Abstract:
A cutting element for an earth-boring drill bit may include a thermally stable cutting table comprising a polycrystalline diamond material. The polycrystalline diamond material may consist essentially of a matrix of diamond particles bonded to one another and a silicon, silicon carbide, or silicon and silicon carbide material located within interstitial spaces among interbonded diamond particles of the matrix of diamond particles. The cutting table may be at least substantially free of Group VIII metal or alloy catalyst material. The cutting element may further include a substrate and an adhesion material between and bonded to the cutting table and the substrate. The adhesion material may include diamond particles bonded to one another and to the cutting table and the substrate after formation of the preformed cutting table.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/751,520, filed Mar. 31, 2010, now U.S. Pat. No. 8,573,333,issued on Nov. 5, 2013, which is a utility conversion of U.S. Provisional Patent Application Ser. No. 61/165,382, filed Mar. 31, 2009, for “Methods For Bonding Preformed Cutting Tables to Cutting Element Substrates and Cutting Elements Formed by Such Processes,” the disclosure of each of which is incorporated in this application in its entirety by this reference. 
    
    
     FIELD 
     The present disclosure relates generally to cutting elements, or cutters, for use with earth-boring drill bits and, more specifically, to cutting elements that include thermally stable, preformed superabrasive cutting tables adhered to substrates with diamond. The present disclosure also relates to methods for manufacturing such cutting elements, as well as to earth-boring drill bits that include such cutting elements. 
     BACKGROUND 
     Conventional polycrystalline diamond compact (PDC) cutting elements include a cutting table and a substrate. The substrate conventionally comprises a metal material, such as tungsten carbide, to enable robust coupling of the PDC cutting elements to a bit body. The cutting table typically includes randomly oriented, mutually bonded diamond (or, sometimes, cubic boron nitride (CBN)) particles that have also been adhered to the substrate on which the cutting table is formed, under extremely high-temperature, high-pressure (HTHP) conditions. Cobalt binders, also known as catalysts, have been widely used to initiate bonding of superabrasive particles to one another and to the substrates. Although the use of cobalt in PDC cutting elements has been widespread, PDC cutting elements having cutting tables that include cobalt binders are not thermally stable at the typically high operating temperatures to which the cutting elements are subjected due to the greater coefficient of thermal expansion of the cobalt relative to the superabrasive particles and, further, because the presence of cobalt tends to initiate back-graphitization of the diamond in the cutting table when a temperature above about 750° C. is reached. As a result, the presence of the cobalt results in premature wearing of and damage to the cutting table. 
     A number of different approaches have been taken to enhance the thermal stability of polycrystalline diamond and CBN cutting tables. One type of thermally stable cutting table that has been developed includes polycrystalline diamond sintered with a carbonate binder, such as a Mg, Ca, Sr, or Ba carbonate binder. The use of a carbonate binder increases the pressure and/or temperature required to actually bind diamond particles to one another, however. Consequently, the diameters of PDC cutting elements that include carbonate binders lack an integral carbide support or substrate and are typically much smaller than the diameters of PDC cutting elements that are manufactured with cobalt. 
     Another type of thermally stable cutting table is a PDC from which the cobalt binder has been removed, such as by acid leaching or electrolytic removal. Such cutting elements have a tendency to be somewhat fragile, however, due to their lack of an integral carbide support or substrate and, in part, due to the removal of substantially all of the cobalt binder, which may result in a cutting table with a relatively low diamond density. Consequently, the practical size of a cutting table from which the cobalt may be effectively removed is limited. 
     Yet another type of thermally stable cutting table is similar to that described in the preceding paragraph, but the pores resulting from removal of the cobalt have been filled with silicon and/or silicon carbide. Examples of this type of cutting element are described in U.S. Pat. Nos. 4,151,686 and 4,793,828. Such cutting tables are more robust than those from which the cobalt has merely leached, but the silicon precludes easy attachment of the cutting table to a supporting substrate. 
     SUMMARY 
     The present disclosure includes embodiments of methods for adhering thermally stable diamond cutting tables to cutting element substrates. As used herein, the phrase “thermally stable” includes polycrystalline diamond cutting tables in which abrasive particles (e.g., diamond crystals, etc.) are secured to each other with carbonate binders, as well as cutting tables that consist essentially of diamond, such as cutting tables from which the cobalt has been removed, with or without a silicon or silicon carbide backfill, or that are formed by chemical vapor deposition (CVD) processes. 
