Diamond film and solid particle composite structure and methods for fabricating same

Porous and non-porous compositions include diamond particles, non-diamond particles, or mixtures of particles consolidated with polycrystalline diamond. The composite compositions of the present invention may be formed by a process which includes the steps of preforming the particles into a preform having a desired shape, and consolidating the preform with polycrystalline diamond. The polycrystalline diamond is preferably formed using CVD techniques including application of sufficient microwave energy to maintain the preform at a temperature of between about 670.degree. and 850.degree. C. The preform may be rotated during a portion of the deposition process.

BACKGROUND OF THE INVENTION 
1. Field Of The Invention 
The present invention relates to compositions of diamond and non-diamond 
particulate solid materials consolidated with polycrystalline diamond, and 
to methods for manufacturing these materials. 
2. The Prior Art 
The advent of methods for formation of polycrystalline diamond films has 
opened up a wide variety of new applications for diamond as an engineering 
material. Thin (.apprxeq.4000 .ANG.) films of this new material have 
become the basis for commercially available X-ray detector windows (sold 
By Crystallume of Menlo Park, Calif.), while thicker diamond films 
(typically 0.3-0.5 mm) are being used to enhance the power dissipation 
capabilities of thermally-limited electronic devices such as laser diodes, 
laser diode arrays, and microwave power amplifier transistors. 
While solid diamond films, produced by chemical vapor deposition methods, 
are finding increasing commercial utility, cost is still a barrier to 
their radiation into wider use. In particular, for applications which 
require very thick sections and/or which require fabrication of complex 
shapes, the polycrystalline CVD diamond materials are often prohibitively 
expensive, due to the excessive deposition time required to grow thick 
sections, and/or due to the extreme expense of mechanically fabricating 
diamond, the hardest known substance. 
Earlier attempts at consolidation of diamond particles using diamond CVD 
are known in the art. The earliest known of these were experiments by 
William G. Eversole, which consisted of passage of methane gas over heated 
diamond dust. These experiments, which led to an issued U.S. Pat. No. 
3,030,188, produced only a thin, hard, mainly graphitic crust of deposited 
material on the exterior of the diamond powder mass, leaving the interior 
unconsolidated. 
Other later attempts by Japanese researchers involving pyrolysis of methane 
and/or benzene on heated diamond dust led essentially to the same 
nonutilitarian results achieved by Eversole, and did not demonstrate a 
useful degree of consolidation of particles (Matsumoto, S; and Setaka, N; 
Consolidation of Diamond Powders by Thermal Decomposition of Methane and 
Benzene; Journal of Materials Science, vol. 15, pp. 1333-1336). 
The lack of success in these attempts at consolidation of particulates by 
formation of a matrix of diamond material stimulated development of 
alternate technologies, including use of "glues" (such as liquid metals) 
which are infiltrated into the particulate mass liquid form and allowed to 
solidify through freezing and shock-consolidation methods, in which 
explosively generated shock waves pass through a diamond particulate mass 
and briefly melt the diamond particles, with solidification and partial 
consolidation occurring after passage of the shock wave (Potter, David K.; 
Ahrens, Thomas, J.; Dynamic Consolidation of Diamond Powder into 
Polycrystalline Diamond, Applied Physics Letters 51 (5), Aug. 3, 1987, pp. 
317-319). This technology has not been capable of producing commercially 
useful diamond composite or consolidated objects due to its inability to 
generate large pieces (e.g., volumes .gtoreq..about.1 cm.sup.3) without 
cracks and other structural flaws. 
BRIEF DESCRIPTION OF THE INVENTION 
This application describes a new class of diamond composite materials in 
which particulates consisting in part or in whole of diamond are 
consolidated, or "glued" together by deposition of a matrix of 
polycrystalline diamond material or other material using chemical vapor 
deposition (CVD) techniques. As will be described herein, this approach 
enables the rapid, cost-effective, production of diamond materials of 
arbitrary thickness, and which exhibit complex shapes and topologies in 
their as-grown state, necessitating little or no post-consolidation 
machining operations. 
