# Patent

## Title
Compacts for producing polycrystalline diamond compacts, and related polycrystalline diamond compacts

## Abstract

A method of forming a PDC cutter having solvent metal catalyst located adjacent the diamond and/or in the diamond and a layer of reactive material on the layer of diamond, the layer of reactive material for promoting the flow of the solvent metal catalyst material from the layer of diamond under high pressure and high temperature. Compacts for producing polycrystalline diamond compacts, and related polycrystalline diamond compacts are also disclosed.

## Background
CROSS-REFERENCE TO RELATED APPLICATION APPLICATIONS
This application is a divisional of U.S. patent application Ser. No. 12/568,966, filed Sep. 29, 2009, now U.S. Pat. No. 8,277,722, issued Oct. 2, 2012, the disclosure of which is hereby incorporated herein by this reference in its entirety. This application is also related to U.S. patent application Ser. No. 12/916,201, filed Oct. 29, 2010, pending.


TECHNICAL FIELD
The present invention, in several embodiments, relates generally to polycrystalline diamond compact (PDC) cutters and methods of making PDC cutters for rotary drag bits for drilling subterranean formations.
BACKGROUND
Rotary drag bits have been used for subterranean drilling for many decades, and various sizes, shapes and patterns of natural and synthetic diamonds have been used on drag bit crowns as cutting elements. In many formations, a drag bit can provide an improved rate of penetration (ROP) of the drill bit during drilling over the ROP of a tri-cone drill bit.
Over the past few decades, rotary drag bit performance has been improved with the use of a polycrystalline diamond compact (PDC) cutting element or cutter, comprised of a planar diamond cutting element or table formed onto a tungsten carbide substrate under high temperature and high pressure conditions. The PDC cutters are formed into a myriad of shapes including, circular, semicircular or tombstone, which are the most commonly used configurations. Typically, the PDC diamond tables are formed so the edges of the table are coplanar with the supporting tungsten carbide substrate. Bits carrying PDC cutters, which for example, may be brazed into pockets in the bit face, pockets in blades extending from the face, or mounted to studs inserted into the bit body, have proven very effective in achieving a high rate of penetration (ROP) in drilling subterranean formations exhibiting low to medium compressive strengths. The PDC cutters have provided drill bit designers with a wide variety of improved cutter deployments and orientations, crown configurations, nozzle placements and other design alternatives previously not possible with the use of small natural diamond or synthetic diamond cutters. While the PDC cutting element improves drill bit efficiency in drilling many subterranean formations, the PDC cutting element is nonetheless prone to wear when exposed to certain drilling conditions, resulting in a shortened life of a rotary drag bit.
PDC cutters comprise combining synthetic diamond grains with a suitable solvent catalyst material to form a mixture. The mixture is subjected to processing conditions of extremely high pressure/high temperature (HPHT) where the solvent catalyst material promotes desired inter-crystalline diamond-to-diamond bonding between the grains, thereby forming a PDC structure. The resulting PDC structure has enhanced properties of wear resistance and hardness. PDC materials are useful in aggressive wear and cutting applications where high levels of wear resistance and hardness are desired. The cutting elements used in such earth-boring tools often include polycrystalline diamond compact (often referred to as “PDC”) cutting elements, which are cutting elements that include cutting faces of a polycrystalline diamond material. Polycrystalline diamond material is material that includes inter-bonded grains or crystals of diamond material. In other words, polycrystalline diamond material includes direct, inter-granular bonds between the grains or crystals of diamond material. The terms “grain” and “crystal” are used synonymously and interchangeably herein.
PDC cutters typically include a metallic substrate material that is joined to a layer or body of the PDC material during the same HPHT process that is used to form the PDC body. The metallic substrate facilitates attachment of the PDC cutter to a drill bit. Techniques are used to improve the wear resistance of the PDC cutter which is known to suffer thermal degradation at a temperature starting at about 400° C. and extending to 1200° C. Conventional PDC cutters are known to have poor thermal stability when exposed to operating temperatures above 700° C. Some of the techniques for improving wear resistance of a PDC cutter are directed to improving the thermal stability of the PDC cutter. One technique of improving thermal stability of a PDC cutter is to leach the uppermost layer of PDC cutter to remove substantially all solvent metal catalyst material from the PDC cutter surface while retaining as much metal catalyst material in the remaining portion of the PDC cutter.
While this technique improves the thermal stability of the treated uppermost layer of a PDC cutter, such a PDC cutter tends to suffer from spalling and de-lamination during use.
Therefore, it is desirable to provide a PDC cutter having improved wear resistance properties and thermal stability which reduces or minimizes spalling and de-lamination of the PDC cutter without leaching the uppermost layer of the PDC cutter to remove solvent metal catalyst material from the PDC cutter.
BRIEF SUMMARY
A PDC cutter having solvent metal catalyst material in the diamond and methods of manufacture thereof.
The advantages and features of the present invention will become apparent when viewed in light of the detailed description of the various embodiments of the invention when taken in conjunction with the attached drawings and appended claims.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a drawing of a PDC compact before pressing;
FIG. 1A is a drawing of various patterns for interfacial barrier designs for the control of catalyst migration to the diamond powder and sink;
FIG. 2 is a drawing of the PDC of FIG. 1 after pressing;
FIG. 3 is a drawing of another embodiment of the present invention of a PDC compact before pressing;
FIG. 4 is a drawing of another embodiment of the present invention of the PDC of FIG. 3 after pressing;
FIG. 5 is a drawing of another embodiment of the present invention of a PDC compact before pressing;
FIG. 6 is a drawing of another embodiment of the present invention of a PDC compact before pressing;
FIG. 7 is a drawing of another embodiment of the present invention of a PDC compact before pressing; and
FIG. 8 is a drawing of another embodiment of the present invention of a PDC compact before pressing.



