Directional catalyst alloy sweep through process for preparing diamond compacts

Disclosed is an improved method for making a polycrystalline diamond compact comprising subjecting a mass of diamond particles, which mass is adjacent a cemented metal carbide mass containing a catalyst, to a high pressure/high temperature process which results in a compact characterized by diamond-to-diamond bonding. The improvement in such process comprises placing a second catalyst source adjacent the diamond mass, said second catalyst having a metal point which is lower than the melting point of the catalyst of the carbide; and subjecting said mass to high pressure/high temperature sintering at a temperature above the melting point of the second catalyst, but below the melting point of the carbide catalyst, for causing said second catalyst to selectively diffuse through said mass for forming said polycrystalline diamond compact. The preferred catalyst is a mixture of cobalt and boron.

BACKGROUND OF THE INVENTION 
The present invention relates to methods of preparing polycrystalline 
diamond compacts made by a high pressure-high temperature process (HP/HT) 
and has special application in the preparation of polycrystalline diamond 
compacts for use in wire dies. 
A polycrystalline diamond compact comprises a mass of diamond-to-diamond 
bonded particles in which the diamond concentration is at least 70 volume 
percent. Representative wire drawing dies made with polycrystalline 
diamond compacts can be found, for example, in U.S. Pat. Nos. 3,831,428, 
4,129,052, 4,144,739, 4,171,973, and 4,231,762. Such wire die compacts 
comprise an inner mass of polycrystalline diamond which inner mass is 
surrounded by and bonded to a mass of cemented metal carbide, such as 
cobalt cemented tungsten carbide. These are referred to as 
carbide-supported wire die compacts. Unsupported polycrystalline diamond 
wire die compacts without a surrounding mass of cemented metal carbide 
also are available. Carbide-supported polycrystalline diamond compacts in 
other configurations are described, for example, in U.S. Pat. Nos. 
3,745,623, 4,108,614, 4,215,999, 4,219,339, 4,229,186, and 4,255,165. 
The formation of diamond-to-diamond bonds between individual abrasive 
grains requires a catalyst/solvent (hereinafter referred to as a catalyst) 
that is able to web the diamond surface as well as dissolve and 
precipitate diamond. This task normally is complicated by the presence of 
inhibiting impurities. The impurities can be in the form of 
surface-adsorbed species including oxygen and water, for example. The 
impurities can block pore passages between the grains and alter the 
diamond surfaces so that catalyst penetration becomes inadequate and 
surfaces are no longer wetted. The problems caused by impurities are 
magnified as the abrasive grain size decreases. Thus, decreasing pore size 
and increasing surface area to volume ratios are contributing factors that 
lead to a higher frequency of poorly bonded diamond compacts as smaller 
grains are used. However, the ease of finishing diamond compacts that have 
been sintered from fine grain diamond, e.g. less than about 10 microns, 
into a desired geometry make such compacts desirable in the marketplace. 
In the case of wire die compacts, the use of fine diamond grains enables 
an improvement in the surface finish of wires that have been drawn 
therethrough, making such compacts especially desirable. In addition to 
the noted affect of diamond particle size, it also has been observed that 
the incidence of flaws during fabrication generally tends to increase with 
overall compact size. 
The high temperature/high pressure (HP/HT) process of sintering diamond 
into a coherent mass in making polycrystalline diamond compacts with a 
catalyst "sweep-through" technique as taught by U.S. Pat. Nos. 3,745,623 
and 3,831,428 is well known in the art. An important feature of the 
sweep-through technique is that the amount of catalyst in the system is 
determined automatically by the available free volume within the mass of 
polycrystalline grains being sintered. The amount of catalyst is 
independent of diamond size, diamond size distribution, and the change in 
free volume during compression and sintering. Diamond bonding during the 
process is enhanced by the pushing of impurities from the diamond 
consolidation zone by the sweeping catalyst solvent front. In this regard, 
commonly assigned application of Gigi et al., U.S. Ser. No. 487,115, filed 
Apr. 27, 1983, now U.S. Pat. No. 4,525,179 based on continuation-in-part 
application U.S. Ser. No. 542,081, filed Oct. 14, 1983, discloses an 
improved sweep-through process which utilizes a pre-sweep of a relatively 
low melting point material, typified by copper, which preceeds a catalyst 
sweep through a diamond particle mass in the production of diamond 
compacts. Another recent commonly-assigned application of Cho, U.S. Ser. 
