JP2594785B2 - Diamond crystal-sintered carbide composite polycrystal - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention is directed to use in operations such as cutting, machining, drilling, and the like, and for use as wear surfaces such as wrapping stops, valve seats, nozzles, and the like. Abrasion and impact resistant materials. In particular, the invention relates to such materials formed by pressing polycrystalline diamond and sintered metal carbide (commonly referred to as cemented carbide) at very high pressures and temperatures.

As used herein, "polycrystalline diamond (CPCD)" does not refer to the type of material produced by placing individual diamond crystals under ultra-high pressure and temperature to cause intercrystalline bonding. It is assumed that. Generally, a catalyst / binder material is used to ensure sufficient intercrystalline bonding. In the art, this material is also often referred to as "sintered diamond". In this specification,
"Pre-sintered carbide" means that carbide grains of any of the IVB, VB or VIB metals are pressed and heated (in the presence of a binder such as Co, Ni or Fe and various alloys thereof). ), Which refers to the type of material obtained in producing the dense unitary piece. The most common and readily available form of pre-sintered carbide is tungsten carbide containing a cobalt binder. This is commonly called a cemented carbide. Pre-sintering refers to being already sintered when used in the present invention.

Prior Art In some applications, polycrystalline diamond has shown particular advantages over single crystal diamond. In particular, polycrystalline diamond PCD has better impact resistance than single crystal diamond. Single crystal diamond has not only its specific cleavage plane, which can cause fracture of the crystal at relatively low stress, but also has relatively low impact resistance due to its very high elastic modulus. On the other hand, polycrystalline diamond, which consists of a collection of randomly oriented individual crystals, alleviates the problems caused by cleavage planes in single crystal form. However, polycrystalline diamond is still
Relatively poor in impact resistance due to its high elastic modulus. This low impact resistance is problematic in many applications because polycrystalline diamond wears not from erosion of the atomic layer but from crushing and spalling that occurs on both macro and micro scales.

It has long been recognized that polycrystalline diamond is relatively brittle, and consequently, the first commercially available polycrystalline diamond products have a metallic backing layer directly bonded to the diamond layer as shown in U.S. Pat.No. 3,745,623. That is, the substrate was included. The most common form of this "composite compact" to date has been the sintering of a plane disc of polycrystalline diamond directly on a pre-sintered tungsten carbide disc by high pressure and high temperature during a press cycle. is there.

This configuration, in which the PCD is supported by a single pre-sintered carbonized body or similar substrate, has also provided advantages for attachment of the PCD to tools and the like. Diamond is relatively inert. As a result, it is difficult, if not impossible, to join a PCD to a tool support or other surface via conventional brazing techniques. Thus, providing the PCD with a metal backing that enables brazing provides a suitable means for brazing the PCD composite compact to a tool support.

Unfortunately, certain problems are found in composite tamps produced as described above, i.e., with the PCD layer applied directly to a single planar substrate.

One problem has been the design constraints of polycrystalline diamond tools, which can only be made in such a form that the diamond layer can be sufficiently supported by the carbide substrate.
Although work has been done to expand the possibilities for morphology (see, for example, US Pat. No. 4,215,999, growing a cylinder of polycrystalline diamond around a core of pre-sintered carbide), The need to provide a pre-sintered carbide substrate for use has identified polycrystalline diamond tool applications that are difficult or impossible to achieve using conventional composite tamped bodies. For example, rotating tools that need to be symmetric about one straight line and whose working surfaces are subjected to tangential forces, such as small grinding wheels and drills, have not been industrially feasible.

Another problem arises because the carbide substrate has a higher coefficient of thermal expansion than polycrystalline diamond. The bond between the diamond layer and the pre-sintered carbide substrate was 1,30 for both materials.
Since formed at temperatures in the range of 0 to 2,000 ° C., stress is generated as the composite compact cools and the carbide substrate shrinks more than diamond. Since the diamond layer is less elastic than the carbide substrate, these stresses often result in cracking of the diamond layer during the cooling of the composite compact, either during brazing or during use.

