GB2270493A - Encapsulation of segmented diamond compact - Google Patents

Abstract

A diamond compact which comprises at least two interlocking segments 1, 2 of thermally stable, polycrystalline diamond encapsulated with a diamond film is provided wherein the diamond segments are bound to form a composite mass which is overcoated with a diamond film. The diamond film provides added shear strength and an enhanced bending moment to the compact. The segments can also be comprised of diamond particles of a different average grain size to provide improvements in impact resistance and abrasion resistance in tools used for drilling and mining. These compacts can be prepared by cutting diamond clusters to provide complementary surfaces, bonding these surfaces together to form one composite mass and overcoating the mass with a diamond layer by chemical vapor deposition. <IMAGE>

Description

ENCAPSULATION OF SEGNENTED DIAMOND COMPACT Cross-Reference to Related ApDlications This application is related to copending application Serial No. (Attorney Docket No. GEMAT 16], entitled Segmented Diamond Compact", and assigned to the same assignee as the present invention, filed concurrently herewith.

Backqround of the Invention This invention relates to an encapsulated diamond compact for tools comprised of interlocking segments and a process for the production of such compacts. More particularly, it is concerned with encapsulated diamond compacts useful as tool components comprising at least two interlocking segments of polycrystalline, self-bonded diamond particles produced independently, preferably with diamond particles of a different average grain size. These segments are encapsulated with a thin diamond layer.

Diamond finds use as an abrasive material in the form of (a) aggregated particles bonded by a resin or metal matrix, (b) compacts, and (c) composite compacts. As bonded aggregates, particles of diamond abrasive are embedded in a grinding or cutting section of a tool such as a grinding wheel or drill bit.

A compact is defined herein as a cluster of diamond crystals bound together either in a self-bonded relationship, by means of a chemically bonded sintering aid or bonding medium, or some combination of the two. Diamond compacts can be made by converting graphite particles directly into a diamond cluster, with or without a metal catalyst or bonding medium. Alternatively, diamond com pacts can be made by first forming diamond particles and subsequently bonding them, with or without a sintering aid or bonding medium. Where a catalyst is used, the diamond compacts formed are polycrystalline.

Compacts which contain residual metal from a catalyst, bonding medium, or sintering aid are thermally sensitive and will experience thermal degradation at elevated temperatures. Compacts which contain self-bonded particles, with substantially no secondary non-abrasive phase, are thermally stable. The "porous compacts" described in U.S.

Patent Nos. 4,224,380 and 4,228,248 are polycrystalline and contain some non-diamond phase (less than 3 wt%), yet they are thermally stable. These compacts have pores dispersed therethrough which comprise 5-3096 of the compact. The porous compacts are made thermally stable by removal of the metallic phase through liquid zinc extraction, electrolytic depletion, or a similar process.

A composite compact is defined herein as a compact bonded to a substrate material such as a cemented tungsten carbide. The bond to the substrate is formed under high pressure/high temperature conditions either during or subsequent to formation of the compact. Examples of composite compacts and methods for making the same are found in Re.

32,380 and U.S. Patent Nos. 3,743,489; 3,767,371; and 3,918,219.

Diamond compacts and aggregated diamond particles are used to provide tools for drilling and boring. There is a continuing effort to enhance the useful life of such tools.

Diamond compacts comprised of coarse-grain diamond are well known to be useful in such tools, as are compacts of fine-grain diamond. Advantages are recognized with each type of compact. Fine-grain compacts often provide the advantage of leaving smooth surfaces in the material cut or abraded and show improved impact resistance over compacts of a coarser grain. In contrast, compacts of a coarsegrain diamond typically show improved wear resistance over fine-grain compacts. In many industries, such as drilling and mining, both impact resistance and abrasion resistance are important properties for the abrasive components.

While fine-grain diamond compacts provide the desired impact resistance, they are relatively expensive, making improvements in wear performance desirable. Coarse-grain diamond compacts provide the desired wear performance; however, these diamond compacts often fracture due to poor impact resistance. It is desirable to provide compacts with improved abrasion and impact resistance over the single-grain compacts used commercially.

U.S. Patent No. 4,505,746 describes a diamond compact for tools such as a wire die comprised of fine-grain diamond particles and coarse-grain diamond particles. U.S.

