Dynamic compaction of composite materials containing diamond

This invention relates to high-hardness, high-toughness, high-density composite materials containing diamond, and a process for making such materials comprising applying shock compression to the composite powders and inducing an exothermic chemical reaction. The process is useful in making metal, ceramic and cermet diamond composite materials.

BACKGROUND OF THE INVENTION 
This invention relates to a process for making high-hardness and 
high-toughness diamond composite materials, and in particular, 
diamond-metal, diamond-ceramic, and diamond-metal-ceramic (cermet) 
composite materials. 
The prior art discloses the manufacture of composite materials by heating 
and compressing the composite powders. Mechanical pressures are generally 
used in the prior art. Various heating means are employed in the prior 
art, including ovens and the like. More recently, in the prior art, the 
heating is achieved by burning exothermic reaction mixtures such as 
thermite compositions, intermetallic reactions and the like. The 
exothermic powder is either mixed in the powder to be compressed, or fired 
as a separate layer adjacent to the composite material. Typical prior art 
methods are described below. 
Certain kinds of ceramic, metal and cermet composite materials can be 
synthesized by utilizing an exothermic reaction between the elemental 
constituents of these materials without any external heating. This 
processing technique is termed "Self-Propagating High-Temperature 
Synthesis," and has been abbreviated as SHS, SHTS and SUS. SHS processing 
has been investigated in the Soviet Union since 1967, and over 200 phases 
have been produced by this technique. Exothermic reactions have been 
utilized for many years in the United States for a variety of heat 
requirements and pyrophoric applications. It is only recently that this 
processing technique has been explored as a method for synthesis and 
sintering of ceramic, metal and cermet composite materials. 
In SHS processing, a strong exothermic reaction, ignited at one end of a 
compact of mixed precursory powders by heating (using electric spark, hot 
wire, ion beam, etc.), propagates spontaneously in the compact and passes 
through the whole sample. An example of this reaction is the synthesis of 
titanium diboride (TiB.sub.2) from titanium and boron powders. This 
reaction can be expressed as: 
EQU Ti+2B.fwdarw.TiB.sub.2 .DELTA.H =66.8 kcal/mol (at 298.degree. K.) 
The adiabatic temperature resulting from this reaction is calculated to be 
3190.degree. K. (assuming that all of the reaction heat contributes to 
increase the temperature of the reaction product), which corresponds to 
the melting point of TiB.sub.2. This particular reaction is 
self-sustaining. Self-sustaining reactions can occur only when a product 
phase is liquid or partially liquid at the reaction temperature. 
Therefore, not all exothermic reactions are self-sustaining. 
Currently, fundamental research and applications of SHS processing are 
progressing. A. P. Hardt and P. V. Phung have proposed a simple, 
diffusion-limited, reaction model and evaluated the exothermic reaction 
rates. They have found that reaction rate depends on two factors: (1) a 
heat transfer which is sufficiently low to allow accumulation of heat in 
the reaction zone; and (2) system characteristics of particle size and 
fusion temperature which are sufficiently small to promote a high rate of 
mass transfer. Hardt and Phung have shown experimentally that reaction 
characteristics can be altered by using suitable additives which alter the 
thermal conductivity. Table 1 shows some influential factors of physical 
and chemical characteristics of precursory powders on SHS reaction and 
product. 
TABLE 1 
______________________________________ 
Relation of SHS Characteristics to the Physical 
and Chemical Properties of the Starting Materials 
INFLUENCE OF INFLUENCE OF 
PRECURSOR PRECURSOR 
PHYSICAL CHAR- 
CHEMICAL CHAR- 
ACTERISTICS ACTERISTICS 
______________________________________ 
REACTION Adiabatic Reaction Rate 
CHARACTER- Temperature Reaction Mechanism 
ISTICS Conductive Heat Loss 
Volatile Evolution 
Reaction Initiation 
PRODUCT Densities Secondary Phases 
CHARACTER- Microstructure Impurity Content 
ISTICS Unreacted Material 
Porosity 
______________________________________ 
In the area of application research, J. D. Walton, Jr. and N. E. Poulos 
have applied the thermite reaction to production of high-temperature 
resistance cermets (1959). Self-bonding zirconium disilicide-aluminum 
oxide cermets (ZrSi.sub.2 -Al.sub.2 O.sub.3) were successfully produced 
from the thermite mixture of ZrO.sub.2, SiO.sub.2, and aluminum. Walton 
and Poulos reported some advantages of this method of production as 
follows: (1) inexpensive precursory powders; (2) low ignition temperature 
(980.degree. C.); (3) high reaction temperature (+2760.degree. C.); (4) 
short firing time; and (5) controlling the atmosphere was unnecessary. 
Therefore, this technique has a significant meaning for industrial 
production of ceramic, metal and cermet composite materials. 