Another limitation on the use of a substrate to support or bond a PCD compact is the requirement that the composition of the substrate must be chemically compatible. Especially,
It is important that the substrate material does not react detrimentally to the diamond or to the catalyst / binder material.
For example, sintering PCD on steel or other iron-based alloy substrates has been difficult, if not impossible. This is because iron has a strong tendency to melt and catalyze the conversion of diamond to graphite. This is unfortunate in that it is easier to process than when the steel is a cemented carbide, and may be an otherwise good substrate material. Steel is also preferred in some applications where it has a low modulus of elasticity and thus encounters high impact forces, such as rock bits. Steel substrates are also preferred because they are easy to settle into the tool with a simple interference fit and easy to weld to the tool.

Furthermore, if the impact resistance of polycrystalline diamond is dependent on a pre-sintered carbide support, the diamond layer is preferably relatively thin so that the diamond is not too far from the support. This restriction on the thickness of the diamond layer naturally limits both the expected life of the composite compact in use and the design for the polycrystalline diamond tool.

Another problem that has limited the thickness of the diamond layer in composite compacts is caused by the "bridging" problem. Bridging refers to a phenomenon that occurs when a fine powder is pressed from multiple directions. It has been observed that the individual particles in the pressed powder tend to accumulate and form arches or bridges, so that the total amount of pressure often does not reach the center of the pressed powder. The present inventors have found that when 1 micron diamond powder is used to make a polycrystalline diamond body exceeding 1.52 mm thick, the polycrystalline diamond toward the center of the piece is better formed as the outer periphery. It was found that it was not normal. This condition may cause cracking or chipping of the diamond layer.

Japanese Patent Application No. 60-78614 describes an improved PCD composite material which partially alleviates the above problems. Briefly, the disclosed material is a polycrystalline diamond matrix or polycrystal in which a mixture of diamond crystals and pre-sintered carbide pieces is pressed under sufficient heat and pressure to disperse the sintered carbides. It is formed by forming a sintered carbide matrix in which diamond is dispersed. This composite PCD / sintered carbide material has been found to have higher toughness than standard PCD, making it attractive for high impact applications such as drilling, cement sawing and the like.

It has also been found that the addition of pre-sintered carbide pieces to the PCD is beneficial for composite compacts with a sintered carbide backing. In particular, PCD caused by the difference in thermal expansion coefficient
The stress at the interface between the layer and the backing is due to the fact that the presence of the pre-sintered carbide pieces dispersed within the PCD layer tends to make the thermal expansion properties of the PCD layer closer to that of the backing.
It is reduced.

In addition, the inclusion of pre-sintered carbide pieces in the PCD has been found to reduce the problems caused by bridging. In particular, the pre-sintered carbide pieces did not appreciably compress, thereby improving the pressure distribution in the pressing cell. Therefore, the new composite PCD material was able to press well even with thicker pieces than before.

Although the wear resistance of this composite is surprisingly higher than the standard PCD even at low dispersed carbide concentrations, the wear resistance is generally inferior to that of the standard PCD. As can be expected, the higher the concentration of cemented carbide, the lower the wear resistance. To achieve increased toughness in many applications
It is acceptable to sacrifice the wear resistance of the PCD body to some extent. However, it is certainly desirable to optimize both wear resistance and impact resistance. Also,
In some wear component applications, such as PCD bearings, it is important that the surface of the PCD component be uniform so that it can wear at a uniform rate.