No. 313,119, filed Oct. 20, 1981 new U.S. Pat. No. 4,534,934, discloses an 
improved process in the manufacture of diamond wire die compacts in which 
catalyst sweeps both axially and radially into a diamond particle mass. 
Another method suggested for decreasing the incidence of flaws, 
particularly in fine grain polycrystalline diamond compacts, is the 
addition of particles designed to inhibit excessive regrowth during sweep 
as proposed by Hara et al., "On the Properties of Fine Grain Sintered 
Diamond Bodies", Proceedings of the 10th Plainsee-Seminar, Hugo M. Ortner, 
Editor, Metal Work Plainsee, Reutte, Austria, Vol. 2, pp 581-589 (1981). 
Another technique proposed to improve the diamond compact portion of the 
wire drawing dies is the use of sintering aids as set forth in U.S. Pats. 
Nos. 3,913,280, 4,268,276, 4,370,149, and South African application No. 
756730. Despite the many benefits which have been achieved in the art, the 
need exists for techniques which substantially enhance the 
reproduceability of well bonded polycrystalline diamond compacts, 
especially those sintered with fine grain diamond. 
BROAD STATEMENT OF THE INVENTION 
The present invention addresses the problems discussed above and provides a 
new selective, uniform controlled directional catalyst sweep-through 
process and an improved compact made therefrom. This process also enables 
a reduction in sintering temperatures and pressures needed for 
satisfactory results. The use of less severe operating conditions can lead 
to improvements in apparatus life with a corresponding decrease in 
manufacturing costs. The present invention is directed to a method for 
making a polycrystalline diamond compact comprising subjecting a mass of 
diamond particles to a high pressure/high temperature (HP/HT) process 
which results in a compact characterized by diamond-to-diamond bonding. 
In this invention the mass of diamond particles is provided in an assembly 
adjacent a mass of cemented metal cabide which includes a catalyst for 
diamond recrystallization. A second catalyst source also is provided 
adjacent the diamond mass. The second catalyst source is selected such 
that the catalyst in the second source melts at a lower temperature than 
the catalyst in the carbide under high pressure, for example above 45 
kbar. The assembly then is subjected to HP/HT sintering at a temperature 
above the melting point of the catalyst in the second source, but below 
the melting point of the catalyst in the carbide to enable a selective, 
controlled sweep of catalyst from the second source into the diamond mass. 
In an exemplary embodiment of this invention, a mass of diamond particles 
is contained within and surrounded by a cobalt-cemented tungsten carbide 
annulus. Depending on the composition of the carbide, the cobalt therein 
can become molten under high pressure conditions at a temperature below 
1350.degree. C. In such an embodiment, a second catalyst source is placed 
adjacent the diamond mass at an open end of the carbide annulus. The 
composition of the second catalyst source is selected such that the 
catalyst therein becomes molten below the temperature of the cobalt 
catalyst in the carbide annulus. While the catalyst source may be a 
lower-melting point catalyst, the source is preferably a mixture 
comprising a catalyst and a diffusion aid, which mixture exhibits a 
melting point below that of the catalyst itself. A preformed alloy may be 
used as can a physical mixture provided the mixture forms an alloy under 
HP/HT sintering conditions. The assembly then is subjected to such 
sintering conditions at a temperature below the melting point of the 
cobalt catalyst in the carbide, but above the melting point of the 
catalyst in the second catalyst source. In this manner, the catalyst from 
the second source selectively axially diffuses or sweeps through the 
diamond mass in a net direction to the opposite opening of the carbide 
annulus, i.e., controlled directional sweep-through or diffusion. 
