
application Ser. No. 07/568,618, which in turn issued as U.S. Pat. No. 
5,066,618 on Nov. 19, 1991, from a continuation of U.S. application Ser. 
No. 07/269,152, filed Ser. No. 07/269,152, filed Nov. 9, 1988 (now 
abandoned), which is a continuation of U.S. Pat. No. 4,818,734, which 
issued Apr. 4, 1989 from U.S. patent application Ser. No. 07/152,518, 
filed Feb. 5, 1988, in the names of Robert C. Kantner et al., which was a 
Continuation-in-Part Application of the above-mentioned Ser. No. 
06/908,454, filed Sep. 17, 1986, having the same title and also being 
Commonly Owned. These Patents and the above-mentioned U.S. application 
Ser. No. 06/908,454, disclose methods for tailoring the constituency of 
the metallic component (both isolated and interconnected) of ceramic and 
ceramic matrix composite bodies during formation thereof to impart one or 
more desirable characteristics to the resulting body. Thus, desired 
performance characteristics for the ceramic or ceramic composite body are 
advantageously achieved by incorporating the desired metallic component in 
situ, rather than from an extrinsic source, or by post-forming techniques. 
As discussed in these Commonly Owned Ceramic Matrix Patent Applications and 
Patents, novel polycrystalline ,ceramic materials or polycrystalline 
ceramic composite materials are produced by the oxidation reaction between 
a parent metal and an oxidant (e.g., a solid, liquid and/or a gas). In 
accordance with the generic process disclosed in these Commonly Owned 
Ceramic Matrix Patent Applications and Patents, a parent metal (e.g., 
aluminum, silicon) is heated to an elevated temperature above its melting 
point but below the melting point of the oxidation reaction product (e.g., 
aluminum oxide, aluminum nitride, silicon nitride, etc.) to form a body of 
molten parent metal which reacts upon contact with an oxidant (e.g., an 
oxygen containing atmosphere, a nitrogenous atmosphere, etc.) to form the 
oxidation reaction product. At this temperature, the oxidation reaction 
product, or at least a portion thereof, is in contact with and extends 
between the body of molten parent metal and the oxidant, and molten metal 
is drawn or transported through the formed oxidation reaction product and 
towards the oxidant. The transported molten metal forms additional fresh 
oxidation reaction product when contacted with the oxidant, at the surface 
of previously formed oxidation reaction product. As the process continues, 
additional metal is transported through this formation of polycrystalline 
oxidation reaction product thereby continually "growing" a ceramic 
structure of interconnected crystallites. The resulting ceramic body may 
contain metallic constituents, such as non-oxidized constituents of the 
parent metal, and/or voids. Oxidation is used in its broad sense in all of 
the Commonly Owned Ceramic Matrix Patent Applications and Patents and in 
this application, and refers to the loss or sharing of electrons by a 
metal to an oxidant which may be one or more elements and/or compounds. 
Accordingly, elements other than oxygen may serve as an oxidant. 
In certain cases, the parent metal may require the presence of one or more 
dopants in order to influence favorably or to facilitate growth of the 
oxidation reaction product. Such dopants may at least partially alloy with 
the parent metal at some point during or prior to growth of the oxidation 
reaction product. For example, in the case of aluminum as the parent metal 
and nitrogen as the oxidant, dopants such as strontium, silicon, nickel 
and magnesium, to name but a few of a larger class of dopant materials, 
can be alloyed with aluminum, and the created growth alloy is utilized as 
the parent metal. The resulting oxidation reaction product of such a 
growth alloy, in the case of using nitrogen as an oxidant, comprises 
aluminum nitride. 
Novel ceramic composite structures and methods of making the same are also 
disclosed and claimed in certain of the aforesaid Commonly Owned Ceramic 
Matrix Patent Applications and Patents which utilize the oxidation 
reaction to produce ceramic composite structures comprising a 
substantially inert filler (note: in some cases it may be desirable to use 
a reactive filler, e.g., a filler which is at least partially reactive 
with the advancing oxidation reaction product and/or parent metal) 
infiltrated by the polycrystalline ceramic matrix. A parent metal is 
positioned adjacent to a mass of permeable filler (or a preform) which can 
be shaped and treated to be self-supporting, and is then heated to form a 
body of molten parent metal which is reacted with an oxidant, as described 
above, to form an oxidation reaction product. As the oxidation reaction 
product grows and infiltrates the adjacent filler material, molten parent 
metal is drawn through previously formed oxidation reaction product within 
the mass of filler and reacts with the oxidant to form additional fresh 
oxidation reaction product at the surface of the previously formed 
oxidation reaction product, as described above. The resulting growth of 
oxidation reaction product infiltrates or embeds the filler and results in 
the formation of a ceramic composite structure of a polycrystalline 
ceramic matrix embedding the filler. As also discussed above, the filler 
(or preform) may utilize a barrier means to establish a boundary or 
surface for the ceramic composite structure. 
The entire disclosures of the above-described commonly owned patents and 
patent applications are expressly incorporated herein by reference. 
Definitions 
As used in the present specification and the appended claims, the terms 
below are defined as follows: 
"Alloy Side", as used herein, refers to that side of a metal matrix 
composite or ceramic matrix composite which initially contacted molten 
metal before that molten metal infiltrated the permeable mass of filler 
material or preform. 
"Aluminum", as used herein, means and includes essentially pure metal 
(e.g., a relatively pure, commercially available unalloyed aluminum) or 
other grades of metal and metal alloys such as the commercially available 
metals having impurities and/or alloying constituents such as iron, 
silicon, copper, magnesium, manganese, chromium, zinc, etc., therein. An 
aluminum alloy for purposes of this definition is an alloy or 
intermetallic compound in which aluminum is the major constituent. 
"Ambient Atmosphere", as used herein in conjunction with the formation of 
metal matrix composites by a self-generated vacuum technique, refers to 
the atmosphere outside the filler material or preform and the impermeable 
container. It may have substantially the same constituents as the reactive 
atmosphere, or it may have different constituents. 
"Balance Non-Oxidizing Gas", as used herein in conjunction with the 
formation of metal matrix composites by a spontaneous infiltration 
technique, means that any gas present in addition to the primary gas 
comprising the infiltrating atmosphere, is either an inert gas or a 
reducing gas which is substantially non-reactive with the matrix metal 
under the process conditions. Any oxidizing gas which may be present as an 
impurity in the gas(es) used should be insufficient to oxidize the matrix 
metal to any substantial extent under the process conditions. 
"Barrier" or "barrier means", as used herein in conjunction with the 
formation of metal matrix composites, means any suitable means which 
interferes, inhibits, prevents or terminates the migration, movement, or 
the like, of molten matrix metal beyond a surface boundary of a permeable 
mass of filler material or preform, where such surface boundary is defined 
by said barrier means. Suitable barrier means may be any such material, 
compound, element, composition, or the like, which, under the process 
conditions, maintains some integrity and is not substantially volatile 
(i.e., the barrier material does not volatilize to such an extent that it 
is rendered non-functional as a barrier). 
Further, suitable "barrier means" includes materials which are 
substantially non-wettable by the migrating molten matrix metal under the 
process conditions employed. A barrier of this type appears to exhibit 
substantially little or no affinity for the molten matrix metal, and 
movement beyond the defined surface boundary of the mass of filler 
material or preform is prevented or inhibited by the barrier means. The 
barrier reduces any final machining or grinding that may be required and 
defines at least a portion of the surface of the resulting metal matrix 
composite product. The barrier may in certain cases be permeable or 
porous, or rendered permeable by, for example, drilling holes or 
puncturing the barrier, to permit gas to contact the molten matrix metal. 
"Barrier " or "barrier means", as used herein in conjunction with the 
formation of ceramic matrix composites, may be any material, compound, 
element, composition, or the like, which, under the process conditions, 
maintains some integrity, is not substantially volatile (i.e., the barrier 
material does not volatilize to such an extent that it is rendered 
non-functional as a barrier) and is preferably permeable to a vapor-phase 
oxidant (if utilized) while being capable of locally inhibiting, 
poisoning, stopping, interfering with, preventing, or the like, continued 
growth of the oxidation reaction product. 
"Bonded", as used herein in conjunction with metal matrix composites, means 
any method of attachment between two bodies. The attachment may be 
physical and/or chemical and/or mechanical. A physical attachment requires 
that at least one of the two bodies, usually in a liquid state, 
infiltrates at least a portion of the microstructure of the other body. 
This phenomenon is commonly known as "wetting". A chemical attachment 
requires that at least one of the two bodies chemically react with the 
other body to form at least one chemical bond between the two bodies. One 
method of forming a mechanical attachment between the two bodies includes 
a macroscopic infiltration of at least one of the two bodies into the 
interior of the other body. An example of this would be the infiltration 
of at least one of the two bodies into a groove or slot on the surface of 
the other body. Such mechanical attachment does not include microscopic 
infiltration or "wetting" but may be used in combination with such 
physical attachment techniques. 
An additional method of mechanical attachment includes such techniques as 
"shrink fitting", wherein one body is attached to the other body by a 
pressure fit. In this method of mechanical attachment, one of the bodies 
would be placed under compression by the other body. 
"Bronze", as used herein, means and includes a copper rich alloy, which may 
include iron, tin, zinc, aluminum, silicon, beryllium, manganese and/or 
lead. Specific bronze alloys include those alloys in which the proportion 
of copper is about 90% by weight, the proportion of silicon is about 6% by 
weight, and the proportion of iron is about 3% by weight. 
"Carcass" or "Carcass of Matrix Metal", as used herein, refers to any of 
the original body of matrix metal remaining which has not been consumed 
during formation of the metal matrix composite body, and typically, if 
allowed to cool, remains in at least partial contact with the metal matrix 
composite body which has been formed. It should be understood that the 
carcass may also include a second or foreign metal therein. 
"Cast Iron", as used herein, refers to the family of cast ferrous alloys 
wherein the proportion of carbon is at least about 2% by weight. 
"Ceramic", as used herein, should not be unduly construed as being limited 
to a ceramic body in the classical sense, that is, in the sense that it 
consists entirely of non-metallic and inorganic materials, but rather 
refers to a body which is predominantly ceramic with respect to either 
composition or dominant properties, although the body may contain minor or 
substantial amounts of one or more metallic constituents (isolated and/or 
interconnected, depending on the processing conditions used to form the 
body) derived from a parent metal, or reduced from an oxidant or a dopant, 
most typically within a range of from about 1-40 percent by volume, but 
may include still more metal. 
"Ceramic Matrix Composite" or "CMC" or "Ceramic Composite Body", as used 
herein, means a material comprising a two- or three-dimensionally 
interconnected ceramic which has embedded a preform or filler material, 
and may further include a parent metal phase embedded therein, possibly in 
a two- or three-dimensionally interconnected network. The ceramic may 
include various dopant elements to provide a specifically desired 
microstructure, or specifically desired mechanical, physical, or chemical 
properties in the resulting composite. 
"Copper", as used herein, refers to the commercial grades of the 
substantially pure metal, e.g., 99% by weight copper with varying amounts 
of impurities contained therein. Moreover, it also refers to metals which 
are alloys or intermetallics which do not fall within the definition of 
bronze, and which contain copper as the major constituent therein. 
"Dopants", as used herein in conjunction with ceramic matrix composites, 
means materials (parent metal constituents or constituents combined with 
and/or included in or on a filler, or combined with the oxidant) which, 
when used in combination with the parent metal, favorably influence or 
promote the oxidation reaction process and/or modify the growth process to 
alter the microstructure and/or properties of the product. While not 
wishing to be bound by any particular theory or explanation of the 
function of dopants, it appears that some dopants are useful in promoting 
oxidation reaction product formation in cases where appropriate surface 
energy relationships between the parent metal and its oxidation reaction 
product do not intrinsically exist so as to promote such formation. 
Dopants may be added to the filler material, they may be in the form of a 
gas, solid, or liquid under the process conditions, they may be included 
as constituents of the parent metal, or they may be added to any one of 
the constituents involved in the formation of the oxidation reaction 
product. Dopants may: (1) create favorable surface energy relationships 
which enhance or induce the wetting of the oxidation reaction product by 
the molten parent metal; and/or (2) form a "precursor layer" at the growth 
surface by reaction with alloy, oxidant, and/or filler, that (a) minimizes 
formation of a protective and coherent oxidation reaction product 
layer(s), (b) may enhance oxidant solubility (and thus permeability) in 
molten metal, and/or (c) allows for transport of oxidant from the 
oxidizing atmosphere through any precursor oxide layer to combine 
subsequently with the molten metal to form another oxidation reaction 
product; and/or (3) cause microstructural modifications of the oxidation 
reaction product as it is formed or subsequently and/or alter the metallic 
constituent composition and properties of such oxidation reaction product; 
and/or (4) enhance growth nucleation and uniformity of growth of oxidation 
reaction product. 
"Filler", as used herein in conjunction with both ceramic matrix composites 
and metal matrix composites, is intended to include either single 
constituents or mixtures of constituents which are substantially 
non-reactive with and/or of limited solubility in the matrix or parent 
metal and may be single or multi-phase. Fillers may be provided in a wide 
variety of forms, such as powders, flakes, platelets, microspheres, 
whiskers, bubbles, fibers, particulates, fiber mats, chopped fibers, 
spheres, pellets, tubules, refractory cloths, etc., and may be either 
dense or porous. "Filler" may also include ceramic fillers, such as 
alumina or silicon carbide, as fibers, chopped fibers, particulates, 
whiskers, bubbles, spheres, fiber mats, or the like, and coated fillers 
such as carbon fibers coated with alumina or silicon carbide to protect 
the carbon from attack, for example, by a molten aluminum matrix metal. 
Fillers may also include metals. 
"Impermeable Container", as used herein, in conjunction with the formation 
of metal matrix composites by a self-generated vacuum technique, means a 
container which may house or contain a reactive atmosphere and a filler 
material (or preform) and/or molten matrix metal and/or a sealing means 
and/or at least a portion of at least one second material, under the 
process conditions, and which is sufficiently impermeable to the transport 
of gaseous or vapor species through the container, such that a pressure 
difference between the ambient atmosphere and the reactive atmosphere can 
be established. 
"Infiltrating Atmosphere", as used herein, in conjunction with the 
formation of metal matrix composites by a spontaneous infiltration 
technique, means that atmosphere which is present which interacts with the 
matrix metal and/or preform (or filler material) and/or infiltration 
enhancer precursor and/or infiltration enhancer and permits or enhances 
spontaneous infiltration of the matrix metal to occur. 
"Infiltration Enhancer", as used herein, in conjunction with the formation 
of metal matrix composites by a spontaneous infiltration technique, means 
a material which promotes or assists in the spontaneous infiltration of a 
matrix metal into a filler material or preform. An infiltration enhancer 
may be formed from, for example, (1) a reaction of an infiltration 
enhancer precursor with an infiltrating atmosphere to form a gaseous 
species and/or (2) a reaction product of the infiltration enhancer 
precursor and the infiltrating atmosphere and/or (3) a reaction product of 
the infiltration enhancer precursor and the filler material or preform. 
Moreover, the infiltration enhancer may be supplied directly to at least 
one of the filler material or preform, and/or matrix metal and/or 
infiltrating atmosphere and function in a substantially similar manner to 
an infiltration enhancer which has formed as a reaction between an 
infiltration enhancer precursor and another species. Ultimately, at least 
during the spontaneous infiltration, the infiltration enhancer should be 
located in at least a portion of the filler material or preform to achieve 
spontaneous infiltration, and the infiltration enhancer may be at least 
partially reducible by the matrix metal. 
"Infiltration Enhancer Precursor" or "Precursor to the Infiltration 
Enhancer", as used herein, in conjunction with the formation of metal 
matrix composites by a spontaneous infiltration technique, means a 
material which when used in combination with (1) the matrix metal, (2) the 
preform or filler material and/or (3) an infiltrating atmosphere forms an 
infiltration enhancer which induces or assists the matrix metal to 
spontaneously infiltrate the filler material or preform. Without wishing 
to be bound by any particular theory or explanation, it appears as though 
it may be necessary for the precursor to the infiltration enhancer to be 
capable of being positioned, located or transportable to a location which 
permits the infiltration enhancer precursor to interact within the 
infiltrating atmosphere and/or the preform or filler material and/or the 
matrix metal. For example, in some matrix metal/infiltration enhancer 
precursor/infiltrating atmosphere systems, it is desirable for the 
infiltration enhancer precursor to volatilize at, near, or, in some cases, 
even somewhat above the temperature at which the matrix metal becomes 
molten. Such volatilization may lead to: (1) a reaction of the 
infiltration enhancer precursor with the infiltrating atmosphere to form a 
gaseous species which enhances wetting of the filler material or preform 
by the matrix metal; and/or (2) a reaction of the infiltration enhancer 
precursor with the infiltrating atmosphere to form a solid, liquid or 
gaseous infiltration enhancer in at least a portion of the filler material 
or preform which enhances wetting; and/or (3) a reaction of the 
infiltration enhancer precursor within the filler material or preform 
which forms a solid, liquid or gaseous infiltration enhancer in at least a 
portion of the filler material or preform which enhances wetting. 