During the American Ceramic Society's 86th Annual Meeting (1984), there 
were seven presentations about thermite reactions and SHS. One of these 
presentations disclosed the self-sintering of materials. TiB.sub.2, TiC, 
and compacts formed from these mixtures have a high potential for weapons 
systems applications. Such materials produced by conventional processes 
are expensive because powders with suitable properties for sintering are 
needed, and high-temperature and high-pressure sintering of these powders 
are required to produce high-strength materials. On the other hand, by 
using SHS processing, it may be possible to produce strongly bonded 
materials with desired phases from precursory powder mixtures by igniting 
only one end of the compact at room temperature. N. D. Carbin et al. 
examined the effect of precursory powder characteristics of resulting 
products in the system Ti-B-C and showed that mixtures containing fine 
titanium powder are easier to ignite and have slower reaction rates, but 
the products are more porous than those containing coarse powder. 
Furthermore, reaction rates in the mixtures using B.sub.4 C for the boron 
and carbon elements decreased about 100 times and partially sintered 
products containing TiB.sub.2 and TiC were produced. The resulting 
products seemed to be considerably porous. 
Recently, high-pressure, self-combustion sintering for ceramics, utilizing 
this SHS processing technique, were demonstrated from cooperative research 
by Osaka University and Sumitomo Electric Industries Ltd. in Japan. Their 
attempt is to eliminate the porosity in products produced by SHS by 
applying high pressure during the SHS process. It is reported that a dense 
TiB.sub.2 sintered compact was produced in a few seconds by electric 
ignition of a pressed titanium and boron mixture at 3 GPa; the relative 
density and microhardness value of the center region in the high pressure 
reaction cell was 95% and 2000 kg/mm.sup.2 for a 200 g load, respectively. 
This result suggests that the application of high pressures to SHS 
processing is very effective in eliminating porosity and has the potential 
of producing strong, dense ceramic compacts. However, in this 
high-pressure, self-combustion process, expensive and complicated 
high-pressure apparatuses and assemblies are required; the expense and 
complication is similar to conventional high-pressure sintering 
techniques. 
U.S. Pat. No. 4,255,374, to Lemcke et al, discloses a method of compacting 
interweldable powder materials into a solid body by using a shock wave. 
This patent does not disclose the use of shock or explosive compression to 
produce an exothermic chemical reaction or alloying between the powder 
ingredients. This patent discloses that such chemical reactions or 
alloying, in particular with respect to diamond powders, would be 
undesirable because of a general decrease in the hardness and wear 
resistance of the resulting product. 
U.S. Pat. Ser. No. 747,558 discloses an inexpensive method for producing 
high density compacts of refractory ceramics, ceramic composites, cermets 
and other high hardness materials. The method comprises applying explosive 
shock to the compact to produce exothermic sintering and bonding of the 
compact powder materials. 
A comprehensive article on the prior art formation of intermetallic 
compounds, most of which are formed exothermically, is an article entitled 
"Intermetallic Compounds: Their Past and Promise," set forth in 
Metallurgical Transactions A, Volume 8A, Sept. 1977, at page 1327 et seq. 
This article records the 1976 Campbell Memorial Lecture at the American 
Society for Metals. Attention is directed particularly to the footnotes 
and the literature references at the end of this article. 
Another article pertaining to prior art exothermic reactions is 
"Propagation of Gasless Reactions in Solids," by A. P. Hardt and P. V. 
Phung, 21 Combustion and Flame, pages 77-89 (1973). This article sets 
forth an analytical study of exothermic intermetallic reaction rates. 
Polycrystalline diamond is tougher than single crystalline diamond because 
of the random orientation of the crystal (no significant cleavage). Both 
polycrystalline and single crystalline diamond have a high hardness. Thus, 
natural and synthesized polycrystalline diamond composite materials are 
useful in cutting tools, wire-drawing dies and rock-drilling bits. 
Particularly in rock-drilling applications, high hardness and high 
toughness materials are required. Diamond cutting tools are being used in 
the automobile, airframe manufacturing and aircraft engine propulsion 
industries. The work materials in these fields are mainly aluminum alloys 
with a high silicon content, nickel- and titanium-based alloys, and gray 
cast irons. In recent years, high speed machine technology has been 
developed in the industries mentioned above in order to reduce machining 
costs and to increase productivity. For this purpose, tool materials with 
a high hardness and high toughness are required. Ceramic tool materials 
such as Si.sub.3 N.sub.4 -based ceramics, ZrO.sub.2 -based ceramics, and 
SiC-whisker reinforced alumina are being successfully developed and 
commercialized for high-speed machining of superalloys and cast irons. 
However, most attractive and effective tool materials comprise 
polycrystalline diamond because of the high hardness and high toughness 
properties. As an example, a comparison of the cutting performance of 
diamond tool and conventional cemented carbide tool is shown in Table 2. 