Desirably, the second catalyst source is selected such that the melting 
point of the catalyst therein is at least 50.degree. C. less than the 
melting point of the catalyst in the cemented metal carbide, 
advantageously about 100.degree. C. less, and preferably about 200.degree. 
C. less. In this manner the process is more controllable and substantially 
no metal from the metal carbide will infiltrate or diffuse into the 
diamond mass during the sintering process. In addition, such a large 
difference in melting point allows the sintering process to proceed at a 
lower temperature than previously possible, resulting in lower cost and 
less stress on the apparatus used. 
The preferred second catalyst source is a physical mixture or preformed 
alloy of cobalt or nickel and boron. The proportion of catalyst and boron 
are adjusted to obtain the desired melting point for achieving the 
selective directional catalyst diffusion. In addition, for achieving 
uniformity and minimizing the undesirable effects of secondary flow paths 
on the resulting compact, longer sweep paths are provided, as detailed 
herein. 
Advantages of the present invention include the ability to achieve a 
uniform and homogeneous sweep-through of catalyst through the mass of 
diamond particles for achieving improved diamond-to-diamond bonding. 
Another advantage is the ability to achieve consistency and 
reproduceability in polycrystalline diamond compact production. A further 
advantage is the ability to utilize fine diamond crystals, e.g. less than 
10 microns, in forming the diamond compact. There also is an advantage in 
increased apparatus life resulting from the ability to operate at lower 
HP/HT conditions. These and other advantages will become readily apparent 
to those skilled in the art based upon the disclosure contained herein.

DETAILED DESCRIPTION OF THE INVENTION 
In conventional systems for sintering diamond in cemented carbide supported 
compacts, a major flow of catalyst infiltrates the diamond mass from the 
carbide support. For example, in a wire die configuration as depicted in 
FIG. 1, flow 15 of catalyst for diamond recrystallization radially 
infiltrates core 14 of diamond particles from annular cemented metal 
carbide support 12. In a typical embodiment the annulus is formed of 
cobalt cemented tungsten carbide from which a portion of the cobalt flows 
during high pressure/high temperature (HP/HT) sintering conditions to act 
as the catalyst. 
More specifically, FIG. 1 depicts a conventional assembly for making a 
polycrystalline diamond wire die compact under HP/HT conditions. Such 
assemblies and HP/HT conditions are well known in the art and are 
described, for example, in U.S. Pat. Nos. 3,745,623, 3,831,428, and 
3,850,591. The assembly depicted comprises enclosure 10 of a refractory 
metal such as molybdenum, tantalum, titanium, tungsten, zirconium, etc., 
in which is contained cemented metal carbide annulus 12 and interiorly 
disposed central core of diamond particles 14. In addition to radial 
catalyst flow 15, a significant catalyst flow 13 across the ends of core 
14 is thought to occur in such a configuration. In smaller wire dies, 
primary radial sweep 15 is thought to be sufficiently rapid that catalyst 
flow 13 across the end of the die blank is not as noticeable. However, in 
diamond dies of larger core construction or utilizing finer diamond 
particles, flow 13 of catalyst across the core end can become more 
significant. Such an alternative catalyst flow path can result in 
non-uniform infiltration of catalyst into diamond core 14, and may hamper 
the full densification of the core, thereby increasing the probability of 
flaw formation. Similarly, such a non-uniform flow hampers the 
concentration of impurities at a point in the diamond core from which they 
might be more easily removed. It also has been suggested that radial 
catalyst flow 15 may cause some cobalt depletion in carbide annulus 12 and 
that some portion of the metal from the metal carbide (for example, 
tungsten in a tungsten carbide annulus) will enter diamond core 14 along 
with radial flow 15 of cobalt. 
A controlled directional sweep-through process according to the invention, 
as depicted in FIG. 2, similarly employs metal enclosure 10 bearing 
cemented carbide annulus 12 and central diamond core 14. However, a 
particular second catalyst source 16 is disposed at one end of enclosure 
10 adjacent an end of annulus 12 and diamond core 14. 