Application requirements which can now be filled using composite diamond 
materials as described herein include large area electronic packaging 
(e.g., multichip modules), ceramic turbine blades and rotors (e.g., 
automotive turbochargers and jet engine components), precision gauge 
blocks, and corrosion-proof porous ceramic filters. According to a first 
aspect of the present invention, both porous and non-porous compositions 
include diamond particles consolidated with polycrystalline diamond. 
According to a second aspect of the present invention, both porous and 
non-porous compositions include non-diamond solid particles consolidated 
with polycrystalline diamond. The solid particles may include any material 
which is compatible with polycrystalline diamond deposition techniques. 
According to a third aspect of the present invention, both porous and 
non-porous compositions include mixtures of different solid particles and 
composite particles consolidated with polycrystalline diamond. The solid 
particles may include diamond or any material which is compatible with 
polycrystalline diamond deposition techniques. 
According to yet another aspect of the present invention, the diamond and 
non-diamond particle compositions of the present invention may be formed 
by a process which includes the steps of arranging the particles into a 
preform having a desired shape, and consolidating the preform with 
polycrystalline diamond. The polycrystalline diamond is preferably formed 
using CVD techniques including application of sufficient energy to 
maintain the preform at a temperature of between about 670.degree. and 
850.degree. C. The preform may be rotated during a portion of the 
deposition process.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
The present invention includes both porous and non-porous compositions 
including diamond and non-diamond particles consolidated with 
polycrystalline diamond. FIG. 1 is a schematic representation of a cross 
sectional view of a diamond consolidated particle composition 10 according 
to the present invention showing particles 12 consolidated by diamond 14. 
The particles may be either solid particles or composite particles, i.e., 
particles formed from a first material coated with a layer of a second 
material. While FIG. 1 shows a composition comprising solid particles, 
FIG. 2 shows a composition 16 in which particles 18 are first coated with 
a layer 20 of different material and consolidated by diamond 14. 
The particles (or the surface portion of composite particles) may comprise 
any material which is compatible with polycrystalline diamond deposition 
techniques. It is presently contemplated that particles comprised of 
materials which work well for diamond deposition as substrates in regular 
flat surface form, including, but not limited to, diamond, silicon 
nitride, tungsten, tungsten carbide, molybdenum, silicon, and aluminum 
will provide suitable particle substrates for consolidation into the 
compositions of the present invention. It is believed that particulate 
quartz and alumina may also be consolidated according to the present 
invention. Particle mixtures of different materials are also consolidated 
within the scope of the present invention. It has been demonstrated that 
diamond and silicon carbide particles may be consolidated into porous and 
non-porous articles according to the present invention. 
According to one embodiment of the present invention, enhancement of 
thermal conductivity and strength of polycrystalline diamond compact, such 
as that sold under the trade name Compax by GE Superabrasives of 
Worthington, Ohio, are accomplished by further consolidating it using the 
present invention. This starting compact material is created by first 
metal-coating diamond particles and then pressing them together under high 
pressure and temperature. The metal coating melts and allows the 
underlying diamond grains to grow partially together. After cooling, the 
metal matrix may be leached away with a solvent, such as an acid or 
mixture of acids, leaving a porous network of diamond particles. 
Consolidation of this material according to the present invention further 
enhances the physical properties of this material. 
The consolidation process of the present invention may be used to 
consolidate a broad range of particle sizes. Particle sizes of 0 to 5 
microns in diameter and particle sizes above 5 microns in diameter may be 
consolidated utilizing the present invention. It is presently believed 
that the optimum particle and pore size will depend on the application to 
which the finished product will be put. For example, the particle and pore 
size distribution which is best for maximum consolidation will probably be 
less useful for producing a porous material for use as a filter. 
Generally, if the particles are too small, the surface will grow over with 
a solid diamond layer and terminate growth in the interior. If the 
particles are too large, impractically long deposition times may be 
required to achieve good consolidation because pore sizes will be large. 
This consideration will also affect the size of the objects to be 
fabricated according to the present invention. The center of thicker 
objects must be assured of consolidation prior to the completion of 
surface consolidation which cuts off the flow of reactant gases. 