DETAILED DESCRIPTION
Illustrated in FIG. 1 is a representation of a compact 10 to be pressed under high pressure and high temperature (HPHT) to form a polycrystalline diamond compact (PDC) for use as a cutter on a rotary drag bit. The compact 10 includes a substrate 14, layer of either powdered solvent catalyst 15 or a solid disc of catalyst 15, a first layer of diamond powder 12, a sacrificial layer or second layer 12′ of diamond powder, and a sink 16. The compact 10 includes two layers of diamond powder, a first layer of diamond powder 12 typically having a particle size in the range of about 5 microns to about 40 microns and a second, more coarse sacrificial layer 12′ of diamond powder having particle size in the range of about 100 microns to about 500 microns or multi-modal particle size distributions thereof for forming a diamond table for cutting. The layer of powdered solvent catalyst 15, such as cobalt, while illustrated as a separate layer of powdered cobalt, may be mixed within primarily the powdered diamond 12, if desired. The sacrificial layer 12′ of diamond powder acts as a catalyst for forming the diamond table and for attaching the polycrystalline diamond table to a substrate 14. The substrate 14 typically comprises a cermet material (i.e., a ceramic-metal composite material) such as, for example, cobalt-cemented tungsten carbide for forming a backup substrate, after pressing. The sink 16 acts as a getter that can react favorably with or adsorb any catalyst, or any suitable metal catalyst, in the diamond powder 12 and in the sacrificial layer 12′ of diamond powder to reduce the concentration of the catalyst, or other suitable metal catalyst, in the diamond powder 12, which may be swept into the diamond grains of diamond powder 12 from either the substrate 14, or the layer of powder solvent catalyst 15, or solid catalyst disc 15, during sintering. During sintering, each of substrate 14 and the layer of catalyst 15 serves as catalyst material for forming the inter-granular diamond-to-diamond bonds and, the resulting diamond table, from the diamond grains. In other methods, a layer of powdered catalyst material 15, or any suitable metal catalyst material 15, may additionally be mixed with the diamond grains prior to sintering in an HTHP process. Upon formation of a diamond table 12 using an HTHP process, catalyst material may remain after pressing and cooling to form a diamond microstructure for the diamond table 12 of the compact 10. The sacrificial layer 12′ may comprise coarse diamond, carbide, graphite, ceramic, metal, or any suitable mixtures thereof as well as any suitable materials that promote fracturing of the sacrificial layer 12′ and allow the migration of catalyst 15 therethrough. The sink 16 may be any suitable material such as fine diamond, graphite, metals, or metal alloys that will react at or, preferably, above the reactivity level of the diamond powder 12. By placing the sink 16 over the diamond powder 12 and sacrificial layer 12′, the sink 16 causes a solvent gradient to occur across the diamond powder 12 and sacrificial layer 12′ for the solvent catalyst 15 in the diamond powder 12 and sacrificial layer 12′ to migrate to the sink 16 during high pressure and high temperature formation of the compact 10. The sacrificial layer 12′ of diamond powder acts as a sacrificial layer to be removed after the High Pressure High Temperature (HPHT) portion of the process by any suitable means, such as direct separation of the sacrificial layer 12′ of diamond powder from diamond layer 12 or cutting or grinding, or lapping, etc. The sacrificial layer 12′ of diamond powder should not remain on the compact 10, although in some instances it may be retained. While coarse diamond powder for the sacrificial layer 12′ is preferred to be used, any diamond powder may be used and may include a minimally reacting material therein, if so desired. The sacrificial layer 12′ of coarse diamond powder may be in powder form, mixed with a suitable metal, layered, or in any combination thereof. The sacrificial layer 12′ of diamond powder should react minimally with the diamond powder layer 12 allowing the catalyst to pass freely through the sacrificial layer 12′ of diamond powder with minimal reactivity therewith and should be easily removable from the diamond powder layer 12. In certain instances, the sacrificial layer 12′ of diamond powder may not be used and only the solvent catalyst layer 15 used, if the solvent catalyst layer 15 may be easily separated from the powdered diamond layer 12 and the solvent catalyst layer 15 retains the activity thereof without the sacrificial layer 12′ of diamond powder after high temperature and high pressure formation of the compact 10.
