Patent Publication Number: US-10773303-B2

Title: Spark plasma sintered polycrystalline diamond compact

Description:
RELATED APPLICATIONS 
     This application is a U.S. National Stage Application of International Application No. PCT/US2015/043802 filed Aug. 5, 2015, which designates the United States, and which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to polycrystalline diamond compact (PDC) including polycrystalline diamond bonded to a substrate by spark plasma sintering. 
     BACKGROUND 
     Polycrystalline diamond compacts (PDCs), particularly PDC cutters, are often used in earth-boring drill bits, such as fixed cutter drill bits. PDCs include diamond formed under high-pressure, high-temperature (HTHP) conditions in a press. In many cases, a PDC includes polycrystalline diamond formed and bonded to a substrate in as few as a single HTHP press cycle. A sintering aid, sometimes referred to in the art as a catalysing material or simply a “catalyst,” is often included in the press to facilitate the diamond-diamond bonds that participate both in forming the diamond and, optionally, in bonding the diamond to the substrate. 
     During use (e.g. while drilling), polycrystalline diamond cutters become very hot, and residual sintering aid in the diamond can cause problems such as premature failure or wear due to factors including a mismatch between the coefficients of thermal expansion (i.e. CTE mismatch) of diamond and the sintering aid. To avoid or minimize this issue, all or a substantial portion of the residual diamond sintering aid is often removed from the polycrystalline diamond prior to use, such as via a chemical leaching process, an electrochemical process, or other methods. Polycrystalline diamond from which at least some residual sintering aid has been removed is often referred to as leached regardless of the method by which the diamond sintering aid was removed. Polycrystalline diamond sufficiently leached to avoid graphitization at temperatures up to 1200° C. at atmospheric pressure is often referred to as thermally stable. PDCs containing leached or thermally stable polycrystalline diamond are often referred to as leached or thermally stable PDCs, reflective of the nature of the polycrystalline diamond they contain. 
     Although the polycrystalline diamond used in a PDC is typically formed on a substrate, the formation substrate may be subsequently removed, for example to facilitate leaching. Even if the PDC contains polycrystalline diamond on the original substrate, the bond between the polycrystalline diamond and the original substrate may have been weakened, for instance by leaching. Thus, attachment of polycrystalline diamond to a substrate or improving an existing attachment of polycrystalline diamond to a substrate is of interest. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete and thorough understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, which are not to scale, in which like reference numbers indicate like features, and wherein: 
         FIG. 1A  is a schematic drawing in cross-section of unleached polycrystalline diamond; 
         FIG. 1B  is a schematic drawing in cross-section of leached polycrystalline diamond adjacent, but not covalently bonded to, a substrate; 
         FIG. 1C  is schematic drawing in cross-section of leached polycrystalline diamond adjacent a substrate in the presence of a reactant gas prior to covalent bonding by spark plasma sintering; 
         FIG. 1D  is a schematic drawing in cross-section of a leached PDC cutter including polycrystalline diamond and a substrate covalently bonded by spark plasma sintering; 
         FIG. 2  is a schematic drawing in cross-section of a spark plasma sintering assembly; 
         FIG. 3  is a schematic drawing of a spark plasma sintering system containing the assembly of  FIG. 2 ; 
         FIG. 4  is a schematic drawing of a PDC cutter formed by spark plasma sintering; 
         FIG. 5  is a schematic drawing of a fixed cutter drill bit containing a PCD cutter formed by spark plasma sintering. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure relates to a s PDC element, such as a PDC cutter, containing leached polycrystalline diamond covalently bonded to a substrate by spark plasma sintering. The plasma used in spark plasma sintering contains carbide structure-forming elements that covalently bond to the polycrystalline diamond and to carbide particles in the substrate, forming covalent carbide bonds between them. 
     Polycrystalline diamond, particularly if leached, more particularly if sufficiently leached to be thermally stable, contains pores in which the carbide structures form. When the pores in the polycrystalline diamond are adjacent to the carbide grains in the substrate, carbide structures form within and covalently bond to the walls of the pores and also covalently bond to the carbide grains in the substrate. Within the polycrystalline diamond, diamond bonds may also form within the pores. 
       FIG. 1A  depicts unleached polycrystalline diamond. Diamond sintering aid  20 , in the form of a catalyst, is located between diamond grains  10 . After leaching, as illustrated in by fully leached polycrystalline diamond  30  of  FIG. 1B , pores  50  are present where diamond sintering aid  20  was previously located. Although  FIG. 1B  illustrates fully leached, thermally stable polycrystalline diamond, partially leached polycrystalline diamond or unleached polycrystalline diamond with pores may also be used with spark plasma sintering processes disclosed herein. The leached portion of the polycrystalline diamond may extend to any depth from the surface of the polycrystalline diamond or even include all of the polycrystalline diamond. Less than 2% or less than 1% of the volume of the leached portion of leached or thermally stable polycrystalline diamond is occupied by diamond sintering aid, as compared to between 4% and 8% of the volume in unleached polycrystalline diamond. 