Diamond particles of 10 .mu. and 100 .mu. and silicon carbide particles of 
100 .mu. in diameter have been successfully consolidated at an average 
deposition rate of approximately 1 .mu./hour. At this deposition rate, the 
100 .mu. particles form better compositions than the 10 .mu. particles 
because deposition at and immediately adjacent to the surface of the 10 
.mu. particles causes premature closure of the surface porosity (i.e., 
within about 6-10 hours), resulting in cessation of deposition, and 
therefore of consolidation, within the interior of the material. 
FIGS. 3a and 3b are scanning electron micrographs of diamond particles 
shown, respectively, prior to and after consolidation with diamond 
according to the present invention. The effect of the diamond coating may 
be seen in FIG. 3b. 
FIGS. 4a and 4b are scanning electron micrographs of silicon carbide 
particles shown, respectively, prior to and after consolidation with 
diamond according to the present invention. The effect of the diamond 
coating may be seen in FIG. 4b. 
Consolidation tests have been performed using irregularly shaped (i.e., 
particles with fracture surfaces and aspect ratios of up to about 3 to 1) 
particles of natural diamond dust and ordinary synthetic silicon carbide 
abrasive particles. The tests demonstrate that irregularly shaped 
particles work well with the current invention. Recent CVI modelling work, 
S. M. Gupte and J. A. Tsamopoulos, Forced Flow Chemical Vapor Deposition 
of Porous Ceramic Materials, J. Electrochem. Soc., Vol. 137, No. 11, 
November 1990, pp. 3675-3682 indicates that pore size distribution (which 
is strongly influenced by particle size and shape) critically determines 
the degree of densification achievable and processing time required. It is 
presently believed that a uniform pore size leads to the greatest 
densification under forced flow conditions. 
Particle shape will also affect the properties of the finished composite. 
If particles have a large length/diameter ratio (in excess of about 7/1), 
they will behave more like fibers and may improve the fracture toughness 
of the composite material. Other properties, like scattering of polarized 
light, and directionality of thermal conductivity, may also be affected by 
use of fiber-like particles. 
The present invention also contemplates consolidation of mixtures of 
diamond and non-diamond particles. Varying the proportions of diamond and 
non-diamond particles in compositions made according to the present 
invention allows for the control of important physical properties of the 
resulting material. For example, thermal expansion, and thermal and 
electrical conductivity of compositions made according to the present 
invention may be controlled by altering the ratio of diamond to 
non-diamond particles from which the composition is made. At a given 
porosity, the thermal impedance of the composition will be approximately 
the weighted average of the thermal impedances of the component materials, 
weighted by volume percent of composition. 
In some circumstances, it may be desirable or necessary to employ particles 
or fibers which are themselves composites of two or more materials. For 
example, nickel and iron are poisonous to the diamond deposition process. 
Consequently, if it is desired to consolidate nickel or iron particles 
with diamond material, it may be necessary to coat each particle prior to 
final diamond consolidation with a material which presents a hospitable 
surface for diamond deposition. Thus a thin layer of metal such as 
molybdenum or ceramic such as silicon carbide, both of which are known to 
support diamond deposition, may be applied to the iron or nickel particles 
to prepare them for consolidation with diamond as earlier described. 
Additional areas of utility for composite particles as precursors to 
densify with diamond include modification of electrical, thermal, or 
mechanical properties through use of appropriate coatings. 
A similar process may be used to form composite fibers which may then be 
used for consolidation with diamond. In this instance, use of composite 
fibers not only allows use of inhospitable fiber materials and/or 
modification of selected properties, but also makes available composite 
fibers which are substantially all diamond for use as elements in the 
manufacture of a diamond-fiber-reinforced, diamond-consolidated composite 
material. 
For example, when 5 .mu. fibers of silicon nitride (HPZ silicon nitride, 
available from Dow Corning) are coated with approximately 25 .mu. of 
diamond through chemical vapor deposition means, a 50 .mu. diameter fiber 
is formed whose greater portion consists of diamond, and whose properties 
are substantially those of a pure diamond fiber. This is useful because 
current technology does not permit the economic manufacture of pure 
diamond fibers. 
Because a critical factor in determining the mechanical properties of fiber 
reinforced materials is the behavior of the interface between the fiber 
and the surrounding matrix, it may be desireable to modify the surface 
chemistry of a diamond composite fiber by applying an outer overcoat layer 
of an appropriate material. For example, use of a silicon carbide overcoat 
or a thin metal layer such as molybdenum will increase the adhesive 
strength between the diamond composite fiber and the surrounding matrix. 