As illustrated in FIG. 1A, if desired, the layer 15 may consist of a solid metal disc 15 or metal alloy disc 15 having reduced catalytic activity, such as a nickel disc 15. The disc 15 includes a plurality of apertures 18 therein to control the migration of catalyst contained within the substrate 14 into the diamond layer 12 and sacrificial layer 12′ to the sink 16. The thickness of the disc 15, or layer of powdered catalyst 15, may be any thickness in the range of approximately 1 micron to approximately 100 microns. The shape of the apertures 18 may be any desired shape, such as circular, square, rectangular, oval, ellipsoid, triangular, or any desired combinations thereof in any desired patterns thereof. The length and width of the apertures 18 may be any desired diameter thereof or length and width thereof convenient for the size of the compact 10. The apertures 18 may have any desired pattern, such as symmetrical, asymmetrical, any desired combinations thereof, etc.
Referring back to FIG. 1, the initial concentration of the solvent catalyst 15 below diamond powder 12 or in the diamond powder 12 is illustrated by the graphic representation of 15′ on the right side of FIG. 1, showing that the diamond powder 12 and sacrificial layer 12′ of diamond powder each have some concentration of solvent catalyst 15 therein while the highest concentration of solvent catalyst 15 is in the catalyst layer 15 at or near the interface of the layer of diamond powder 12. If desired, the wettability of the diamond powder 12 and sacrificial layer 12′ can be enhanced with a graphite coating or any other agent to allow the catalyst 15 to migrate more easily to the sink 16 from the diamond powder 12 and sacrificial layer 12′.
Illustrated in FIG. 2 is a representation of a compact 10 of FIG. 1, or with the solid disc 15 of FIG. 1A, after high pressure and high temperature pressing of the compact 10. As illustrated on the right side of the compact 10, during high pressure and high temperature pressing of the compact 10, the affinity of the sink material 16 has caused the solvent catalyst material 15 to migrate to the sink 16. As illustrated, the sink 16 has the highest concentration of the cobalt solvent catalyst 15, after high pressure and high temperature pressing of the compact 10. As illustrated, the polycrystalline diamond table 12 formed from the diamond powder 12 and sacrificial layer 12′ of diamond powder includes, at or near the WC substrate 14, a first level 12A of concentration of catalyst material having a level of concentration of catalyst of about two times or more of the level of concentration of catalyst in the WC substrate 14, a second level 12B of concentration of catalyst having a level 12B of concentration of about the same level of concentration of catalyst as in the WC substrate 14, and a third level 12C of concentration of catalyst having a level 12C of concentration of catalyst decreasing from about the same level of concentration 12B of catalyst as in the WC substrate 14 to a minimum level of concentration approaching almost no catalyst in the diamond table 12 at the upper end or upper surface thereof, although the amount or concentration of catalyst is as minimal as required for foimation of the diamond table 12 of the compact 10. The level of concentration of catalyst in the sacrificial layer 12′ of coarse diamond powder 12′ is significantly less than that of the level of concentration of the catalyst in the WC substrate 14 with the sink 16 having a level of concentration of catalyst peaking at a level of about three times or more of the level of concentration of the catalyst, in the WC substrate 14. The solvent catalyst layer 15 may be deleted, if desired, when sufficient catalyst material from the substrate 14 is available during HPHT of the compact 10. It will be appreciated that the volume or mass of the material comprising the sink 16 must be at least approximately equal to or larger than the volume or mass of catalyst material, such as from the catalyst layer 15 and any catalyst that may migrate from the substrate 14 that is to be to be removed from the diamond powder 12 and sacrificial layer 12′ of diamond powder. Otherwise, the volume or mass of the sink 16 will not be effective for the removal of the desired amount of catalyst material from the layer of catalyst powder 15, or from a solid disc 15, from the layer of diamond powder 12, and from sacrificial layer 12′ of diamond powder.
Illustrated in FIG. 3 is another representation of an alternative embodiment of the present invention where a compact 10 is to be pressed under high pressure and high temperature to form a PDC for use as a cutter on a rotary drag bit. The compact 10 includes a substrate 14, a powdered catalyst layer 15, a diamond powder layer 12, a sacrificial layer or second layer 12′ of coarse diamond powder, and a sink or reactive layer 16. As illustrated, the compact 10 includes at least two layers of diamond, one of diamond powder 12 (PDC FEED), typically having a particle size of about 5 microns to about 40 microns, and another of sacrificial layer 12′ of coarse diamond particles, typically having a particle size of about 100 microns to about 500 