     Pores  70  may be present in substrate  40  surrounding carbide grains  60 . Alternatively, substrate  40  may lack pores or may contain other material around carbide grains  60 . In either case, substrate  40  may be a cemented carbide containing a matrix in which carbide grains  60  and pores  70  are located. 
     During a spark plasma sintering process, pores  50  and  70  are filled with reactant gas  80 , as shown in  FIG. 1C . Although all pores  50  and  70  are illustrated as filled in  FIG. 1C , not all pores need necessarily be filled. At least a portion of the pores, at least 25% of the pores, at least 50% of the pores, at least 75% of the mores, or at least 99% of the pores in either polycrystalline diamond  30 , substrate  40 , or both may be filled with reactant gas. Alternatively, at least 95% of the pores, at least 90% of the pores, or at least 75% of the pores in polycrystalline diamond  30  within 500 μm of the interface between polycrystalline diamond  30  and substrate  40  may be filled with reactive gas. Pore filling is evidenced by formation of diamond bonds or carbide structures in the pores after spark plasma sintering. 
     Although substrate  40  may have pores throughout in some instances, in others it may also generally lack pores, in which case it may be modified or prepared to introduce pores  70  near its surface adjacent polycrystalline diamond  30 , for instance within 500 μm of the substrate surface adjacent polycrystalline diamond  30 . Preparation or modification may include dissolving a portion of the substrate, for instance using an acid. In the case of a cemented carbide substrate, acid typically dissolves the matrix before it dissolves carbide grains  60 , leaving pores where the matrix once was. Preparation or modification may also include mechanical abrasion, which may not selectively remove matrix from a cemented carbide. These modifications or preparations typically take place prior to placing substrate  40  adjacent to polycrystalline diamond  30 . 
     If substrate  40  generally lacks pores and is not modified or prepared to form pores on its surface adjacent the polycrystalline diamond, carbide structures  100  will covalently bond to available carbide grains  60 , typically those at the surface of substrate  40  adjacent polycrystalline diamond  30 . 
     Finally, in the spark plasma sintered PDC illustrated in  FIG. 1D , pores  50  are filled with diamond bonds  90  and/or carbide structures  100  that are formed from reactant gas  80 . In addition pores  70  in substrate  40  are filled with carbide structures  100  that are formed from reactant gas  80 . Carbide structures  100  at the interface between polycrystalline diamond  30  and substrate  40  may covalently bond to carbide grains  60  and diamond grains  10 . These structures spanning the interface may be particularly useful in covalently bonding polycrystalline diamond  30  to substrate  40 . 
     In  FIG. 1D , carbide structures  100  are illustrated as distinguishable from carbide grains  60 , but they may be so similar and/or may fill any pores so thoroughly that they are not distinguishable, particularly if carbide grains  60  and carbide structures  100  are formed from the same material. Similarly, although diamond bonds  90  are illustrated as distinguishable from diamond grains  10 , they may not be in some instances. 
     Furthermore, although each filled pore in  FIG. 1D  is illustrated as not entirely filled, it is possible for each filled pore to be substantially filled in one or both of the polycrystalline diamond  30  and substrate  40 . Furthermore, although  FIG. 1D  illustrates some pores as unfilled, the disclosure include embodiments in which diamond bonds and/or carbide structures fill at least 25% of the pores, at least 50% of the pores, at least 75% of the mores, or at least 99% of the pores in polycrystalline diamond  30  and/or substrate  40 . 
     A higher percentage of filled pores and more complete filling of filled pores  50  and  70  adjacent substrate  40  and polycrystalline diamond  30 , respectively, typically results in a stronger covalent bonding between the polycrystalline diamond and the substrate, making the bonded area less likely to fail during use of the PDC. It may also result in a more dense PDC or a PDC with higher impact strength. 
     Diamond grains  10  may be of any size suitable to form polycrystalline diamond  30 . They may vary in grain size throughout the polycrystalline diamond or in different regions of the polycrystalline diamond. For example, diamond grains  10  may be larger near the interface between polycrystalline diamond  30  and substrate  40  in order to provide more or larger pores  50 , and smaller near the working surface of polycrystalline diamond  30  to provide beneficial properties, such as higher abrasion resistance, than are achievable with larger diamond grains. 