FIG. 5 is a schematic representation of a cross sectional view of a mixed 
fiber and particle composition 22 consolidated with polycrystalline 
diamond 14. Non-diamond fibers, for example silicon carbide, silicon 
nitride, or alumina, are shown at reference numeral 24. 
Diamond-consolidated fibers are shown at reference numeral 26 coated with 
a layer of diamond 28. Diamond-consolidated fibers, coated with a layer of 
diamond 28 and overcoated with non-diamond layer 32, comprising 
substances, for example quartz, silicon carbide, silicon nitride, or 
alumina, are shown at reference numeral 30. For illustrative purposes 
only, the composition 22 of FIG. 5 is shown comprising several types of 
fibers and particles which may be consolidated according to the present 
invention. Those of ordinary skill in the art will recognize that an 
actual composition 22 formed according to the present invention may 
contain one or more of the types of particles and/or fibers actually shown 
in FIG. 5. 
There appears to be no inherent limitation regarding the ratio of diamond 
to non-diamond particles which may be consolidated according to the 
present invention, so long as the material of which the non-diamond 
particles are comprised is compatible with diamond deposition, and is of a 
size range which will allow proper consolidation. With respect to size 
range ratios, there will be various optimum particle size distributions 
depending on specific process operating conditions. By properly tailoring 
the pore size distribution as a function of position within the mass being 
consolidated to compensate for deposition rate differences, it may be 
possible to achieve higher densification than with a simple uniform pore 
size distribution. 
For example, a higher overall degree of consolidation may be achieved by 
fabricating preforms such that pores most distant from the source of 
reactant gases are smaller than those closest to the source of reactant 
gases. This average reduction of pore size with increasing distance from 
the reactant gas source compensates for the reduction in growth rate which 
occurs with increasing distance from reactants. This technique may be used 
in combination with imposed thermal gradients and/or controlled gas flow 
methods, but is particularly useful when thermal gradients and/or 
controlled gas flow techniques cannot be employed due to specific 
application or engineering requirements. 
One major controlling factor in the process according to the present 
invention is the deposition rate. For example, if the average particle and 
pore size are about 100 .mu., a growth rate of 1 .mu./hr will close off 
the average pore in 50 hours. A presently preferred maximum growth rate is 
about 1% of the average particle size, expressed in microns/hr. Thus, a 
particle preform having average particle sizes of about 100 .mu. can be 
consolidated using a process with a deposition rate of about 1 .mu./hr. 
This is a rule of thumb rather than a hard and fast rule, and departures 
from this rule will be fairly common, depending on particle shape, whether 
more than one particle size is present, and on whether thermal gradients 
and gas flows in the process are arranged to modify local deposition 
rates. 
For example, a way to increase the degree of consolidation of a composition 
according to the present invention is to arrange for the region most 
distant from the plasma or other reactant source to be the hottest. 
Because deposition rate is a strong function of temperature, this 
compensates for the tendency for the regions nearest to the plasma to grow 
more quickly, and postpones premature termination of consolidation 
resulting from closure of gas diffusion passages. Under these 
circumstances, a faster deposition rate may be useable. 
Although the foregoing discussion of consolidation of particulates by 
chemical vapor infiltration has focused on the use of polycrystalline 
diamond as a matrix material, those of ordinary skill in the art will 
recognize that operative embodiments of the present invention can be used 
to consolidate diamond particles in the variety of forms discussed herein 
by chemical vapor infiltration of non-diamond matrix materials such as 
silicon carbide. This process produces a further variety of diamond 
composite materials having desireable properties and broadens the 
commercial utility and application of diamond composite materials. A 
specific example of such a system is the consolidation of diamond 
particles by chemical vapor infiltration of silicon carbide matrix 
material, using methane and silane gas chemistry as is well known in the 
art. 
According to a presently preferred embodiment of the present invention, a 
composition comprising polycrystalline diamond and either diamond or 
non-diamond solid or composite particles may be fabricated using CVD 
techniques. Those of ordinary skill in the art will recognize that, while 
the preferred embodiment disclosed herein utilizes microwave power, other 
sources of energy, such as combustion flames, plasma torches, etc., may be 
used to drive the deposition of diamond. The present invention 
contemplates formation of the composite material using any known diamond 
deposition process. 