Patent No. 3,885,637 describes boring tools wherein coarsegrain abrasives are embedded in a matrix layer also containing fine-grain abrasives embedded therein. U.S. Patent No. 4,696,352 describes a coated insert for a drilling tool used in mining and boring, wherein the coating is a refractory material formed on the substrate of tool steel, cemented carbide, and the like.

U.S. Patent 4,976,324 (Tibbitts), entitled "Drill Bit Having Diamond Film Cutting Surface, describes coating a diamond bit with a diamond film by chemical vapor deposition. The diamond film is deposited on the cutting face and is said to improve the cutter's leading edge, help resist wear, improve impact resistance and reduce friction.

The film is said to increase toughness by reducing the surface porosity of a substrate and filling the anomalies which are nucleation points of fracture. The film is also said to cover joints between diamond pieces.

Summarv of the Invention It is an object of the present invention to provide diamond compacts with high impact resistance and abrasion resistance to enhance the useful life of the tools in which they are used.

It is another object of the present invention to provide improved diamond compacts for tools used in drilling and mining industries that exhibit a longer useful life than diamond compacts currently employed in tools.

It is a further object of the present invention to provide diamond compacts which comprise at least two segments of bonded diamond particles, preferably of a different average grain size, which are encapsulated by a thin diamond film.

It is another object of the present invention to provide a process for producing an encapsulated, polycrystalline diamond compact comprised of bonded segments of diamond particles.

The above objects are achieved by producing a diamond compact with at least two interlocking segments of bonded diamond particles, preferably with diamond particles of differing average grain size. These segments are prepared from one or more clusters of bonded diamond particles produced under independent high temperature/high pressure processes, with.the aid of a catalyst. The clusters of bonded diamond particles are cut into interlocking segments with geometric patterns, and the catalyst is leached therefrom. The geometric patterns of the interlocking diamond segments are matched, and the matched diamond sections are bonded together. The bonded segments are overcoated with a thin diamond film, preferably by chemical vapor deposition of diamond.

Brief Descrintion of the Drawings Figures 1-7 are perspective views of diamond segments suitable for use in an encapsulated diamond compact of the present invention; Figure 8 is a perspective representation of bonded diamond segments which can be used in an encapsulated diamond compact of the present invention; Figure 9 is a perspective representation of diamond segments suitable for use in an encapsulated diamond compact of the present invention; and Figure 10 is a perspective representation of an encapsulated diamond compact of the present invention.

Detailed Descrintion of the Invention The encapsulated diamond compacts of the present invention comprise at least two segments of bonded diamond particles. Compacts with more than twenty segments are within the scope of this invention; however, the practical limit may be about six segments for most applications due to the costs of preparing and handling compacts. Special applications may call for compacts with many more segments.

Unlike multiple diamond compact segments used to form abrasive tools, such as in U.S. Patent No. 4,246,004, the segments of the present invention are preferably interlocked to form a single compact. The term "interlocked" as used herein is intended to define geometric shapes wherein the surface area of the interface between segments is greater than the cross sectional area at the interface. Preferably, the surface area at the interface is more than 150% of the cross sectional area and, more preferably, the surface area is more than twice (200%) the cross sectional area at the interface. The amount of surface area desired at the interface will depend on the intended use of the tool assembled with these compacts.

This can be accomplished with a variety of geometric designs, as shown in Figures 1-7. The geometric designs include dovetail joints, as shown in Figures 2 and 9; keyhole joints, as shown in Figure 4; tongue-and-groove joints, as shown in Figures 3 and 5; and modifications thereof, as in Figure 6. Figures 7 and 8 show modifications of the dovetail joint. Figure 1 shows a corrugated joint with corrugations of a sinusoidal wave form. Figures 1 and 3 illustrate geometries which provide moderate levels of surface area at the interface. Such geometries are more than adequate where the compact will not experience shear forces in the plane of the interface during use.