As noted above, cemented carbide annuli typically are cemented with a metal 
which is a catalyst for diamond recrystallization, cobalt being the metal 
of choice predominant in the industry. The simple supply of a second 
catalyst source at 16 likely would result in a relatively random 
combination of radial and axial sweep-through, as can be envisioned by the 
combination of sweep paths shown in FIG. 1 and FIG. 2. The resulting 
infiltration process would be replete in control difficulties. The 
selective directional catalyst sweep of the present invention, as shown in 
FIG. 2, is achieved by utilizing a particular type of catalyst source at 
one end of core 14 in a form such that this second catalyst has a melting 
point less than the melting point of the catalyst in cemented carbide 
annulus 12. Known catalysts in this art may be selected from the group 
consisting of cobalt, iron, nickel, ruthenium, rhodium, osmium, iridium, 
palladium, platinum, chromium, manganese, tantalum, and mixtures and 
alloys thereof. Cobalt, iron, and nickel catalyst predominate in use with 
cobalt being the most preferred. Utilizing cobalt or nickel catalyst, a 
preferred second catalyst source 16, according to this invention, is 
obtained by alloying with boron. Of course, this second catalyst source 
may be in the form of a pre-formed alloy, or may be in the form of a 
mixture of powders sufficient to form an alloy under HP/HT conditions. 
A number of technical reasons for preferring a metal/boron system exist and 
include: such alloy efficiently dissolves and precipitates diamond; boron 
has a high affinity towards carbon; boron is effective in lowering the 
melting point of the catalyst; thermodynamically stable cobalt/boron 
carbides are formed; the composition remains homogeneous throughout the 
core when used in a cobalt-cemented carbide; boron is a diamond grain 
regrowth inhibitor; and the stable cobalt boron alloys formed are very 
hard phases. A table summarizing the effect of composition on melting 
point of cobalt-boron alloys, as taken from Elliott, "Constitution of 
Binary Alloys, First Supplement", McGraw-Hill Book Company, pp 115-116 
(1958) is set forth below: 
TABLE 1 
______________________________________ 
Weight Percent Melting 
Boron in a Point 
CO--B Alloy .degree.C. 
______________________________________ 
0 1495 
1 1340 
2 1220 
3 1140 
4 1095 
5 1130 
6 1190 
7 1240 
8 1250 
______________________________________ 
As will be observed from Table 1, the composition with the lowest melting 
point in the cobalt-boron alloy system contains about 4 weight percent 
boron. However, a 4 weight percent pre-formed boron alloy is brittle and 
difficult to fabricate. Therefore, a 3 weight percent boron alloy which is 
more ductile is preferred. A sufficiently depressed melting point is 
experienced with such an alloy system. Between about 2% and 7% boron 
should prove useful in the process when a cobalt cemented tungsten carbide 
annular support is employed. The low melting point of a cobalt-boron alloy 
(3 weight percent boron) of about 1150.degree. C. minimizes the 
opportunity for cobalt or other metal from the carbide support annulus to 
radially infiltrate the central diamond core provided that the sintering 
temperature is at least initially less (under high pressure conditions) 
than the melting point of cobalt in the carbide annulus and above the 
melting point of the named alloy for an amount of time sufficient to 
enable the alloy containing the catalyst to flow into diamond core 14. 
Alternate sweep paths of cobalt or other metal from the carbide annulus 
also are thereby reduced since available free areas within diamond core 14 
already are filled by the low melting point alloy. Temperature windows for 
sintering processes using other second catalyst sources 16 in conjunction 
with various carbide structures can be similarly calculated for achieving 
controlled directional sweep or infiltration of the catalyst alloy through 
the central diamond core while not providing an opportunity for the 
catalyst or other metal from the carbide annulus to substantially 
infiltrate therein. 
