Patent Document

TECHNICAL FIELD 
       [0001]    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 
       [0002]    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. 
         [0003]    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. 
         [0004]    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 application 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. 
         [0005]    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. 
         [0006]    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. 
         [0007]    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 
       [0008]    A PDC cutter having solvent metal catalyst material in the diamond and methods of manufacture thereof. 
         [0009]    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 
         [0010]      FIG. 1  is a drawing of a PDC compact before pressing; 
           [0011]      FIG. 1A  is a drawing of various patterns for interfacial barrier designs for the control of catalyst migration to the diamond powder and sink; 
           [0012]      FIG. 2  is a drawing of the PDC of  FIG. 1  after pressing; 
           [0013]      FIG. 3  is a drawing of another embodiment of the present invention of a PDC compact before pressing; 
           [0014]      FIG. 4  is a drawing of another embodiment of the present invention of the PDC of  FIG. 3  after pressing; 
           [0015]      FIG. 5  is a drawing of another embodiment of the present invention of a PDC compact before pressing; 
           [0016]      FIG. 6  is a drawing of another embodiment of the present invention of a PDC compact before pressing; 
           [0017]      FIG. 7  is a drawing of another embodiment of the present invention of a PDC compact before pressing; and 
           [0018]      FIG. 8  is a drawing of another embodiment of the present invention of a PDC compact before pressing. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    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  14  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 a HTHP process. Upon formation of a diamond table  12  using a HTHP process, catalyst material may remain after pressing and cooling to form 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 which will react at or, preferably, above the reactivity level of the diamond powder. 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 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 . 
         [0020]    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. 
         [0021]    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  15 ′ on the right side  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 ′. 
         [0022]    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  12 A 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  12 B of concentration of catalyst having a level  12 B of concentration of about the same level of concentration of catalyst as in the WC substrate  14 , and a third level  12 C of concentration of catalyst having a level  12 C of concentration of catalyst decreasing from about the same level of concentration  12 B 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 formation 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. 
         [0023]    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. A sink  16  which 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  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 which will react at or, preferably, above the reactivity level of the diamond powder. By placing the sink over the tungsten carbide powder, the catalyst layer  15 , the diamond powder layer  12 , and sacrificial layer  12 ′, the sink 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 formation process. 
         [0024]    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 formed from tungsten carbide powder  14  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 as a sink  16  which 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 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 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. 
         [0025]    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 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. 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 permeability 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. 
         [0026]    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. 
         [0027]    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  (PDC 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. 
         [0028]    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. 
         [0029]    While particular embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Accordingly, it is intended that the invention be limited in terms of the appended claims.

Technology Category: 8