This table was obtained from 208 Science, R. H. Wentorf, R. C. DeVries and 
F. P. Bundy, p. 873 (1980). 
TABLE 2 
______________________________________ 
Cutting Performance of Sintered Diamond 
Compared to Cemented Carbide 
Total Number 
of Pieces 
Work Material Cut Per Tool 
______________________________________ 
Silicon-Aluminum SAE 332 
Compax Diamond Tool 412000 
Cemented Carbide 2400 
Rubber filled with nickel and aluminum powder 
Compax Diamond Tool 6000 
Cemented Carbide 140 
Type 390 Aluminum 
Compax Diamond Tool 12000-14000 
Cemented Carbide 3000 
Glass Filled Polypropylene 
Compax Diamond Tool 7000 
Cemented Carbide 400 
______________________________________ 
Some kinds of natural polycrystalline diamonds such as framesite, carbonado 
and ballas, are available for cutting tools and rock-drilling bits, but 
the amount of these materials is limited. Thus, most of the 
polycrystalline diamond for industrial applications has to be produced by 
means of high-pressure sintering techniques using diamond powder. Diamond 
is a typical, strong, covalently bonded material, and is unstable at high 
temperatures under ambient pressure. The sintering of diamond powders at 
high pressures and high temperatures has been studied by many 
investigators in the prior art. Stromberg and Stevens, 49 Ceramic 
Bulletin, p. 1030 (1970) and Hall, 169 Science, p. 868 (1970) reported the 
sintering of diamond with and without additives which were not useful as 
catalysts for diamond formation. The additives in their compacts served 
solely as a binder of diamond grains. Sintered diamond compacts with 
densities of 3.29 to 3.48 g/cm.sup.3 and compressive strengths of 4.4 to 
5.8 GPa were produced. However, these references pointed out that the 
surface transformation of diamond particles into low pressure forms during 
the sintering was a major problem in using this technique. On the other 
hand, Katzman and Libby, 172 Science, p. 1132 (1971), and Notsu et al., 12 
Materials Research Bulletin, p. 1079 (1977) reported the sintering of 
diamond powders using additives such as iron, nickel and cobalt, which can 
act as a catalyst for diamond formation. In this prior art sintering 
technique, the mechanical properties of the resulting compacts strongly 
depend upon the amount of additives. It is reported that extensive 
diamond-diamond bonding was successfully produced in the compacts during 
the sintering process. Sintered polycrystalline diamond compacts produced 
by this technique are being commercialized and used for many industrial 
applications in the prior art. 
The use of sintered diamond compacts can be expected to gradually increase 
in the automobile and aerospace industries in order to machine 
high-performance superalloys. Such compacts will also be useful in the 
high-speed machining of conventional and new materials. Especially, in 
these industries, there will be an increased demand for materials which 
are capable of cutting high-performance structural ceramics such as 
Al.sub.2 O.sub.3, Si.sub.3 N.sub.4 and SiC based ceramics and their pure 
materials. Sintered diamond appears to be the most effective and promising 
tool material for such machining due to its excellent mechanical and 
thermal properties. However, in the prior art, the extremely high price of 
sintered diamond compacts, compared to that of conventional cemented 
carbide and ceramic tools (about 20 times higher per corner available to 
cutting), is one of the factors preventing a wide usage of this material 
in industry. The high price of this material in the prior art is partially 
due to the high capital and operating costs of high pressure apparatuses 
in producing polycrystalline diamond compacts. 
SUMMARY OF THE INVENTION 
This invention relates to improved composite materials containing diamond. 
This invention further relates to a process of making composite materials 
containing diamond through dynamic compaction of powder materials and 
exothermic reaction sintering. Dynamic compaction is achieved by utilizing 
a shock compression technique. The diamond composite materials formed by 
the process of the invention have a high hardness, high toughness, and 
high density. 
In accordance with the invention, a powder mixture containing diamond 
powder with exothermically reactive additives is dynamically compressed. 
The dynamic compression induces and allows an exothermic chemical reaction 
between the powder materials to proceed throughout the compact. This 
chemical reaction produces a composite material having improved mechanic 
properties due to strong interparticle bonding. 
The preferred exothermically reactive additives are boron, silicon, 
aluminum, transition metals, and mixtures and compounds thereof, including 
but not limited to carbides, oxides, nitrides, carbonitrides, borides, and 
silicides. The preferred particle size of the starting diamond powder is 
between 0.05 to 1000 microns. 
The starting materials are thoroughly mixed and placed into a capsule or 
container which can be shock compressed. The capsule is then dynamically 
compressed by shock wave means, common to the art. The shock wave 
initiates or induces an exothermic chemical reaction which proceeds 
throughout the compact without requiring external heating. 
The primary object of the present invention is an improved composite 
material containing diamond, having high hardness, high toughness, and 
high density. 
It is a further object of the invention to produce diamond composite 
materials which are useful in cutting tools and rock-drilling bits. 
Yet another object of the present invention is to produce diamond composite 
materials by means of a dynamic shock compression and exothermic sintering 
process. 
Other objects and further scope of applicability will become apparent from 
the detailed description to follow and the accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
This invention relates to improved composite materials containing diamond, 
and a process for making such improved composite materials. The improved 
composite materials have improved mechanical properties, including high 
hardness, high toughness, and high density. 