     Some embodiments of such methods include preparation of the surface of a substrate to which a cutting table is to be bound before the cutting table is secured to that surface. In specific embodiments, preparation of the surface of the substrate may include removal of one or more contaminants or materials from the surface that may weaken or otherwise interfere with optimal bonding of the cutting table to the surface. In other specific embodiments, a substrate surface may be prepared to receive a cutting table by increasing a porosity or an area of the surface. 
     In such methods, preformed cutting tables, which are also referred to herein as “wafers,” are secured, under HTHP conditions, to substrates (e.g., tungsten carbide, etc.) with an intermediate layer of diamond grit. In some embodiments, a powder, particles, or a thin element (e.g., foil, etc.) comprising cobalt or another suitable binder may be used with the diamond grit. In other embodiments, cobalt or another suitable binder material that is present (e.g., as part of a binder, etc.) in the substrate may be caused to sweep into the cutting table as heat and pressure are applied to the cutting table. In further embodiments, a preformed diamond wafer formed by a CVD process may be disposed on a surface of a conventional PDC cutting table previously formed on a substrate. The CVD wafer may then be bonded to the PDC cutting table under HTHP conditions. 
     The present disclosure also includes various embodiments of cutting elements. One embodiment of a cutting element according to the present disclosure includes a substrate, a thermally stable cutting table and an adhesion layer therebetween. The adhesion layer includes diamond particles bonded to the diamonds of the thermally stable cutting table and to the substrate. In addition to diamond, the adhesion layer may include cobalt. The substrate may comprise a cemented carbide, such as tungsten carbide with a suitable binder, such as cobalt. In another embodiment, a preformed cutting table comprising CVD diamond and bonded to a PDC layer comprising cobalt under HTHP conditions is carried by a cemented carbide substrate. 
     Other features and aspects, as well as advantages, of embodiments of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the ensuing description, the accompanying drawings, and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIGS. 1 and 1A  illustrate an embodiment of a process for manufacturing PDC cutting elements from preformed cutting tables, with a specific embodiment of preformed cutting table being shown; 
         FIG. 1B  depicts another specific embodiment of a preformed cutting table that may be used to manufacture a PDC cutting element in accordance with various embodiments of teachings of the present disclosure; 
         FIG. 2  is a carbon phase diagram; 
         FIG. 3  depicts a PDC cutting element that includes a substrate, a preformed cutting table, and a diamond adhesion layer between the substrate and the preformed cutting table; 
         FIGS. 4 and 4A  depict another embodiment of a process for manufacturing cutting elements that include preformed wafers that consist of diamond; 
         FIG. 5  illustrates an embodiment of a cutting element that includes a substrate, a PDC cutting table, and a wafer that consists of diamond atop the PDC cutting table; and 
         FIG. 6  shows an embodiment of an earth-boring rotary drill bit including at least one PDC cutting element that incorporates teachings of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIG. 1 , an embodiment of a process for securing a preformed cutting table  20  to a substrate  30  is illustrated. In that process, at least one “cutter set,” which includes a substrate  30  and its corresponding preformed cutting table  20 , is assembled. 
     In the method of  FIGS. 1 and 1A , at least one substrate  30  is introduced into a canister assembly, or synthesis cell assembly  50 , formed from a refractory metal or other material that will withstand and substantially maintain its integrity (e.g., shape and dimensions) when subjected to HTHP processing. Each substrate  30  may comprise a cemented carbide (e.g., tungsten carbide) substrate for a PDC cutting element, or any other material that is known to be useful as a substrate for PDC cutting elements. In some embodiments, substrate  30  may include a binder material, such as cobalt. 
     Particles  40  of diamond grit are placed on substrate  30 . More specifically, particles  40  are placed on a surface  32  to which a preformed cutting table  20  is to be secured. Particles  40  may be placed on surface  32  alone or with a fine powder or particles  42  of a suitable, known binder material, such as cobalt, another Group VIII metal, such as nickel or iron, or alloys including these materials (e.g., Ni/Co, Co/Mn, Co/Ti, Co/Ni/V, Co/Ni, Fe/Co, Fe/Mn, Fe/Ni, Fe (Ni.Cr), Fe/Si 2 , Ni/Mn, Ni/Cr, etc.). 