The segments can vary in size and proportion depending on the intended use. Preferably, the segments comprise from 10-90 wt% of the completed compact, and are typically from 40-60 wt%, i.e., about 50 wt%, of the completed compact. Where a dovetail joint, keyhole joint, or tongueand-groove joint is used, the cross sectional area at the base of any protrusion may fall within the range of 20-80% of the total cross sectional area of the compact. The size of the bases for opposing protrusions may be balanced as desired to provide a bond with high shear strength across the plane of the interface.

Two or more of the segments of the bonded diamond particles may be produced independently, i.e., they are produced in separate high pressure/high temperature processes. The processes used and the segments obtained can be the same or different. Particular advantage is obtained where the segments are comprised of diamond particles of a different grain size to provide a balance of different features available from each segment. Also included in this invention are multisegmented compacts, wherein at least two segments are of identical composition and sandwich one or more segments of a distinct composition. The identical segments can be produced simultaneously or cut from the same cluster of bonded diamond particles.

The average particle size for the diamond within each segment can vary widely. The particles can be of submicron size to as large as 1000 Am in diameter. Typically, the average particle diameter falls within the range of 0.25-200 Mm. Preferably, at least one segment has diamond particles of an average grain size in the range of 30-150 mesh. Such segments are preferably interlocked with segments having diamond particles of an average particle diameter of less than 20 m, and preferably from 1-15 pm.

These diamond compacts, which comprise fine-grain diamond segments and coarse-grain diamond segments, show improved impact resistance and/or abrasion resistance over singlegrain diamond compacts.

The impact strength of a diamond compact is lowered with an increase in the average grain size of the diamond particles therein. A compact of fine diamonds is excellent in transverse rupture strength, as well as in toughness.

However, since individual grains are held by small skeletons, their bonding strengths are weak, and the individual grains can fall off relatively easily during cutting, resulting in a relatively low overall wear resistance. On the other hand, in a compact of coarse diamond grains held by large skeletons, individual diamond grains have the high bonding strength to impart excellent wear resistance; but cracks, once formed, tend to be propagated due the large skeleton parts, thus leading to breakage of the edge.

Therefore, fine diamond grains with a particle diameter of 20 ,um or less provide good impact resistance, and coarse diamond grains provide high toughness. The average grain size of coarse diamond particles used in the compacts of the present invention should have an average particle diameter of 20 pm or more. A typical example of a bimodal compact of the present invention is one comprised of two segments, wherein one segments has diamond particles of an average particle diameter of 80-120 mesh, and the other segment comprises diamond particles with an average grain size of 4-12 ,um.

The segments of the bonded diamond particles utilized in this invention can be those obtained by converting graphite directly into a diamond by high pressure/high temperature techniques or by two-step procedures whereby graphite is first converted to diamond, with or without a catalyst, and the resultant diamond particles are bonded in a cluster, with the aid of a bonding agent, sintering aid, or residual conversion catalyst. U.S. 'Patent Nos.

3,136,615 and 3,233,988 describe examples of suitable methods for producing diamond compacts or clusters with the aid of a bonding medium or sintering aid.

The materials that function as the sintering aid can vary widely. Any metal or ceramic thereof can form the metallic phase. However, preferred materials used as a sintering aid typically include metals recognized as catalysts for converting graphite into a stronger, more compact state or for forming compact masses thereof and, in addition, include ceramics of such metals such as the carbides and nitrides of Ti, Ta, Mo, Zr, V, Cr, and Nb.

Reference made herein to a compact segment with a metallic phase is intended to include those containing more than one metal.

The amount of material which forms the metallic phase can vary widely and is preferably below 3 wt% to maintain thermal stability. The upper limit on the amount of the metallic phase within a particular segment is defined by the performance and effectiveness expected of the tool component. The presence of any metallic phase is expected to cause some instability at temperatures greater than 700'C. For example, less than 0.05 vol% of a metallic phase will cause instability under such conditions.

It is preferable that the bonded segments of diamond particles be thermally stable so that they can be coated with a diamond film by CVD. Thermally stable diamonds include clusters of bonded diamond particles which are porous, as defined in U.S. Patent Nos. 4,224,380 and 4,288,248. The abrasive in these porous clusters comprises about 70-95 volt of the cluster, which is bonded to form a network of interconnected empty pores. For porous clusters of bonded diamond particles, suitable sintering materials include those catalysts described in U.S. Patent Nos.