The particle substrate material is first selected. Natural diamond powder, 
such as 100 .mu. type N diamond powder available from Flat-Tech Systems of 
Glenview, Ill., or commercial silicon carbide abrasive powder, such as 
Meccarb Nero grana P 225 available from Samatec of Milan, Italy have been 
successfully employed in the practice of the present invention. Where 
diamond particles are to be consolidated, natural diamond is preferred in 
order to avoid impurities which are sometimes present in the 
high-pressure, high-temperature synthetics which reduce thermal 
conductivity. 
The particles may be precleaned by rinsing them with isopropyl alcohol and 
drying them on filter paper. The particles may then be premixed as 
required. To prepare particle mixtures, the appropriate amounts are 
weighed out in the dry state and the weighted amounts are transferred into 
a beaker or crucible for subsequent mixing. 
Small amounts of a liquid, such as isopropyl alcohol or polyvinyl alcohol 
are preferably added to the dry particle mix to form a pourable slurry. 
The properties of the ideal slurry-forming liquid, or vehicle, include 
somewhat elevated viscosity (to prevent rapid settling of particles after 
mixing) and complete, residue-free evaporation from the slurry after 
pouring into a mold. 
The slurry is then poured into a mold having the desired shape of the 
finished consolidated article and the slurry vehicle is allowed to 
evaporate, either unaided, or with the assistance of vacuum and/or heat, 
to leave a particle preform. Too rapid vehicle removal causes bubble or 
void formation in the finished preform. For uniform thickness, the mold 
must be kept level. This is especially important for thin, wide items, as 
slight tilts cause the slurry to pile up at one side of the mold. 
On the other hand, deliberate mold tilting may be employed to obtain linear 
thickness variation if desired. In addition, a circular mold may be spun 
to obtain a parabolic thickness distribution through the interaction of 
centrifugal force and gravity. 
Mold material and surface finish can be important, depending on the desired 
result. Ideally, a mold should be made of a material to which diamond does 
not strongly adhere or grow upon, to ease post-deposition mold separation. 
The mold surface texture is replicated in the adjacent consolidated 
material, so smooth finishes may be obtained in the completed material if 
a mold with a polished surface is employed. Molds can also include shapes 
of various types which give contour and relief to the finished material. 
This is an especially important capability in that it reduces or 
eliminates the need for post-deposition machining, an important 
cost-reduction consideration in view of the hardness of the finished 
product. 
A circular copper gasket with an inner diameter of 2.25 inches centered on 
the polished surface of a silicon wafer has been shown to function 
satisfactorily as a mold. A copper gasket about 2 mm thick has been 
employed, although other thicknesses may be employed. The gasket is simply 
placed on the wafer and is kept in place by gravity. The silicon surface 
is extremely flat and smooth, and is compatible with the diamond 
deposition environment. It is easily etched away following deposition. 
The isopropyl alcohol vehicle may be removed by evaporation accelerated 
with gentle heating. The mold is placed on a levelled hot plate, and the 
slurry is poured into the mold. Generally, the seal between the copper 
gasket and the wafer surfaces is good enough that very little liquid leaks 
out. The particles are too large to be carried along small leak paths. 
After the slurry is poured and levelled (if needed), the hot plate is 
turned on and the slurry temperature is allowed to increase to about 40-45 
C. Evaporation takes about 2 hours. 
When the vehicle has evaporated, the copper gasket is carefully removed by 
lifting it vertically off the wafer. This leaves a disc of loosely-bound 
particles on the wafer. The copper gasket is removed because copper is not 
compatible with the diamond deposition process. The preform particle 
composite disc is placed, still on the underlying wafer, in a diamond 
deposition system. Any deposition system capable of producing diamond may 
be used. 
The polycrystalline diamond deposition process is preferably carried out in 
a CVD reactor capable of depositing diamond, such as a model HPMS, 
available from Applied Science and Technology, Inc., of Woburn, Mass. 
According to a presently preferred embodiment of the invention, deposition 
proceeds in two stages. 