"Macrocomposite" or "Macrocomposite Body", as used herein in conjunction 
with metal matrix composites, means any combination of two or more 
materials selected from the group consisting of a ceramic matrix body, a 
ceramic matrix composite body, a metal body, and a metal matrix composite 
body, which are intimately bonded together in any configuration, wherein 
at least one of the materials comprises a metal matrix composite body. The 
metal matrix composite body may be present as an exterior surface and/or 
as an interior surface. Further, the metal matrix composite body may be 
present as an interlayer between two or more of the materials in the group 
described above. It should be understood that the order, number, and/or 
location of a metal matrix composite body or bodies relative to residual 
matrix metal and/or any of the materials in the group discussed above, can 
be manipulated or controlled in an unlimited fashion. 
"Matrix Metal" or "Matrix Metal Alloy", as used herein means that metal 
which is utilized to form a metal matrix composite (e.g., before 
infiltration) and/or that metal which is intermingled with a filler 
material to form a metal matrix composite body (e.g., after infiltration). 
When a specified metal is mentioned as the matrix metal, it should be 
understood that such matrix metal includes that metal as an essentially 
pure metal, a commercially available metal having impurities and/or 
alloying constituents therein, an intermetallic compound or an alloy in 
which that metal is the major or predominant constituent. 
"Matrix Metal/Infiltration Enhancer Precursor/Infiltrating Atmosphere 
System" or "Spontaneous System", as used herein, in conjunction with the 
formation of metal matrix composites by a spontaneous infiltration 
technique, refers to that combination of materials which exhibits 
spontaneous infiltration into a preform or filler material. It should be 
understood that whenever a "/" appears between an exemplary matrix metal, 
infiltration enhancer precursor and infiltrating atmosphere that, the "/" 
is used to designate a system or combination of materials which, when 
combined in a particular manner, exhibits spontaneous infiltration into a 
preform or filler material. 
"Maximum Operating Temperature" or "MOT", as used herein, is related to the 
predominant failure mode of composite rotors (e.g., metal matrix composite 
rotors) which is by surface scuffing. As a rotor is subjected to 
progressively more severe conditions, the temperature of the rotor 
continues to rise until it reaches a temperature at which the glaze on the 
rotor surface breaks down and scuffing ensues. The temperature at which 
the breakdown occurs is referred to as the maximum operating temperature 
(MOT). The breakdown of a rotor is accompanied by excessive noise, sparks 
and dust. The rotor breakdown may be followed by rapid wear of the pads 
and a rise in temperature measured by the pad thermocouples. The MOT is 
primarily dependent on the material composition and not on the rotor 
design or the test conditions. 
"Metal Matrix Composite" or "MMC", as used herein, means a material 
comprising a two- or three-dimensionally interconnected alloy or matrix 
metal which has embedded a preform or filler material. The matrix metal 
may include various alloying elements to provide specifically desired 
mechanical and physical properties in the resulting composite. 
A Metal "Different" from the Matrix Metal or from the parent metal means a 
metal which does not contain, as a primary constituent, the same metal as 
the matrix or parent metal (e.g., if the primary constituent of the matrix 
metal is aluminum, the "different" metal could have a primary constituent 
of, for example, nickel). 
"Oxidant", as used herein, means one or more suitable electron acceptors or 
electron sharers and may be a solid, a liquid or a gas or some combination 
of these (e.g., a solid and a gas) at the oxidation reaction conditions. 
Typical oxidants include, without limitation, oxygen, nitrogen, any 
halogen or a combination thereof, sulphur, phosphorus, arsenic, carbon, 
boron, selenium, tellurium, and or compounds and combinations thereof, for 
example, silica or silicates (as sources of oxygen), methane, ethane, 
propane, acetylene, ethylene, propylene (the hydrocarbon as a source of 
carbon), and mixtures such as air, H.sub.2 /H.sub.2 O and CO/CO.sub.2 (as 
sources of oxygen). The latter two (i.e., H.sub.2 /H.sub.2 O and 
CO/CO.sub.2) being useful in reducing the oxygen activity of the 
environment. 
"Oxidation", as used herein means a chemical reaction in which an oxidant 
reacts with a parent metal, and that parent metal has given up electrons 
to or shared electrons with the oxidant. 
"Oxidation Reaction Product", as used herein, means one or more metals in 
any oxidized state wherein the metal(s) has given up electrons to or 
shared electrons with another element, compound, or combination thereof. 
Accordingly, an "oxidation reaction product" under this definition 
includes the product of the reaction of one or more metals with one or 
more oxidants. 
"Parent Metal", as used herein, means that metal(s) (e.g., aluminum, 
silicon, titanium, tin, zirconium, etc.) which is the precursor of a 
polycrystalline oxidation reaction product and includes that metal(s) as 
an essentially pure metal, a commercially available metal having 
impurities and/or alloying constituents therein, or an alloy in which that 
metal precursor is the major constituent. When a specified metal is 
mentioned as the parent or precursor metal (e.g., aluminum, etc.), the 
metal identified should be read with this definition in mind unless 
indicated otherwise by the context. 
"Nonreactive Vessel for Housing Matrix Metal", as used herein, in 
conjunction with the formation of metal matrix composites by a spontaneous 
infiltration technique, means any vessel which can house or contain molten 
matrix metal under the process conditions and not react with the matrix 
and/or the infiltrating atmosphere and/or infiltration enhancer precursor 
and/or filler material or preform in a manner which would be significantly 
detrimental to the spontaneous infiltration mechanism. 
"Preform" or "Permeable Preform", as used herein in conjunction with both 
metal matrix composite and ceramic matrix composite materials, means a 
porous mass of filler or filler material which is manufactured with at 
least one surface boundary which essentially defines a boundary for 
infiltrating matrix metal, such mass retaining sufficient shape integrity 
and green strength to provide dimensional fidelity without any external 
means of support prior to being infiltrated by the matrix metal. The mass 
should be sufficiently porous to permit infiltration of the matrix metal. 
A preform typically comprises a bonded array or arrangement of filler, 
either homogeneous or heterogeneous, and may be comprised of any suitable 
material (e.g., ceramic and/or metal particulates, powders, fibers, 
whiskers, etc., and any combination thereof). A preform may exist either 
singularly or as an assemblage. 
"Reaction System", as used herein, in conjunction with the formation of 
metal matrix composites by a self-generated vacuum technique, refers to 
that combination of materials which exhibit self-generated vacuum 
infiltration of a molten matrix metal into a filler material or preform. A 
reaction system comprises at least an impermeable container having therein 
a permeable mass of filler material or preform, a reactive atmosphere and 
a matrix metal. 
"Reactive Atmosphere", as used herein, in conjunction with the formation of 
metal matrix composites by a self-generated vacuum technique, means an 
atmosphere which may react with the matrix metal and/or filler material 
(or preform) and/or impermeable container to form a self-generated vacuum, 
thereby causing molten matrix metal to infiltrate into the filler material 
(or preform) upon formation of the self-generated vacuum. 
"Reservoir", as used herein in conjunction with both metal matrix composite 
and ceramic matrix composite materials, means a separate body of metal 
positioned relative to a mass of filler or a preform so that, when the 
metal is molten, it may flow to replenish, or in some cases to initially 
provide and subsequently replenish, that portion, segment or source of 
matrix metal which is in contact with the filler or preform. 
"Seal" or "Sealing Means", as used herein in conjunction with the formation 
of metal matrix composites by a self-generated vacuum technique, refers to 
a gas-impermeable seal under the process conditions, whether formed 
independent of (e.g., an extrinsic seal) or formed by the reaction system 
(e.g., an intrinsic seal), which isolates the ambient atmosphere from the 
reactive atmosphere. The seal or sealing means may have a composition 
different from that of the matrix metal. 
"Seal Facilitator", as used herein in conjunction with the formation of 
metal matrix composites by a self-generated vacuum technique, is a 
material that facilitates formation of a seal upon reaction of the matrix 
metal with the ambient atmosphere and/or the impermeable container and/or 
the filler material or preform. The material may be added to the matrix 
metal, and the presence of the seal facilitator in the matrix metal may 
enhance the properties of the resultant composite body. 
"Second Body" or "Additional Body", as used herein, means another body 
which is capable of being bonded to a metal matrix composite body by at 
least one of a chemical reaction and/or a mechanical or shrink fit. Such a 
body includes traditional ceramics such as sintered ceramics, hot pressed 
ceramics, extruded ceramics, etc., and also, non-traditional ceramic and 
ceramic composite bodies such as those produced by the methods described 
in Commonly Owned U.S. Pat. No. 4,713,360, which issued on Dec. 15, 1987, 
in the names of Marc S. Newkirk et al.; Commonly Owned U.S. Pat. No. 
4,851,375, which issued on Jul. 25, 1989, from U.S. patent application 
Ser. No. 819,397, filed Jan. 17, 1986 in the names of Marc S. Newkirk et 
al. and entitled "Composite Ceramic Articles and Methods of Making Same"; 
Commonly Owned U.S. Pat. No. 5,017,526, which issued on May 21, 1991, from 
U.S. patent application Ser. No. 07/338,471, filed Apr. 14, 1989, as a 
continuation of U.S. patent application Ser. No. 861,025, filed May 8, 
1986 in the names of Marc S. Newkirk et al. and entitled "Shaped Ceramic 
Composites and Methods of Making the Same"; Commonly Owned U.S. Pat. No. 
4,818,734, which issued on Apr. 4, 1989, from U.S. patent application Ser. 
No. 152,518 filed on Feb. 5, 1988 in the names of Robert C. Kantner et al. 
and entitled "Method For In Situ Tailoring the Metallic Component of 
Ceramic Articles and Articles Made Thereby"; Commonly Owned U.S. Pat. No. 
4,940,679, which issued on Jul. 10, 1990, from U.S. patent application 
Ser. No. 137,044, filed Dec. 23, 1987 in the names of T. Dennis Claar et 
al. and entitled "Process for Preparing Self-Supporting Bodies and 
Products Made Thereby"; and variations and improvements on these processes 
contained in other Commonly Owned U.S. Patent Applications and Patents. 
For the purpose of teaching the method of production and characteristics 
of the ceramic and ceramic composite bodies disclosed and claimed in these 
commonly owned applications and Patents, the entire disclosures of the 
above-mentioned applications and Patents are hereby incorporated by 
reference. Moreover, the second or additional body of the instant 
invention also includes metal matrix composites and structural bodies of 
metal such as high temperature metals, corrosion resistant metals, erosion 
resistant metals, etc. Accordingly, a second or additional body includes a 
virtually unlimited number of bodies. 
"Second Material", as used herein, refers to a material selected from the 
group consisting of a ceramic matrix body, a ceramic matrix composite 
body, a metal body, and a metal matrix composite body. 
"pontaneous Infiltration", as used herein, means that the infiltration of 
matrix metal into the permeable mass of filler or preform occurs without 
requirement for the application of pressure or vacuum (whether externally 
applied or internally created). 
"Wetting Enhancer", as used herein in conjunction with the formation of 
metal matrix composites by a self-generated vacuum technique, refers to 
any material, which when added to the matrix metal and/or the filler 
material or preform, enhances the wetting (e.g., reduces surface tension 
of molten matrix metal) of the filler material or preform by the molten 
matrix metal. The presence of the wetting enhancer may also enhance the 
properties of the resultant metal matrix composite body by, for example, 
enhancing bonding between the matrix metal and the filler material. 
SUMMARY OF THE INVENTION 
The present invention comprises improved composite brake rotors useful for 
ground vehicles. Specifically, the present invention comprises a brake 
rotor comprising an interconnected metal or ceramic matrix embedding at 
least one filler material (e.g., such as a ceramic material), wherein in 
the case of metal matrix composites the at least one filler material 
comprises at least about 26% by volume of the brake rotor for most 
applications, and at least about 20% by volume for applications involving 
passenger cars and trucks. Such a brake rotor demonstrates properties 
which are unexpectedly superior to the properties demonstrated by brake 
rotors having lower volumetric percentages of filler material when such 
brake rotors are used in similar applications. 
Although any process capable of forming metal matrix composites containing 
at least about 20% by volume filler material may be used to form the metal 
matrix composites of the present invention, a particularly preferable 
technique comprises contacting a molten matrix metal with a mass of filler 
material or a preform which is in communication with an infiltration 
enhancer and/or an infiltration enhancer precursor and/or an infiltrating 
atmosphere at least at some point during the process which permits molten 
matrix metal to spontaneously infiltrate the mass of filler material or 
preform to form the metal matrix composite (sometimes referred to herein 
as "spontaneous infiltration"). 
Without wishing to be bound by any particular theory or explanation, it is 
believed that when the volume percent of filler material in a metal matrix 
composite reaches a certain level (e.g., at least about 26% by volume, and 
preferably at least about 28% by volume, for most applications, and at 
least about 20% by volume for applications involving passenger cars and 
trucks, however, in some cases, even more preferably at least about 30% by 
volume), the overall performance level of the metal matrix composite 
material may be unexpectedly enhanced (i.e., in comparison to metal matrix 
composite materials having lower, or in some cases even higher, filler 
loadings and used in similar applications) to a level which renders the 
metal matrix composite material suitable for certain uses or applications, 
such as brake rotors for both the front and rear braking systems on, for 
example, automobiles and trucks. It is further believed that the overall 
performance level may be influenced by one or more of thermal 
conductivity, heat capacity wear or abrasion resistance, high temperature 
strength, stiffness, coefficient of friction, elastic modulus, yield 
strength, density, hardness, resistance to heat cracking, ultimate tensile 
strength, fatigue strength and fracture toughness. 
The above disclosure is directed generally to brake rotors for ground 
vehicles. In view of this, the lower end of the applicable filler material 
range has been generally limited to about 26% by volume, where the 
increased performance of the brake rotors justifies their use in a wide 
variety of ground vehicles (e.g., automobiles, trucks, trains, trolleys, 
motorcycles, military vehicles and all other ground vehicles that use 
brake rotors). The lower end of the filler material range which may be 
used in the brake rotors of the present invention when the end use of the 
brake rotors is for passenger cars and trucks has been limited to about 
20% by volume. This is because the necessary performance level for brake 
rotors in certain passenger cars and trucks is, typically, not as high as 
in other types of ground vehicles (e.g., heavy trucks, buses and trains). 
Accordingly, when the brake rotor of the present invention is intended for 
use in passenger cars and trucks (or in any other application which 
requires an equivalent or lesser amount of brake rotor performance), a 
filler material loading of at least about 20% may be necessary to achieve 
the required performance levels. However, in many passenger car and light 
truck applications, a brake rotor may require filler material loadings of 
at least about 30% by volume or more, depending upon the specific 
performance requirements that the rotor must meet. In this regard, the 
aforementioned physical properties which contribute to the overall 
performance of the rotors are related in a complex way. Specifically, the 
presence of one filler material verses another filler material in a rotor 
affects virtually all of the properties discussed above herein. 
Accordingly, in some cases, a greater amount of one filler material may be 
required to achieve similar rotor performances in comparison to a 
different filler material. While the complex interrelationship of 
properties is difficult to quantify with respect to different rotor 
performances, one item which is readily quantifiable is the Maximum 
Operating Temperature ("MOT") which a rotor can experience. For example, 
under a given set of testing conditions, every rotor can be caused to fail 
and the temperature at which such rotor fails gives an indication of which 
application (e.g., front brake rotor or back brake rotor for automobiles) 
the rotor is suited for. The rotors of the present invention reach 
unexpectedly high MOT's of at least about 900.degree. F. (482.degree. C.) 
and above. Specifically, rotors of the present invention readily achieve 
MOT's of 925.degree. F. (496.degree. C.), 950.degree. F. (510.degree. C.) 
1000.degree. F. (538.degree. C.) and above. These MOT's have never before 
been achieved by prior art rotors and permit new design/weight formulation 
to occur. Accordingly, the present invention is a significant achievement 
in the rotor art because weight savings can be achieved without 
sacrificing performance. 
The predominant failure mode of composite material brake rotors and 
particularly metal matrix composite brake rotors is by surface scuffing. 
As a brake rotor is subjected to progressively more severe conditions 
(e.g., high inertial loads), the temperature of the brake rotor continues 
to rise until it reaches a temperature at which a glaze (typically formed 
on the rubbing surfaces of the rotor at preburnish, for example, as 
Section 6.3 Preburnishment of SAE J212) on the rotor surface breaks down 
and scuffing ensues. The temperature at which the breakdown occurs is 
referred to as the Maximum Operating Temperature or MOT. The breakdown of 
a rotor accompanies excessive noise, sparks and dust. The rotor breakdown 
is followed by rapid wear of the pads and a rise in temperatures measured 
by the pad thermocouples (as discussed further below). The Maximum 
Operating Temperature or MOT is primarily dependent on the material 
composition and not on the rotor design or the test conditions. 