SUMMARY OF THE INVENTION According to the present invention, there is provided a composite polycrystal comprising at least one exposed surface in contact with a workpiece and comprising a mixture of diamond crystals and pre-sintered carbide pieces bonded together and dispersed together. The concentration of diamond crystals from the material is varied, the diamond concentration is increased including 100% closer to the exposed surface, (A) comprising at least one exposed surface in contact with the workpiece and the diamond crystal and pre-sintered carbide pieces A mixture of polycrystalline materials, wherein adjacent portions of the exposed surface are only bonded with diamond crystals, and (B) contacting with a workpiece. At least one exposed surface and bond the mixture of diamond crystals and pre-sintered carbide pieces together and Wherein the volume percentage of diamond crystals in the mixture is reduced away from the exposed surface. A substrate for supporting the composite polycrystal can be provided. The volume percentage of diamond crystals in the mixture is reduced stepwise or continuously away from the exposed surface.

The present invention is a composite of polycrystalline diamond and pre-sintered carbide for engagement with a workpiece. The composite has a first surface having an exposed surface adapted to contact the workpiece.
Layer. This layer consists of polycrystalline diamond, ie, a diamond crystal pressed at a temperature and pressure sufficient to allow adjacent diamond crystals to bond together. The composite also includes a second layer adjacent to the first layer and comprising a mixture of polycrystalline diamond and pre-sintered carbide. That is, the second layer comprises a mixture layer of diamond crystals and pre-sintered carbide pieces pressed under sufficient heat and pressure to bond adjacent diamond crystals to one another and also to the pre-sintered carbide pieces. As a result, the diamond crystal and the pre-sintered carbide pieces are dispersed to each other. Either the pre-sintered carbide pieces or the diamond crystals constitute the matrix for the composite.

According to one embodiment of the present invention, the first layer also includes a pre-sintered carbide, but at a lower concentration than the second layer. That is, the volume% of the PCD in the first layer is the PCD in the second layer.
% By volume.

According to another embodiment of the present invention, a third layer is added to the composite. This third layer is adjacent to the second layer and consists of PCD and pre-sintered carbide and has a lower diamond concentration in the second layer.

According to yet another embodiment of the present invention, the volume percentage of PCD is 2%.
Uneven throughout each of the three layers. In the first layer,
The volume percentage of PCD is maximum (almost preferably 100%) when defined at the exposed or working (working) surface and decreases toward the interface with the second layer. Similarly, also in the second layer, the volume percentage of PCD is greatest at the interface with the first layer and decreases with distance from the interface. In a highly preferred form, the boundary between the two layers is not distinguished. That is, the change in the volume percentage of diamond in each layer and the diamond concentration is such that the volume percentage of diamond in the first layer at the interface is the volume percentage of diamond in the second layer at the interface.
It is selected to be only slightly higher or equivalent.
Consequently, this embodiment can be defined as having only one polycrystalline layer such that the volume percentage of diamond decreases away from the exposed surface. Alternatively, this can be defined as having an exposed layer having a maximum diamond volume percent and the remaining layers having a plurality of thin layers, each with a slight decrease in diamond concentration. .

According to yet another embodiment of the present invention, the composite is composed of two or more distinct layers. In this case, each layer has a relatively uniform diamond volume percentage, maximizing the exposed layer.

In yet another aspect, the composite also includes a substrate. Such a substrate may be constructed as a cemented carbide, steel, or other metallic, ceramic or cermet material. In one preferred embodiment, the substrate comprises sintered tungsten carbide. In another preferred embodiment, the substrate comprises steel or another iron-based metal and the composite further comprises a pre-sintered carbide barrier layer disposed between the substrate and the PCD-containing closest layer.

According to yet another embodiment, the layer that exhibits an exposed surface for engagement with the workpiece is narrowed between the two PCD / carbide composites. This particular example is an insert for a spade drill such that the cutting edge protrudes from the middle layer and the two composite side layers support and facilitate the attachment of the spade drone insert to the drill shaft. Useful for applications.

Description of specific examples Referring to the drawings, FIG.
A prior art composite tamped body 10 consisting of 12 and a sintered carbide backing or substrate 11 supporting it is illustrated. See, for example, U.S. Patent No. 3,745,623. Diamond layer 12 is obtained by treating individual diamond crystals under heat and pressure sufficient to provide intercrystalline bonding. The cemented carbide backing 11 is tightly bonded to the diamond layer 12 at the interface 13. During the press cycle, a strong chemical bond is formed at the interface 13 between the two layers 11,12. Because the cemented carbide backing 11 shrinks more than the diamond layer 12, residual stresses are created between the two layers that can lead to premature cracking in the diamond layer.

