BRAKE ROTORS, CLUTCH PLATES AND LIKE PARTS AND METHODS FOR MAKING THE SAME

Abstract: This invention relates to metal and metal matrix composite materials that are useful as, for example, brake rotors, clutch plates and other similar uses which benefit from material properties of the invention. In the case of metal matrix composite materials, clutch plates and brake rotors made according to the invention comprise an interconnected matrix metal embedding at least one filler material. For example, the at least one filler material comprises numerous acceptable filler materials present in a sufficient quantity to provide desired performance. The brake rotors and clutch plates according to the invention further comprise a coating on the surface thereof causing the metal or metal matrix composite body to function as a substrate. The coatings may be applied by various conventional techniques. Desirable results of placing a coating on a metal or metal matrix composite substrate brake rotor or clutch plate include a significant increase in the maximum operating temperature of the brake rotor or clutch plate and/or a significant reduction in weight in comparison to conventional materials, etc.

Description: DESCRIPTION BRAKE ROTORS, CLUTCH PLATES AND LIKE PARTS AND METHODS FOR MAKING THE SAME Technical Field This invention relates to metal and metal matrix composite materials that are useful as, for example, brake rotors, clutch plates and other similar uses which benefit from material properties of the invention. In the case of metal matrix composite materials, clutch plates and brake rotors made according to the invention comprise an interconnected matrix metal embedding at least one filler material. For example, the at least one filler material comprises numerous acceptable filler materials present in a sufficient quantity to provide desired performance. The brake rotors and clutch plates according to the invention further comprise a coating on the surface thereof causing the metal or metal matrix composite body to function as a substrate. The coatings may be applied by various conventional techniques. Desirable results of placing a coating on a metal or metal matrix composite substrate brake rotor or clutch plate include a significant increase in the maximum operating temperature of the brake rotor or clutch plate and/or a significant reduction in weight in comparison to conventional materials, etc. Background Art 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 achieved 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, for example, automotive brake rotors and clutch plates 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 or clutch plate is relatively heavy. Specifically, 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. Moreover, a heavy clutch plate is considered to be undesirable for at least two reasons. The first reason is that a heavy clutch plate contributes to the overall weight of a vehicle and thus reduces the fuel efficiency of the vehicle and correspondingly increases emissions levels of the vehicle. The second reason is that the clutch plate is part of the drive train which requires direct rotation by the engine. Thus, a heavier clutch plate requires the use of additional energy to increase and decrease its rotational speed. The search for desirable materials to replace cast iron in brake rotors and clutch plates has identified several possible candidates. Steel, titanium, aluminum alloys and magnesium alloys have been considered as potential brake rotor and clutch plate materials because of the excellent strength to weight properties of these materials. Various polymeric materials have also been considered as brake rotor and clutch plate materials due to the relatively inexpensive nature of these materials. In addition, various ceramic and ceramic matrix composite materials have been considered as brake rotor and clutch plate materials due to their excellent wear resistance properties and ability to withstand extremely high temperatures. Recently, aluminum and magnesium metal matrix composite materials have been considered as potential brake rotor and brake caliper 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 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. 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 U.S. patents: U.S. Patent No. 5,028,392, in the names of Lloyd et al. ; U.S. Patent No. 5,028,494, in the names of Tsujimura et al.; U.S. Patent No. 4,865,806, in the names of Skibo et al.; U.S. Patent No. 4,759,995, in the names of Skibo et al.; U.S. Patent No. 4,961,461, in the names of Klier et al.; U.S. Patent No. 4,473,103, in the names of Kenney et al.; U.S. Patent No. 4,404,262, in the name of Watmough; U.S. Patent No. 3,970,136, in the names of Cannell et al.; U.S. Patent No. 3,915,699, in the names of Umehara et al.; U.S. Patent No. 3,718,441, in the name of Landingham; U.S. Patent No. 5,042,561, in the name of Chandley; U.S. Patent No. 4,862,945, in the names of Greanias et al.; U.S. Patent No. 3,547,180, in the name of Cochran; and U.S. Patent No. 3,364,976, in the names of Reding et al. 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. Patent No. 5,028,494, which issued on July 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 the performance of brake rotors and clutch plates made from a substrate material comprising a metal or metal matrix composite material can be enhanced by placing an appropriate coating thereon. Specifically, such coatings tend to ameliorate unacceptable surface scoring (e.g., surface disfigurements, such as scratches or grooves) after fade tests have been performed on the brake rotor. The present invention enhances the maximum operating temperature of substrate metal ' and metal matrix composite materials. Accordingly, the increasing demand for higher fuel efficiency and reduced emissions has created a need for brake rotors and clutch plates 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 and clutch plates currently in use. The present invention provides brake rotors and clutch plates 