The Maximum Operating Temperature or MOT of a material formed as a brake 
rotor or disc is determined using dynamometer tests adopted from SAE J212, 
"Brake System Dyanamometer Test Procedure"--Passenger Cars--SAE J212 
JUN80, SAE 1980 (which is herein incorporated by reference), with some 
modifications. These tests are discussed in greater detail later herein. 
In addition, certain rotor formulations relating to the present invention 
achieve performances never before thought to be obtainable with 
conventional materials. These rotor formulations include both novel metal 
matrix composites and ceramic matrix composites made by the methods 
discussed herein.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS 
The present invention comprises improved metal matrix or ceramic matrix 
composite brake rotors useful for ground vehicles. Specifically, with 
regard to metal matrix composites, the present invention comprises a brake 
rotor comprising an interconnected metal matrix (e.g., aluminum) embedding 
at least one filler material (e.g., such as a ceramic material), wherein 
the at least one filler material comprises at least about 26% by volume of 
the brake rotor for most applications, and at least about 20% by volume 
for applications involving passenger cars and trucks. Such a brake rotor 
demonstrates properties which are unexpectedly superior to the properties 
demonstrated by brake rotors having lower volumetric percentages of filler 
material when such brake rotors are used in similar applications. 
Although any process capable of forming metal matrix composites containing 
at least about 20% by volume filler material may be used to form the metal 
matrix composites of the present invention, a particularly preferable 
technique comprises contacting a molten matrix metal with a mass of filler 
material or a preform which is in communication with an infiltration 
enhancer and/or an infiltration enhancer precursor and/or an infiltrating 
atmosphere at least at some point during the process which permits molten 
matrix metal to spontaneously infiltrate the mass of filler material or 
preform to form the metal matrix composite. 
Without wishing to be bound by any theory, it is believed that when the 
volume percent of filler material in a metal matrix composite reaches a 
certain level (e.g., at least about 26% by volume, and preferably at least 
about 28% by volume, for most applications, and at least 20% by volume for 
applications involving passenger cars and trucks and even more preferably, 
for some applications, greater than about 30% by volume), the overall 
performance level of the metal matrix composite material is enhanced 
(i.e., in comparison to metal matrix composite materials having lower 
filler loadings and used in similar applications) to a level which renders 
the metal matrix composite material suitable for certain uses or 
applications, such as brake rotors. It is further believed that the 
overall performance level may be influenced by one or more of thermal 
conductivity, heat capacity, wear or abrasion resistance, high temperature 
strength, density, stiffness, coefficient of friction, elastic modulus, 
yield strength, hardness, resistance to heat cracking, filler particle 
size, filler particle distribution, filler particle loading, filler 
particle geometry, ultimate tensile strength, fatigue strength and 
fracture toughness. 
However, in many passenger car loadings and light truck applications, a 
brake rotor may require filler material loadings of at least about 30% by 
volume or more, depending upon the specific performance requirements that 
the rotor must meet. In this regard, the aforementioned physical 
properties which contribute to the overall performance of the rotors are 
related in a complex manner. Specifically, the presence of one filler 
material verses another filler material in a rotor affects virtually all 
of the properties discussed above herein. Accordingly, in some cases, a 
greater amount of one filler material may be required to achieve similar 
rotor performances in comparison to a different filler material. While the 
complex interrelationship of properties is difficult to quantify with 
respect to different rotor performances, one item which is readily 
quantifiable is the Maximum Operating Temperature ("MOT") which a rotor 
can experience. For example, under a given set of testing conditions, 
every rotor can be caused to fail and the temperature at which such rotor 
fails gives an indication of which application (e.g., front brake rotor or 
back brake rotor for automobiles) the rotor is suited for. The rotors of 
the present invention reach unexpectedly high MOT's of at least about 
900.degree. F. (482.degree. C.) and above. Specifically, rotors of the 
present invention readily achieve MOT's of 925.degree. F. (496.degree. 
C.), 950.degree. F. (510.degree. C.) 1000.degree. C.) and above. These 
MOT's have never before been achieved by prior art rotors and permit new 
design/weight formulation to occur. Accordingly, the present invention is 
a significant achievement in the rotor art because weight savings can be 
achieved without sacrificing performance. 
Although the filler materials that may be used in the brake rotors of the 
present invention comprise a wide variety of shapes, sizes and geometries 
(e.g., particulate, fibers, cloth etc.), a preferred type of filler 
material is particulate or powdered filler material. Such filler material 
usually has an average diameter of about 1 to 5,000 microns and preferably 
has an average diameter of about 5 to 500 microns. Several tests have 
indicated that equiaxed or rounded filler materials may be desirable and 
may provide enhanced brake rotor performance. 
A preferred embodiment of the present invention comprises a metal matrix 
composite brake rotor comprising an aluminum metal matrix embedding a 
silicon carbide filler material which comprises at least about 26% by 
volume of the brake rotor for most applications, and at least about 20% by 
volume for applications involving passenger cars and trucks and even more 
preferably, at least of 30% by volume for some more severely performed 
applications. The filler material may be in a wide variety of forms and 
sizes. A particularly preferred silicon carbide filler is silicon carbide 
particulate. The silicon carbide filler material may be present as a mass 
of filler material or a preform and at least one of an infiltration 
enhancer, infiltration enhancer precurser and infiltrating atmosphere may 
be located within the mass of filler material or preform. 
Another preferred embodiment of the present invention comprises a metal 
matrix composite brake rotor comprising an aluminum metal matrix embedding 
an alumina filler material which comprises at least about 26% by volume of 
the brake rotor for most applications, and at least about 20% by volume 
for applications involving passenger cars and trucks and even more 
preferably, at least of 30% by volume for some more severely performed 
applications. The filler material may be in a wide variety of forms and 
sizes. A particularly preferred form of alumina filler material is 
particulate alumina. The alumina filler material may be present as a mass 
of filler material or a preform and at least one of an infiltration 
enhancer, infiltration enhancer precursor and infiltrating atmosphere may 
be located within the mass of filler material or preform. 
Although the present disclosure focusses primarily upon aluminum matrix 
metals, it should be understood that any metal may be used as the matrix 
metal in the brake rotor of the present invention. Representative matrix 
metals include, but are not limited to, aluminum, magnesium and titanium. 
Moreover, although the present disclosure focusses primarily upon metal 
matrix composite materials, it should be understood that macrocomposite 
materials which include a metal matrix composite material which is 
integrally attached or bonded to at least one other material (e.g., a 
ceramic material, a ceramic matrix composite material, a metal etc.) may 
be used as the brake rotor of the present invention. 
Still further, ceramic matrix composite rotors made according to various 
methods including these methods discussed above relating to the Commonly 
Owned Patents and Patent Applications, also function as desirable rotors 
(e.g., give unexpectantly high MOT's). 
The above disclosure is directed generally to brake rotors for ground 
vehicles. In view of this, the lower end of the applicable filler material 
range has been generally limited to about 26% by volume, where the 
increased performance of the brake rotors justifies their use in a wide 
variety of ground vehicles (e.g., automobiles, trucks, trains, trolleys, 
motorcycles, military vehicles and all other ground vehicles that use 
brake rotors). The lower end of the filler material range which may be 
used in the brake rotors of the present invention when the end use of the 
brake rotors is for passenger cars and trucks has been limited to about 
20% by volume. This is because the necessary performance level for brake 
rotors in some passenger cars and trucks is, typically, not as high as in 
other types of ground vehicles (e.g., heavy trucks, buses and trains). 
Accordingly, when the brake rotor of the present invention is intended for 
use in passenger cars and trucks (or in any other application which 
requires an equivalent or lesser amount of brake rotor performance), a 
filler material loading of at least about 20% may be necessary to achieve 
the required performance levels. 
However, in many passenger car and light truck applications, a brake rotor 
may require filler material loadings of at least about 30% by volume or 
more, depending upon the specific performance requirements that the rotor 
must meet. In this regard, the aforementioned physical properties which 
contribute to the overall performance of the rotors are related in a 
complex manner. Specifically, the presence of one filler material verses 
another filler material in a rotor affects virtually all of the properties 
discussed above herein. Accordingly, in some cases, a greater amount of 
one filler material may be required to achieve similar rotor performances 
in comparison to a different filler material. While the complex 
interrelationship of properties is difficult to quantify with respect to 
different rotor performances, one item which is readily quantifiable is 
the Maximum Operating Temperature ("MOT") which a rotor can experience. 
For example, under a given set of testing conditions, every rotor can be 
caused to fail and the temperature at which such rotor fails gives an 
indication of which application (e.g., front brake rotor or back brake 
rotor for automobiles) the rotor is suited for. The rotors of the present 
invention reach unexpectedly high MOT's of at least about 900.degree. F. 
(482.degree. C.) and above. Specifically, rotors of the present invention 
readily achieve MOT's of 925.degree. F. (496.degree. C.), 950.degree. F. 
(510.degree. C.) 1000.degree. F. (538.degree. C.) and above. These MOT's 
have never before been achieved by prior art rotors and permit new 
design/weight formulation to occur. Accordingly, the present invention is 
a significant achievement in the rotor art because weight savings can be 
achieved without sacrificing performance. 
The predominant failure mode of composite material brake rotors and 
particularly metal matrix composite brake rotors is by surface scuffing. 
As a brake rotor is subjected to progressively more severe conditions 
(e.g., high inertial loads), the temperature of the brake rotor continues 
to rise until it reaches a temperature at which a glaze (typically formed 
on the rubbing surfaces of the rotor at preburnish, for example, as 
Section 6.3 Preburnishment of SAE J212) on the rotor surface breaks down 
and scuffing ensues. The temperature at which the breakdown occurs is 
referred to as the Maximum Operating Temperature or MOT. The breakdown of 
a rotor accompanies excessive noise, sparks and dust. The rotor breakdown 
is followed by rapid wear of the pads and a rise in temperatures measured 
by the pad thermocouples (as discussed further below). The Maximum 
Operating Temperature or MOT is primarily dependent on the material 
composition and not on the rotor design or the test conditions. 
The Maximum Operating Temperature or MOT of a material as a brake rotor or 
disc is determined using dynamometer tests adopted from SAE J212, "Brake 
System Dyanamometer Test Procedure"--Passenger Cars--SAE J212 JUN80, SAE 
1980 (which is herein incorporated by reference), with some modifications. 
The current SAE J212 test has two fade/recovery sequences, each conducted 
at a cooling air speed of 8 mph (12.8 km/h). In the present test, an 
additional fade/recovery sequence is added at a cooling air speed of 2 mph 
(3.2 km/h). The rubbing surface temperature of the test rotor is measured 
by a thermocouple located 0.040 inch (1 mm) below the surface at the 
center of the inboard side, since most of the failures in the metal matrix 
composite rotors has been determined to initiate on this side (this 
rubbing surface is designated as the inner rotor rubbing surface or IRRS). 
A second thermocouple is located at the intersection of the outer rubbing 
surface and the rotor hub. This thermocouple is also recessed 0.040" (1 
mm) under the rotor surface. Both braking pads are fitted with 
thermocouples located at the center of each pad, approximately 0.040" (1 
mm) under the rubbing surface. For examples of the placement of 
thermocouples in the brake rotor and brake pads, see FIGS. 3 and 4, 
respectively. FIG. 3 is a schematic of the thermocouple placement in the 
rotor during the determination MOT and corresponds to a vented front brake 
rotor for 1991 model year Ford Escort. FIG. 4 is taken from SAE J212 and 
is a schematic of the thermocouple placement in the brake pad during the 
determination of the Maximum Operating Temperature or MOT. 
The Maximum Operating Temperature or MOT of a material is determined during 
the fade segments of the modified SAE J212 test and, therefore, the fade 
segments are described in detail. There are three fade segments in the 
test. The test conditions, except for the inertial load, during each fade 
segment are summarized in Table 1. 
TABLE 1 
______________________________________ 
Test Conditions During Fade Segments 
Test Conditions 
______________________________________ 
Initial IRRS 
150 (65.5.degree. C.) 
150 (65.5.degree. C.) 
150 (65.5.degree. C.) 
Temp., .degree.F. 
Initial Speed, mph 
60 (97 km/h) 
60 (97 km/h) 
60 (97 km/h) 
Deceleration, ft/s.sup.2 
15 (4.6 m/s.sup.2) 
15 (4.6 m/s.sup.2) 
15 (4.6 m/s.sup.2) 
No. of stops 
10 15 15 
Cycle Time, s 
35 35 35 
Cooling Air 8 (12.8 km/h) 
8 (12.8 km/h) 
2 (12.8 km/h) 
Speed, mph 
______________________________________ 
An inertial load of at least that specified by Section 5.7, "Test Moment of 
Inertia" of SAE J212 is used during the determination of Maximum Operating 
Temperature or MOT for a particular rotor material. If that inertial load 
is insufficient to cause the failure of the rotor a higher inertial load 
is applied on the rotor until failure is observed. The temperature 
measured at failure corresponds to Maximum Operating Temperature or MOT. 
The tests for determining Maximum Operating Temperature or MOT are 
conducted using compact dynamometers, for example, with DC drives and at 
commercial laboratories (e.g., Link Testing Laboratory and Greening 
Testing Laboratory). The speed, acceleration (or deceleration), torque, 
cooling air speed, cooling air temperature, rotor and pad temperatures are 
continuously monitored and recorded. 
Before a test to determine the Maximum Operating Temperature or MOT of a 
rotor material, the rotor and the mating pads are thoroughly characterized 
for: 
1. weight 
2. dimensions, particularly the rotor thickness 
3. surface roughness 
4. density 
5. microstructure and reinforcement loading 
After the Maximum Operating Temperature or MOT for a rotor material is 
determined, all of the above parameters are remeasured to assess the 
damage and wear to the rotor and the pads. 
The following Examples demonstrate certain preferred fabrication techniques 
for forming brake rotors according to the present invention, however, 
these Examples should be viewed as being illustrative of the invention and 
not be viewed as limiting the scope of the invention as defined in the 
appended claim. 
The following Examples further demonstrate the unexpected superior 
performance of brake rotors made according to the present invention. 
Specifically, never before have metal matrix composites (e.g., especially 
aluminum metal matrix composite materials) and ceramic matrix composite 
materials been fabricated to function as desirable brake rotor materials. 
The present invention is a significant enhancement to the art. 
EXAMPLE 1 
The present Example demonstrates the fabrication of cast brake rotors or 
discs from a metal matrix composite material produced in a "two step" 
process. In a first step, a highly loaded metal matrix composite is 
prepared by spontaneously or pressurelessly infiltrating a matrix metal 
into a permeable mass of filler material and thereafter solidifying the 
matrix metal. In a second step, the formed highly loaded metal matrix 
composite is reheated and dispersed into a melt of second matrix metal. 
The assemblies used to carry out these two steps are depicted 
schematically in FIGS. 1, 2A, 2B, 2C and 2D, respectively. 
Specifically, in reference to FIG. 1, about 25.5 kilograms of a filler 
material mixture 124 comprising by weight about 98% 500 grit (average 
particle diameter of about 17 microns) super strong "39 CRYSTOLON.RTM." 
green silicon carbide particulate (Norton Co., Worcester, Mass., and 
hereinafter "SiCp) and about 2 percent -100 mesh (particle diameter less 
than about 150 microns) magnesium powder (-100 mesh, Hart Metals 
Materials, Rumson, N.J.) was blended for about 15 minutes in an 
approximately 1 cubic foot (28.32 liter) capacity V-blender. 
The interior of a graphite mold 120 having inner dimensions measuring about 
7.25 inches (184 mm) square and about 7 inches (178 mm) high was lined 
with a graphite foil box 122 made from "PERMA-FOIL.TM." graphite foil 
(TTAmerica, Portland, Oreg.). About 4550 grams of the filler material 
mixture 124 were poured into the lined graphite mold 120 and levelled. An 
additional piece of graphite foil 126 made of "PERMA-FOIL.TM." graphite 
foil (TTAmerica, Portland, Oreg.) measuring about 7 inches (178 mm) square 
by about 0.015 inch (0.38 mm) thick and having five through holes 129 
(only three depicted in FIG. 1) was placed on top of the levelled filler 
material mixture 124. A hole in the center of the graphite foil 126 
measured about 1.5 inches (38 mm) in diameter while the four remaining 
holes, one located in the center of each quadrant of the graphite foil, 
measured about 1 inch (25 mm) in diameter. Magnesium powder 128 (+50 mesh, 
Hart Metals) was sprinkled evenly over the top of the exposed filler 
material mixture 124 at each of the five holes. Two ingots of a first 
matrix metal 130 comprising by weight about 10 percent silicon and the 
balance aluminum and each measuring about 6 inches (152 mm) square by 
about 2 inches (51 mm) thick, were stacked on top of the graphite foil 126 
to form a setup. Five additional and substantially equivalent setups were 
then formed. 