FIG. 2 shows a cross section of a pressing unit 20 that can be used to produce the composite polycrystalline diamond body of the present invention. The pressing unit 20 is cylindrical and may be ultra-high such as those described in US Pat. No. 3,913,280 (for use in a cubic press) or US Pat. No. 3,745,623 (for use in a belt-type press). Designed to fit within the central cavity of the pressure and temperature cell.
The pressing unit 20 includes a hollow tube 14 on which disks 15, 16 are placed. Tube 14 and disks 15 and 16
Serves as a plastic pressure transmitting medium and preferably consists of pressed NaCl. However, talc or hexagonal boron nitride can also be used.

Disposed within the tube 14 is a protective metal enclosure 17, also cylindrical and closed at the bottom end. This enclosure 17
Is preferably made of molybdenum because of its high melting point,
Other metals such as zirconium or tantalum may also be used successfully. A disk 18 usually made of the same metal as the enclosure 17 is placed as a lid on the upper end of the enclosure 17.

The substrate 21 is placed on the bottom of the enclosure 17. This substrate is made of sintered tungsten carbide (a so-called cemented carbide) using a cobalt binder in a preferred embodiment. It has been found that substrates of this composition can be chemically compatible with many of the catalyst / binder systems used to form polycrystalline diamond. Substrates made of other metals, ceramics or cermets can also be used. For example, steel or other iron-based alloys may be used. However, when using steel or other materials that are chemically reactive or otherwise incompatible with the catalyst / binder system used to generate the PCD, an additional barrier that acts as a barrier between the substrate and diamond It is desirable to include a layer. A layer of pre-sintered carbide grains has been successfully used to do this. The substrate 21 can serve as a support for the compacted body to be produced. Also, the substrate
21 can be used to join the tamped body to the tool.

Adjacent to the substrate 21 is a pre-sintered carbide piece 22 and a diamond crystal 23 as well as a transition layer 24 comprising a mixture of a catalyst / binder material for the formation of polycrystalline diamond. This mixture can be produced by ball milling a pre-sintered carbide piece 22 with diamond crystals 23 and a suitable catalyst / binder material. This pulverized mixture is injected into the metal enclosure 17 on the substrate 21. In this preferred embodiment, the diamond crystal 23 and the pre-sintered carbide pieces
A ratio of 22 can be expressed as carbide pieces occupying about 60% by volume of this transition layer. That is, diamond occupies about 40% by volume with its catalyst / binder.

Pre-sintered carbide pieces 22 consist of sintered tungsten carbide using a cobalt binder. At present, for chemical compatibility reasons, it is preferred that the pre-sintered carbide pieces 22 have the same composition as the substrate 21, including the binder phase. However, it may also be desirable to vary the binder content in the pre-sintered carbide piece so that the elastic modulus of the carbide piece 22 has different properties than that of the substrate 21. Also, in other embodiments having more than one transition layer, the binder content or tungsten carbide grain size in the pre-sintered carbide pieces can be varied from layer to layer to achieve the same result.

The size and shape of the pre-sintered carbide pieces 22 can be varied to achieve various results. Even if the shape is regular,
It can be irregular. Irregular shaped pieces are presently preferred because the most economical source of pre-sintered carbide pieces is crushed or fire-blasted pre-sintered grit. For convenience and clarity, the dimensions of the carbide pieces 22 are shown straddling in the drawing. In practice, they are preferably small enough to be invisible without magnification. In particular, a particle size of -325 mesh (US sieve standard) is preferred.
In addition, it may seem preferable to use carbide pieces that are sufficiently larger than the diamond crystal to reduce the extent to which the carbide pieces prevent the formation of diamond-to-diamond bonds.