2,947,609 and 2,947,610, such as Group IIIA metals, chromium, manganese, and tantalum. The porous clusters of bonded diamond particles are not thermally stable until the second phase is removed.

Upon formation of the individual clusters of bonded diamond particles by high temperature/high pressure processes, the metallic phase may be removed first. The individual diamond clusters are cut using a laser into interlocking segments having geometric patterns.

Conventional power intensities and beam widths can be used.

Alternatively, the individual clusters may be cut to a desired shape with a traveling wire electron discharge machine (EDM) before leaching the metallic phase. Such individual clusters are not thermally stable, and complex geometric shapes can be obtained. Once the clusters are shaped, the metal phase is leached away to provide a thermally stable segment.

Matching segments are then bonded together to form a compact. The individual segments are preferably bonded together with the aid of an intermediate metal layer, such as a carbide former, under high pressure and high temperature or a low temperature sintering metal such as nickel.

The intermediate metal layer may be applied by conventional techniques such as chemical vapor deposition, electrolytic deposition, electroless deposition, or salt bath deposition. The pressures and temperatures utilized to bond the segments are consistent with those used to form conventional sintered bonds within compacts of diamond particles.

A thin diamond film is applied to the bonded segments to encapsulate the composite mass. The diamond film covers at least 75% of the outer surfaces of the bonded segments.

This film serves to increase the bond shear strength between segments and to enhance the bending moment of the compact. Complete encapsulation of the bonded segments is suitable. This film can be applied by conventional processes, preferably by CVD of diamond. The thickness of the layer typically falls within the range of 200-2500 corm, preferably 1000-2000 Am.

High temperature/high pressure apparatus suitable for forming the clusters of bonded diamond particles used to form the segments herein are described in U.S. Patent No.

2,941,248. Suitable devices are typically capable of providing pressures in excess of 100 kilobars and temperatures in excess of 2000it. Common components of the device in dude a pair of cemented tungsten carbide punches and a die member of the same material which can withstand extreme temperatures and pressures.

Reaction conditions used to form the clusters of bonded diamond particles and the duration of reaction can vary widely with the composition of the starting materials, i.e., graphite types, and the desired end product. Temperatures and pressures of from 1000-2000'C and pressures greater than 10 kilobars, such as from 50-95 kilobars, are typical. The actual conditions are dictated by pressure/ temperature phase diagrams for carbon, as described in U.S.

Patent Nos. 4,188,194; 3,212,852; and 2,947,617.

The compacts produced find use in dies, cutting tools, drill bits, and dressers. The compacts can be brazed directly to a tool substrate such as a tungsten carbidecobalt substrate. A chemically bonded metal layer may be applied to the diamond film to aid adhesion. The position and configuration of the compacts in the tool substrate can vary widely, depending on the intended use. Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.

In the foregoing and in the following example, all temperatures are set forth in degrees Celsius; and, unless otherwise indicated, all parts and percentages are by weight.

The entire disclosure of all applications, patents and publications, cited above and below, are hereby incorporated by reference.

EXAMPLE Clusters of bonded, non-thermally stable polycrystalline diamond particles, produced by conventional methods, such as those of U.S. Patent No. 4,224,380, are selected for cutting into geometric shapes with a traveling wire EMD. One cluster has diamond particles of from 80-120 mesh size. Another cluster has diamond particles of an average diameter of from 4-12 ,um.

The clusters to be cut are about 1 g in total weight and about 1 cm3 in size. The clusters are cut to a desired shape with a conventional automatic traveling wire electron discharge machine (EDM). The power and speed of the EDM can vary over conventional operating conditions. The wire cuts a geometric pattern into the surface of each of the clusters which complements the other such that the surface area at the interface is more than 150% of the cross sectional area. The clusters are cut in the shape of a sinusoidal wave form, as shown in Figure 1. The cut clusters are then leached of the metallic phase therein to provide thermally stable interlocking segments by conventional methods such as in U.S. Patent No. 4,224,380.

The cut surface is coated with a metal interlayer by chemical vapor deposition at a thickness of about 1-10 ym, and the two cut segments are assembled and sintered at a conventional sintering temperature and pressure.