The six setups comprising the lined graphite molds 120 (only one depicted 
in FIG. 1) and their contents were then placed into a graphite tray 136 
measuring about 22.25 inches (565 mm) wide by about 42.63 inches (1083 mm) 
long by about 2 inches (51 mm) high to form a lay-up. 
The graphite tray 136 and its contents were placed into a retort lined 
resistance heated furnace. The retort door was closed, and a nitrogen gas 
flow rate of about 70 standard cubic feet per hour (1982 liters per hour) 
was established through the retort chamber at about one pound per square 
inch (0.0703 kilograms per square centimeter) overpressure. The furnace 
and its contents were then heated from about room temperature to about 
200.degree. C. at a rate of about 200.degree. C. per hour; held at about 
200.degree. C. for about 3 hours; heated from about 200.degree. C. to 
about 550.degree. C. at about 150.degree. C. per hour; held at about 
550.degree. C. for about 2 hours; heated from about 550.degree. C. to 
about 790.degree. C. at about 450.degree. C. per hour; held at about 
790.degree. C. for about 16 hours; and cooled from about 790.degree. C. to 
about 680.degree. C. at about 250.degree. C. per hour. During the heating 
sequence and while the nitrogen flow rate was maintained, the matrix metal 
alloy spontaneously or pressurelessly infiltrated the filler material 
mixture to produce a highly loaded metal matrix composite. 
The graphite tray 136 and its contents were retrieved from the furnace at a 
temperature of about 680.degree. C. and placed on a heat sink made from 
graphite plates. The still-molten carcasses of matrix metal were covered 
with a ceramic blanket insulation to establish a temperature gradient 
during cooling to directionally solidify the formed highly loaded metal 
matrix composites. After cooling to substantially room temperature, the 
formed metal matrix composite bodies and the carcasses of matrix metal 
were removed from their respective graphite boats, and the composite 
bodies comprising highly loaded silicon carbide reinforced aluminum metal 
matrix composite (hereinafter "SiCp/Al MMC") were separated from the 
carcasses. 
With reference to FIG. 2A, several second matrix metal ingots weighing 
about 99 kilograms (218 pounds) and comprising by weight about 10 percent 
silicon and the balance aluminum were placed into a silicon carbide 
crucible 200 measuring about 21 inches (533 mm) in inner diameter at the 
top, about 10 inches (254 mm) in inner diameter at the base, and about 26 
inches (660 mm) high. The crucible 200 was in an oil fired remelting 
furnace chamber. Once the second matrix metal ingots had melted to form a 
body of molten second matrix metal 202, a rotary graphite lance (not shown 
in FIG. 2A) was inserted into the bottom of the resultant melt and 
nitrogen gas was flowed through the melt to degas the melt. Then, surface 
dross was scraped from the surface of the melt and about 36.3 kilograms 
(80 pounds) of regularly shaped pieces of highly loaded SiCp/Al MMC 204 
(dried overnight at about 300.degree. C. and preheated to about 
450.degree. C.), formed as described above, were added to the melt. During 
the melting of the initial pieces of the highly loaded SiCp/Al MMC 204, 
additional pieces of the highly loaded SiCp/Al MMC 204 were added to the 
contents of the crucible and melted. A total of about 173 kilograms (381 
pounds) of highly loaded SiCp/Al MMC 204 were added to the body of molten 
second matrix metal 202 in the crucible. During the melting of the highly 
loaded SiCp/Al MMC 204, a preheated stainless steel rod 206 (shown in FIG. 
2A) coated with commercially available mold wash (to minimize any 
interactions between the stainless steel rod 206 and the contents of the 
crucible) and measuring about 1 inch (25 mm) in diameter and about 60 
inches (1524 mm) long was inserted into the crucible and used to disperse 
the highly loaded SiCp/Al MMC 204. The coated stainless steel rod 206 was 
removed from the crucible and, as depicted in FIG. 2B, a mixing unit 208 
was then placed into the crucible, said mixing unit 208 comprising an 
about 6 inch (152 mm) diameter stainless steel dispersion blade (Hockmeyer 
Equipment Co., Harrison, N.J., Style F) coated with plasma sprayed alumina 
(PP-30 by Standard Engineering and Machine Co., Wilmington, Del.) and 
mounted to an about 5/8 inch (16 mm) diameter, 36 inch (914 mm) long 
shaft. While maintaining the temperature of the crucible and its contents 
at about 650.degree. C., the mixing unit 208 was rotated at about 1050 rpm 
for about 1 hour by using an about 1.5 horsepower air motor (Eclipse 
System Inc., Franklin, N.J., Model No. 9-4300-14A) attached thereto (not 
shown in FIG. 2b) and located external to the furnace thereby forming a 
diluted SiCp-matrix metal suspension 210, depicted in FIG. 2C. The 
suspension 210 comprised the former highly loaded SiCp/Al MMC 204 now 
substantially uniformly dispersed within the second matrix metal. The 
mixing unit 208 was removed from the SiCp-matrix metal suspension 210 and 
the oxide fillers on top of the suspension was removed by skimming. A 
portion of the metal matrix composite suspension 210 was cast, using a 
ladle 220, as depicted in FIG. 2D, into about fifteen conventional sand 
molds to cast brake rotors or disc for the 1991 model year "ESCORT" 
compact size automobile. After cooling to substantially room temperature, 
the about fifteen cast brake rotors or disc comprising the SiCp/Al MMC 
were removed from the molds. The loading of the silicon carbide filler 
material in each of the cast SiCp/Al MMC brake rotors or disc was about 30 
percent by volume. 
EXAMPLE 2 
The present Example demonstrates, among other things, a method for forming 
a metal matrix composite brake rotor or disc with a Maximum Operating 
Temperature (MOT) of at least about 482.degree. C. (900.degree. F.). The 
present Example presents the method for forming an aluminum oxide 
particulate reinforced aluminum metal matrix composite brake rotor or 
disc. The formation of the aluminum oxide particulate reinforced aluminum 
metal matrix composite (also designated "Al.sub.2 O.sub.3 p MMC") rotor or 
disc includes, among other things, filler material preparation, preform 
formation, and spontaneous infiltration of the preform with a molten 
matrix metal. The present Example also presents the Maximum Operating 
Temperature (MOT) of the Al.sub.2 O.sub.3 p/Al MMC brake rotor or disc as 
determined by using the modified SAE J212 testing procedure. 
A pressing mixture comprising by weight about 94.33 percent C-73 unground 
aluminum oxide (Alcan Chemicals, a division of Alcan Aluminum Corporation 
Cleveland, Ohio and hereinafter "C-73 "Al.sub.2 O.sub.3 p"). about 2.83 
weight percent -325 mesh (particle diameter less than about 45 microns) 
ground magnesium powder (Hart Corporation, Tamaque, Pa., and hereinafter 
"Mgp"), about 2.83 weight percent "LANXIDE" CERASET.RTM.-SN" 
polyureasilazane pre-ceramic polymer (Lanxide Corporation, Newark, Del.) 
and 0.01 percent "DICUP.TM.-" dicumyl peroxide (Hercules Incorporated, 
Wilmington, Del.) was prepared. 
The preparation of a pressing mixture included the preparation of an C-73 
Al.sub.2 O.sub.3 p-Mgp mixture. Specifically, about 6060 grams of a 
material mixture comprising by weight of about 39.53 percent C-73 Al.sub.2 
O.sub.3 p (Alcan Chemicals of Alcan Aluminum Corporation, Cleveland, 
Ohio), about 1.19 percent -325 mesh (particle diameter less than about 45 
microns) Mgp (Hart Corporation, Tamaque, Pa.) and about 59.29 percent 3/8 
inch (9.5 mm) diameter by about 3/8 inch (9.5 mm) long alumina milling 
media were placed into an about 2-gallon (7.6 liter) capacity ceramic 
milling jar (Standard Ceramic Supply Co., Pittsburgh, Pa.). The ceramic 
milling jar and its contents were placed on a jar mill (ROMCO, 
Poughkeepsie, N.Y.) for about 2 hours. The ceramic jar was then removed 
from the jar mill and its contents were passed through a 20 mesh (average 
opening of about 850 microns) sieve to separate the alumina milling media 
from the C-73 Al.sub.2 O.sub.3 p-Mgp mixture. The C-73 Al.sub.2 O.sub.3 
p-Mgp mixture was then set aside. 
Simultaneously, a pre-ceramic polymer binder was prepared. Specifically, 
about 120 grams of a mixture comprised by weight of about 99.5 percent 
"LANXIDE.TM. CERASET.TM.-SN" polyureasilazane pre-ceramic polymer and 
about 0.5 percent "DICUP.RTM.-R" dicumyl peroxide were combined in a 
"NALGENE.RTM." 1-pint (0.47 liter) plastic jar. The sealed plastic jar and 
its contents were then placed on a jar mill and roll mixed for about 30 
minutes, that is, until the dicumyl peroxide had substantially completely 
dissolved into polyureasilazane pre-ceramic polymer. The contents of the 
plastic jar were then ready to be combined with the C-73 Al.sub.2 O.sub.3 
p-Mgp mixture as a binder. 
About 2060 grams of the C-73 Al.sub.2 O.sub.3 p-Mgp mixture were then 
placed into the mixing bowl of a Model RV02 "EIRICH.RTM." mixer (Eirich 
Machines, Maple, Ontario, Canada). The speed of the mixing paddles was 
then set at mixing speed setting 1, low. Simultaneously, the about 120 
grams of the binder comprising the pre-ceramic polymer and the dicumyl 
peroxide were placed into a syphon cup of a Model 62 Binks spray gun 
(Binks Corporation, U.S.A.). As the C-73 Al.sub.2 O.sub.3 p-Mgp mixture 
was agitated in the mixing bowl, about 40 grams of the binder were sprayed 
onto the C-73 Al.sub.2 O.sub.3 p-Mgp mixture at a rate of about 13 grams 
per minute. The air pressure supply to the spray gun was at about 40 psi 
(276 kilopascal). After the binder had been sprayed onto the C-73 Al.sub.2 
O.sub.3 p-Mgp mixture, the mixer was turned off. The sidewalls of the 
mixing bowl were then scrapped so that the C-73 Al.sub.2 O.sub.3 
p-Mgp-binder mixture was in the bottom of the mixing bowl. The mixing bowl 
was then covered and the mixer was set at a 4 minutes. The C-73 Al.sub.2 
O.sub.3 p-Mgp-binder mixture was then screened through a 20 mesh (average 
opening of about 850 microns) sieve which produced a pressing mixture. The 
pressing mixture was then placed into a sealable plastic bags (e.g., 
"ZIPLOC.RTM." plastic bags) for storage until it could be used for preform 
formation. 
A four-piece pressing mold with major components machined from Grade ATJ 
graphite (Union Carbide Corp., Cleveland, Ohio) was fabricated to form 
preforms from the pressing mixture. The pressing mold 501 is depicted in a 
cross-sectional schematic in FIG. 5 and comprised a base plate 502, a 
mandrel 504, a mold wall 503, and a mandrel extension 505. The base plate 
502, the mandrel 504 and the mold wall 503 were machined from Grade ATJ 
graphite; however, the mold mandrel extension 506 was machined from 
commercially available aluminum. 
Base plate 502 had an outer diameter measuring about 13 inches (330 mm), an 
inner diameter of about 1.75 inches (44.5 mm) and a height of about 0.5 
inch (13 mm). The base plate 502 also had a lip measuring about 0.25 inch 
(6.4 mm) high and extending about 0.75 inch (19 mm) in from the 13 inch 
(330 mm) outer diameter toward the inner diameter. The machined surface 
finish of the base plate 502 was about 63 rms. 
Mandrel 504 comprised a base plate engaging portion, a hub small diameter 
defining portion and a hub large diameter defining portion. The hub small 
diameter defining portion was located between the base plate engaging 
portion and the hub large diameter defining portion. The three portions 
also shared a common axis of rotational symmetry. The base plate engaging 
portion measured about 1.75 inches (44.5 mm) in diameter and was about 0.5 
inch (13 mm) high. The hub small diameter defining portion measured about 
2.125 inches (53.98 mm) in diameter and about 0.46 inch (11.7 mm) high. 
The hub large diameter defining portion had a diameter measuring about 
4.32 inches (109.7 mm) at about 2.75 inches (70 mm) at the end of the 
mandrel 504 farthermost from the base engaging portion. The hub large 
diameter defining portion also had an about 5.degree. draft extending from 
the 4.32 inches (109.7 mm) end toward the hub small diameter defining 
portion. 
Mold wall 502 comprised three defining diameters including an outer 
diameter, an intermediate diameter and an inner diameter. The outer 
diameter and the intermediate diameter defined a thin wall portion 
measuring about 4.25 inches (108 mm) high while the outer diameter and the 
inner diameter defined thick wall portion measuring about 1.25 inches 
(31.8 mm) high. The intermediate diameter mold wall 502 measuring about 
9.63 inches (245 mm) of was measured about 1.25 inches (31.8 mm) from the 
portion of the mold wall 502 that engaged the base plate 502. An about 
2.degree. draft was machined on the inner diameter of the thick wall 
portion and the inner diameter of the thin wall portion of the mold wall 
502. 
The mold mandrel extension 505, as mentioned earlier, was machined from 
commercially available aluminum. Mold mandrel extension 505 had a diameter 
measuring about 4.32 inches (109.7 mm) and a height of about 0.5 inch (13 
mm). Machined in the center of mold mandrel extension 505 was alignment 
pin 506 measuring about 0.25 inches (6.4 mm) in diameter. 
Base plate 502, mandrel 504, mold wall 503 and mold mandrel extension 506 
were assembled as schematically depicted in FIG. 5 in preparation for 
pressing a preform from the pressing mixture comprising the C-73 Al.sub.2 
O.sub.3 p-Mgp-binder mixture. 
In preparation for pressing a green preform, pressing mold 501 was lined 
with "PERMAFOIL.TM." graphite foil (TTAmerica, Portland, Oreg.) measuring 
about 0.010 inch (0.25 mm) thick and designated in FIG. 5 with by numerals 
507, 508, 509, 510, 511, 512 and 513. The graphite foil lining of pressing 
mold 501 facilitated the release of the preform 514 formed from pressing 
mold 501. 
After the pressing mold 501 had been lined with the graphite foil, some 
pressing mixture was placed into the lower portion of pressing mold 501. 
The press mixture was gently handpacked around the hub smaller diameter 
defining portion of mandrel 504. Additional pressing mixture was placed 
into the pressing mold 501. The additional pressing mixture was then first 
gently packed using a commercially available foam brush, then leveled and 
finally tamped using a tamping tool machined from aluminum. The pressing 
mixture was then leveled to coincide with the top surface of mold mandrel 
extension 505. An annulus 515 comprising "PERMAFOIL.TM." graphite foil 
(TTAmerica, Portland, Oreg.) was then placed onto the pressing mixture. A 
punch 516, also having an annulus shape, and machined from commercially 
available aluminum, was engaged with the annulus 515 within the pressing 
mold 501. Four load transferring rods 517 were then attached to punch 516. 
The load transferring members 517 were evenly spaced along the annulus of 
punch 516. Pressing mold 501 and its contents were then placed on a Carver 
50-ton laboratory press (Fred S. Carver, Inc., Menome Falls, Wis.). A load 
was applied to the pressing mixture by engaging the platens of the 
laboratory press with the mold base 502 and the four load transferring 
rods 517. The load was adjusted to produce a pressure of about 100 psi 
(689.5 kPa) on the pressing mixture and was maintained for about 30 
seconds. 
After the load was removed from the pressing mixture, the pressing mold 501 
and its contents were placed into an air atmosphere furnace to cure the 
pre-ceramic polymer binder within the pressing mixture. The curing was 
effected by heating the furnace and it contacts at a rate of about 
100.degree. C. per hour to about 150.degree. C., holding the furnace and 
its contents at about 150.degree. C. for about 2 hours and cooling the 
furnace and its contents to about 85.degree. C. at about 100.degree. C. 
per hour. Pressing mold 501 and its contents were then removed from the 
air atmosphere furnace. While still at about 85.degree. C., the pressing 
mold 501 was disassembled and preform 514 was removed. The shape of 
preform 514 corresponded to the shape of a brake rotor or disc. Preform 
514 was comprised of the C-73 Al.sub.2 O.sub.3 p-Mgp mixture bonded with 
cured pre-ceramic polymer. Preform 514 was stored at about 85.degree. C. 
prior to incorporation into a lay-up to form the C-73 Al.sub.2 O.sub.3 
p/Al MMC brake rotor or disc. 