The two deposition stages differ with respect to sample motion. During the 
first stage, the sample is stationary because it does not have the 
mechanical integrity to withstand rotation. During the second stage, the 
sample is strong enough to endure rotation when spun at up to 600 rpm. The 
rotational motion substantially increases deposition area and uniformity 
by reducing temperature gradients in the preform article. 
During the first stage of deposition, a mixed gas containing hydrogen 
(99.9995+% purity) at a flow rate of between about zero and 10 slm, 
preferably about 150 sccm, and methane (99.99+% purity) at a flow rate of 
between about 0.001 sccm and 1,000 sccm, preferably about 0.75 sccm is 
introduced into the deposition chamber at a pressure of between about 0.5 
and 100 torr. While it is presently preferred to conduct the deposition in 
the presence of a carbon-containing gas, it is believed that even without 
addition of methane or another carbon bearing gas, some diamond carbon 
will be gassified by the hydrogen plasma and will redeposit as diamond. 
The chamber is preferably pumped down slowly (over about a five minute 
period) to avoid explosively decompressing the preform article through 
rapid release of entrapped gases. Similarly, the gas flow into the chamber 
is initiated slowly to avoid blowing the unconsolidated powder of the 
preform all over the interior of the chamber. 
A plasma is ignited using about 800 watts of microwave energy at a 
frequency of above about 50 Mhz, preferably about 2.45 Ghz in a manner 
well known in the art. Following the establishment of a stable plasma, 
pressure is increased over a period of about two minutes until a pressure 
of about 60 torr is obtained. Simultaneously, microwave power is increased 
to maintain the temperature of the preform article to between about 
600.degree. C. and 850.degree. C. Typical microwave power levels necessary 
to achieve this operating substrate temperature are from about between 800 
to 1,500 watts, and depend on the specific composition and dimensions of 
the preform article to be densified. For example, a 3 mm thick, 2.25 inch 
diameter preform consisting of diamond particles required approximately 
1,400 watts of microwave power to maintain a measured temperature of 
approximately 735.degree. C. A 2 mm thick, 1 inch diameter preform 
consisting of silicon carbide particles required approximately 900 watts 
of microwave power to maintain a measured temperature of approximately 
770.degree. C. 
The power required to maintain a specific temperature changes during 
consolidation as the thermal conductivity and radiation properties of the 
consolidating material change during the process. In experience with 
particles consolidated by the inventor, microwave power was initially 
fixed at 850 watts. Other initial power levels, and other variation of 
power levels applied during consolidation may be required or advisable in 
light of the requirements of specific applications or process variations. 
After initial consolidation of the particulate preform article has been 
achieved and the preform article mass has acquired an enhanced degree of 
mechanical integrity (about twelve hours), the second stage of deposition 
includes rotating the support platform upon which the preform article 
rests. In a presently preferred embodiment, the rotational speed is 
between about 60 and 2,000 rpm, preferably about 300-600 rpm. In a 
presently preferred embodiment, the plasma may be simultaneously displaced 
from the center of the support platform to a position at about one half 
the radius of rotation of the preform article. The combination of rotation 
and plasma displacement provides more uniform heating of the preform 
article and leads to better deposition uniformity. In another preferred 
embodiment, the plasma position may be rapidly varied over the rotating or 
stationary preform through means of phase modulation of either or both the 
incident or reflected microwave energy which define the plasma location 
within the deposition chamber. This has the effect of increasing 
deposition area and uniformity. 
As the mass and densification of the preform article increases, the heat 
flow from it increases. Microwave power is therefore increased to maintain 
the preform article temperature at between about 600.degree. and 
850.degree. C. A power level of about 1,200 watts is presently preferred 
for a preform diameter of 2.25 inches. 
After continuation of the second deposition phase for between approximately 
48 to 168 hours, depending on the degree of porosity desired, the preform 
thickness, particle size, and growth rate achievable under required 
process conditions, during which microwave power is increased to maintain 
sample temperature, deposition is terminated by switching off the 
microwave power supply and discontinuing the flow of methane gas. The 
excess methane gas may be removed from the chamber by momentarily opening 
a high flow rate valve between the chamber and the vacuum pump. The sample 
is allowed to cool, preferably under flowing hydrogen gas at a pressure of 
about 100 torr. 