microns, for forming a diamond table for cutting. A layer of powdered solvent catalyst 15, such as cobalt powder, or a solid solvent catalyst disc 15, such as an iron and cobalt alloy disc, contacts the powdered diamond 12 for forming the diamond table from the diamond powder 12 and sacrificial layer 12′ of diamond powder and attaching the diamond table to a substrate 14, which is formed from tungsten carbide powder for forming a backup substrate for the diamond table after pressing. The sink 16 acts as a getter that can react favorably with the cobalt solvent catalyst 15 to reduce the concentration of the cobalt solvent catalyst 15 in the diamond powder 12 and sacrificial layer 12′, after pressing and cooling to form the diamond microstructure of a diamond table 12 of the compact 10. The sink 16 may be any suitable material, such as fine diamond, graphite, metals, or metal alloys that will react at or, preferably, above the reactivity level of the diamond powder 12. By placing the sink 16 over the tungsten carbide powder, the catalyst layer 15, the diamond powder layer 12, and sacrificial layer 12′, the sink 16 causes a solvent gradient to occur across the tungsten carbide powder 14 for the cobalt solvent catalyst therein and the catalyst in the catalyst layer 15 to migrate to the sink 16 during high pressure and high temperature formation of the compact 10. Because the coarse diamond powder of the sacrificial layer 12′ has a particle size in the range of about 100 microns to about 500 microns, the sacrificial layer 12′ will not strongly bond to the diamond layer 12 at the interface therebetween during high pressure and high temperature pressing. The overall permeability of the diamond layer 12 and the permeability of the sacrificial layer 12′ of coarse diamond powder is determined by the mean free path of open porosity, which is formed by the interstitial regions between individual grain boundaries between grains, and fractures that form under pressure and determines the effectiveness at which any solvent catalyst migrates therethrough during the high pressure and high temperature process of forming the compact 10, as the closed porosity of the diamond layer 12 and the closed porosity of the sacrificial layer 12′ of coarse porous diamond prevents any substantial migration of the catalyst 15 thereacross. When there is a greater amount of permeability in the diamond layer 12 and permeability in the sacrificial layer 12′ of coarse porous diamond particle layer, the solvent catalyst 15 will migrate through the diamond layer 12 and the sacrificial layer 12′ of coarse porous diamond. If a diamond powder 12 is used that has a mean free path of open porosity below the percolation threshold for the grain size distribution, the permeability of the diamond layer 12 may be such that the catalyst 15 cannot effectively migrate thereacross in any reasonable period of time for the compact 10 formation process.
Illustrated in FIG. 4 is another representation of an alternative embodiment of the present invention where a compact 10 is to be pressed under high pressure and high temperature to form a PDC for use as a cutter on a rotary drag bit. The compact 10 includes a substrate 14, a layer of powdered cobalt catalyst 15, a layer of diamond powder 12, another layer of coarse diamond powder 12′, and a sink 16 of fine graphite powder. The compact 10 includes at least two layers of diamond, one of diamond powder 12 having a particle size of about 5 microns to about 40 microns and another of sacrificial layer 12′ of coarse diamond particles having a particle size of about 100 microns to about 500 microns for forming a diamond table for cutting. A layer of powdered cobalt solvent catalyst 15 contacts the powdered diamond 12 for attaching a diamond table to a substrate 14 formed from tungsten carbide powder for forming a backup substrate for the diamond table formed from the diamond powder 12 and sacrificial layer 12′ of coarse diamond particles having the diamond table secured thereto after pressing. A fine graphite powder, such as a sink 16, acts as a getter that can react favorably with the cobalt solvent catalyst 15 to reduce the concentration of the cobalt solvent catalyst in the diamond powder 12, after pressing and cooling to form a diamond microstructure of a diamond table of the compact 10. The fine crystalline graphite powder 16 will react at or, preferably, above the reactivity level of the diamond powder 12 (PCD FEED). By placing the sink 16 opposite the tungsten carbide powder for forming the substrate 14, the cobalt catalyst layer 15, the diamond powder 12, and the sacrificial layer 12′ of coarse diamond powder, the sink 16 causes a solvent gradient to occur across the tungsten carbide powder 14, the cobalt powder catalyst layer 15, the diamond powder layer 12 and the sacrificial layer 12′ for any cobalt solvent catalyst to migrate to the sink 16 during high pressure and high temperature formation of the compact 