Preform 514 was infiltrated with an aluminum matrix metal using the 
"PRIMEX.TM." pressureless metal infiltration process to form a C-73 
Al.sub.2 O.sub.3 p/Al MMC brake rotor or disc. A cross-sectional schematic 
of the lay-up 601 used to infiltrate preform 514 is illustrated in FIG. 6. 
Lay-up 601 comprised preform 514, catch tray 602, setup tray 603, setup 
tray lining 604, small preform support ring 605, large preform support 
ring 606, barrier powder 607, barrier mixture 608, barrier coating 609 
applied to the outer surfaces of preform 514, cylinder 610, support boxes 
611, matrix metal containment 612, sealing beads 613, matrix metal guide 
cone 614, shim 615, matrix metal supply tray 617, matrix metal supply tray 
lining 616 and matrix metal ingots 618. 
The inner dimensions of catch tray 602 measured about 21.25 inches (539.8 
mm) long, 12.5 inches (317.5 mm) wide and about 2 inches (51 mm) high. 
Catch tray 602 had walls of two thicknesses. The walls along the 21.25 
inch (539.8 mm) sides measured about 0.25 inch (6.4 mm) thick, and the 
walls along the about 11.5 inch (305 mm) sides measured about 3/8 inch 
(9.5 mm). 
Setup tray 603 measured about 19.5 inches (495.3 mm) long, about 9.875 
inches (250.8 mm) wide and about 2 inches (51 mm) deep. Unlike catch tray 
602, setup tray 603 had walls of a single thickness. The walls measured 
about 0.25 inch (6.4 mm) thick. 
Setup tray lining 604 within setup tray 603 comprised "GRAFOIL.RTM." 
graphite foil (Union Carbide Corporation, Cleveland, Ohio) measuring about 
0.015 inch (0.38 mm) thick. Setup tray lining 604 substantially covered 
the inner surfaces of setup tray 604. 
Small preform support ring 605 and large preform support ring 606 comprised 
"PERMAFOIL.TM." graphite foil (TTAmerica, Portland, Oreg.) measuring about 
0.01 inch (0.25 mm) thick. Strips of graphite foil measuring about 0.25 
inch (6.4 mm) high were cut and shaped into rings corresponding 
substantially to the inner and outer diameter of the hub portion of the 
preform 514 (see FIG. 6 for clarification). Small preform support ring 605 
and large preform support ring 606 were placed concentrically within setup 
tray 603 and on setup tray lining 604 to support preform 514 during the 
pressureless metal infiltration process. 
Graphite powder 607 comprised "LONZA.RTM." KS 44 graphite powder (Lonza, 
Inc., Fairlawn, N.J.). 
Barrier coating 609 was applied to preform 514, as is discussed in more 
detail below, prior to incorporating preform 514 into lay-up 601. Barrier 
coating 609 comprised at least one of "AERODAG.RTM.-G" (Acheson Colloids, 
Port Huron, Mich.) and "DAG.RTM." 154 colloidal graphite (Acheson 
Colloids, Port Huron, 
Barrier mixture 608 comprised by weight about 95 percent 90 grit (average 
particle diameter of about 216 microns) "38 ALUNDUM.RTM." alumina (Norton 
Co., Worcester, Mass.) and about 5 percent F-69 glass frit (Fusion 
Ceramics, Inc., Carllton, Ohio). 
Containment cylinder 610 was formed from a piece of "GRAFOIL.RTM." graphite 
foil (Union Carbide Corporation, Cleveland, Ohio) measuring about 39.4 
inches (1000 mm) long, 3.3 inches (80 mm) high and about 0.015 inch (0.38 
mm) thick. Containment cylinder 610 was placed concentrically around 
preform 514 in a manner as depicted in FIG. 6. The graphite foil 
comprising containment cylinder 610 was secured around preform 514 using 
commercially available staples by stapling the graphite foil. 
Support boxes 611 comprised open ended boxes machined from commercially 
available graphite and measuring about 6 inches (152 mm) square by about 
2.75 inches (69.9 mm) high. 
Matrix metal containment wall 612 comprised "PERMAFOIL.TM." graphite foil 
(TTAmerica, Portland, Oreg.) material formed into a ring measuring about 1 
inch (25.4 mm) tall and placed concentrically with containment cylinder 
610 to form a gap measuring about 0.25 inch (6.3 mm) wide along the 
outermost perimeter of preform rotor 514. 
Sealing beads 613 comprised "DAG.RTM." 154 colloidal graphite (Acheson 
Colloids, Port Huron, Mich.) applied at the outermost perimeter of preform 
514 and along the intersection of preform 514 and containment cylinder 
610. Barrier material mixture 608 was then placed in the space between 
matrix metal containment 612 and containment cylinder 610. 
Matrix metal guide cone 614 comprised "PERMAFOIL.TM." graphite foil 
(TTAmerica, Portland, Oreg.). Matrix metal containment cone 614 was 
fabricated to facilitate efficient use of molten matrix metal in contact 
with preform 514 during the pressureless metal infiltration process. 
Shim 515 was in engaging contact with matrix metal guide cone 614 and 
matrix metal supply tray 617 and comprised "PERMAFOIL.TM." graphite foil 
(TTAmerica, Portland, Oreg.). 
The inner dimension of matrix metal supply tray 617 measured about 13.25 
inches (337 mm) long, about 8.5 inches (216 mm) wide and about 1.5 inches 
(38 mm) deep. As catch tray 602 and setup tray 603, the matrix metal 
supply tray 617 had walls with two thicknesses. The wall along the 13.25 
inch (337 mm) sides measures 0.25 inch (6.3) thick and the walls along the 
8.5 inch (216 mm) sides were 3/8 inch (9.5 mm) thick. Within the bottom of 
matrix metal supply tray 617 were two holes each having about 1 inch (25.4 
mm) diameter. The centers of holes were located along the intersection of 
diagonals in each half of matrix metal supply tray 617. The inner surface 
of supply tray 617 was lined with matrix metal supply tray lining 616. The 
supply tray lining comprised "PERMAFOIL.TM." graphite foil (TTAmerica, 
Portland, Oreg.) having holes measuring about 1 inch (25.4 mm) diameter 
and coinciding with the holes within matrix metal supply tray 617. 
To prepare preform 514 for incorporation in lay-up 601, all of the surfaces 
of preform 514 were substantially completely sprayed with a barrier 
coating 609 comprising "AERODAG.RTM." G colloidal graphite (Acheson 
Colloids, Port Huron, Mich.). Three applications of "DAG.RTM." 154 
colloidal graphite (Acheson Colloids, Port Huron, Mich.) were brushed to 
the surfaces of preform 514 which would face away from matrix metal ingots 
618 when preform 514 was incorporated into lay-up 601. The outer perimeter 
of preform 514 was also brush coated. Two applications comprising 
"DAG.RTM." 154 colloidal graphite were brushed onto the surfaces of 
preform 514 facing matrix metal ingots 518 as depicted in FIG. 6. A third 
application comprising "DAG.RTM." 154 was brushed onto the surfaces having 
two applications. While the surfaces were still moist, -50 +100 mesh 
(having particle diameters between about 150 and 300 microns) magnesium 
powder was sprinkled onto the surface. This -50 +100 mesh magnesium powder 
(Hart Co., Tamaqua, Pa.) is designated as 619 in FIG. 6. 
After the lay-up 601 was formed, as illustrated in FIG. 6, and comprising a 
preform 514 weighing about 2000 grams and two matrix metal ingots 618 
together weighing about 3500 grams and comprising by weight about 1 weight 
percent magnesium and the balance aluminum, the lay-up 601 and its 
contents were placed into a controlled atmosphere furnace. The furnace 
door was closed, and the furnace and its contents were evacuated to about 
30 inches (762 mm) of mercury. The vacuum was ended when nitrogen gas 
flowing at about 10 liters per minute was introduced into the furnace. The 
furnace and its contents were then heated from about 150.degree. C. to 
about 250.degree. C. at about 100.degree. C. per hour, held at about 
250.degree. C. for about an hour, heated from about 250.degree. C. to 
about 450.degree. C. at about 100.degree. C. per hour, held at about 
450.degree. C. for about 5 hours, heated from about 450.degree. C. to 
about 800.degree. C. at about 100.degree. C. per hour and held at about 
800.degree. C. for about 6 hours. Throughout the entire heating procedure, 
a nitrogen flow rate of about 10 liters per hour was maintained. After 
about 6 hours at about 800.degree. C., the nitrogen flow rate was 
interrupted and the lay-up 601 was removed from the furnace and 
transferred to a chill plate. The matrix metal supply tray 617 was 
removed. A remaining molten matrix metal reservoir was then covered with 
an about 1 inch (25.4 mm) hot topping mixture comprising "FEEDOL" 9 
exothermic hot topping compound (Feesco Corporation, Cleveland, Ohio). The 
matrix metal that had infiltrated preform 514 was then allowed to solidify 
during cooling to about room temperature. At about room temperature, 
lay-up 601 was disassembled further and it was revealed that the matrix 
metal had infiltrated preform 514 to form a near net shape C-73 Al.sub.2 
O.sub.3 p/Al MMC composite rotor or disc. 
The resulting metal matrix composite body was then machined to the 
specification of front brake rotors or discs compatible with the 1991 
Model year Escort automobile (Ford Motor Co., Detroit, Mich.). The 
surfaces of the brake rotor or disc that would be in contact with braking 
pads were machined to a surface finish of 63 rms. The thickness of the 
braking disc measured about 0.8 inch (20 mm). 
The brake rotor or disc was subjected to the modified SAE J212 brake system 
dynamometer test as described in the "Summary of the Invention" and the 
"Detailed Description of the Invention" sections of the present 
application. The results of the test indicated that the C-73 Al.sub.2 
O.sub.3 p/Al MMC brake rotor or disc made by the method of the present 
Example had an unexpected Maximum Operating Temperature (MOT) of about 
532.degree. C. (990.degree. F.). 
Thus, the present Example demonstrates that a C-73 Al.sub.2 O.sub.3 p/Al 
MMC brake rotor or disc (i.e., C-73 UNG alumina embedded by an aluminum 
magnesium matrix metal) unexpectedly high temperature performance 
capability. Furthermore, these high temperature performance or operation 
capabilities indicate that the brake rotor or disc formed by the methods 
of the present Example are superior to the commercially available metal 
matrix composite brake rotors or discs. Additionally, these results 
indicate that brake rotors of disc made by the methods of the present 
Example can be subjected to higher inertial loading than commercially 
available metal matrix composite brake rotors or disc. 
EXAMPLE 3 
The present Example demonstrates, among other things, a method for forming 
a preform shaped as a brake rotor or disc and spontaneously or 
pressurelessly infiltrating the shaped preform with molten aluminum alloy 
to form a silicon carbide particulate reinforced aluminum metal matrix 
composite (hereinafter in this Example "SiCp/Al MMC") brake rotor or disc 
that exhibits unexpected superior performance characteristics in 
accordance with the present invention. Furthermore, the present Example 
demonstrates that a SiCp/Al MMC brake rotor or disc made in accordance 
with the present Example has a Maximum Operating Temperature (MOT) of at 
least about 482.degree. C. (900.degree. C.). 
Methods similar to the methods for forming the C-73 Al.sub.2 O.sub.3 p/Al 
MMC brake rotor or disc of Example 2 were used to fabricate the rotor of 
the present Example. The methods of the present Example and Example 2 were 
identical in at least the following respects: 1) a pressing mixture was 
prepared; 2) the pressing mixture was formed into a shaped green preform 
in a pressing mold 501 as depicted in FIG. 5; 3) the green preform was 
heat treated to form a preform 514 for incorporation into a lay-up similar 
to the lay-up 601 depicted in FIG. 6; 4) the preform 514 was infiltrated 
by molten matrix metal by the "PRIMEX.TM." pressureless metal infiltration 
process; and 5) the resultant brake rotor or disc was machined prior to 
subjecting the brake rotor or disc to the modified SAE J212 test to 
determine the Maximum Operating Temperature (MOT). 
The methods of the present Example and Example 2 differed in at least the 
following respects: 1) the filler material comprised 360 grit (average 
particle diameter of about 27 microns) "39 CRYSTOLON.RTM." green silicon 
carbide (Norton Co., Worcester, Mass.); 2) the binder comprised an 
organic-inorganic binder system comprising a phenolic resin, a diphenyl 
phosphite and a colloidal silica; 3) the pressed preform was fired at 
elevated temperatures to at least partially oxidize the silicon carbide 
filler to give sufficient strength to the preform for handling during 
incorporation into the infiltration lay-up; 4) the matrix metal comprised 
an aluminum silicon-magnesium alloy; and 5) the infiltration lay-up did 
not include the matrix metal supply tray 617 as depicted in FIG. 6, but 
rather the matrix metal ingot contracted the preform. 
The following discussion elaborates on the methods of the present Example 
which differ from the methods of Example 2. 
A first binder mixture was prepared by adding about 7.2 grams of diphenyl 
phosphite (Aldrich Chemical Co., Milwaukee, Wis.) and about 30 grams of 
"NYACOL.RTM." 1034A colloidal silica (Nyacol Prod. Inc., Ashland, Mass.) 
to a plastic jar. After thoroughly mixing the contents of the jar, the 
first binder mixture was allowed to sit at room temperature for about 30 
minutes. 
A pressing mixture was prepared by placing about 3000 grams of 360 grit "39 
CRYSTOLON.RTM." green silicon carbide particulate (Norton Co., Worcester, 
Mass.) and about 60 grams of a second binder comprising the developmental 
"DURITE.TM." SL-870A liquid phenolic resin (Bordon Chemical, Columbus, 
Ohio), into the mixing bowl of an Eirich.RTM. mixer (Model #RV02, Eirich 
Machines, Maple, Ontario, Canada). The mixer was turned on low, mixing 
speed setting 1, and the mixture was subjected to mixing for about 1 
minute. After about 1 minute, the mixer was turned off and the mixture was 
scraped from the sides and bottom of the mixing bowl towards the center of 
the bowl. Then the mixer was turned onto high, mixing speed setting 2, for 
about 1 minute. After about 1 minute, the mixer was turned off, the 
mixture was scraped from the sides and bottom of the mixer bowl towards 
the center of the bowl and the first binder mixture comprising the 
diphenyl phosphite-"NYACOL.RTM." 1034A colloidal silica mixture was added 
to the contents of the mixing bowl. The mixer was turned onto high, mixing 
speed setting 2, for about 2 minutes. After about 2 minutes, the mixer was 
turned off and the contents of the mixer bowl was sieved through a 14 mesh 
(average openings of about 1400 microns) sieve utilizing a RO-TAP.RTM. 
testing sieve shaker (12 inch model, W. S. Tyler, Gastovia, N.C.) to 
ultimately produce the pressing mixture. 
Utilizing a metal spoon, a quantity of the pressing mixture was then placed 
into the pressing mold 501 depicted in FIG. 5 and described in Example 2. 
The pressing mixture was leveled within the mold utilizing a soft bristle 
brush and a straight edge. The pressing mixture within the pressing mold 
501 was then compacted into a green preform by subjecting the mixture to a 
pressure of about 100 psi (689.5 kPa). After subjecting the pressing 
mixture to a pressure of about 100 psi (689.5 kPa) for about 1 minute, the 
pressure was released and the pressing mold 501 and its contents were 
placed into an air atmosphere furnace at temperature of about 150.degree. 
C. After remaining in the furnace for about 2 hours, the pressing mold 501 
and its contents were removed from the air atmosphere furnace, the 
pressing mold 501 was disassembled and a green preform was recovered. 
A bed of 36 grit (average particle diameter of about 710 microns) "38 
ALUNDUM.RTM." alumina (Norton Company, Worcester Mass.) was poured into a 
refractory boat and leveled. The green preform was placed on the bed of 36 
grit "38 ALUNDUM.RTM." alumina. The refractory boat and its contents were 
placed into an air atmosphere furnace at a temperature of about 
100.degree. C. The temperature within the furnace was raised from about 
100.degree. C. to about 680.degree. C. at about 100.degree. C. per hour, 
held at about 680.degree. C. for about 5 hours, heated from about 
680.degree. C. to about 1200.degree. C. at a rate of about 100.degree. C. 
per hour. After maintaining a furnace temperature of about 1200.degree. C. 
for about 5 hours, the furnace and its contents were naturally cooled to 
about 150.degree. C. and the refractory boat and its contents were removed 
from the furnace and allowed to cool to about room temperature, thus 
producing a preform 514. 
The preform 514 was incorporated into a lay-up substantially the same as 
the lay-up 601 depicted in FIG. 6 and discussed in Example 2. However, and 
as discussed earlier, the matrix metal ingots 618 contacted the preform 
514, no -50, +100 mesh Mg powder was applied the surface of the brake 
rotor or disc preform. The weight of preform 514 comprising fired silicon 
carbide was about 3000 grams. The weight of the matrix metal was about 
4100 grams. The matrix metal used for pressurelessly infiltrating preform 
514 comprised by weight about 12 percent silicon, about 5 percent 
magnesium and the balance comprised aluminum. 