In accordance with the invention, diamond powder is preferably mixed with 
exothermically reactive additives and other starting materials and 
dynamically compressed. The diamond powder may be natural or synthesized 
(man-made) single crystalline or polycrystalline diamond. The diamond in 
the starting mixture is at a high pressure phase. After release of the 
shock pressure, a portion of the diamond powder is transformed into the 
low pressure phases of carbon at a residual temperature (called "reverse 
transformation"). These low pressure phases exothermically and chemically 
react with the additives, in accordance with the invention, to produce 
strong interparticle bonding and the improved mechanical properties of the 
resulting compacts produced by the invention. 
Exothermically reactive additives, useful in the invention, comprise at 
least one of the following: 
(1) Boron, silicon, or aluminum, or mixtures or compounds thereof; 
(2) Transition metals, or mixtures or alloys thereof; 
(3) Non-stoichiometric carbides, oxides, nitrides or carbonitrides of the 
materials in (1); and 
(4) Non-stoichiometric carbides, oxides, nitrides, carbonitrides, borides 
or silicides of the materials in (2). 
Non-stoichiometric compound additives, rather than stoichiometric compound 
additives, are preferable constituents in the starting materials of the 
invention, because of the interparticle bonding which occurs during the 
exothermic chemical reaction. This interparticle bonding is partially 
responsible for the improved mechanical properties of the composite 
product. 
The size of the additive powders are preferably smaller than the diamond 
powder in the starting mixture to allow for uniform mixing. To obtain 
uniform distribution of the additives, the additives may be coated on the 
diamond grains. Coating might be more effective than mechanical mixing of 
the powders, especially for fine grain diamond powders. The particle size 
of the diamond is preferably between 0 grade to 1000 grade. The starting 
powders should be thoroughly mixed before dynamic compaction. The powders 
may be compressed, by means common to the art, prior to the dynamic 
compaction process. Typical initial densities of the powder materials, 
prior to dynamic compaction, range between 30% to 90%, and preferably 
between 40% to 80%. 
The amount of the exothermically reactive additives to be mixed with the 
starting materials containing diamond depends on the characteristics of 
the powders (diamond and additives), the content of the diamond in the 
starting materials and the dynamic compaction conditions. The preferred 
amount of additive is between 0.05% to 40% by volume of the diamond 
content in the starting materials. Preferably, the content of diamond in 
the starting mixture is between 40.0% to 99.9% by volume. 
The addition of exothermically reactive additives, which can be chemically 
reacted with reverse-transformed carbon and/or graphite, into the starting 
composite powder mixtures containing diamond has two primary effects. One 
effect is an increase in microhardness of the resulting compact. This is 
most likely due to the formation of substantial interparticle bonding 
during the compaction process. The other effect is a reduction of macro- 
and micro-cracks in the recovered compacts. This is most likely due to the 
increase in fracture toughness of compacted diamond powders because of the 
additives. 
Starting materials, useful in the invention, in addition to diamond and 
exothermically reactive additives, are ceramic, metal and cermet 
compounds, common to the art. 
Dynamic compaction is the powder compaction process used in making the 
diamond composite materials of the present invention. This process, 
disclosed in U.S. patent application Ser. No. 747,558, involves unique 
densification and consolidation processes for powder materials. The 
dynamic compaction process comprises the passage of a shock wave through 
the powder composite materials or compact. The shock wave may be generated 
by the detonation of an explosive or by high velocity impact. In the 
dynamic compaction process, powder compacts are mainly densified by 
particle fracture and/or plastic deformation at the shock front. 
Subsequently, the powders are consolidated into strong compacts, sometimes 
through interparticle bonding associated with a localized high temperature 
rise during the dynamic-compaction process. The shock wave induces the 
exothermic sintering of the powder materials, and allows the chemical 
reaction between the additives and the diamond and between the additives 
and reverse-transformed carbon and/or graphite to proceed throughout the 
compact. 
The dynamic compaction process is useful in the consolidation and 
densification of diamond powders, with or without additives. With dynamic 
compaction, the high-pressure and high-temperature conditions required for 
sintering diamond powders are relatively easy and fast to produce; a shock 
wave is used to compress powders in the dynamic compaction process rather 
than the prior art method of utilizing static high pressure sintering 
techniques. The duration of the shock pressure is extremely short, 
generally only a few microseconds. Furthermore, in dynamic compaction, the 
expensive processing equipment or apparatuses, such as the high-pressure 
apparatus used in static high-pressure sintering, is not required. 
In conventional shock compression techniques, temperatures during and after 
shock compression cannot be independently controlled. This results in 
significant undesirable effects on dynamically compacted materials such as 
diamond and cubic boron nitride (c-BN), because high pressure phases are 
converted to low pressure phases at the high temperatures present after 
release of the shock pressure (called "residual temperature"). In the case 
of diamond, the diamond is at a high pressure phase, and it converts into 
low pressure phases such as carbon and/or graphite at high temperatures. 