After cooling and removal from the reaction chamber, the silicon or other 
substrate support may be removed by etching. Where the support substrate 
is a silicon substrate, it may be dissolved in a 2:1 mixture by volume of 
concentrated reagent grade HNO.sub.3 and HF, which is sufficient to remove 
the silicon substrate without attacking the densified ceramic diamond 
article. 
Two diamond/non-diamond particle mixtures including 100 .mu. diamond 
particles intermixed with about 1 weight % of about 1 .mu. silicon 
carbide particles as nucleation aids were consolidated according to the 
present invention using slightly different process parameters. In the 
first process, 0.75 g of 1 .mu. silicon carbide particles, from Buehler 
Ltd., of Evanston Ill., comprising 1% by weight of the starting material 
were consolidated with 75 g of 100 .mu. N diamond particles from Flat-Tech 
Systems. A 3 mm thick preform having a 2.25 inch diameter was prepared as 
described above and placed in a CVD reactor. A gas mixture of 0.5 sccm 
CH.sub.4 and 150 sccm H.sub.2 was introduced in to the reactor at a 
pressure of 80 torre, and microwave power of 1500 watts was applied for a 
total time of 58.4 hours. After 2 hours, the workpiece was rotated at 
about 300 rpm for an additional 56.4 hours. The resulting composition was 
found to be hard, with considerable mechanical integrity. The top and side 
surfaces of the particulate preform could not readily be damaged by 
application of pressure with sharp probes. During exposure of the 
densified composite to mixed acids as described previously to free the 
composite from its silicon mold, no attack by the acids was noted on the 
composite, although the underlying silicon mold was rapidly and completely 
removed. After removal of the silicon mold, the surface of the composite 
adjacent to the polished silicon mold was found to be substantially smooth 
and hard, indicating that consolidation and densification processes had 
occurred at the region of the preform which was furthest from the plasma. 
The composite dimensions and weight were measured and the densified article 
was found to be approximately 63% dense, based upon an assumption of 100% 
diamond composition of solid materials present. The composite was stressed 
to fracture, and scanning electron micrographs were taken of particles 
within the interior of the article. This inspection disclosed diamond 
growth over all of the interior particles. 
In the second process, 0.75 g of 1 .mu. silicon carbide particles, from 
Buehler Ltd., of Evanston Ill., comprising 1% by weight of the starting 
material were consolidated with 75 g of 100 .mu. N diamond particles from 
Flat-Tech Systems. A 3 mm thick preform having a diameter measuring 2.25 
inches was prepared as described above and placed in a CVD reactor. A gas 
mixture of 0.5 sccm CH.sub.4 and 150 sccm H.sub.2 was introduced in to the 
reactor at a pressure of 90 torr, and microwave power of 1800 watts was 
applied for a total time of 83.4 hours. After 1.5 hours, the workpiece was 
rotated at about 300 rpm for an additional 82 hours. The resulting 
composition was found to exhibit substantial mechanical integrity, and 
compared to the first composition, was similarly consolidated throughout 
its interior, ascertained after fracture of the densified article and 
scanning electron microscopy inspection. 
Although the consolidation process proceeds most efficiently within the 
temperature ranges cited herein, it will be appreciated by those of 
ordinary skill in the art that the particulate preform temperature must be 
such as to be compatible with the thermal tolerance limits of the 
materials comprising the particulates. Thus, if aluminum particles are to 
be consolidated with diamond, it is desirable never to exceed 
approximately 450.degree. C. to avoid softening and solid state 
diffusional bonding of the aluminum particles into a less penetrable mass. 
The consolidation process proceeds as at higher temperatures with other 
materials, subject to the expected reduction in growth rate of 
polycrystalline diamond at reduced temperatures for any given diamond 
growth process. 