10. If desired, a solid solvent catalyst disc 15 may be placed between the diamond layer 12 and the substrate 14, rather than a layer of powdered cobalt catalyst 15. If the sacrificial layer 12′ of coarse porous diamond powder has an average particle size in the range of about 100 microns to about 500 microns, the sacrificial layer 12′ of coarse porous diamond particle layer will not strongly bond to the diamond layer 12 at the interface therebetween. The overall permeability of the diamond layer 12 and the permeability of the sacrificial layer 12′ of coarse diamond powder determines the effectiveness at which any solvent catalyst migrates therethrough during the high pressure and high temperature process of forming the compact 10, as the closed porosity of the diamond layer 12 and the closed porosity of the sacrificial layer 12′ of coarse diamond powder prevents or limits any migration of the catalyst 15 thereacross. When there is greater permeability of the diamond layer 12 and the permeability of the sacrificial layer 12′ of coarse diamond powder, the solvent catalyst 15 will migrate with greater effectiveness through the diamond layer 12 and the sacrificial layer 12′ of coarse diamond powder. If a diamond powder 12 is used that has a mean free path of open porosity below the percolation threshold for the grain size distribution, the permeability of the diamond layer 12 may be such that the solvent catalyst 15 cannot effectively migrate thereacross in any reasonable period of time for the compact formation process.
Illustrated in FIG. 5 is another representation of an alternative embodiment of the present invention where a compact 10 is to be pressed under high pressure and high temperature to form a PDC for use as a cutter on a rotary drag bit. The compact 10 includes a substrate 14, a layer of diamond powder 12, a small or thin sacrificial layer of coarse diamond powder 12′, when compared to the thickness of the layer 12 of diamond powder, and a reactive sink layer 16. The compact 10 includes at least two layers of diamond, one of diamond powder 12, typically having a particle size of about 5 microns to about 40 microns, and another of sacrificial layer 12′ of coarse diamond powder, typically having a particle size of about 100 microns to about 500 microns that are used for forming a diamond table for cutting. A powdered solvent catalyst, such as cobalt powder, is mixed with the diamond powder 12. A sacrificial layer 12′ of coarse diamond powder is for forming the diamond table from the diamond powder 12 and sacrificial layer 12′ of coarse diamond powder and attaching the diamond table to a substrate 14 formed from tungsten carbide powder for forming a backup substrate for the diamond table after pressing. A sink 16 (a reactive layer) acts as a getter that can react favorably with any cobalt solvent catalyst to reduce the concentration of the cobalt solvent catalyst in the diamond powder 12 and sacrificial layer 12′ of diamond powder after pressing and cooling to form a diamond microstructure of a diamond table 12 of the compact 10. The sink 16 may be any suitable material such as fine diamond, graphite, metals, or metal alloys that will react at or, preferably, above the reactivity level of the diamond powder. By placing the sink 16 opposite the tungsten carbide powder of the substrate 14, diamond powder 12, the sacrificial layer 12′ of coarse diamond powder, the sink 16 causes a solvent gradient to occur across the diamond powder layer 12 (PCD FEED) having cobalt solvent catalyst therein for the cobalt solvent catalyst to migrate to the sink 16 during high pressure and high temperature formation of the compact 10. Because the sacrificial layer 12′ of coarse diamond powder has a particle size in the range of about 100 microns to about 500 microns, the sacrificial layer 12′ of coarse porous diamond particle layer 12′ will not strongly bond to the diamond layer 12 at the interface therebetween. The overall permeability of the diamond layer 12 and the permeability of the sacrificial layer 12′ of diamond powder determines the effectiveness at which the solvent catalyst migrates therethrough during the high pressure and high temperature process of forming the compact 10 as the closed porosity of the diamond layer 12 and the closed porosity of the sacrificial layer 12′ of coarse diamond powder prevents any substantial migration of the catalyst thereacross. When there is a large amount of peimeability in the diamond layer 12 and permeability in the sacrificial layer 12′ of coarse diamond powder, any solvent catalyst in the diamond powder 12 will migrate with a greater effectiveness through the diamond layer 12 and the sacrificial layer 12′ of coarse diamond powder. If a diamond powder 12 or a sacrificial layer 12′ of coarse diamond powder is used that has mean free path of open porosity below the percolation threshold for the grain size distribution, the permeability of the diamond layer 12 and the sacrificial layer 12′ may be such that the catalyst cannot effectively migrate thereacross in any reasonable period of time for the compact formation process.