The dimensions of the diamond crystal 23 used can also be varied by known means to meet the needs of a particular application. In a preferred embodiment, a 1-100 micron, and preferably 4-12 micron, diamond mixture is used. Various catalyst / binder materials for the formation of PCD are well known in the art. In this preferred embodiment, the catalyst / catalyst comprising cobalt powder and present in a 1 to 10 volume ratio in the case of a diamond-cobalt mixture
A binder is mixed with the diamond crystals.

Alternatively, the catalyst for bonding the diamond crystals together in this layer 24 may be partially or entirely derived from the binder present in the pre-sintered carbide pieces. In other words, the cobalt or other binder in the pre-sintered carbide pieces 22 may be taken from the pre-sintered carbide pieces in an amount sufficient to act as a catalyst / binder for the diamond crystals 23 during the press cycle.

Adjacent to the mixture is another layer 25 of an amount of diamond crystals and a suitable catalyst / binder material, preferably the same catalyst / binder material as in the transition layer. Again, the catalyst / binder in this layer 25 may be supplied in part or in whole from a binder which is introduced from the pre-sintered carbide pieces 22. This layer 25 is
What is necessary is just to implant in the transition layer 24 in 17. This layer 25 forms the exposed or working surface of the resulting composite compact.

In this embodiment, the diamond crystals are present as a mixture of comparable dimensions as in the transition layer. However, since this layer contains the working surface of the final product,
It would also be desirable to vary the diamond grain size to suit a particular application. For example, 0-5 to improve the finish of the exposed surface for applications such as precision grinding, wire drawing, etc.
It would be preferable to use fine diamond crystals, such as microns. In addition, it may be desirable to include more than one diamond crystal layer with an upper layer comprising the smallest diamond crystal.

FIG. 3 is a perspective view of a composite 30 made in accordance with the present invention. A composite 30 suitable for cutting, grinding, crushing, machining, and other applications requiring severe wear and impact resistance, such as bearings, includes a substrate 31. The substrate shown here comprises a tungsten carbide sinter with cobalt as a binder. As described above, other materials can be used for the substrate 31. In some applications, the substrate 31 is soldered to a tool holder or other support.

Immediately adjacent to the substrate 31, there is a transition layer. Transition layer 34 comprises polycrystalline diamond 37 and pre-sintered carbide pieces 36.
(Preferably much smaller than illustrated). Specifically, transition layer 34 is formed by pressing a mixture of diamond crystals and catalyst / binder material and pre-sintered carbide pieces under heat and pressure sufficient to bond adjacent diamond crystals to each other and to the pre-sintered carbide pieces. It is composed. The transition layer 34 also includes residual catalyst / binder material left in the polycrystalline structure after pressing. Transition layer 34
The concentration of polycrystalline diamond (including slight perforations and residual catalyst / binder) is between 20 and 60%, and preferably around 40%. However, for various reasons discussed in the application, this concentration may be adjusted up or down to suit a particular application.

Adjacent to the transition layer 34 is an upper layer (as shown) 35 that includes an exposed or working surface 39. This upper layer 35 is made of polycrystalline diamond 38. Specifically, the polycrystalline diamond 38 is formed by pressing the diamond crystal and catalyst / binder material under sufficient heat and pressure to bond the adjacent diamond crystals together. Preferably, the catalyst / binder material is cobalt powder and is present in the upper and transition layers in a 1 to 10 volume ratio to diamond. Alternatively, the catalyst / binder for this upper layer may be partially or wholly obtained from a binder that migrates from the transition layer.

FIG. 4 is a sectional view taken along the line 4-4 in FIG. Transition layer 34 faces substrate 31 at interface 32. As noted above, in typical prior art composite compacts, the interface between the substrate and the PCD layer could be a weak point in the structure due to the stress caused by the differential thermal expansion. However, the use of the transition layer 34 of the present invention alleviates the thermal expansion problem due to the fact that the transition layer as a whole has a thermal expansion characteristic intermediate between that of the sintered carbide substrate 31 and the polycrystalline diamond layer 35. That is, during the cooling stage after pressing of the compact 30, the transition layer has a smaller degree of shrinkage than the substrate 31 which shrinks more than the PCD layer 35. As a result, the strain on the composite compact is
At a large decrease.