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 U.S. Patent No. 4,828,008, which issued on May 9, 1989, in the names of White et al. , and entitled "Metal Matrix Composites. " Moreover, an example of suitable barrier means for use with metal matrix composite formation is described in Commonly Owned U.S. Patent No. 5,141,819, and Commonly Owned U.S. Patent No. 4,935,055, both entitled "Method of Making Metal Matrix Composite with the Use of a Barrier". The method of U.S. Patent No. 4,828,008, was improved upon by Commonly Owned and Copending U.S. Patent No. 5,298,339, in the names of Michael K. Aghajanian and Marc S. Newkirk and entitled "Metal Matrix Composites and Techniques for Making the Same. " Further improvements in metal matrix technology can be found in commonly owned U.S. Patent No. 5,249,621, 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." Commonly Owned U.S. Patent No. 5,222,542, and Commonly Owned U.S. Patent No. 5,000,247, both 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" also relate to a novel method for forming metal matrix composite bodies. 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. Patent No. 4,998,578, and Commonly Owned U.S. Patent No. 4,871,008, by Dwivedi et al., both entitled "Method of Making Metal Matrix Composites". A method of forming macrocomposite bodies by a somewhat related process is disclosed in Commonly Owned U.S. Patent No. 5,040,588 on August 20, 1991, in the names of Marc S. Newkirk et al., and entitled "Methods for Forming Macrocomposite Bodies and Macrocomposite Bodies Produced Thereby". A method of forming metal matrix composite bodies by a self-generated vacuum process is disclosed in Commonly Owned U.S. Patent No. 5,224,533, 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". Methods of forming macrocomposite bodies by somewhat related processes are disclosed in Commonly Owned U.S. Patent No. 5,247,986, entitled "A Method of Forming Macrocomposite Bodies by Self-Generated Vacuum Techniques, and Products Produced Therefrom" in the names of Robert C. Kantner et al. and Commonly Owned U.S. Patent No. 5,188,164, 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". Methods of forming shaped metal matrix composite bodies by a self-generated vacuum process are disclosed in Commonly Owned U.S. Patent No. 5,316,069, entitled "Method of Making Metal Matrix Composite Bodies With Use of A Barrier" . A novel approach to the formation of ceramic materials is disclosed generically in Commonly Owned U.S. Patent No. 4,713,360, in the names of Marc S. Newkirk et al. and entitled "Novel Ceramic Materials and Methods for Making Same". This method was improved upon in Commonly Owned U.S. Patent No. 4,853,352, in the names of Marc S. Newkirk et al., and entitled "Methods of Making Self-Supporting Ceramic Materials". Further, 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 U.S. Patent Nos. 5,187,130, 4,916,113, and 4,851,375. A method for producing ceramic composite bodies having a predetermined geometry or shape is disclosed in Commonly Owned U.S. Patent No. 5,162,273, and Commonly Owned U.S. Patent No. 5,162,273. 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 No. 4,923,832. Moreover, 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. Patent Nos. 5,051,382, 4,828,785, 4,859,640. 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. Patent Nos. 4,918,034 and 4,900,699. Moreover, a method for tailoring the constituency of the metallic component of a ceramic matrix composite structure is disclosed in Copending U.S. Patent No. 5,017,533. Moreover, U.S. Patent Nos. 5,185,303, 5,066,618 and 4,818,734 also 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. The entire disclosures of all 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: "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. "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. "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. "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. "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. "Filler", as used herein in conjunction with 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. "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 interlay er 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. "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. "Preform" or "Permeable Preform", as used herein in conjunction with both metal 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. " 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. 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. "Spontaneous 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). Summary of the Invention The present invention comprises improved materials useful as, for example, brake rotors and clutch plates for ground vehicles. Specifically, the present invention comprises substrate brake rotor and clutch plate materials that are coated with an appropriate material by an appropriate process to result in a lower metal content at or near the friction surfaces thereof. It should be noted that this application focuses primarily on brake rotors and clutch plates; however, an artisan of ordinary skill will understand that other acceptable similar uses are possible, even though such uses are not discussed expressly herein. Specifically, by providing a second material as a coating on an appropriate substrate material (e.g., metals or metal matrix composites) a surface enhancement of the brake rotors and clutch plates is achieved. This type of surface enhancement may result in the formation of a physical barrier which prevents scuffing and/or scarring which normally would occur on a softer material. Moreover, this surface enhancement may result in the production of a thermal barrier which at least partially thermally insulates a lower melting substrate from high heat generated by, for example, frictional forces. Accordingly, it is believed that the overall performance level of metals and metal matrix composites utilized as materials for brake rotors and clutch plates is significantly enhanced by placing one or more specific