Illustrated in FIG. 6 is another representation of an alternative embodiment of the present invention where a compact 10 is to be pressed under high pressure and high temperature to form a PDC for use as a cutter on a rotary drag bit. The compact includes a substrate 14, a catalyst layer 15, a layer of powdered diamond 12, a sacrificial layer 12′ of diamond powder extending around the top surface and circumference of the layer of powdered diamond 12, extending around the circumference of the catalyst layer 15, and extending around the circumference of the substrate 14, and a reactive layer forming a sink 16 extending over the top or upper surface and over or around the entire circumference of the sacrificial layer 12′ of diamond powder. The compact 10 includes at least two layers of diamond, one of diamond powder 12, typically having a particle size of about 5 microns to about 40 microns, and another of sacrificial layer 12′ of coarse diamond powder, typically having a particle size of about 100 microns to about 500 microns, for forming a diamond table for cutting, each layer 12 and 12′ extending around a portion of the tungsten carbide powder 14. A layer of powdered solvent catalyst 15, such as cobalt powder, or solid solvent catalyst disc 15, such as an iron and cobalt alloy disc, contacts the substrate 14 and contacts the powdered diamond 12 for forming the diamond table from the diamond powder 12 and sacrificial layer 12′ of diamond powder and attaching the diamond table to a substrate 14 formed from tungsten carbide powder for forming a backup substrate for the diamond table after pressing. A sink or reactive layer 16 extends around the diamond layers 12 and 12′ as well as the tungsten carbide powder 14 with the sink or reactive layer 16 acting as a getter that can react favorably with the solvent catalyst 15 to reduce the concentration of the solvent catalyst in the diamond powder 12 and sacrificial layer 12′ of coarse diamond powder after pressing and cooling to form diamond microstructure of a diamond table 12 of the compact 10. The sink may 16 be any suitable material such as fine diamond, graphite, metals, or metal alloys which will react at or, preferably, above the reactivity level of the diamond powder. By placing the sink 16 opposite and around the diamond powder 12 and sacrificial layer 12′ of diamond powder, the sink 16 causes a solvent gradient to occur across the tungsten carbide powder 14 the diamond powder 12, and the sacrificial layer 12′ for any solvent catalyst 15 to migrate to the sink or reactive layer 16 during high pressure and high temperature formation of the compact 10. Because the coarse diamond powder 12′ has a particle size in the range of about 500 microns to about 1000 microns, the sacrificial layer 12′ of coarse diamond powder will not strongly bond to the diamond layer 12 at any interface therebetween. The overall permeability of the diamond layer 12 and the permeability of the sacrificial layer 12′ of coarse diamond powder determines the effectiveness at which solvent catalyst 15 migrates therethrough during the high pressure and high temperature process of forming the compact 10 as the closed porosity of the diamond layer 12 and the closed porosity of the sacrificial layer 12′ of coarse diamond powder prevents any substantial migration of the solvent catalyst 15 thereacross. When there is a large amount of permeability in the diamond layer 12 and permeability in the sacrificial layer 12′ of coarse diamond powder, the solvent catalyst 15 will migrate with greater effectiveness through the diamond layer 12 and the sacrificial layer 12′ of coarse diamond powder. If a diamond powder 12 and/or sacrificial layer of coarse diamond powder 12′ is used that has a mean free path of open porosity below the percolation threshold for the grain size distribution, the permeability of the diamond layer 12 and/or the sacrificial layer 12′ of coarse diamond powder may be such that the catalyst 15 cannot effectively migrate thereacross in any reasonable period of time for the compact formation process.