These low pressure phases have a lower hardness and density than the high 
pressure phase of diamond. Conversion to the low pressure phase also 
significantly reduces interparticle bonding of the composite materials 
because this transformation takes place preferentially at grain 
boundaries. These effects result in a significant degradation of the 
mechanical properties of the resulting composite. In the present 
invention, which uses dynamic compaction of diamond powders, with or 
without additives, the diamond structure is preserved. The low pressure 
phases, which are transformed from the diamond (high pressure phase) due 
to an increased temperature, are converted into hard, refractory materials 
by a chemical reaction. The additives, mixed into the diamond composite 
starting materials, enhance the consolidation of the composite materials 
and enable the formation of extensive interparticle bonding of the powders 
during the dynamic compaction process. The resulting composite materials 
have excellent mechanical properties. 
The dynamic compaction process, useful in forming the diamond composite 
materials of the present invention, is described in detail in U.S. patent 
application Ser. No. 747,558. For purposes of dynamic compaction in the 
present invention, shock wave generators, common to the art, may be 
utilized. The theory and practice of shock wave generators and their use 
for other purposes is described throughout the explosive literature. A 
typical disclosure is that made by Dr. M. A. Cook in his book entitled The 
Science of High Explosives, published by the Reinhold Company. Chapter 10 
of the first edition is particularly comprehensive in its explanation. 
Shock wave generators, however, have not been used in the prior art to 
induce the exothermic sintering of compactable powders, and in particular 
composite materials containing diamond. 
In one shock wave generator described in U.S. patent application Ser. No. 
747,558, detonation of an explosive propels glass into a main explosive, 
resulting in a plane detonation. By the detonation of the main explosive, 
the flyer plate is propelled against a capsule containing the powder 
sample at a particular velocity, causing a plane shock wave to be 
transmitted to the sample through the capsule. 
Another common type of plane shock wave generator has two different 
explosives: an inside explosive with a detonation velocity (Vd1) which is 
lower than the detonation velocity (Vd2) of an outside explosive. The 
angle .phi. is determined by the following equation: Sin .phi. is equal to 
(Vd1/Vd2). Plane detonation is transmitted to the outside explosive. By 
this detonation the flyer plate is propelled against a capsule containing 
the powder sample at a determined velocity. The plane shock wave is 
transmitted to the sample through the capsule. 
A typical cylindrical shock wave assembly, useful in the present invention, 
functions as follows: A detonator is ignited, the detonation top travels 
down the tube wall at a determined velocity and thereby generates a 
cylindrical shock wave which compresses the powder sample and capsule. 
EXAMPLE 1 
Diamond powders with various grain sizes (2-4 .mu.m, 10-20 .mu.m and 40-60 
.mu.m grades) were dry-mixed with exothermically reactive additives 
(mixtures of titanium and boron (Ti-B) or silicon and carbon (Si-C)) and 
with TiC or SiC powders in the compositions shown in Table 3. These 
exothermically reactive materials (Ti-B and Si-C), had a stoichiometric 
composition corresponding to TiB.sub.2 and SiC. The mixtures and pure 
diamond powders (for comparison) were pressed into stainless steel 
capsules with initial densities of 60-69% of theoretical density and then 
shock-compressed. 
Shock treatments were carried out using a mouse-trap planewave generator 
and a momentum-trap recovery system. An iron flyer plate with a 4.3 mm 
thickness was impinged upon capsules containing composite materials at 
velocities of 2.1 km/sec. Shock pressure induced in the stainless steel 
capsules was estimated to be about 50 GPa from a one-dimensional impedance 
matching method. Immediately after impact, fixtures containing the 
capsules were plunged into a water basin and quickly cooled before being 
recovered. After the shock treatments, samples were carefully taken out of 
the capusles using a lathe. 
Shock loading tests in the prior art have shown than in using the above 
shock treatment fixture, the pressure and the temperature induced by shock 
loading depends strongly upon the position within the powder compact. Most 
noticeably, shock temperatures at the top and bottom regions at a given 
impact velocity differ significantly. These positions correspond to the 
direction or propagation of the shock wave. Powder in the bottom region 
has a temperature of about two times higher than in the top region at an 
impact velocity of 2.5 km/sec. secause of this difference, the 
shock-compacted materials were examined with respect to the top and bottom 
regions by using x-ray diffraction, scanning electron and optical 
microscopy, and Vicker's microhardness testing. 
Both surfaces of each recovered sample were ground using a diamond wheel 
and then polished with a diamond paste. Vicker's microhardness 
measurements were taken on the polished surfaces of the compacts using a 
4.8 Newton load with a loading time of 15 seconds. Microhardness values of 
the resulting compacts are summarized in Table 3. Microstructures of the 
fractures and polished surfaces of the compacted materials were observed 
by scanning and optical microscopy. Microphotographs are shown in the 
figures of the drawing. 