coating(s) thereon. Desirable coating methods useful for practicing the present invention include anodizing techniques, plasma spraying techniques, flame spraying techniques, electrolytic coating techniques, dip coating techniques and the use of preceramic polymer based coatings. While each of these techniques has specific advantages and disadvantages, common to each of the techniques is the resultant coating which provides desirable surface properties which differ from one or more properties of the substrate material itself. The coating also should be capable of adhering to the substrate material under conditions which are typical for the operation of the article. The desirable thickness of such coatings will vary depending upon the particular application (e.g., environmental conditions) to which the article will be exposed. For example, with regard to brake rotors, if the substrate material comprises aluminum or an aluminum metal matrix composite, desirable coating thicknesses should be from about 5 microns to about 200 microns. However, the coating thickness needs to be analyzed with regard to several factors, including amount of thermal insulation provided by the coating, the ability of the coating to adhere to the substrate (e.g., the thermal expansion coefficients of the substrate and the coating should be similar (i.e., not differ by more than about 5-50 percent)), etc. In this regard, depending on a particular application and the materials involved, the performance of the brake rotor and clutch plate can be a function of the thickness of the coating on the substrate materials. Brief Description of the Drawings Figure 1 is a schematic of the thermocouple placement in the rotor during the determination of the MOT and corresponds to a vented front brake rotor for the 1991 model year Ford Escort; Figure 2 is taken from SAE J212 and is a schematic of the thermocouple placement in the brake pad during the determination of the MOT. Detailed Description of the Invention and Preferred Embodiments The present invention comprises improved materials useful as, for example, brake rotors and clutch plates for ground vehicles. Specifically, the present invention comprises substrate brake rotor and clutch plate materials that are coated with an appropriate material by an appropriate process to result in a lower metal content at or near the rubbing surfaces thereof. It should be noted that this application focuses primarily on brake rotors and clutch plates; however, an artisan of ordinary skill will understand that other acceptable similar uses are possible, even though such uses are not discussed expressly herein. Specifically, by providing a second material as a coating on an appropriate substrate material (e.g., metals or metal matrix composites) a surface enhancement of the brake rotors and clutch plates is achieved. This type of surface enhancement may result in the formation of a physical barrier which prevents scuffing and/or scarring which normally would occur on a softer material. Moreover, this surface enhancement may result in the production of a thermal barrier which at least partially thermally insulates a lower melting substrate from high heat generated by, for example, frictional forces. Accordingly, it is believed that the overall performance level of metals and metal matrix composites utilized as materials for brake rotors and clutch plates is significantly enhanced by placing one or more specific coating(s) thereon. Desirable coating methods useful for practicing the present invention include anodizing techniques, plasma spraying techniques, flame spraying techniques, electrolytic coating techniques, dip coating techniques and the use of preceramic polymer based coatings. While each of these techniques has specific advantages and disadvantages, common to each of the techmques is the resultant coating which provides desirable surface properties which differ from one or more properties of the substrate material itself. The coating also should be capable of adhering to the substrate material under conditions which are typical for the operation of the article. The desirable thickness of such coatings will vary depending upon the particular application (e.g. , environmental conditions) to which the article will be exposed. For example, with regard to brake rotors, if the substrate material comprises aluminum or an aluminum metal matrix composite, desirable coating thicknesses should be from about 5 microns to about 200 microns. However, the coating thickness needs to be analyzed with regard to several factors, including amount of thermal insulation provided by the coating, the ability of the coating to adhere to the substrate (e.g., the thermal expansion coefficients of the substrate and the coating should be similar (i.e., not differ by more than about 5-50 percent)), etc. In this regard, depending on a particular application and the materials involved, the performance of the brake rotor and clutch plate can be a function of the thickness of the coating on the substrate materials. It should be recognized that a complex interrelationship of properties is difficult to quantify with respect to rating the performance of brake rotors and clutch plates; however, one item which is readily quantifiable for brake rotors and clutch plates is the Maximum Operating Temperature ("MOT") which a material can experience. For example, under a given set of testing conditions, every brake 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. Rotors of the present invention utilizing aluminum and/or aluminum metal matrix composites as substrates with appropriate coatings thereon readily achieved MOT's of 1000°F (538°C) and above. These MOT's having never before been achieved by prior art rotors having similar compositions to the substrate compositions of the present invention. Accordingly, the present invention is a significant achievement in the rotor art (as well as in the clutch plate art because similar considerations apply) 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 MOT is primarily dependent on the