The bonded segments are then overcoated with a 10002000 ,um CVD diamond layer applied by conventional techniques. The resulting compact can be bonded to a tool body in a manner consistent with conventional compacts.

The preceding example can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding example.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, withput departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt'it to various usages and conditions.

Claims (18)

1. A diamond compact which comprises at least two interlocking segments of thermally stable, polycrystalline diamond encapsulated with a diamond film.

2. A diamond compact as in claim 1 wherein at least 75% of the outer surface of the segments is coated by the diamond film to provide encapsulation.

3. A diamond compact as in claim 1, wherein the diamond film is deposited by chemical vapor deposition.

4. A diamond compact as in claim 1, wherein the diamond film has a thickness of 200-2500 clam.

5. A diamond compact which comprises at least two interlocking segments of thermally stable, polycrystalline diamond coated completely with a CUD diamond film at a thickness in the range of 1000-2000 im which encapsulates said segments.

6. A diamond compact as in claim 1, wherein at least two of the interlocking segments comprise diamond particles of a different average grain size.

7. A diamond compact which comprises interlocking segments of thermally stable, polycrystalline diamond, wherein at least one segment comprises diamond particles of an average grain size within the range of 30-150 mesh, and at least one segment comprises diamond particles of an average particle diameter of less than 20 Sm.

8. A diamond compact as in claim 7, wherein the surface area at the interface between the interlocking segments is more than 150% of the cross sectional area at the interface.

9. A diamond compact as in claim 7, wherein the surface area at the interface between interlocking segments is at least two times that of the cross sectional area of the compact at the interface.

10. A drill bit which comprises a diamond compact of claim 1.

11. A method for preparing a diamond compact of at least two interlocking segments of thermally stable, polycrystalline diamond encapsulated with a diamond film which comprises: forming two or more individual clusters of nonthermally stable bonded diamond particles of a different average grain size with a metallic phase; cutting each of the clusters of non-thermally stable bonded diamond particles, to provide a geometrically shaped surface which complements a geometrically shaped surface of another cluster of non-thermally stable bonded diamond particles, wherein the geometrically shaped surfaces have a surface area of more than 150% of the cross sectional area at the interface; leaching the metallic phase from the cut clusters of non-thermally stable bonded diamond particles to provide thermally stable interlocking segments;; bonding the two or more thermally stable interlocking segments across the complementary surfaces to form a composite mass; and depositing a diamond film over at least 75% of the outer surfaces of salid composite mass at a thickness of from 200-2500 ,um.

12. A method as in claim 11, wherein at least one segment comprises diamond particles of an average grain size within the range of 30-150 mesh, and at least one segment comprises diamond particles of an average particle diameter of less than 20 Am.

13. A method as in claim 11, wherein the thermally stable interlocking segments are bonded by the application of a metal interlayer between the segments and sintering the interlayer.

14. A method as in claim 11, wherein each cluster of non-thermally bonded diamond particles is cut into the desired surface configuration with a traveling wire electron-discharge machine to form interlocking segments before the metal phase is leached from the cut segments to provide thermal stability.

15. A method as in claim 11, wherein the diamond film is deposited by chemical vapor deposition to a thickness of 1000-2000 im over the entire composite mass.

16. A method for preparing.a diamond compact of at least two interlocking segments of thermally stable, polycrystalline diamond encapsulated with a diamond film which comprises: forming two or more individual clusters of nonthermally stable bonded diamond particles of a different average grain size with a metallic phase; leaching the metallic phase from the individual clusters of non-thermally stable bonded diamond particles to provide clusters of thermally stable bonded diamond particles; cutting each of the clusters of thermally stable bonded diamond particles in a geometric shape which complements another cluster to provide thermally stable interlocking diamond segments, wherein the thermally stable interlocking semgents have a surface area of more than 150% of the cross sectional area at the interface; ; bonding the thermally stable interlocking diamond segments across the complementary surfaces to form a composite mass; and depositing a diamond film over at least 75% of the outer surfaces of said composite mass at a thickness of from 200-2500 pm.

17. A diamond compact according to claim 1 substantially is described herein.

18. A method for preparing a diamond ccxqpact according to Claim 11 or Claim 16 substantially as described herein.