     Carbide grains  60  may include any carbide, particularly tungsten carbide (WC) or another carbide also capable of forming a carbide structure as described below. Substrate  40  may include one or more matrix materials (not shown), such as binders and/or infiltrants, in addition to carbide grains  60 . These matrix materials surround carbide grains  60  to form a cemented carbide. The binder and/or infiltrant may, in particular, be a metallic composition, such as a metal or metal alloy. 
     Reactant gas  80  may include a carbide-forming metal in gas form alone or in combination with hydrogen gas (H 2 ) and/or a hydrocarbon gas. The carbide-forming metal may include zirconium (Zr), titanium (Ti), silicon (Si), vanadium (V), chromium (Cr), boron (B), tungsten (W), tantalum (Ta), manganese (Mn), nickel (Ni), molybdenum (Mo), halfnium (Hf), rehenium (Re) and any combinations thereof. The gas form may include a salt of the metal, such as a chloride, or another compound containing the metal rather than the unreacted element, as metal compounds often form a gas more readily than do unreacted elemental metals. The hydrocarbon gas may include methane, acetone, methanol, or any combinations thereof. 
     Carbide structures may include transitional phases of metal elements, such as zirconium carbide (ZrC), titanium carbide (TiC), silicon carbide (SiC), vanadium carbide (VC), chromium carbide (CrC), boron carbide (BC), tungsten carbide (WC), tantalum carbide (TaC), manganese carbide (MnC), nickel carbide (NiC), molybdenum carbide (MoC), halfnium carbide (HfC), rhenium carbide (ReC), and any combinations thereof. 
     Prior to spark plasma sintering, polycrystalline diamond  30  and substrate  40  are placed in a spark plasma sintering assembly  100 , such as the assembly of  FIG. 2 . The assembly includes a sealed sintering can  110  containing polycrystalline diamond  30  and substrate  40  with a reactant gas  80  adjacent to polycrystalline diamond  30 . Sealed sintering can  110  includes port  120  through which reactant gas  80  enters sealed sintering can  110  before it is sealed. Reactant gas  80  may be introduced into sealed sintering can  110  before it is placed in spark plasma sintering assembly  200  of  FIG. 3  by placing can  110  in a vacuum to remove internal air, then pumping reactant gas  80  into the vacuum chamber. The vacuum chamber may be different from chamber  210  of spark plasma sintering assembly  200 , or it may be chamber  210 . Port  120  may be sealed with any material able to withstand the spark plasma sintering process, such as a braze alloy. 
     Sealed sintering can  110  is typically formed from a metal or metal alloy or another electrically conductive material. However, it is also possible to form sealed sintering can from a non-conductive material and then place it within a conductive sleeve, such as a graphite sleeve. A conductive sleeve or non-conductive sleeve may also be used with a conductive sintering can  110  to provide mechanical reinforcement. Such sleeves or other components attached to or fitted around all or part of sintering can  110  may be considered to be part of the sintering can. 
     During spark plasma sintering (also sometimes referred to as field assisted sintering technique or pulsed electric current sintering) a sintering assembly, such as assembly  100  of  FIG. 2 , is placed in a spark plasma sintering system, such as system  200  of  FIG. 3 . Spark plasma sintering system  200  includes vacuum chamber  210  that contains assembly  100  as well as conductive plates  220  and at least a portion of presses  230 . 
     Presses  230  apply pressure to sintering can  100 . The pressure may be up to 100 MPa, up to 80 MPa, or up to 50 MPa. Prior to or after pressure is applied, vacuum chamber  210  may be evacuated or filled with an inert gas. If sintering can  100  is filled with reactant gas  80  and sealed in vacuum chamber  210 , then before substantial pressure is applied, chamber  210  is evacuated and filled with reactant gas, then port  120  is sealed. Pressure may be applied before or after chamber  210  is evacuated again and/or filled with inert gas. 
     After vacuum chamber  210  is prepared, a voltage and amperage is applied between electrically conductive plates  220  sufficient to heat reactant gas  80  to a temperature at which reactant gas  80  within pores  50  and  70  forms a plasma. For example, the temperature of the reactant gas may be 1500° C. or below, 1200° C. or below, 700° C. or below, between 300° C. and 1500° C., between 300° C. and 1200° C., or between 300° C. and 700° C. The temperature may be below 1200° C. or below 700° C. to avoid graphitization of diamond in polycrystalline diamond  30 . 
     The voltage and amperage are supplied by a continuous or pulsed direct current (DC). The current passes through electrically conductive components of assembly  100 , such as sealed sintering can  110  and, if electrically conductive, polycrystalline diamond  30  and/or substrate  40 . The current density may be at least 0.5×10 2  A/cm 2 , or at least 10 2  A/cm 2 . The amperage may be at least 600 A, as high as 6000 A, or between 600 A and 6000 A. If the current is pulsed, each pulse may last between 1 millisecond and 300 milliseconds. 