Illustrated in FIG. 7 is another representation of an alternative embodiment of the present invention where a compact 10 is to be pressed under high pressure and high temperature to form a PDC for use as a cutter on a rotary drag bit. The compact 10 includes a substrate 14, a catalyst layer 15, a layer of diamond powder 12 (PCD FEED), and a reactive layer forming a sink 16. The compact 10 includes a layer of diamond powder 12, typically having a particle size of about 5 microns to about 40 microns, for forming a diamond table for cutting. A powdered solvent catalyst 15, such as cobalt powder, extends around the diamond powder 12 on all sides thereof including the circumference thereof and an upper portion of the tungsten carbide powder 14 for forming a backup substrate for 14 the diamond table after pressing. A sink or reactive layer 16 extending around the upper surface and circumference of the powdered solvent catalyst layer 15, and a portion of the tungsten carbide powder 14. The sink or reactive layer 16 acts as a getter that can react favorably with the solvent catalyst 15 to reduce the concentration of the solvent catalyst 15 in the diamond powder 12 after pressing and cooling to form diamond microstructure of a diamond table 12 of the compact 10. The sink may be any suitable material such as fine diamond, graphite, metals, or metal alloys which will react at or, preferably, above the reactivity level of the diamond powder. By placing the reactive sink layer 15 around the solvent catalyst 15 and the tungsten carbide powder 14, the sink causes a solvent gradient to occur across the tungsten carbide powder 14 for the any solvent catalyst 15 to migrate to the sink 16 during high pressure and high temperature formation of the compact 10. The overall permeability of the diamond layer 12 determines the effectiveness at which the solvent catalyst migrates therethrough during the high pressure and high temperature process of forming the compact 10 as the closed porosity of the diamond layer 12 prevents any substantial migration of the solvent catalyst 15 thereacross. When there is a large amount of permeability in the diamond layer 12, the solvent catalyst 15 will migrate with greater effectiveness through the diamond layer 12. If a diamond powder 12 is used that has a mean free path of open porosity below the percolation threshold for the grain size distribution, the permeability of the diamond layer 12 may be such that the solvent catalyst 15 cannot effectively migrate thereacross in any reasonable period of time for the compact formation process.
Illustrated in FIG. 8 is another representation of an alternative embodiment of the present invention where a compact 10 is to be pressed under high pressure and high temperature to form a PDC for use as a cutter on a rotary drag bit. The compact 10 includes a substrate 14, a layer of diamond powder 12, a layer of powdered catalyst 15 contacting the layer of diamond powder 12 on the top side and circumference thereof and an upper portion of the substrate 14, and a reactive layer forming a sink 16. The compact 10 includes a layer of diamond powder 12 (PCD FEED), typically having a particle size of about 5 microns to about 40 microns, for forming a diamond table for cutting, a powdered solvent catalyst 15, such as cobalt powder extending around the diamond layer 12 on the upper surface thereof and around the circumference and an upper portion of the tungsten carbide powder 14, any desired amount, for forming the diamond table from the diamond powder 12 and attaching the diamond table to a substrate 14 formed from tungsten carbide powder for forming a backup substrate for the diamond table after pressing. A sink or reactive layer 16 extending around the solvent catalyst layer 15, and a portion of the tungsten carbide powder 14, any desired amount, acting as a getter that can react favorably with the solvent catalyst 15 around the diamond powder layer 12 and any solvent catalyst in the substrate 14 to reduce the concentration of the solvent catalyst 15 in the diamond powder 12 after pressing and cooling to form diamond microstructure of a diamond table 12 of the compact 10. The sink 16 may be any suitable material such as fine diamond, graphite, metals, or metal alloys which will react at or, preferably, above the reactivity level of the diamond powder 12. By placing the sink 16 around the diamond powder 12 and the substrate 14, the sink 16 causes a solvent gradient to occur across the tungsten carbide powder of the substrate 14 for any solvent catalyst 15 to migrate to the sink 16 during high pressure and high temperature formation of the compact 10. The overall permeability of the diamond layer 12 determines the effectiveness at which the solvent catalyst 15 migrates through the diamond powder 12 during the high pressure and high temperature process of forming the compact 10 as the closed porosity of the diamond powder of the layer 12 prevents any substantial migration of the catalyst thereacross. When there is a large amount of permeability in the diamond powder layer 12, any solvent catalyst 15 will migrate with greater effectiveness through the diamond layer 12. If a diamond powder 12 is used that has a mean free path of open porosity below the percolation threshold for the grain size distribution, the permeability of the diamond powder layer 12 may be such that the catalyst cannot effectively migrate thereacross in any reasonable period of time for the compact formation process.
While particular embodiments of the invention have been shown and described, numerous variations and alternative embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited in terms of the appended claims.