This is an important advantage. In our experience,
The difference in shrinkage rate between the cemented carbide substrate and the PCD layer in prior art compacts resulted in cracks in the PCD layer, resulting in high reject rates as high as 30%. In contrast, batches of composite tamped bodies made with the transition layer according to the present invention only showed a rejection rate of less than 5% due to cracking.

FIG. 4 also illustrates another advantage of the present invention. As shown, at the interface 32 between the substrate 31 and the transition layer 34, there are a number of pre-sintered carbide pieces 36 adjacent to the substrate 31. During the press cycle, these adjacent carbide pieces burn into the substrate 31. As a result, the carbide substrate-diamond interface becomes non-planar. Thus, the potential stress between the two is further reduced.

Another important advantage of the present invention is the fact that it has become possible to realize the benefits of a composite PCD / carbide material while retaining a working surface of 100% PCD. This is advantageous because it alleviates some of the problems of prior art PCD compacts while maximizing maximum wear resistance. A 100% PCD working surface is particularly important in applications such as bearings where a homogeneous surface is also desired.

FIG. 5 is a cross section of a composite compact 50 made in accordance with another embodiment of the present invention. In particular, this embodiment does not have two distinct diamond layers,
It comprises a single polycrystalline diamond layer 53 consisting of a mixture of PCD 54 and pre-sintered carbide 55. The PCD concentration is greatest at the exposed or working surface 59. Preferably,
The concentration of PCD54 was 100% by volume (residual catalyst /
(Including binder material). The concentration of PCD 54 gradually decreases in a direction away from the exposed surface and toward interface 52 with substrate 51. Conversely, volume% of pre-sintered carbide
Increases in the same direction. More preferably, the volume% of PCD54
At the interface 52 is 0% or more.

Alternatively, this embodiment may be defined as a collection of several thin layers, each decreasing the PCD concentration as one moves away from the layer containing the exposed surface 59. In practice, this is an easy way to implement this embodiment. That is, this concentration gradient is generated by sequentially placing several thin layers of increasing polycrystalline diamond concentration in the pressing cell, and finally the concentration gradient compact 50 is produced.

Another method of producing the gradient compact 50 is to vary the proportion of diamond and pre-sintered carbide pieces added to the pressing cell with careful control. Yet another approach is to use a carefully controlled centrifugal action of the diamond and pre-sintered carbide mixture. This centrifugation method will require a dispersing medium such as acetone, which can be easily removed prior to pressing.

FIG. 6 is a cross-sectional view of an insert 60 made in accordance with yet another embodiment of the present invention and suitable for use in roller cone crushed bits. The insert 60 includes a base or insert body 61. In a preferred embodiment, the fuselage 61 is made of steel. Steel is preferred over sintered carbide. Reason,
Steel is easier to make, can be joined by welding, and has a lower elastic modulus, which makes the insert more impact resistant and can be suitably mounted in the bit by an interference fit. It is. According to well-known technology,
The fuselage 61 is properly shaped to be suitable for use in a specific cutting structure of roller cone rock bits.

A barrier 62 exists immediately adjacent to the body 61. In this case, the barrier layer is constructed by welding pre-sintered carbide grit to one another during a press cycle. This barrier layer plays an important role in separating polycrystalline diamond from steel. This is required due to the strong tendency of the iron element from the steel to melt and thereby trigger the graphitization of the diamond. This result would otherwise occur if the iron came into contact with the diamond during the press cycle. It is also important to keep the steel isolated from the polycrystalline diamond during use of the compacted body, as the PCD adjacent to the steel is likely to produce the graphite encountered during use.