Some slight infiltration from the annulus is thought to occur as depicted 
at 17 in FIG. 2 when a cobalt/boron alloy as source 16 is used. It is 
assumed that the infiltrated boron from the second catalyst source makes 
itself available to the cobalt near the surface of annulus 12 enabling the 
cobalt to flow from the carbide as a eutectic. This, in turn, beneficially 
affects a bond between diamond core 14 and supporting carbide annulus 12. 
The lower sintering temperature additionally minimizes the risk to the 
apparatus used to achieve HP/HT sintering conditions resulting in a 
decrease in the costs of the process. 
Without limitation, additional sweep alloy compositions which may find 
utility in accordance with the precepts of the present invention include, 
for example, nickel/boron, cobalt/palladium, cobalt/tantalum/boron, 
iron/nickel/boron, cobalt/boron (optionally with copper), 
cobalt/beryllium, cobalt/manganese, nickel/manganese, 
cobalt/tantalum/boron, cobalt/niobium/boron, cobalt/molbydenum/boron, 
cobalt/boron/tungsten, and nickel/iron/chromium/phosphorous/boron/silicon. 
It should be noted that the selection of a second catalyst source according 
to this invention must be based on the melting point of the catalyst in 
the context of the system in which they are present. Thus, the melting 
point of a cobalt catalyst in a cemented tungsten carbide will typically 
be less than the melting point of cobalt itself. Similarly, the melting 
point of a catalyst in a second catalyst source, such as cobalt in a 
cobalt/boron alloy, will be at a eutectic temperature below that for 
cobalt alone. As already noted, the temperature differential between the 
melting point of the catalyst in the second catalyst source and that in 
the cemented carbide mass should be at least 50.degree. C., advantageously 
at least about 100.degree. C., and preferably at least about 200.degree. 
C. 
As depicted in FIG. 2, sintering is accomplished directionally from second 
catalyst source 16 and completed at the oppositely disposed end of the 
assembly. The opposite end of the diamond core 14 may contain a flawed 
area, generally in the center. The shape and location of the flawed area 
suggests that the sweep front of catalyst from source 16 does not move as 
a uniform wave-front, but travels preferentially along the interior wall 
of carbide annulus 12. The flow path of catalyst from disc 16 along the 
annulus die wall then proceeds across metal enclosure 10 at the oppositely 
disposed end. Such flow path of catalyst up to and across the oppositely 
disposed end is thought to occur prior in time to the sweep up the core 
center and may lead to a soft, non-bonded inner core at the end. The finer 
the particle size of the diamond in core 14, the more likely is this 
phenomenon to occur. 
As depicted in FIG. 3, upper layer 18 of material such as a diamond, or 
B.sub.4 C powder advantageously may be used to increase the sweep path 
length as sweep path 20 in FIG. 3 shows. Increasing the sweep path length 
has the effect of displacing the flawed area from position a to position b 
to position c, etc. until a position is reached within material 18 which 
can be removed during finishing operations by conventional techniques such 
as lapping. Additionally, with smaller diamond particles, the greater 
resistance to flow and corresponding increase in path length assists in 
ensuring good quality diamond cores. The use of such a layer also serves 
to concentrate impurities pushed by the flow of catalyst outside of 
diamond core 14. 
Preferred forms of high pressure/high temperature apparatus in which the 
diamond wire drawing compacts of the present invention may be prepared are 
known in the art, as typified by U.S. Pat. No. 2,941,248 which describes a 
"belt apparatus". Operational techniques for simultaneously applying both 
high pressure and high temperature in this type of apparatus also are well 
known to those skilled in the super pressure art. In practice, a number of 
assemblies as depicted in FIG. 3 normally are combined in a charge 
assembly and placed in a belt apparatus as described, for example, in U.S. 