## Claims

1. A polycrystalline diamond compact comprising:
a substrate comprising a metal catalyst; and
a diamond layer on the substrate and comprising:
a first region comprising a first concentration of the metal catalyst equal to about twice a concentration of the metal catalyst in the substrate;
a second region comprising a second concentration of the metal catalyst about the same as the concentration of metal catalyst in the substrate; and
a third region comprising a third concentration of the metal catalyst that decreases from a value about the same as the second concentration of the metal catalyst to about a zero value.

2. The polycrystalline diamond compact of claim 1, wherein the metal catalyst comprises cobalt.

3. The polycrystalline diamond compact of claim 1, further comprising another diamond layer on the diamond layer.

4. The polycrystalline diamond compact of claim 1, wherein the first region of the diamond layer is proximate the substrate, the third region of the diamond layer is distal from the substrate, and the second region is between the first region of the diamond layer and the third region of the diamond layer.

5. A compact for producing a polycrystalline diamond compact, comprising:
a substrate comprising a metal catalyst;
a layer of catalyst over the substrate;
a first layer of diamond powder over the layer of catalyst;
a second layer of diamond powder over the first layer of diamond powder; and
a sink over the second layer of diamond powder.

6. The compact of claim 5, wherein the layer of catalyst comprises cobalt powder.

7. The compact of claim 5, wherein the first layer of diamond powder comprises diamond powder having a particle size within a range of from approximately 5 microns to approximately 40 microns.

8. The compact of claim 5, wherein the second layer of diamond powder comprises diamond powder having a particle size within a range of from approximately 100 microns to approximately 500 microns.

9. The compact of claim 5, wherein the second layer of diamond powder comprises coarse diamond, carbide, graphite, ceramic, metal, or a mixture thereof.

10. The compact of claim 5, wherein the sink comprises fine diamond powder, graphite powder, metal powder, or metal alloy powder formulated to react at or above the reactivity level of the first layer of diamond powder.

11. The compact of claim 5, wherein the layer of catalyst comprises a solid disc of a metal or a metal alloy.

12. The compact of claim 11, wherein the solid disc defines a plurality of apertures.

13. The compact of claim 11, wherein the solid disc comprises iron and cobalt.

14. The compact of claim 11, wherein the solid disc comprises nickel.

15. A compact for producing a polycrystalline diamond compact, comprising:
a substrate comprising a metal catalyst;
a layer of powder catalyst over the substrate;
a layer of diamond powder over the layer of powder catalyst;
a layer of material over an upper surface and a circumference of the layer of diamond powder and over a circumference of the substrate; and
a sink over the layer of material.

16. The compact of claim 15, wherein the sink overlies at least a portion of the circumference of the substrate.

17. The compact of claim 15, wherein the layer of material comprises another layer of powder catalyst.

18. The compact of claim 15, wherein the layer of material comprises another layer of diamond powder.

19. The compact of claim 18, wherein the another layer of diamond powder comprises diamond particles of greater size than that of other diamond particles of the layer of diamond powder.

20. The compact of claim 15, wherein a mass of the sink is greater than or equal to an overall mass of catalyst material in the substrate, the layer of powder catalyst, the layer of diamond powder, and the layer of material.