TABLE 3 
__________________________________________________________________________ 
Vicker's Microhardness of Diamond Compacts (50 GPa) 
Microhardness (kg/mm.sup.2) 
Grain Size (.mu.m) 
Constituents 
Do** (%) 
Top Bottom 
__________________________________________________________________________ 
2-4 100% Diamond 
65 1860-2400 (2030)* 
1990-2370 (2070)* 
2-4 Diamond-(Ti--B) 
66 1140-1330 (1210) 
1750-2130 (1930) 
6.5 vol % 
10-20 100% Diamond 
65 1820-2190 (2020) 
(1200) 
10-20 Diamond-(Ti--B) 
60 880-960 (920) 
1290-1520 (1390) 
6.5 vol % 65 1210-1500 (1330) 
2570-2790 (2660) 
66 1170-1260 (1210) 
2700-2960 (2830) 
69 1060-1150 (1100) 
2400-2960 (2600) 
Diamond-(Ti--B) 
66 1080-1130 (1090) 
2150-2380 (2230) 
13 vol % 
Diamond-(Ti--B) 
66 680-770 (710) 
1250-1280 (1260) 
19.5 vol % 
40-60 100% Diamond 
65 1970-2040 (2040) 
(1200) 
40-60 Diamond-(Ti--B) 
66 1130-1350 (1220) 
2700-3000 (2850) 
6.5 vol % 
10-20 Diamond + TiC 
66 (1100) (820) 
6.0 vol % 
10-20 Diamond + TiC 
66 (800) (700) 
18.0 vol % 
10-20 Diamond + SiC 
66 1350-1400 (1380) 
1910-2220 (2010) 
10.8 vol % 
10-20 Diamond + (Si--C) 
60 1780-2060 (1930) 
2450-2790 (2470) 
10.8 vol % 
66 1760-2130 (1980) 
4120-4730 (4590) 
__________________________________________________________________________ 
(*Average Value) 
(**Initial Density) 
Dependencies of microhardness on initial density of the starting powder, 
diamond content and diamond grain size are apparent from Table 3. These 
dependencies of microhardness are almost the same as those observed in 
dynamic compaction of c-BN powders containing exothermically reactive 
materials in U.S. patent application Ser. No. 747,558. Microhardness of 
the compacted samples increased with the additions of exothermically 
reactive materials, especially for larger grain-sized diamond powder. A 
maximum microhardness value of 4730 kg/mm.sup.2 was obtained in the 
compacted 10-20 .mu.m grain size diamond powder containing 10.8% by volume 
Si-C. There was a great difference in hardness values between the top and 
bottom surfaces of these samples, as shown in Table 3. Except for the 
compacted pure diamond powders, the higher microhardness values of the 
bottom surfaces of the resulting compacts compared to the top surfaces 
strongly suggest that for effective dynamic compaction of these powder 
materials to occur, higher shock temperatures than the temperatures 
reached at 50 GPa would be required to cause the exothermic reaction to 
proceed and to consolidate the powders. 
X-ray diffraction patterns were taken for the compacted 10-20 .mu.m grade 
diamond powders containing 10% by volume (Ti-B) or (Si-C). The exothermic 
reaction between titanium and boron was expected to occur during the 
dynamic-compaction process, analogous to the shock treatment of c-BN 
powders containing (Ti-B). However, x-ray diffraction patterns indicated 
that the titanium powders, in fact, reacted with diamond powders or 
reverse-transformed carbon and/or graphite to produce TiC, but did not 
react with boron which was intentionally added into the starting powders. 
Nevertheless, the formation energy of TiB.sub.2 from Ti-B is lower than 
that of TiC from Ti-C at high temperatures under ambient pressure. Part of 
the TiC in the recovered compacts was possibly produced from the reaction 
between titanium and diamond during shock compression, but most was formed 
from the reaction between titanium and reverse-transformed carbon and/or 
graphite at a residual temperature. The preferential reaction of titanium 
with reverse-transformed carbon and/or graphite observed in the recovered 
compacts is probably due to the fact that the conversion of diamond to low 
pressure forms occurs preferentially at the grain boundaries and the 
transformed carbon and/or graphite grains have a high chemical reactivity. 
The results obtained in the diamond-(Ti-B) system suggest that in the 
mixture system of diamond and (Si-C), Si also possibly reacted with 
reverse-transformed carbon and/or graphite, and not with intentionally 
added carbon. 
In each compact obtained from the mixture of diamond and (Ti-B) or (Si-C), 
the amount of the TiC and SiC produced in the bottom region was greater 
than in the top region. This most likely occurred because the temperature 
in the bottom region in the shock-treatment fixture was higher than in the 
top region during and after shock compression. The amount of the TiC in 
the compacts increased with increasing initial density of the powder 
compacts, which corresponds to a decrease in shock and residual 
temperatures. Although the reason why the amount of TiC and SiC formed in 
the recovered compacts increased with decreasing shock and residual 
temperatures cannot be readily explained, these results suggest that for 
dynamic compaction of the mixture of diamond and (Ti-B) or (Si-C), higher 
pressures than 50 GPa are required to produce a well-bonded composite 
material containing diamond. Results of diamond powders with 
exothermically reactive additives compacted at higher pressures are 
described in the following examples. 