material composition and not on the rotor design or the test conditions. The MOT of a material formed as a brake rotor or disc is determined using dynamometer tests adopted from SAE J212, "Brake System Dynamometer 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. The MOT of a material as a brake rotor or disc is determined using dynamometer tests adopted from SAE J212, "Brake System Dynamometer 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 have 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 Figures 1 and 2, respectively. Figure 1 is a schematic of the thermocouple placement in the rotor during the determination of the MOT and corresponds to a vented front brake rotor for 1991 model year Ford Escort. Figure 2 is taken from SAE J212 and is a schematic of the thermocouple placement in the brake pad during the determination of the MOT. The 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 Temp., °F 150 (65.5°C) 150 (65.5°C) 150 (65.5 °C) Initial Speed, mph 60 (97 km/h) 60 (97 km/h) 60 (97 km/h) Deceleration, ft/s 2 15 (4.6 m/s 2 ) 15 (4.6 m/s 2 ) 15 (4.6 m/s 2 ) No. of stops 10 15 15 Cycle Time, s 35 35 35 Cooling Air Speed, mph 8 (12.8 km/h) 8 (12.8 km/h) 2 (12.8 km/h) 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 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 the MOT. The tests for determining 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 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 Substrate metal matrix composite materials can be fabricated according to any of the metal matrix composite formation techniques discussed above herein. However, preferred techniques for forming the metal matrix composite substrate portions can be found in the Examples set forth in U.S. Patent Application Serial No. 08/127,655, which was filed on September 27, 1993, in the names of Dwivedi et al., and entitled "Brake Rotors and Methods For Making The Same", the subject matter of which is herein expressly incorporated by reference. One preferred technique for forming a desirable coating on a substrate metal matrix composite material is an anodizing technique. Specifically, U.S. Patent No. 5,225,069, which issued on July 6, 1993, in the names of Haupt et al. and entitled "Process for the Production for Oxide Ceramic Surface Films on Silicon-Containing Light Metal Cast Alloys" disclosed a desirable coating method. Particularly, this patent discloses an anodizing procedure which results in the production of oxide ceramic surface films on substrate metals. The resultant surface films provide desirable properties for the brake rotors and clutch plates of the present invention. The subject matter of U.S. Patent No. 5,225,069 is herein expressly incorporated by reference. It has been unexpectedly discovered that by placing a desirable coating (e.g., an anodized layer according to U.S. Patent No. 5,225,069) on an aluminum metal matrix composite reinforced with silicon carbide filler results in unexpected desirable performance as a brake rotor. Specifically, by forming an anodized layer having an approximate thickness of about 10 microns a desirable brake rotor and/or clutch plate can be formulated.

Claims: WHAT IS CLAIMED IS: 1. A component comprising: a substrate comprising at least one of a metal and a metal matrix composite; and * 5 at least one coating covering at least a frictional contact portion of said component. 2. The component of claim 1, wherein said at least one coating provides at least one surface enhancement to said substrate selected from (1) a physical barrier which 10 prevents scuffing and scarring of said substrate, and (2) a thermal barrier which at least partially thermally insulates said substrate. 3. The component of claim 1 or claim 2, wherein said at least one coating has a thickness of from about 5 microns to about 200 microns. 15 4. The component of any of the preceding claims, wherein the thermal expansion coefficients of said substrate and said at least one coating do not differ by more than about 5 to 50 percent. 20 5. The component of any of the preceding claims, wherein said at least one coating comprises at least one anodized oxide ceramic surface film. 6. The component of any of the preceding claims, wherein said component comprises a brake rotor, said substrate comprises metal, and said at least one coating acts 25 as a physical barrier and a thermal barrier. 7. The component of any of the preceding claims, wherein said component comprises a brake rotor, said substrate comprises a metal matrix composite, and said at least one coating acts as a thermal barrier. 30 8. The component of any of claims 1-5, wherein said component comprises a clutch plate, said substrate comprises metal, and said at least one coating acts as a physical barrier and a thermal barrier. 35 9. The component of any of claims 1-5, wherein said component comprises a clutch plate, said substrate comprises a metal matrix composite, and said at least one coating acts as a thermal barrier. 10. The component of claim 6 or claim 8, wherein said metal comprises aluminum. 11. The component of claim 7 or claim 9, wherein said metal matrix composite comprises an aluminum metal matrix composite. 12. The component of claim 10 or claim 11, wherein said component has a maximum operating temperature of at least 1000°F (538°C) 13. The component of claim 11, wherein said aluminum metal matrix composite comprises at least one filler selected from the group consisting of oxides, carbides, borides and nitrides. 14. The component of claim 13, wherein said at least one filler comprises at least one material selected from silicon carbide and aluminum oxide. 15. The component of claim 5, wherein said coating has a thickness of about 10 microns.

Inventors: DWIVEDI RATNESH KUMAR, GRAY THOMAS M, HOLLINS MICHAEL JOHN, IRICK VIRGIL JR, DWIVEDI, RATNESH, KUMAR, GRAY, THOMAS, M., HOLLINS, MICHAEL, JOHN, IRICK, VIRGIL, JR.
Applicants: LANXIDE TECHNOLOGY CO LTD, LANXIDE TECHNOLOGY COMPANY, L.P.
Application year: 1995
Main classification: F16D65
IPC codes: C22C32, C23C30, C25D11, F16D13, F16D65, F16D69