Since CBN is known to have low solubility in molten iron-based alloys, polycrystalline as a barrier to carbon diffusion
Other embodiments incorporating a CBN (sintered during press cycle) transition layer would also be desirable.

This separation effect will also be achieved by a polycrystalline layer as shown in FIG. That is, if the gradient concentration of the pre-sintered carbide pieces reaches 100% before contacting the substrate, steel, another iron-based alloy or another incompatible material can be used as the substrate.

Next, a transition layer 63 is provided immediately adjacent to the barrier layer 62. The transition layer is constructed by pressing a mixture of pre-sintered carbide pieces and diamond crystals at heat and pressure sufficient to produce an interdispersed matrix of both. Preferably, the transition layer comprises about 40% PCD by volume.

Immediately adjacent to the transition layer 63, an actuation layer 64 is provided.
This layer 64 includes a working surface 65 that will actually make contact with the rock to be cut or ground. This layer 64 comprises another pre-sintered carbide-PCD mixture than in the transition layer. However, in this layer, the PCD is at a higher volume percentage, preferably at 60%. It may be preferable to include a pre-sintered carbide piece in the working layer because of the high impact forces on the insert during rock drilling operations. High carbide transition layers have been found to be beneficial in improving the insert's ability to withstand high impact forces.

Applying these layers 62, 63 and 64 to the fuselage 61 prior to pressing may require the use of traces of temporary binders such as paraffin to hold these layers in place for pressing. unknown. However, even without the use of such temporary binders, it was observed that these mixtures adhered and stayed to some extent. This is probably due to the presence of the cobalt powder catalyst / binder or the fineness of the powder.

Example 1 A sintered carbide substrate was placed on the bottom of a pressing unit as described above. This substrate was a pre-sintering plate of tungsten carbide using a cobalt binder of 14% by weight. This disc was obtained from Tungsten Carbide Manifacturing as Code No. 614.

The mixture of diamond crystals, catalyst / binder material and pre-sintered carbide pieces is completely milled (pulverized and mixed) of diamond, cobalt powder and pre-sintered tungsten carbide pieces in a tungsten carbide lined ball mill. Obtained. The resulting mixture had a diamond grain size of 65% at 4-8 microns and 35% at 0.5-1 micron. The catalyst / binder in the form of cobalt powder was included as 13% by weight of the diamond cobalt mixture. The pre-sintered carbide pieces had an average size of 30 microns and a cobalt binder content of 11%. Pre-sintered carbide pieces accounted for 60% by volume of the mixture.

The mixture was clarified and reduced at 800 ° C. by alternating treatment with hydrogen gas and vacuum. 0.4mm
Was injected into the upper surface of the substrate to form a transition layer.

Then a mixture of diamond crystals and cobalt powder (grain size and cobalt content in transition layer (similar)
Was poured onto the transition layer. This upper layer was also 0.4 mm thick.

The pressing cell is placed between the anvils of a cubic press and pressurized to about 60 Kbar and at about 1450 ° C.
Heated for a minute. Thereafter, the pressure and temperature were reduced and the cell was allowed to cool.

The recovered compact did not show any signs of cracking. In a wear test against the rotating Hanaokaiwa round material, this compact showed the same abrasion resistance as the standard PCD compact.

Example 2 A compact was produced in the same manner as in Example 1 except that the upper layer contained a pre-sintered carbide piece in an amount of 40% by volume. The recovered compact did not show any signs of cracking.

Example 3 A compacted body was produced in the same manner as in Example 1 except that four layers were formed on a steel substrate. Specifically, a 0.25 mm thick layer of pre-sintered tungsten carbide grit (ie, 100%) was placed on a steel substrate. A layer of similar thickness consisting of 60% by volume pre-sintered tungsten carbide grit and 40% by volume diamond crystal and cobalt binder was then placed in the cell. A 0.25 mm thick layer of 40% by volume pre-sintered tungsten carbide grit and 60% by volume diamond and its cobalt binder was formed thereon. Finally 100% by volume
An upper layer consisting of diamond and its cobalt binder was added. The recovered compact did not show any signs of cracking. In addition, no negative effects were seen with the use of steel substrates.