In conclusion, the microhardness of the compacted diamond powders was 
increased by the addition of an exothermically reactive material into the 
starting powders. From x-ray diffraction patterns, it was shown that this 
effect resulted from the reaction between the reverse-transformed carbon 
and/or graphite and one of the elemental constituents of the 
exothermically reactive materials which were intentionally added to the 
starting mixture. Higher microhardness values in the bottom regions of the 
compacted samples than in the top regions, and an increase in 
microhardness values with an increase in the amount of reaction products, 
suggest that higher temperature and pressure conditions are required for 
dynamic compaction of diamond powders with exothermically reactive 
additives which can be reacted with reverse-transformed carbon and/or 
graphite. 
EXAMPLE 2 
Diamond powders having different grain sizes were dry mixed with 
exothermically reactive additives (Ti or Si) in the compositions shown in 
Table 4. The starting powders, diamond, Ti, and Si were the same as in 
Example 1. The mixed powders and pure diamond powders (for comparison) 
were pressed into stainless steel capsules with initial densities of 
60-69% of the theoretical density and then shock compressed. Shock 
treatments were carried out using the same shock-treatment fixture as in 
Example 1. The impact velocity employed in this example was 2.5 km/sec. 
Shock pressures induced in the stainless steel capsules were estimated to 
be 60 GPa. 
It was found that the microhardness of the compacted samples substantially 
increased with the samples containing exothermically reactive additives 
and also increased with a decreasing grain size of the starting diamond 
powders. A maximum microhardness value of 6330 kg/mm.sup.2 was obtained in 
the compacted 2-4 .mu.m grade diamond powder containing 7.2% by volume 
silicon. Another distinguishing and desirable effect of the exothermically 
reactive additives was the reduction of macro- and micro-cracks in the 
resulting compacts. This effect was predominant in the compacted fine 
diamond powders mixed with additives. The microhardness values for the 
resulting compacts are summarized in Table 4. 
TABLE 4 
__________________________________________________________________________ 
Vicker's Microhardness of Diamond Compacts (60 GPa) 
Grain 
Size 
Si Ti Do** Microhardness (kg/mm.sup.2) 
(.mu.m) 
(vol %) 
(vol %) 
(%) Top Bottom 
__________________________________________________________________________ 
2-4 -- -- 65 4190-4600 (4380)* 
4660-5080 (4580)* 
2-4 7.2 -- 60 4200-4890 (4600) 
4760-5400 (5020) 
65 4870-5740 (5330) 
5750-6330 (6030) 
69 4200-5200 (4630) 
4620-5460 (4940) 
10-20 
-- -- 60 670-690 (680) 
1180-1440 (1280) 
65 720-820 (770) 
2100-2890 (2550) 
69 760-1180 (960) 
2460-2890 (2650) 
10-20 
3.6 -- 60 1190-1300 (1230) 
2810-3180 (3040) 
65 1150-1230 (1190) 
2860-3170 (3050) 
69 830-870 (840) 
1700-1990 (1890) 
7.2 60 1500-1610 (1560) 
2150-2390 (2280) 
65 2540-3030 (2700) 
3260-3530 (3380) 
69 800-830 (810) 
1930-2940 (2460) 
14.1 60 2700-3220 (2920) 
3190-3710 (3390) 
65 3200-3800 (3540) 
5610-5850 (5740) 
69 2390-2490 (2450) 
2940-3660 (3360) 
-- 7.2 60 2860-3240 (3030) 
3860-3960 (3890) 
65 2990-2590 (2438) 
3780-4790 (4170) 
69 2380-2680 (2500) 
3690-4630 (4300) 
40-60 
-- -- 65 750-800 (770) 
2300-2960 (2610) 
40-60 
7.2 -- 60 2350-2540 (2440) 
3140-3340 (3250) 
65 2160-2550 (2380) 
2820-3060 (2910) 
69 1200-1410 (1330) 
2310-3060 (2740) 
__________________________________________________________________________ 
(*Average Value) 
(**Initial Density) 
For pure diamond powders, it was found that the microhardness values of the 
compacted 10-20 .mu.m grade and 40-60 .mu.m grade powders were similiar. 
When the grain size of the starting diamond powders was decreased from 
10-20 .mu.m to 2-4 .mu.m, the microhardness increased significantly. 
Microhardness values of the compacted diamond powders were increased by the 
additions of silicon and titanium additives into the starting diamond 
powders, and also increased with a decrease in the grain size of the 
starting diamond powder. This is the same tendency as was shown with the 
compacted pure diamond powders discussed above. An advantage of using 
fine-grain diamond powder is that the difference in microhardness values 
between the top and bottom regions in each recovered compact is 
diminished. 
It was found that the addition of titanium was more effective in increasing 
the microhardness of the resulting compact than the addition of silicon. 