The lay-up was then placed into a controlled atmosphere vacuum furnace at a 
temperature of about 150.degree. C. The furnace and its contents were 
evacuated to about 30 inches (762 mm) Hg and backfilled with nitrogen gas 
to about atmospheric pressure. The furnace and its contents were evacuated 
a second time to about 30 inches (762 mm) Hg and backfilled with nitrogen 
gas to about atmospheric pressure and a nitrogen gas flow rate of about 10 
liters per minute was established through the furnace. 
The furnace temperature was increased from about 150.degree. C. to about 
825.degree. C. at a rate of about 100.degree. C. per hour. After 
maintaining a temperature of about 825.degree. C. for about 20 hours, the 
lay-up was removed from the furnace and treated substantially in 
accordance with the methods of Example 2. 
At room temperature, the lay-up was disassembled to reveal that the 
aluminum matrix metal had spontaneously infiltrated the preform 514 to 
form a near-net shape brake rotor or disc. After the brake rotor or disc 
was machined to the specification for a front brake rotor or disc for a 
1991 model year "ESCORT" compact car as described in Example 2, the brake 
rotor or disc was subjected to testing according to the modified SAE J212 
method. The results of that test indicated that the Maximum Operating 
Temperature for a rotor made according to the methods of the present 
Example was about 498.degree. C. (928.degree. F.). 
While the preceding discussion includes very particular disclosures, 
various modifications to the disclosure should occur to an artisan of 
ordinary skill, and all such modifications should be considered to be 
within the scope of the claims appended hereto. 
EXAMPLE 4 
The present Example demonstrates the fabrication of cast brake rotors or 
discs from a metal matrix composite material produced in a "three step" 
process. The metal matrix composite brake rotors or discs made in 
accordance with the methods of the present Example comprised composites 
having filler loadings ranging by volume percent from about 15 percent to 
about 30 percent at about 5 percent increments. In a first step, a billet 
comprising highly loaded metal matrix composite integrally attached to 
excess matrix metal was prepared by spontaneously or pressurelessly 
infiltrating a sufficient amount of molten matrix metal into a permeable 
mass of filler material and solidifying the matrix metal. In a second 
step, the billet comprising the highly loaded metal matrix composite 
integrally attached to excess matrix metal was reheated above the melting 
temperature of the matrix metal. The filler material of the highly loaded 
portion of the billet was then dispersed homogeneously throughout the 
molten matrix metal, which included some additional matrix metal to 
produce a lower loaded metal matrix composite. Some of the assemblies for 
carrying out the first and second steps were substantially the same as 
those depicted schematically in FIGS. 1, 2A, 2B, 2C and 2D. Some 
additional assemblies for carrying out the fabrication process are 
depicted in FIGS. 7, 8, 9A, 9B and 10. In a third or final step, the lower 
loaded metal matrix composite was remelted and either cast directly into a 
sand mold to make brake rotors or discs or dispersed further with 
additional matrix metal before casting into a sand molds to make brake 
rotors or discs. 
About 25.5 kilograms of a filler material mixture comprising by weight 
about 98% 500 grit (average particle diameter of about 16 microns) round, 
strong "39 CRYSTOLON.RTM." green silicon carbide particulate (Norton Co., 
Worcester, Mass., and hereinafter "SiCp") and about 2 percent -325 mesh 
(particle diameter less than about 45 microns) magnesium powder (Hart 
Metals Materials, Rumson, N.J.) were blended for about 15 minutes, but no 
more than about 17 minutes, under an argon-oxygen gas mixture comprising 
about 2 volume percent oxygen and the balance argon in an approximately 1 
cubic foot (28.32 liter) capacity V-blender. This procedure was repeated 
to produce a sufficient quality of filler material mixture to be used to 
form billets. 
The interior of a graphite mold having inner dimensions measuring about 
7.25 inches (184 mm) square and about 7 inches (178 mm) high was lined 
with a box comprising "PERMA-FOIL.TM." graphite foil (TTAmerica, Portland, 
Oreg.). About 4550 grams of the filler material mixture were poured into 
the lined graphite mold and levelled. About 5.4 grams of -50, +100 mesh of 
(particle diameters between about 150 microns and 300 microns) magnesium 
powder (Hart Corporation, Tamaque, Pa.) were sprinkled evenly over the top 
of the exposed surface of the leveled filler material mixture. Two ingots 
of matrix metal comprising by weight about 10 percent silicon and the 
balance aluminum (nominally an Aluminum Association Alloy 360), each 
measuring about 6 inches (152 mm) square by about 2 inches (51 mm) thick 
and having a combined weight of about 5460 grams, were stacked on the 
leveled filler material mixture to form a setup. Five additional and 
substantially equivalent setups were then formed. The six setups 
comprising the lined graphite molds and their contents were placed into a 
graphite tray measuring about 22.25 inches (565 mm) wide, about 42.63 
inches (1083 mm) long and about 2 inches (51 mm) high to form a lay-up. 
The lay-up comprising the graphite tray and its contents were placed into a 
retort lined resistance heated furnace. After the retort door was closed, 
a nitrogen gas flow rate of about 70 standard cubic feet per hour (1982 
liters per hour) was established through the retort chamber. The pressure 
within the retort chamber was maintained at about one pound per square 
inch (6.895 kPa) above atmospheric pressure. The furnace and its contents 
were then heated from about room temperature to about 200.degree. C. at a 
rate of about 200.degree. C. per hour; held at about 200.degree. C. for 
about 3 hours; heated from about 200.degree. C. to about 550.degree. C. at 
about 150.degree. C. per hour; held at about 550.degree. C. for about 2 
hours; heated from about 550.degree. C. to about 790.degree. C. at about 
450.degree. C. per hour; held at about 790.degree. C. for about 16 hours; 
and cooled from about 790.degree. C. to about 680.degree. C. at about 
250.degree. C. per hour. During the heating sequence and while the 
nitrogen flow rate was maintained, the matrix metal melted and 
spontaneously or pressurelessly infiltrated the filler material mixture to 
produce six substantially identical billet comprising highly loaded metal 
matrix composite integrally attached to excess matrix metal. 
The graphite tray and its contents were removed from the furnace at a 
temperature of about 680.degree. C. and placed on a heat sink comprising 
graphite slabs. The excess matrix metal of each setup, which was molten, 
was covered with a commercially available blanket of ceramic insulation to 
establish a temperature gradient during cooling to directionally solidify 
and form billets comprising highly loaded metal matrix composite 
integrally attached to excess matrix metal. After cooling to substantially 
room temperature, the formed billets were removed from their respective 
graphite boats. The above procedure was repeated to produce a stockpile of 
billets to be used as feedstock to produce lower loaded metal matrix 
composite ingots. 
Equipment for producing the lower loaded metal matrix composite is depicted 
schematically in FIGS. 2A, 28, 2D, 7, 8, 9A, 9B and 10. 
FIG. 10 depicts an apparatus 1001 comprising a furnace cover 1002 
supporting baffles 801. Furnace cover 1002 was formed from 11 gauge 304 
stainless steel. Furnace cover 1002 comprised halves each having an outer 
diameter of about 28 inches (712 mm) and an inner diameter of about 8 
inches (264 mm). Each half of furnace cover 1002 incorporated two slots 
measuring about 3 inch (76 mm) long and about 3/4 inch (19 mm) wide to 
accommodated baffles 801. The slots were located along a radius about 5.75 
inches (146 mm) from the axis of rotational symmetry of furnace cover 
1002. The slot spacing was set such that line segments parallel to the 3 
inch (76 mm) sides of each slot were perpendicular. Each half of furnace 
cover 1002 had a thickness of about 1.25 inches (31.8 mm) which was formed 
by welding about 14 gauge 314 stainless steel strips along its inner and 
outer diameter. A cover for the hole in furnace cover 1002 was fabricated 
from a piece of 14 gauge 314 stainless steel measuring about 10 inches 
(254 mm) square with a slot measuring about 1 inch (25.4 mm) wide and 
extending from one side of the cover to the center of the cover. This 
cover aligned with the hole in furnace cover 1002 defined by its 8 inch 
(204) inner diameter while accommodating the rotating shafts which 
supported the rotating tools used at least during the dispersion step for 
forming lower loaded metal matrix composite bodies. 
Baffles 801 incorporated in apparatus 1001 were machined from graphite to 
the configuration depicted in FIG. 8. Prior to incorporation, baffles 801 
were subjected to a coating process described commonly owned U.S. Pat. No. 
5,242,710, issued Sep. 7, 1993, from U.S. patent application Ser. No. 
07/880,479, in the names of Terry Dennis Claar et al. and entitled 
"Methods for Making Self-Supporting Composite Bodies and Articles Produced 
Thereby". The subject matter of U.S. Pat. No. 5,242,710 is hereby 
incorporated by reference in its entirety. The process described in U.S. 
Pat. No. 5,242,710 was used to produce a titanium carbide coating 802 on 
substantially all the surfaces of baffle 801. The graphite substrate 
comprised Grade AXF-5Q graphite (POCO Inc., Decatur, Tex.). To produce the 
baffle depicted in FIGS. 8 and 10, the graphite was machined about 22 
inches (559 mm) long, about 2.75 inches (69.9 mm) wide and about 3/8 inch 
(9.5 mm) thick. The lower portion 803 of baffle 801 was formed by cutting 
a segment from the about 22 inches (551 mm) long side to an about 16 
inches (406 mm) along opposite side of the graphite piece. Three holes 805 
were drilled at the top portion 804 of baffle 801. Each hole had a 
diameter of about 5/8 inch (15.9 mm). 
A first hole 805 was spaced about 3/4 inch (19 mm) from the top and about 
1.38 inches (35 mm) from each side of baffle 801. A second and a third 
hole 805 were spaced about 1.75 inches (44.4 mm) from the top and about 
0.63 inch (16 mm) from the side of baffle 801. The second and third holes 
were also spaced about 1.5 inches (38 mm) from each other. 
Also depicted in FIG. 10 is rotating means 1003, shaft 904 and blade 905 or 
701. Shaft 904 corresponds to the shaft used with blade 905 schematically 
depicted in FIGS. 9A and 9B. In the present Example, rotating means 1003 
comprised a drive unit Model No. HVI-15 (Hockmeyer Equipment Co., 
Elizabeth, N.C.). Blade 701 is schematically depicted in FIG. 7. 
In regard to shaft 904 and blade 905, a more detailed discussion follows. 
Shaft 904, which measured about 30 inches (762 mm) long and about 5/8 inch 
(16 mm) in diameter, was cut from 316 stainless steel. Blade 905 had an 
outermost diameter of about 5 inches (127 mm), for example, the distance 
between narrowest portion of segments 902D and 902B, and an intermediate 
diameter of about 3 inches (76 mm), for example, the distance from the 
axis of rotation of blade 905 to that portion of any of the 902 or 903 
which is perpendicular to a diagonal running through the rotational axis. 
The material used to fabricate blade 905 was about 1/8 inch (3.2 mm) 
thick. As with shaft 904, blade 905 was fabricated from 316 stainless 
steel. Shaft 904 was welded to blade 905. Additional features of blade 905 
included alternating segments 902 and 903. Segment 903A, 903B, 903C and 
903D extend upward while segment 902A, 902B, 902C and 902D extended 
downward from the plane of blade 905. After blade 905 was welded to shaft 
904, both were coated with an alumina material formed by a plasma 
deposition technique (PP-30 coating applied by Standard Engineering and 
Machine Co., Wilmington, Del.). 
In regard to blade 701 depicted in FIG. 7, blade 701 was machined from 
commercially available graphite (e.g., Grade AXF-5Q graphite from POCO 
Graphite Inc., Decatur, Tex.). Blade 701 measured about 6 inches (152 mm) 
in diameter and about 3/4 inch (19 mm) thick. Angles phi and theta marked 
in FIG. 7 measure about 90.degree. and 45.degree., respectively. 
Extensions 703 were formed along blade 701 by machining an about 10/32 
inch (7.9 mm) radius 702 every 45.degree. along the outer diameter an 
about 6 inch (152 mm) diameter disc of graphite. During the machining of 
radius 702, flat 704 was formed. Flat 704 was substantially perpendicular 
to radial segment 706. After machining, blade 701 was secured to a 5/8 
inch (15.9 mm) diameter rod measuring about 31 inches (787 mm) long and 
compositionally comprising 316 stainless steel. 
About 550 pounds (1213 kg) of ingot casting stock comprising by volume 
about 30 percent silicon carbide particulate and the balance aluminum 
matrix metal were produced in accordance with the following discussion. A 
600 pound capacity crucible, having an inner diameter measuring about 21 
inches (533 mm) and a height measuring about 27 inches (686 mm) made from 
a commercially available silicon carbide material and contained within an 
electrical resistance heated furnace, was charged with about 119 pounds 
(262 kg) of an aluminum alloy comprising by weight about 10 percent 
silicon and the balance aluminum (nominally Aluminum Association 360 
alloy). The crucible, which had been subjected to a prior wash melt in 
preparation for use, and its contents were heated from about room 
temperature to about 700.degree. C. in about 12 hours while a cover gas 
comprising nitrogen flowing at a rate of about 40 standard cubic feet per 
hour (1133 liters per hour) was provided to the contents of the crucible. 
Simultaneously, about 486 pounds of billet comprising highly loaded metal 
matrix composite integrally attached to excess matrix metal were dried by 
preheating in a second resistance heated furnace to about 300.degree. C. 
in about 12 hours and then to about 450.degree. C. in about 2 hours. 
When the 119 pounds (262 kg) of aluminum alloy continued within the 
available was molten, the flow of the nitrogen cover gas was stopped and 
any dross or oxide that may have formed during the melting of the aluminum 
alloy and present on the surface of the melt was removed from the melt 
surface using commercially available foundry tools comprising steel coated 
with a commercially available "ZIRCWASH.RTM." mold wash (ZYP Coatings, Oak 
Ridge, Tenn.). Incrementally, billets comprising the highly loaded metal 
matrix composite integrally attached to excess matrix metal preheated to 
about 450.degree. C. were added to the molten aluminum alloy. Throughout 
this procedure, an argon cover gas flowing at about 30 standard cubic feet 
per hour (849.8 liters per hour) was provided to the melt surface. Also, 
about 30 minutes after the addition to the crucible, the billets were at 
least partially dispersed into the melt using a plunging lance (for 
example, lance 206 depicted in FIG. 2A). The procedure was repeated until 
a total of about 486 pounds (1071 kg) of billet had been added to the 
contents of the crucible. 
After the 486 pounds (1071 kg) of billets were substantially molten, four 
preheated graphite baffles 801, which had been covered by a commercially 
available mold wash, were secured to furnace cover 1002. A portion of 
baffle 801 was submerged into the melt which was at a temperature of about 
625.degree. C. 
After baffles 801 were sufficiently secured to furnace cover 1002, blade 
905 was attached to rotational mean 1003 through shaft 904. Rotation mean 
1003 was lowered so that blade 905 was about 12.5 inches (317.5 mm) from 
the bottom of the containment crucible. Blade 905 was rotated about 650 
rounds per minute (rpms) during this step. When it became apparent that 
the filler material from the highly loaded metal matrix composite was 
becoming dispersed throughout the melt, blade 905 was lowered from about 
12.5 inches (317.5 mm) from the bottom of the containment crucible to 
about 7 inches (178 mm) from the bottom of the crucible. The rotation 
speed of shaft 904 and blade 905 was increased from about 650 rpm to about 
1000 rpm. Blade 905 was used for about 75 minutes and then removed. Blade 
701 was then attached to rotation means 1003. Unlike blade 905, the 
rotational speed of blade 701 was maintained at about 1600 rpm. Blade 701 
was maintained at the 1600 rpm speed for about 60 minutes to produce a 
molten suspension of castable material. 
The castable material, after heating to about 700.degree. C., was then hand 
ladled (see, for example, FIG. 2D) into ingot molds to form pigs of lower 
loaded metal matrix composite comprising by volume about 30 percent filler 
(optionally designated "SiC(30)360"). 
A similar procedure was employed to produce additional lower loaded metal 
matrix composites. However, in addition to the about 6 inch (152 mm) 
diameter blade 701, about 4 inch (102 mm) diameter and about 5 inch (127 
mm) blades having a design substantially the same as blade 701 were used. 
Table 2 below summarizes the parameters relating to the formation of lower 
loaded metal matrix composite bodies. 
TABLE 2 
__________________________________________________________________________ 
MMC 
Alloy Billet 4" Blade 
5" Blade 
Volume 
Change 
Charge 
Blade 705 
Blade 905 
Mixing 
Mixing 
Percent 
Weight 
Weight 
Mixing Mixing Time Time 
Filler 
lbs. (Kg.) 
lbs. (Kg.) 