Although all of the illustrated embodiments include a substrate, there are many uses for the PCD composite compacts of the present invention that do not require such a substrate. In effect, the present invention provides the advantage that the carbide-containing transition layer can be brazed directly to the support. That is, the braze can adhere to the carbide pieces in the composite material, and thus can be directly brazed to the transition layer.

Although all of the illustrated embodiments show the working surface constituting the main surface of the compacted body, it is also possible to make the secondary surface of the compacted body the working surface. For example, when making inserts for spade drills, the cutting layer of high PCD concentration is flanked on its two major sides by a composite layer having a low PCD concentration. The cutting layers project beyond the side layers and are supported by them. In addition, the side layers can be used to facilitate mounting the spade drill insert within the drill shaft.

It should be noted that many modifications can be made within the scope of the present invention.

[Brief description of the drawings]

FIG. 1 is a perspective view of an example of a composite compacted body of the prior art. FIG. 2 is a cross-sectional view of a press cell used for producing the composite of the present invention. FIG. 3 is a perspective view of one embodiment of the present invention. FIG. 4 is a sectional view taken along the line 4-4 in FIG. FIG. 5 is a cross-sectional view of yet another embodiment of the present invention in which the diamond volume percentage decreases away from the exposed surface. FIG. 6 is a cross-sectional view of a roller cone rock bit insert made in accordance with yet another embodiment of the present invention. 10: Conventional compacted compact 11: Substrate 12: Diamond layer 13: Interface 20: Pressing unit 21: Substrate 22: Pre-sintered carbide piece 23: Diamond crystal 24 Transition layer 25: Upper layer 31: Substrate 34: Transition Layer 35: Upper layer 39: Working surface 36: Pre-sintered carbide pieces 37: Diamond 38: Polycrystalline diamond

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C04B 37/00 C04B 37/00 A

Claims (12)

(57) [Claims] 1. A polycrystalline diamond having an exposed surface in contact with a workpiece and formed by pressing a mixture of diamond crystals and pre-sintered carbide pieces under heat and pressure to bond adjacent diamond crystals together. A composite polycrystalline material having the material bonded to a pre-sintered carbide piece such that the polycrystalline diamond material and the pre-sintered carbide piece increase the volume percent of diamond crystals in the mixture toward the exposed surface. A composite polycrystal which is dispersed in each other. 2. The composite polycrystal according to claim 1, further comprising a substrate for supporting the composite polycrystal. 3. The composite polycrystalline body according to claim 2, wherein said substrate is made of a cemented carbide. 4. The composite polycrystalline body according to claim 2, wherein said substrate is made of steel. 5. The composite polycrystalline body according to claim 1, wherein no pre-sintered carbide pieces exist in a portion adjacent to the exposed surface. 6. The composite polycrystal according to claim 5, wherein the total volume of the diamond crystal in the remaining portion other than the portion adjacent to the exposed surface is in the range of 20 to 80%. 7. The composite polycrystal according to claim 5, wherein the total volume of the diamond crystal in the remaining portion other than the portion adjacent to the exposed surface is in the range of 35 to 45%. 8. The composite polycrystal of claim 1, wherein the volume percent of diamond crystals in the mixture is increased stepwise in a direction toward said exposed surface. 9. A first layer proximate to the exposed surface having a uniform diamond crystal percentage in the range of 70-98% by volume;
9. The composite polycrystal of claim 8, comprising a second layer bonded to said first layer having a uniform diamond crystal percentage in the range of 70% by volume. 10. The composite polycrystal of claim 1, wherein the volume percent of diamond crystals in the mixture is continuously increased in a direction toward said exposed surface. 11. The composite polycrystal according to claim 10, wherein the total volume of the diamond crystal is in the range of 20 to 80%. 12. The composite polycrystal according to claim 10, wherein the total volume of the diamond crystal is in the range of 40 to 50%.