Pat. No. 3,609,818. Thereafter, the pressure and then the temperature are 
increased and held at desired conditions for a time sufficient for diamond 
sintering to occur. It should be noted that a slower, step-wise heating 
sequence has been found to be desirable when practicing the present 
invention in order to ensure complete and uniform melting of the second 
catalyst source for diffusion through the diamond particles of the 
compacts being sintered. In this manner the temperature gradually can be 
increased to over the melt temperature of the metal in carbide support 12 
to ensure a joining with diamond core 14 as noted above. Thereafter, the 
sample is allowed to cool under pressure for a short period of time 
followed by a gradual release of pressure to atmospheric pressure. The 
compact is recovered and the shield metal sleeve manually removed. Any 
adhering metal from the shield metal cup or disc can be ground or lapped 
off. Distortion or surface irregularity may be removed in a similar 
manner. 
After removal of adhering materials from the compacts resulting from the 
process and finishing, the recovered wire die compacts comprise sintered 
polycrystalline diamond contained within and bound to a cemented metal 
carbide mass. Thereafter, formation of a wire drawing hole through the 
sintered mass of polycrystalline diamond may be accomplished by a laser or 
other conventional technique or may be preformed during the sintering, as 
is well known in this art. 
The following examples show how the present invention can be practiced, but 
should not be construed as limiting. 
EXAMPLES 
Example 1 
A cobalt cemented tungsten carbide annulus with an inner diameter of 14 mm, 
outer diameter of 25 mm, and a height of 18 mm was placed into a 
refractory metal container (Ta, Zr, Nb as examples). 10.0 gm of less than 
75 micron size diamond was loaded into the core of the carbide annulus and 
container. Approximately 2.5 gms of 10 mesh powdered cobalt with 4% boron 
was placed above the ring and diamond. The complete assembly was sealed 
with a refractory metal lid, loaded into a HP/HT apparatus, and heated to 
at least the melting point of the cobalt/4% boron and maintained at about 
1100.degree. C. in the apparatus at about 50 kB for 30 minutes. 
Examination of the exposed and polished diamond core revealed a well 
bonded and homogeneous structure at a magnification of 500.times.. 
To obtain wire drawing dies having fine grain sintered diamond, the central 
diamond core normally is formed from diamond particles having a grain size 
of less than about 10 microns and generally such particles range in size 
from about 2-4 microns or less. While it should be understood, however, 
that the process of the present invention permits use of such fine grain 
diamond particles which is a decided benefit in favor of the present 
invention, it also should be understood that the process beneficially can 
be used for larger grain size diamond particles as well. Thus, the process 
of the present invention retains the ability and flexibility to utilize 
larger grain diamond particles while permitting the reproduction of 
diamond wire drawing dies from very fine grain diamond particles. With 
very fine crystal size of diamond particles, e.g. 2-4 microns, reduction 
of impurity levels to less than 1 ppm even may be unacceptable. It is 
apparent to those skilled in this art that conventional diamond and 
assembly part preparation is an important factor in obtaining 
reproduceably good dies, especially for the fine particle size of diamond 
which may be used in the present invention. 
Example 2 
Approximately 0.20 gm of a -10 mesh powder of 60% manganese and 40% nickel 
was placed on the bottom of a refractory metal container (Ta, Zr, Nb, as 
examples). A cobalt cemented tungsten carbide annulus with an inner 
diameter of 4.5 mm, an outer diameter of 8.7 mm, and a height of 4.8 mm 
was placed on top of the powder. The core of the annulus was charged with 
approximately 0.25 gm of less than 4 micron diamond. The container was 
sealed with a refractory metal lid, placed into a cell following the 
techniques of U.S. Pat. No. 3,831,428, and was heated to approximately 
1150.degree. C. at about 50 kB for about 15 minutes. Examination of the 
exposed diamond core revealed a homogeneous and well bonded structure at a 
magnification of 2000.times.. Additional observations of the polished 
cross-section of the diamond core demonstrated that the core was free of 
any poorly bonded zones and that undesirable features such as grain growth 
were notably absent. Experience suggests that conventional configurations 
under similar conditions without the second catalyst source in which 
cobalt from the support annulus freely infiltrates radially into the 
diamond core typically would yield unacceptable cores. 