Time(Speed) 
Time(Speed) 
(Speed) 
(Speed) 
__________________________________________________________________________ 
30 486(220.5) 
119(54.0) 
75 min(1000) 
60 min(1600) 
-- -- 
30 476(215.9) 
117(53.1) 
65 min(1000) 
60 min(1637) 
-- -- 
25 417(189.2) 
176(79.8) 
80 min(1000) 
30 min(1500) 
30 min 
-- 
(2050) 
20 321(145.6) 
242(109.8) 
70 min(1000) 
30 min(1300) 
*30 min 
-- 
(2000) 
__________________________________________________________________________ 
*blade diameter of about 4.75 inches (121 mm). 
The pigs of lower loaded metal matrix composite were then used to cast 
brake rotors or discs. The casting procedure paralleled commercially 
acceptable casting procedures for aluminum alloy or aluminum metal matrix 
composites. For example, brake rotors or discs comprising an about 30 
volume percent reinforced metal matrix composite (hereinafter either 
"SiCp/Al MMC" or "SiC(30)/360")were cast into a box mold 1101 as 
schematically in FIG. 11. 
Box mold 1101 comprised cope 1103 and drag 1102 containing metal filter 
1108 between gate portion 1107 and gate portion 1109. When vented brake 
rotor or discs were cast, vent core 1112 was used. In all instances, hub 
core 1113 was used. 
The cope 1103, drag 1102 and hub core 1113 comprised 97.5-99 weight percent 
foundry grade pure silica sand combined with sodium silicate binder. A 
vent core 1112 comprises foundry grade silicon sand combined with "PEPSET" 
sand binder (Ashland Chemical Co., Columbus, Ohio). The sand sodium 
silicate used in these items cured or set by exposing it to a carbon 
dioxide atmosphere. 
The 30 volume percent metal matrix composite, SiC(30)/360, was prepared for 
casting by charging about 520 pounds (236 kg) of pig into an electrical 
resistance heated melting furnace (Thermtronix, Adelento, Calif.) having 
an about 530 pound (240 kg) capacity. The furnace and its contents were 
heated from about room temperature to about 751.degree. C. (1385.degree. 
F.) under a gaseous argon blanket or shroud. After the 30 volume percent 
metal matrix composite SiC(30)/360 had substantially completely melted, a 
mixing blade having a configuration substantially the same as the 
configuration of blade 701 depicted in FIG. 7 and four (4) baffles 801 
were lowered into the molten metal matrix composite. The rotational speed 
of the blade was then brought to 1400 rpm. The molten metal matrix 
composite was then mixed for about 46 minutes while maintaining the melt 
under an argon gas blanket or shroud. The mixing blade and the baffles 801 
were then removed and the re-melting furnace was tilted so that the first 
surface of the melt could be skimmed from the second so that molten metal 
matrix composite could be ladled into box molds substantially as depicted 
in FIG. 11. Specifically, molten metal matrix composite was poured into 
sprue cup 1104. The molten metal matrix composite was flowed into particle 
trap 1106, runner 1107, filter 1108 (either a 20 pre per inch reticulated 
ceramic from Foseco, Inc., Cleveland, Ohio, or a 15 pore per inch 
reticulated ceramic from Selec Corp., Hendersonville, N.C.) runners 1109, 
1110 and 1111, past vent core 1112 and hub core 1113 and into rises 1114. 
The molten metal matrix composite body was at a temperature of about 
751.degree. C. (1385.degree. F.) while the box mold 1101 was at about 
25.degree. C. After the metal matrix composite solidified, the mold box 
1101 was disassembled and the riser, gates, runners and sprue were cut 
away using diamond saws. The resultant brake rotor or disc, after cleaning 
to remove any residual mold sand, was machined to substantially the 
finishes described in Example 2. Additional brake disc or rotors having 
volume percent loading from about 15 to about 25 volume percent were cast 
substantially as the 30 volume percent brake rotors or discs except that 
in some instances liquid argon was used to blanket or shroud the metal 
matrix metal rather than gaseous argon. Table 3 below summarizes some of 
the parameters used to form these lower loaded brake rotors or discs. 
TABLE 3 
______________________________________ 
Charge 
Filler Loading 
Blanket Mixing Weight 
Casting 
Volume Percent 
or Shroud Time (lbs) Temperature 
______________________________________ 
30 gaseous argon 
46 min. 520 752.degree. C. 
25 gaseous argon 
45 min. 415 757.degree. C. 
20.sup.+ gaseous argon 
40 min. 164 757.degree. C. 
15* liquid argon 
30 min. 140 757.degree. C. 
______________________________________ 
*formed by charging 25 vol. % SiCp/Al MMC, 20 vol. % SiCp/Al MMC and 
additional matrix metal. 
*formed by charging 20 vol. % SiCp/Al MMC and additional matrix metal. 
The above discussion described the methods used to form brake rotors or 
discs using a casting technique. Some of the brake rotors or discs 
produced in accordance with the present Example were subjected to the 
modified J212 dynamometer test. The results of the tests are discussed in 
Example 6. 
Furthermore, it should be understood that the methods of the present 
Example may also be employed to form metal matrix composite brake rotor or 
discs reinforced with, for example, Al.sub.2 O.sub.3, MgAl.sub.2 O.sub.4, 
Si.sub.3 N.sub.4, etc, in a range of volume percent loadings. 
EXAMPLE 5 
The present Example demonstrates, among other things, a method for forming 
a metal matrix composite brake rotor or disc using a loose filler material 
mixture comprising an alumina particulate (Al.sub.2 O.sub.3 p) combined 
with a magnesium powder (Mgp). Specifically, the present Example 
demonstrates formation of a brake rotor or disc by spontaneously 
infiltrating an Al.sub.2 O.sub.3 p filler material with a molten aluminum 
matrix metal and a nitrogenous atmosphere. 
FIG. 12 is a cross-sectional schematic of the lay-up used to form brake 
rotor or disc of the present Example. Lay-up 1201 comprised a catch tray 
1202 containing two molds 1205 fabricated from stainless steel and lined 
with a commercially available graphite foil (not depicted in FIG. 12). 
Contained within mold 1205 was a filler material mixture 1207, a graphite 
core 1208 and a hub insert 1209. Hub insert 1209 was also fabricated from 
stainless steel and substantially completely lined with commercially 
available graphite foil (not depicted in FIG. 12). On molds 1205 was 
placed an alloy trough 1206 for containing matrix metal ingots 1210 and 
1211 for setups 1203 and 1204, respectively. 
Catch tray 1202 had inner dimensions measuring about 21.25 inches (539.8 
mm) long, 12.5 inches (317.5 mm) wide and about 2 inches (51 mm) deep. The 
wall thickness of catch tray 1202 was about 3/8 inches (9.5 mm). 
Mold 1205 was fabricated from stainless steel sheet having a thickness of 
about 1/16 inch (1.59 mm) thick. The hub diameter of mold 1205 measured 
about 6.25 inches (158.8 mm), while the rotor diameter of mold 1205 
measured about 10 inches (254 mm). The height of the hub portion of mold 
1205 was about 1.5 inches (38 mm), while the height of the rotor portion 
measured about 4.25 inches (108 mm). The hub insert 1209 was also 
manufactured from 1/16 inch (1.59 mm) thick stainless steel. Hub insert 
1209 measured about 47/8 inches high (123.8 mm) and had an outer diameter 
of about 4.25 inches (107.9 mm). Graphite core 1208 was machined from 
commercially available graphite to an outer diameter of about 95/8 inches 
(244.5 mm) and an inner diameter of about 45/8 inches (117.5 mm). Graphite 
core was about 3/8 inch (9.5 mm) thick. Slots measuring about 17/16 inches 
(36.5 mm) long by about 0.25 inch (6.4 mm) wide were machined to project 
radially at about 0.25 inch (6.3 mm) from the outer diameter extending in 
toward the inner diameter. Twenty-nine substantially identical slots were 
equally spaced along graphite core 1209. 
Alloy troughs 1206 were made from commercially available copper foil and 
spanned the space between the rotor portion of mold 1205 and hub insert 
1209. Trough 1206 provide a means for supporting pieces of matrix metal 
ingots 1210 and 1211. 
A filler material mixture 1207 was made by combining by weight about 96 
percent Type AS10 alumina (average particle diameter of about 44.3 
microns, Showa Denko America Inc., New York, N.Y.) and about 4 percent 
-325 mesh magnesium powder (particle diameter less than about 45 microns) 
in a milling jar. The Al.sub.2 O.sub.3 p was dried under a vacuum of about 
30 inches (762 mm) Hg at about 150.degree. C. for about 18 hours. Also 
placed in the milling jar were alumina milling media measuring about 3/8 
inches (9.5 mm) in diameter and about 3/8 inches (9.5 mm) high. The weight 
of the milling media was twice the weight of the Al.sub.2 O.sub.3 p-Mgp 
mixture. The jar and its contents were then placed on a jar mill for about 
2 hours. To separate the Al.sub.2 O.sub.3 -Mgp filler material mixture 
from the alumina milling media, the contents of the jar were passed 
through a 20 mesh sieve. 
Simultaneously, two molds 1205 were lined with "PERMAFOIL.RTM." graphite 
foil (TTAmerica Inc., Portland, Oreg.) having a thickness of about 0.010 
inch (0.25 mm). The outer diameter and bottom surface of hub insert 1209 
was lined with the same type of graphite foil. A portion of the Al.sub.2 
O.sub.3 p-Mgp filler material mixture was poured into the bottom of molds 
1205 to about the height of the hub portion of steel mold 1205. After the 
filler material mixture 1207 was substantially leveled, hub insert 1209 
was placed in contact with the level surface and co-axially with mold 
1205. Additional filler material mixture was poured into steel mold 1205 
to create an annulus of filler material mixture defined by mold 1205 and 
hub insert 1209. After that filler material had been substantially 
completely leveled, graphite core 1208 placed into the steel mold 1205 and 
on the leveled filler material 1207. Additional filler material mixture 
was then placed in mold 1205 to substantially completely cover graphite 
core 1208 and fill the slotted portions of graphite core 1208. Filler 
material mixture 1207 was placed in mold 1205 to yield equal thicknesses 
of filler material mixture 1207 on both sides of graphite core 1208. The 
total amount of filler material mixture per setup comprised about 3500 
grams. 
Pieces of commercially available copper foil measuring about 0.005 inch 
(0.127 mm) thick (ALL-FOILS, Inc.) was shaped into a trough 1206 to span 
the distance between mold 1205 and hub insert 1209. Ingots of matrix metal 
1210 in setup 1203 and 1211 in setup 1204 were then placed in trough 1206. 
Matrix metal ingots 1210 comprises by weight about 3 percent magnesium, 
1.7 percent silicon and the balance aluminum, while matrix metal ingots 
1211 comprised by weight about 0.8 percent manganese, 0.12 percent chrome 
and 3 percent magnesium. Total weight of each of matrix metal ingots 1210 
and 1211 was about 6000 grams. Setups 1203 and 1204 were then placed on 
catch tray 1202 to form lay-up 1201. 
Lay-up 1201 was then placed into a controlled atmosphere furnace at a 
temperature of about 150.degree. C. After the furnace door was closed, the 
furnace and its contents were evacuated to about 30 inches (762 mm) 
mercury for about 70 hours. The vacuum pump was then disengaged from the 
furnace and the furnace and its contents, while being heated to about 
200.degree. C. at about 100.degree. C. per hour, were exposed to a 
nitrogen atmosphere flowing at a rate of about 10 liters per minute. 
Flowing nitrogen gas of about 10 liters per minute was maintained for the 
remainder of the time that lay-up 1201 spent in the controlled atmosphere 
furnace. After about 2 hours at about 200.degree. C., the furnace and its 
contents were then heated from about 200.degree. C. to about 500.degree. 
C., maintained at about 500.degree. C. for about 5 hours, heated from 
about 500.degree. C. to about 800.degree. C. at about 100.degree. C. per 
hour and held at about 800.degree. C. for about 10 hours. After about 10 
hours at about 800.degree. C., the power to the furnace was disconnected 
and the flowing nitrogen gas interrupted. The lay-up 1201 and its contents 
comprising set-up 1203 and 1204 were then removed from the furnace and 
hot-topping material as described in Example 3 was placed on molten matrix 
metal which had now infiltrated the filler material. 
After the matrix metal had solidified, set-ups 1203 and 1204 were 
disassembled to reveal that the matrix metal had spontaneously or 
pressurelessly infiltrated filler material to form an alumina particulate 
reinforced aluminum metal matrix composite (hereinafter Al.sub.2 O.sub.3 
p-Al MMC). Graphite core 1208 was then removed by sand blasting and the 
resulting brake rotor or disc was machined for testing according to the 
methods described in the present application. The results of some of this 
testing for an Al.sub.2 O.sub.3 /Al MMC, Al.sub.2 O.sub.3 (60)/6061, made 
in accordance with the methods of the present Example are presented in 
Example 6. 
EXAMPLE 6 
Automotive brake rotors or discs produced from metal matrix composites 
(MMCs) made by the methods of the previous Examples were subjected to 
dynamometer tests. The thermal response during fade stops, the failure 
temperature, and the wear performance of the brake rotors or discs were 
measured as functions of various material and design parameters, such as 
rotor thickness, composition of the brake rotors or discs, applied 
inertial load, and cooling air speed. The performance of the MMC brake 
rotors or discs was also compared with that of commercially available 
production cast iron brake rotors or discs. Data related to the maximum 
operating temperature (MOT) as a function of the silicon carbide volume 
percent loading in a composite brake rotor or disc was obtained. The 
results of testing demonstrate, among other things, that metal matrix 
composite materials are strong candidates for brake rotors or discs in 
future models of motor vehicles. 
Use of lightweight materials such as aluminum-based metal matrix composites 
(MMCs) in brake systems is one of the ways of reducing unsprung weight of 
motor vehicles. The brake rotor or disc is one of the components widely 
selected for weight reduction because of significant weight savings 
brought about by replacing the current brake rotor or disc material, gray 
cast iron, with a metal matrix composite (MMC) based on an aluminum alloy 
(e.g., density of cast iron is about 7-8 g/cm.sup.3 while the density of 
an aluminum MMC can be about 2.5 g/cm.sup.3 and higher). 
Despite the widespread interest in the subject, very few studies dealing 
with fabricating, machining and performance testing of MMC brake rotors or 
discs have been reported. Most of the published studies deal with cast 
silicon carbide reinforced aluminum brake rotors or discs containing less 
than about 20 volume percent of reinforcement. None of these studies deal 
with the effect of material parameters, such as alloy chemistry, 
reinforcement chemistry, reinforcement size and shape, and the volume 
fraction of reinforcement, on the performance of metal matrix brake rotors 
or discs. Also, the effects of design parameters, such as inertial load 
(related to the vehicle weight), brake rotor or disc thickness, and 
cooling air speed, on brake rotor or disc performance have not been 
extensively dealt in the open literature and are therefore not understood. 
The present Example presents the results of a comprehensive study 
undertaken to understand the effects of some of the aforementioned 
parameters on brake rotor or disc performance in dynamometer tests. The 
dynamometer tests used in the present Example were adopted from SAE J212 
(1) with some modifications and were discussed above. The test conditions 
during each fade segment were as summarized in Table 1 above. 
The wear test used in the present Example involved 400 stops from an 
initial speed of 60 mph (91 km/h) using a deceleration of 12 fpsps (3.7 
m/s.sup.2). The initial brake rotor or disc temperature was maintained at 
about 500.degree. F. (260.degree. C.) and the cooling air speed was 
maintained at about 8 mph (12.8 km/h). 
The tests were conducted using compact dynamometers with DC drives at Link 
Testing Laboratory, Inc. (Detroit, Mich.) and Greening Testing Laboratory, 
Inc. (Detroit, Mich.). The speed, acceleration (or deceleration), torque, 
cooling air speed, cooling air temperature, and brake rotor or disc and 
pad temperatures were continuously monitored and recorded. 
Prior to a test, a brake rotor or disc and the mating pads were thoroughly 
characterized for: 
1. weight, 
2. dimensions, particularly the brake rotor or disc thickness, 
3. surface roughness, 
4. density, 
5. and microstructure and reinforcement loading. 
After the test, all of the above parameters were remeasured to assess the 
damage and wear to the brake rotor or disc and the pads. 
The brake rotors or discs tested in the present Example were of 1991 Ford 
Escort design. Unless specifically noted, all the brake rotors or discs 
used in the present Example were the standard vented design. The inertial 
loads were varied to simulate the operating conditions of both a front and 
a rear brake rotor or disc. 
A number of metal matrix composites were evaluated as a part of the present 
Example. The metal matrix composites have been designated in the present 
Example by the reinforcement chemistry, followed by volume percentage of 
the reinforcement in parentheses and the matrix alloy designation. The 
alloy designation system adopted by the Society of Automotive Engineers 
has been used wherever applicable. Following this scheme a 360 alloy 
reinforced with 30 volume percent of silicon carbide is designated by 
SiC(30)/360. Similarly, a Al-12% Si-5% Mg alloy reinforced with 40 volume 
percent silicon carbide will be denoted by SiC(40)/Al-12% Si-5% Mg. 