The difference in powder characteristics of both powders and the chemical 
affinity between titanium, silicon and reverse-transformed carbon and/or 
graphite may have caused this result. 
It was found that the optimum amount of exothermically reactive additives 
in the starting material powders to attain a high microhardness, strongly 
depends upon the volume content of diamond, grain size, size distribution 
of the diamond and additive powders, and dynamic compaction conditions. In 
the dynamic compaction of 10-20 .mu.m grade diamond powders, with and 
without additives, a maximum hardness value was obtained with a 14.1% by 
volume silicon addition. X-ray diffraction of this compact showed that 
some amounts of elemental silicon remained after the dynamic compaction 
process. Presence of such unreacted silicon in recovered compact would 
result in the degradation of its mechanical properties. Thus, the optimum 
amount of the silicon additive in 10-20 .mu.m grade diamond powder is most 
likely lower than 14.1% by volume. 
X-ray diffraction patterns for the compacted diamond powders containing 
silicon or titanium were obtained. The amount of the reaction between the 
exothermically reactive additives and the reverse-transformed carbon 
and/or graphite was estimated from the ratio of the diffraction 
intensities of the peaks for SiC and Si shown in the diffraction patterns. 
Broadening peaks ranging from 24 to 28 degrees in 2.theta., observed in 
some of these x-ray diffraction patterns, were evidence of the presence of 
low pressure phases of carbon transformed from diamond. Although the 
maximum microhardness value of 6330 kg/mm.sup.2 was obtained in the 
compacted 2-4 .mu.m grade diamond powder with 7.2% silicon by volume, the 
diffraction pattern showed that the silicon added into the starting powder 
mixture was not completely reacted with reverse-transformed carbon and/or 
graphite and traces of low pressure phases of carbon remained in the 
recovered compact. This may have resulted from insufficient mixing prior 
to the dynamic compaction, because the grain size of silicon powder used 
may have been too large to mix sufficiently with 2-4 .mu.m diamond powder. 
It was shown from x-ray diffraction patterns that the amount of the 
reaction increased with a decrease in the grain size of the diamond. 
Sectional views of the polished top and bottom surfaces of the compacted 
diamond powders, with and without additives, are shown in the 
microphotographs of FIGS. 1-3. FIG. 1 shows the surfaces of a compact 
containing 100% by volume diamond; FIG. 2 shows the surface of a compact 
containing diamond and 7.2% silicon by volume; and FIG. 3 shows the 
surfaces of a compact containing diamond and 7.2% by volume titanium. Two 
notable effects of the exothermically reactive additives are shown in the 
above figures. One effect is an increase in microhardness of the compacts 
with additives. The other effect was a reduction of macro- and 
micro-cracks in the recovered compacts, as seen by comparing the 
photographs of the compacted samples with additives (FIGS. 2 and 3) to 
compacted samples without additives (FIG. 1). The latter effect was 
predominant in the compacted 2-4 .mu.m grade diamond powders with silicon 
additives. (Compare FIG. 4 (100% by volume diamond) to FIG. 5 (7.2% by 
volume silicon as an additive)). The larger number of cracks in the bottom 
surfaces of the compacted diamond powders, with and without additives, 
than in the top surfaces, as shown in FIGS. 1-5, is apparently due to the 
difference in the pressure and temperature conditions within the powder 
compacts during dynamic compaction. 
Optical micrographs of polished top and bottom surfaces of the compacted 
samples are shown in FIGS. 6-8. FIG. 6 shows the surfaces of a compact 
containing 100% by volume diamond; FIG. 7 shows the surfaces of a compact 
containing diamond and 7.2% by volume silicon as an additive; and FIG. 8 
shows the surfaces of a compact containing diamond and 7.2% by volume 
titanium. Light-colored regions (domains) in these photographs correspond 
to the polished diamond grains, and continuous light-colored regions 
indicate a formation of interparticle bonding in compacted powders. In the 
compacted 10-20 .mu.m grade diamond powders with silicon or titanium 
additives, interparticle bonding apparently increased by these additions. 
(Compare FIGS. 7 and 8 to FIG. 6.) Scanning electron microphotographs of 
the fracture surfaces of the compacted samples clearly show the difference 
in fracture morphology due to the difference in the degree of 
interparticle bonding produced during the dynamic-compaction process. 
Fracture morphology was changed from intergranular to transgranular 
fracture by the addition of titanium and silicon and transgranular 
fracture increased with an increasing amount of additive 0%-14% by volume 
silicon. 
It will be appreciated from the foregoing description of the invention, as 
contrasted with the description of the prior art, that the present 
invention has achieved many improvements over the prior art. Notably, the 
invention permits the achievement of improved diamond composite materials 
with respect to toughness, hardness, decreased porosity and appearance. 
Furthermore, it permits the use of less expensive and less complicated 
powders. It permits the achievement of these improvements while 
eliminating the more expensive and complicated pressure devices of the 
prior art. It also simplifies the heating of the ingredients as contrasted 
with the more complicated furnaces of the prior art.