     Surface  32  may be processed to enhance subsequent adhesion of a preformed cutting table  20  thereto. Such processing of surface  32  may, in some embodiments, include removal of one or more contaminants or materials that may weaken or otherwise interfere with optimal bonding of cutting table  20  to surface  32 . In specific embodiments, metal carbonate binder, silicon, and/or silicon carbide may be removed from surface  32  of substrate  30 , as these materials may inhibit diamond-to-diamond intergrowth, which is desirable for adhering preformed cutting table  20  to surface  32  of substrate  30 . The removal of such materials may be effected substantially at surface  32 . In such embodiments, one or more materials may be removed to a depth, from surface  32  into substrate  30 , that is about the same as a dimension of a diamond particle of preformed cutting table  20 , or to a depth of about one micron to about ten microns. In other embodiments, the removal of undesirable materials may extend beyond surface  32 , and into substrate  30 . Such preparation, in even more specific embodiments, may include leaching of one or more materials from the surface of the substrate. 
     In other embodiments, an area of surface  32  of substrate  30  may be increased. Chemical, electrical, and/or mechanical processes may, in some embodiments, be used to increase the area of surface  32  by removing material from surface  32 . Specific embodiments of techniques for increasing the area of surface  32  include, but are not limited to, laser ablation of surface  32 , blasting surface  32  with abrasive material, and exposing surface  32  to chemically etchants. 
     The removal of such materials may, in some embodiments, enable cobalt or another binder to penetrate into substrate  30  to facilitate the bonding of preformed cutting table  20  to surface  32 . 
     A base surface  22  of preformed cutting table  20  is placed over particles  40  on surface  32  of substrate  30 . Base surface  22  of preformed cutting table  20  is of a complementary topography to the topography of surface  32  of substrate  30 . Preformed cutting table  20  may be substantially free of metallic binder. 
     Without limiting the scope of the present disclosure, preformed cutting table  20 , in one embodiment, may comprise a PDC with abrasive particles that are bound together with a carbonate (e.g., calcium carbonate, a metallic carbonate (e.g., magnesium carbonate (MgCO 3 ), barium carbonate (BaCO 3 ), strontium carbonate (SrCO 3 ), etc.) binder, etc.). Despite the extremely high pressure and extremely high temperature that are required to fabricate PDCs that include calcium carbonate binders, as this type of PDC is fabricated without a substrate (i.e., is free-standing), it may be formed with standard cutting table dimensions (e.g., diameter and thickness) in a suitable HPHT apparatus, as known in the art. 
     In another embodiment, depicted by  FIG. 1B , a preformed cutting table  20 ′ may comprise a PDC having a face portion  27 ′ and a base portion  23 ′. Face portion  27 ′ of preformed cutting table  20 ′ is adjacent to and includes a cutting surface  26 ′, which may be filled with silicon and/or silicon carbide. Base portion  23 ′ of preformed cutting table  20 ′ is adjacent to and includes a base surface  22 ′, which consists essentially of diamond. Such an embodiment of preformed cutting element may be manufactured by removing (e.g., by leaching, electrolytic processes, etc.) cobalt or other binder material (e.g., another Group VIII metal, such as nickel or iron, or alloys including these materials, such as Ni/Co, Co/Mn, Co/Ti, Co/Ni/V, Co/Ni, Fe/Co, Fe/Mn, Fe/Ni, Fe (Ni.Cr), Fe/Si 2 , Ni/Mn, and Ni/Cr) from face portion  27 ′ without leaching binder material from base portion  23 ′. This may be accomplished, for example, by preventing exposure of base portion  23 ′ to leaching conditions and limiting the duration of the leaching conditions. Silicon or silicon carbide is then introduced into the pores that result from the leaching process, such as by the processes described in U.S. Pat. Nos. 4,151,686 and 4,793,828, the entire disclosures of both of which are hereby incorporated herein by this reference. Thereafter, binder material may be leached from base portion  23 ′, leaving pores therein or the binder material may remain. The porous base surface  22 ′ is placed adjacent the surface  32  of substrate  30  ( FIGS. 1 and 1A ). 
     With returned reference to  FIGS. 1 and 1A , if desired, one or more other cutter sets  12  including a preformed cutting table  20 , a quantity of diamond grit particles  40  (and, optionally, binder material powder or particles  42 ), and a substrate  30  may then be introduced into synthesis cell assembly  50  so that a plurality of cutting elements may be manufactured with a single HTHP process. In embodiments where multiple cutter sets  12  are introduced into a single synthesis cell assembly  50 , the order of components of each cutter set  12  may be reversed from the order of components of each adjacent cutter set  12 . The cutter sets  12  that are located at ends  52  and  54  of a synthesis cell assembly  50  may be arranged with substrates  30  at ends  52  and  54 , or as the outermost elements, to minimize impact upon and the potential for damage to the expensive preformed cutting tables  20 . 