The metal matrix composites tested during this study were produced using 
both the cast (approximately 10-40 volume percent reinforcement) and the 
infiltrated (20-70 volume percent reinforcement) compositions produced via 
the PRIMEX CAST.TM. casting (see, for example, Example 4) and the 
PRIMEX.TM. pressureless metal infiltration processes (see, for example, 
Examples 3 and 5), respectively. Commercial cast iron brake rotors or 
discs were tested to serve as the baseline reference and to calibrate the 
performance of the dynamometers. 
The brake pads were supplied by Allied-Signal Corp. and were specially 
formulated for aluminum-based MMC brake rotors or discs. The brake pad 
material was designated C0792J. The pads used with the cast iron brake 
rotors or discs were also supplied by Allied-Signal and were designated 
XD-7901. 
For MMC brake rotors or discs to be adopted in commercial vehicles, they 
must show performance similar to that of production cast iron brake rotors 
or discs. For this reason, the performance of the MMC brake rotors or 
discs was compared to that of the cast iron brake rotors or discs. The key 
findings of the present Example include: 
1. The overall performance of the MMC brake rotor or disc was comparable to 
the cast iron production brake rotors or discs. This strongly suggests 
that the metal matrix composite brake rotors or discs may find use in 
future production vehicles. In fact, the brake rotors or discs 
successfully passed the SAE J212 test under the loads typically seen in a 
rear brake rotor or disc (Ford Escort). 
2. With appropriately formulated brake pads, the MMC brake rotors or discs 
yield coefficients of friction between about 0.34 to about 0.40 during all 
but the fade/recovery segments of the present test. This value of 
coefficient of friction was noted to be in the same range as that measured 
for the cast iron brake rotors or discs. During a fade/recovery segment, 
the MMC brake rotors or discs showed slightly higher fade characteristics. 
The recovery of the coefficient of friction was rapid during the eight 
recovery stops of a fade/recovery segment for the MMC brake rotors or 
discs. 
3. The MMC brake rotors or discs were found to quieter than the cast iron 
brake rotors or discs during all phases of the test. No squeals or groans 
were noted. 
4. In general, the MMC brake rotors or discs showed lower rubbing surface 
temperatures as compared to the cast iron brake rotors or discs under 
identical test conditions. 
5. The wear losses in the MMC brake rotors or discs were less than those in 
the cast iron brake rotors or discs. 
6. The effectiveness in stopping a vehicle of the MMC brake rotors or discs 
was comparable to that of the cast iron brake rotors or discs. 
7. In tests where the MMC brake rotors or discs were taken to failure, 
majority of the failures in the MMC brake rotors or discs took place by 
surface scuffing when the surface temperature (temperature measured 0.040" 
(1 mm) under the brake rotor or disc surface) exceeded a temperature 
defined as the `maximum operating temperature` (MOT). A detailed 
discussion on the influence of various material parameters on maximum 
operating temperature will follow in the subsequent paragraphs. 
The MOT is one of the key parameters characterizing the performance of a 
brake rotor or disc material under severe service conditions. The other 
key factor influencing the performance of a brake rotor or disc is the 
thermal response of a brake rotor or disc system (rotor/pad combination) 
as a function of various material and design parameters. That is, how fast 
does a brake rotor or disc system heat up and how quickly the heat is 
dissipated under the influence of various material and design parameters. 
Since this effect is most clearly demonstrated during fade sequence of the 
modified SAE J212 test, most of the discussion pertains to this phase of 
testing. 
The thermal response of a MMC brake rotors or discs during fade strongly 
depends on the material chemistry which determines the heat capacity and 
thermal conductivity of a brake rotor or disc material. Tests were 
conducted to study differences in thermal response of various brake rotor 
or disc materials under the test conditions listed in Table 1 (Fade I and 
II). 
FIG. 13 shows the rise in inboard brake rotor or disc rubbing surface 
(IRRS) temperature during fade along with rises in hub, inboard pad and 
outboard pad for a 25 mm thick brake rotor or disc comprised of a 
SiC(30)/360. This represents a typical response of a brake rotor or disc 
produced from a material with high thermal conductivity (160 
W/m.degree.K.). The hub and the brake rotor or disc surface temperatures 
are relatively close to each other because high thermal conductivity 
enables the material to quickly conduct heat away from the rubbing 
surfaces. 
The thermal response of a similar cast iron brake rotor or disc under an 
identical set of test conditions is shown in FIG. 14. Note that due to a 
lower thermal conductivity (52 W/m.degree.K.), the cast iron brake rotor 
or disc does not distribute the heat to the hub region, keeping it cooler 
than the corresponding region in a SiC(30)/360 rotor. As a result, the 
IRRS temperature of a cast iron brake rotor or disc is higher than that of 
a SiC(30)/360 rotor by about 50 C. in the later stages of the fade 
sequence. This is illustrated in FIG. 15. 
Tests similar to those described above were conducted to compare the 
thermal response of a 29 mm thick SiC(30)/360 rotor with that of an 
alumina(60)/6061 rotor of identical dimensions. Again, due to a lower 
thermal conductivity (55 W/m.degree.K.), the alumina(60)/6061 rotor showed 
higher IRRS temperatures than the SiC(30)/360 rotor, as shown in FIG. 16. 
The brake rotor or disc thickness is one of the factors determining the 
thermal capacity of a brake rotor or disc. The brake rotors or discs with 
higher thermal capacity are expected to show lower temperature rise during 
the fade sequence and, thus, be safer to use in severe braking conditions. 
To study the effect of brake rotor or disc thickness on the thermal 
response of a brake rotor or disc, two brake rotors or discs, 25.41 and 
28.96 mm in thickness, were tested under the conditions described above 
(Table 1 Fade I and II). The IRRS temperature rise during fade for the two 
brake rotors or discs is shown in FIG. 17. As expected, the rate of 
temperature rise and the IRRS temperature were slightly lower for the 
thicker brake rotor or disc because of its higher thermal capacity. Under 
the test condition used in this study, a 14% increase in the brake rotor 
or disc thickness resulted in a 40-50 C. reduction in the IRRS 
temperature. 
The heat generated during a fade stop is dissipated in form of the 
following three components: 
1. heat absorbed by the brake rotor or disc, 
2. heat lost to the surroundings via convection, 
3. and heat lost to the surroundings via radiation. 
A solid brake rotor or disc is expected to have a higher mass and, thus, a 
higher thermal capacity than a vented brake rotor or disc of the same 
thickness. Therefore, when the heat absorption into the brake rotor or 
disc is the predominant mode of heat dissipation, solid brake rotors or 
discs are expected to show a lower temperature rise than vented brake 
rotors or discs. This may happen during early fade stops when the brake 
rotor or disc temperature is close to that of the surroundings and, 
therefore, convective and radiative components of the heat transfer are 
small. During the later fade stops, a vented brake rotor or disc is 
expected to cool faster because of its larger surface area. 
To quantify the thermal response of vented and solid brake rotors or discs, 
two 29 mm thick SiC(30)/360 brake rotors or discs were subjected to 
identical test conditions during fade sequence described above (Table 1, 
Fade I). The rise in IRRS temperatures of the two brake rotors or discs 
are shown in FIG. 18. The temperature of the solid brake rotor or disc was 
lower in the early stages of the fade sequence, but approached the IRRS 
temperature of the vented brake rotor or disc during the tenth stop. The 
trend clearly suggests that in the subsequent stops, the IRRS temperature 
of the solid brake rotor or disc would have exceeded the IRRS temperature 
of the vented brake rotor or disc. The rate of temperature rise in the 
vented brake rotor or disc, particularly towards the later parts of the 
fade sequence, continues to drop as the brake rotor or disc continues to 
cool at increasingly fast rates. 
In summary, the advantage of a solid brake rotor or disc with higher 
thermal capacity is lost as the brake rotor or disc temperature rises 
towards the later part of the fade test sequence. 
As stated in the previous section, convective heat transfer from the brake 
rotor or disc surfaces starts to dominate heat dissipation when the brake 
rotor or disc temperature is high compared to the surroundings and/or the 
cooling air speed is high. To quantify the effect of the cooling air 
speed, two identical SiC(30)/360 rotors (29 mm thick) were subjected to 
identical conditions during fade, except that one of the brake rotors or 
discs was cooled using a cooling air speed of 2 mph (3.2 km/h) while the 
other one was subjected to a cooling air speed of 8 mph (12.8 km/h). FIG. 
19 shows the IRRS temperatures of the two brake rotors or discs. Clearly 
in the later stage of the fade sequence when convective heat loss begins 
to dominate the heat dissipation mechanism, the brake rotor or disc 
subjected to 12.8 km/h cooling air shows 40-50 C. lower temperature as 
compared to the brake rotor or disc cooled with 3.2 km/h air. During the 
early stages of the fade sequence, when heat absorption into the brake 
rotor or disc is the primary heat dissipation mode, cooling air has 
virtually no influence on the temperature of the brake rotors or discs. 
The work done or the heat generated during a fade stop is directly 
proportional to the inertial load. Therefore, the brake rotor or disc 
temperatures are progressively increased as the inertial load is 
increased. During the present study, SiC(30)/360 rotors of 29 mm thickness 
were tested using four different inertial loads. These were 23, 33, 37, 
and 46 kg.multidot.m.sup.2. The cooling air speed was maintained at 8 mph 
(12.8 km/h) during the fade stops. The inertial load of 46 
kg.multidot.m.sup.2 corresponds to the front brake rotor or disc load of a 
1992 Ford Escort whereas 33 kg.multidot.m.sup.2 corresponds to the 
projected front brake rotor or disc load of a future model. The rear brake 
rotor or disc load of the future model is expected to correspond to an 
inertial load of about 17 kg.multidot.m.sup.2. As FIG. 20 shows, the 
inertial load has a great influence on increasing the final IRRS 
temperatures of the brake rotors. At the two highest inertial loads, the 
brake rotors or discs failed before the fade sequence was completed. The 
failure took place between 480 and 490 C. At the lower inertial loads, the 
brake rotors or discs completed the fade sequence without failure. This 
indicated that the SiC(30)/360 rotors are likely to operate satisfactorily 
in the future model of Escort both in front and rear, provided that the 
brake rotors or discs can be cooled using air at 8 mph (12.8 km/h) or 
higher. 
The final IRRS temperature at each fade stop (time elapsed between each 
consecutive stop is 35 seconds) can be plotted as function of the inertial 
load, as shown in FIG. 21. The final IRRS temperature was found to be a 
linear function of the inertial load. Also shown in FIG. 21 is the failure 
temperature range of the SiC(30)/360 rotors. Clearly, the brake rotors or 
discs can go through all the 15 fade stops at the lower two inertial 
loads, as discussed above. 
As stated earlier in this application, the predominant failure mode of the 
MMC brake rotors or discs is by surface scuffing. As a brake rotor or disc 
is subjected to progressively more severe conditions, the temperature of 
the brake rotor or disc continues to rise until it reaches a temperature 
at which the glaze on the brake rotor or disc surface breaks down and 
scuffing ensues. The temperature at which the breakdown occurs is referred 
to as the maximum operating temperature (MOT). The breakdown of a brake 
rotor or disc accompanies excessive noise, sparks and dust. The brake 
rotor or disc breakdown is followed by rapid wear of the pads and rise in 
temperatures, as measured by the pad thermocouples. The MOT is primarily 
dependent on the material composition, and not on the brake rotor or disc 
design or the test conditions. 
The MOT was studied as a function of the volume fraction of reinforcement 
for the silicon carbide reinforced brake rotors or discs. The compositions 
studied are shown in Table 4. 
TABLE 4 
______________________________________ 
Maximum Operating Temperatures for Various Compositions 
Volume % 
Silicon Matrix Solidus Temp. of 
MOT 
Carbide Composition Matrix Alloy (.degree.C.) 
(.degree.C.) 
______________________________________ 
20 360 580 449 
30 360 580 482 
47 Al-12% Si-5% Mg 
535 498 
______________________________________ 
The matrix alloys of the composites reinforced with 20 and 30 volume 
percent silicon carbide were the same, namely alloy 360, whereas the 
matrix of the composite reinforced with 47 volume percent of silicon 
carbide consisted of Al-12% Si-5% Mg alloy. The solidus temperatures (ST) 
of the matrix alloys are listed in Table 4. Since it was expected that the 
solidus temperature (ST) of the matrix alloy would influence the MOT of a 
composite brake rotor or disc, the MOT of various compositions were 
normalized with respect to the solidus temperature by dividing the 
measured values of MOT by the solidus temperatures of the respective 
matrix alloys. The normalized MOT (NMOT) is plotted as a function of 
volume fraction of reinforcement in the composite in FIG. 22. 
Interestingly, the NMOT is a linear function of the volume fraction of 
reinforcement in a composite. This relationship between NMOT and the 
volume fraction of reinforcement is valid for NMOT less than 1 because the 
MOT is not expected to exceed the solidus temperature of the matrix alloy. 
Linear regression analysis of the data yields: 
NMOT=MOT/ST=0.668+0.00564 (% SiC) 
or MOT=ST (0.668+0.00564 (% SiC)). 
This data clearly shows that the MOT bears a strong relationship with the 
volume fraction of silicon carbide and the solidus temperature of the 
matrix alloy in silicon carbide reinforced brake rotors or discs. Based on 
this relationship, silicon carbide reinforced brake rotors or discs using 
360 alloy as the matrix are predicted to have failure temperatures shown 
in Table 5. Similar relationships are expected to exist among the 
composites reinforced with fillers other than silicon carbide. 
TABLE 5 
______________________________________ 
Calculated MOT of SiC Reinforced Brake rotors or discs 
Volume % 
Silicon Carbide 
Calculated MOT (.degree.C.) 
______________________________________ 
10 420 (788.degree. F.) 
20 453 (847.degree. F.) 
30 486 (907.degree. F.) 
40 518 (964.degree. F.) 
50 551 (1023.degree. F.) 
______________________________________ 
To study the effect of volume fraction of reinforcement on wear performance 
of a brake rotor or disc system, brake rotors or discs containing 15, 20, 
25, 30, and 35 volume % silicon carbide in 360 alloy matrix were cast 
(see, for example, Example 4). These brake rotors or discs were then 
subjected to the wear test described in a previous section. The initial 
brake rotor or disc temperature was maintained at 260 C. (500 F.). The 
final brake rotor or disc temperature at the end of each stop was 
approximately 349 C. (660 F.) and was relatively independent of the volume 
fraction of reinforcement. 
The weight losses from the brake rotors or discs and the corresponding 
linings are shown in FIG. 23. FIG. 24 shows the reduction in lining 
thickness as a function of volume fraction of silicon carbide. From these 
results it appears that the overall wear of the rotor/lining system is 
very small and relatively independent of the silicon carbide level under 
the test conditions used in this study. At higher initial temperatures 
wear levels are likely to increase but are expected to remain low. 
A comprehensive investigation was undertaken to study the effect of various 
material and design parameters on the thermal response, failure 
temperatures, and the wear performance of metal matrix composite brake 
rotors. The results related to the effects of various material and design 
parameters on the thermal response of MMC brake rotors or discs indicated 
that: 
1. the brake rotors or discs with lower thermal conductivities show higher 
temperatures at the two rubbing surfaces; however, the hub temperatures 
are lower, 
2. a solid brake rotor or disc shows higher surface temperatures when 
convective heat transfer is the primary heat dissipation mode as compared 
to a vented brake rotor or disc of the same thickness. 
3. the brake rotor or disc temperatures increase as the thickness of the 
brake rotor or disc and the cooling air speed are decreased, 
4. the brake rotor or disc rubbing surface temperatures increase as the 
inertial loads increase, 
There is a strong correlation between the solidus temperature (ST) and the 
volume fraction of silicon carbide and the maximum operating temperature 
(MOT) of silicon carbide reinforced brake rotors or discs. This 
relationship is given by: 
MOT=ST (0.668+0.00564 (% SiC)). 
A similar relationship is expected to exists in MMC systems involving other 
reinforcements (see, for example, FIG. 25 which presents the results for 
the MOT testing of a brake rotor or disc formed in accordance with the 
methods of Example 2). 
Wear of the MMC brake rotor or disc systems (brake rotors or discs and 
pads) was found to be very small under the test conditions used in this 
Example. The wear resistance of the brake rotor or disc systems was 
relatively insensitive to the silicon carbide levels in the composites. 
The MOT of highly loaded SiCp/Al MMC has been determined to be superior to 
lower loaded MMCs. 
While the preceding discussion includes very particular disclosures, 
various modifications to the disclosure should occur to an artisan of 
ordinary skill, and all such modifications should be considered to be 
within the scope of the claims appended hereto.