Example 3 
A disc containing 74% cobalt, 4% boron, and 22% tantalum was placed on the 
bottom of a refractory metal container (Ta, Zr, Nb, as examples). An 
annulus of cobalt cemented tungsten carbide with an inner diameter of 4.5 
mm, outer diameter of 14 mm, and a height of 6 mm was placed on top of the 
disc. The core of the carbide mass was loaded with 1.0 gm of less than 2 
micron diamond. The container was sealed with a refractory metal lid and 
was placed into an HP/HT apparatus. The assembly was heated to 
approximately 1250.degree. C. at a pressure of about 55 kB. The heating 
duration was about 20 minutes. The exposed diamond core was visually 
examined after sintering using optical and scanning election microscopy. 
Diamond-to-diamond bonding was excellent and the microstructure 
homogeneous. The diamond core uniformity was confirmed using transmission 
x-radiographic techniques. 
While the foregoing examples all have described configurations adapted for 
the production of a polycrystalline diamond wire die compact, the present 
invention also is applicable to other polycrystalline diamond 
configurations. For example, it could be used in a configuration such as 
described in U.S. Pat. No. 4,219,339, in which a polycrystalline diamond 
layer is sandwiched between two support layers of a cemented metal 
carbide. In such a configuration, the provision of a second catalyst 
source according to the present invention adjacent an edge of the 
polycrystalline diamond not covered by the carbide supports should provide 
a directional flow of catalyst during HP/HT processing parallel to the 
carbide support layers. More particularly, FIG. 4 shows such a sandwich 
configuration wherein carbide supports 50, 52, and 54 support diamond 
layers 56, 58, and 60, respectively. The container and remaining structure 
of the HP/HT apparatus are not shown in FIG. 4, but are to be provided in 
conventional fashion. Second catalyst source 62 is placed adjacent the 
sandwich carbide/diamond layers such that exposed edges of diamond layers 
56, 58, and 60 are adjacent such second catalyst source. Second catalyst 
source 62, being essentially perpendicular to the carbide support and 
diamond layers, should provide a directional flow of catalyst during HP/HT 
processing parallel to the carbide support layers and through the diamond 
layers. The following is an example using another configuration. 
Example 4 
A refractory metal container (Zr, Ta, Nb, as examples) was charged with 0.6 
gm of a 20% of -2 micron and 80% of 800 to 1000 micron diamond feed. A 0.5 
mm thick disc of cobalt with 3% boron was placed directly above the 
diamond. A cobalt cemented tungsten carbide disc with a diameter of 14 mm 
and a thickness of 3 mm was inserted on top of the Co/B disc and the 
container was sealed with a refractory metal lid. Such a configuration is 
depicted in FIG. 5 wherein diamond layer 74 and carbide support 70 has 
second catalyst source 72 interposed therebetween. After placing the 
container into a high pressure cell, the sample was heated to about 
1150.degree. C. for 10 minutes at approximately 55 kB. The exposed diamond 
surface of the received product was examined and found to be uniform and 
well-sintered with an excellent degree of diamond-to-diamond bonding. 
Performance tests using turning experiments on hard cobalt cemented 
tungsten carbide (6% cobalt) with this tool demonstrated that its cutting 
abilities were good and that sintering was complete. Under the HP/HT 
conditions used to manufacture this tool, cobalt extraction from a support 
carbide using a conventional technique would not be possible. 
As used herein, the term "adjacent" is intended to describe a 
configuration in which a cemented metal carbide or second catalyst source 
is positioned in any assembly sufficient to enable a flow of catalyst 
material therefrom into a mass of diamond particles. Thus, for example, a 
second catalyst source may be placed in direct contact with a mass of 
diamond particles. Similarly, a cemented metal carbide layer would be 
considered adjacent to a mass of diamond particles if an intervening layer 
of tantalum, titanium, etc. as described in U.S. Pat. No. 4,108,614, which 
intervening layer is pervious to a flow of cobalt from the carbide, were 
placed between the carbide and the diamond mass. 
In this application, all percentages and proportions are by weight and all 
units are in the metric system, unless otherwise expressly indicated. 
Additionally, all references cited herein are expressly incorporated 
herein by reference.