     Once each cutter set  12  has been assembled within synthesis cell assembly  50 , the contents of synthesis cell assembly  50  may be subjected to known HTHP processes. The temperature and pressure of such processes are sufficient to cause particles  40  (and, optionally, any binder material powder or particles  42 ) to bind each preformed cutting table  20  within synthesis cell assembly  50  to its corresponding substrate  30 . In some embodiments, the combination of temperature and pressure that are employed in the HTHP process are within the so-called “diamond stable” phase of carbon. A carbon phase diagram, which illustrates the various phases of carbon, including the diamond stable phase D, and the temperatures and pressures at which such phases occur, is provided as  FIG. 2 . 
     An embodiment of a PDC cutting element  10  resulting from such processing is shown in  FIG. 3 . PDC cutting element  10  includes substrate  30 , a binder layer  45 , and preformed cutting table  20 . Binder layer  45  secures preformed cutting table  20  to substrate  30 , and may be bonded to preformed cutting table  20  and integrated into the material of substrate  30  at surface  32  (see  FIGS. 1 and 1A ). In some embodiments, binder layer  45  consists of diamond (e.g., polycrystalline diamond (PCD)). In other embodiments, binder layer  45  consists essentially of diamond. Other embodiments of binder layer  45  include diamond and lesser amounts of a suitable binder material. 
     In another embodiment of a method encompassed by the present disclosure, which is shown in  FIGS. 4 and 4A , at least one cutting element  110  that includes a substrate  30  with a PDC table  120  already secured thereto is introduced into a synthesis cell assembly  50 . 
     A base surface  142  of preformed wafer  140 , which may consist essentially of or consist entirely of diamond that has been deposited by known chemical vapor deposition (CVD) processes, is placed over a surface  122  of PDC table  120 . Base surface  142  of preformed wafer  140  is of a complementary topography to the topography of surface  122  of PDC table  120 . 
     As described in reference to the embodiment shown in  FIGS. 1 and 1A , one or more other cutter sets  112  including a preformed wafer  140  and a cutting element  110  may be introduced into synthesis cell assembly  50  so that a plurality of cutting elements  110  may be manufactured with a single HTHP process. Once each cutter set  112  has been assembled within synthesis cell assembly  50 , the contents of synthesis cell assembly  50  may be subjected to known HTHP processes, as described in reference to  FIGS. 1 and 1A . 
     An embodiment of a cutting element  10 ′ resulting from such processing is shown in  FIG. 5 . Cutting element  10 ′ includes substrate  30 , a PDC table  120 , and a performed wafer  140  that consists essentially of, or consists of, diamond. Base surface  142  of preformed wafer  140  may be secured to surface  122  of PDC table  120  by diamond-to-diamond bonding that occurs during the HTHP process, in which diamond from preformed wafer  140  is bonded with diamond-to-diamond bonding, to diamond crystals of PDC table  120 . Although the resulting structure may include cobalt or another binder material that may, if it were present on the face of preformed wafer  140 , compromise thermal stability, its presence beneath preformed wafer  140  during use of cutting element  10 ′ is at a location which is not subjected to temperatures that are known to be problematic for cutting tables that include cobalt binders. 
     Turning now to  FIG. 6 , an embodiment of a rotary type, earth-boring drill bit  60  of the present disclosure is shown. Among other features that are known in the art, bit  60  includes at least one cutter pocket  62 . A cutting element  10 ,  10 ′ according to an embodiment of the present disclosure is received within cutter pocket  62 , with substrate  30  (see  FIG. 1 ) bonded or otherwise secured to the material of bit  60 . As used herein, the term “earth-boring drill bit” includes without limitation conventional rotary fixed cutter, or “drag” bits, fixed cutter core bits, eccentric bits, bicenter bits, reamer wings, underreamers, roller cone bits, and hybrid bits including both fixed and movable cutting structures, as well as other earth-boring tools configured with cutting structures according to embodiments of the disclosure. 
     Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present disclosure, but merely as providing illustrations of some embodiments. Similarly, other embodiments of the disclosure may be devised which do not exceed the scope of the present disclosure. Features from different embodiments may be employed in combination. The scope of specifically claimed embodiments encompassed by this disclosure is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the embodiments disclosed herein which fall within the meaning and scope of the claims are to be embraced thereby.