The composite articles of the present invention may be formed in holes or 
other recesses of non-diamond materials prepared by etching, drilling or 
other mechanical processes to accept regions of diamond or non-diamond 
solid or composite particles. According to this aspect of the invention, a 
substrate material, such as silicon carbide, beryllium, aluminum, or other 
material compatible with diamond forming processes is prepared by forming 
one or more holes or other recesses. Particles to be consolidated are 
placed in the hole or recess and the loaded substrate material is placed 
in the diamond growth reactor. Consolidation of the particles is performed 
as disclosed herein. Where the substrate material is one to which 
deposited diamond will adhere, no other means need be used to secure the 
position of the consolidated mass in the hole or recess of the substrate 
material. Where the substrate material is one to which diamond has poor 
adhesion, the hole or recess can be formed using undercuts, i.e., its 
diameter increases with its depth below its surface. The diamond 
consolidated particle mass will be interlocked with the substrate material 
and thus be held thereto by a mechanically stable bond. 
One limitation on-the production of diamond consolidated particle 
compositions by chemical vapor infiltration is that there exists a limit 
on the thickness of the article which can be produced. This limitation 
occurs because, at some thickness determined by the particular process 
parameters in use, it is no longer possible to transport the necessary 
growth species from the surface of the article to its interior. This 
places limits on the commercial usefulness of diamond composite materials 
because there are items which, by their nature, require substantial 
section thicknesses for their manufacture. Examples of such articles which 
may require thick sections include turbine blades, metrology gauge blocks, 
and ceramic vacuum tube envelopes. 
According to another aspect of the present invention, articles having 
sectional portions of arbitrary thickness may be formed if the process is 
carried out by addition of new particulate material to the surface of the 
article undergoing consolidation. Such a process is illustrated in FIGS. 
6a-6e, a series of cross sectional views of a diamond consolidated article 
at various points in the process. 
Referring first to FIG. 6a, the initially unconsolidated particles are 
shown formed into a preform of a desired shape. FIG. 6b shows the article 
after particle consolidation has been completed according to the teachings 
of the present invention. 
Next, as shown in FIG. 6c, additional particles are added to the surface of 
the now consolidated article and further particle consolidation of the 
newly placed particles is accomplished, resulting in the thicker 
consolidated article shown in FIG. 6d. It is presently contemplated that 
two possible modes of operation of this phase of the process are possible. 
In a first batch mode, the consolidated article of FIG. 6b is removed from 
the deposition chamber, or the chamber is at least opened, and the 
additional particles are placed on the surface of the article. The 
deposition chamber is then closed and further deposition is performed to 
consolidate the new particles. Performance of this variation in the 
process will result in discernable boundaries within the article at the 
locations across the cross section of the article representing the 
surfaces where the new particles were placed. 
In certain applications, the boundaries within the article may have 
deleterious effects on the strength of the finished composite article. 
Where these features are undesirable in the finished article, a continuous 
process may be performed wherein additional particles are continuously 
added to the surface of the article at a rate determined by the progress 
of the consolidation process. For example, a consolidation process may be 
carried out in which particles to be consolidated are, dispensed in a slow 
continuous fashion using any of a number of particle dispenser mechanisms, 
including vibrating hoppers, impact hoppers, screw-driven particle feeds, 
or gas puff particle feeds. The particle feed rate is adjusted such that 
the average particle feed rate is not greater than the effective 
consolidation rate, i.e., such that particles are substantially fully 
incorporated into the underlying consolidated mass before an excessive 
depth of new particles are added. In this fashion, a continuous densified 
layer is formed by accretion of particles and infiltration of 
polycrystalline diamond matrix material. The particulars of particle feed 
rate are determined by such factors as matrix deposition rate, particle 
shape, particle size, and reaction temperature. A further advantage of 
continuous particle feed and consolidation is that the average depth of 
porous material which must be consolidated can be kept relatively shallow 
compared with the sections consolidated in batch processes, and therefore 
will be less subject to matrix material compositional variation with 
depth, producing a more uniform product. 
Where batch processing is employed, the process steps illustrated by FIGS. 
6c and 6d may be repeated as many times as necessary to obtain a finished 
article having a desired thickness as shown in FIG. 6e. Where continuous 
processing is utilized, the particle feed is stopped when enough material 
is present in the article to achieve the desired end thickness. 
While a presently-preferred embodiment of the invention has been disclosed, 
those of ordinary skill in the art will, from an examination of the within 
disclosure and drawings be able to configure other embodiments of the 
invention. These other embodiments are intended to fall within the scope 
of the present invention, which is to be limited only by the scope of the 
appended claims.