     The passing current heats the electrically conductive components, causing reactant gas  80  to reach a temperature, as described above, at which it forms a plasma. The plasma formed from reactant gas  80  contains reactive species, such as atomic hydrogen, protons, methyl, carbon dimmers, and metal ions, such as titanium ions (Ti 4+ ), vanadium ions (V 4+ ), and any combinations thereof. The reactive species derived from hydrogen gas or hydrocarbon gas form diamond bonds  90 . The metal reactive species form carbide structures  100 , at least a portion of which covalently bond to both diamond grains  10  and carbide grains  60 . 
     Because spark plasma sintering heats assembly  100  internally as the direct current passes, it is quicker than external heating methods for forming a plasma. Assembly  100  may also be pre-heated or jointly heated by an external source, however. The voltage and amperage may only need to be applied for 20 minutes or less, or even for 10 minutes or less, or 5 minutes or less to form a spark plasma sintered PDC. The rate of temperature increase of assembly  100  or a component thereof while the voltage and amperage are applied may be at least 300° C./minute, allowing short sintering times. These short sintering times avoid or reduce thermal degradation of the polycrystalline diamond. 
     The resulting PDC containing covalently bonded polycrystalline diamond  30  and substrate  40  may in the form of a cutter  300  as shown in  FIG. 4 . Although the interface between polycrystalline diamond  30  and substrate  40  is shown as planar in  FIG. 4 , the interface may have any shape and may even be highly irregular. In addition, although PDC cutter  300  is shown as a flat-topped cylinder in  FIG. 4 , it may also have any shape, such as a cone or wedge. Polycrystalline diamond  30  and/or substrate  40  may conform to external shape features. Furthermore, although polycrystalline diamond  30  and substrate  40  are illustrated as generally uniform in composition, they may have compositions that vary based on location. For instance, polycrystalline diamond  30  may have regions with different levels of leaching or different diamond grains (as described above), including different grain sizes in different layers. Substrate  40  may include reinforcing components, and may have different carbide grain sizes. 
     If polycrystalline diamond  30  in PDC cutter  300  is thermally stable prior to its attachment to substrate  40 , it may remain thermally stable after attachment, or experience a much lesser decrease in thermal stability than is typically experienced if an elemental metal or metal alloy is reintroduced during attachment because the carbide structures do not negatively affect thermal stability to the degree elemental metals or metal alloys do. 
     Furthermore, if there is reason to further leach polycrystalline diamond  30  after its attachment to substrate  40 , such additional leaching may be performed. Although care may be taken to avoid dissolving or damaging the carbide structures that covalently bond polycrystalline diamond  30  to substrate  40 , these structures may be more resistant to dissolution or damage than elemental metal or metal alloy structures. 
     A PDC cutter such as cutter  300  may be incorporated into an earth-boring drill bit, such as fixed cutter drill bit  400  of  FIG. 5 . Fixed cutter drill bit  400  contains a plurality of cutters coupled to drill bit body  420 . At least one of the cutters is a spark plasma sintered PDC cutter  300  as described herein. As illustrated in  FIG. 5 , a plurality of the cutters are cutters  300  as described herein. Fixed cutter drill bit  400  includes bit body  420  with a plurality of blades  410  extending therefrom. Bit body  420  may be formed from steel, a steel alloy, a matrix material, or other suitable bit body material desired strength, toughness and machinability. Bit body  420  may also be formed to have desired wear and erosion properties. PDC cutters  300  may be mounted on blades  410  or otherwise on bit  400  and may be located in gage region  430 , or in a non-gage region, or both. 
     Drilling action associated with drill bit  400  may occur as bit body  420  is rotated relative to the bottom of a wellbore. At least some PDC cutters  300  disposed on associated blades  410  contact adjacent portions of a downhole formation during drilling. These cutters  300  are oriented such that the polycrystalline diamond contacts the formation. 
     Spark plasma sintered PDC other than that in PCD cutters may be attached to other sites of drill bit  400  or other earth-boring drill bits. Suitable attachment sites include high-wear areas, such as areas near nozzles, in junk slots, or in dampening or depth of cut control regions. 
     The present disclosure provides an embodiment A relating to a method of covalently bonding polycrystalline diamond and a substrate via a cemented carbide, by placing polycrystalline diamond having pores adjacent a cemented carbide substrate with a reactant gas including a carbide-forming metal in gas form adjacent one another with a reactant gas comprising a hydrocarbon gas form in an assembly, and applying a voltage between the conductive plates sufficient to heat the reactant gas to a temperature of 1500° C. or less at which the reactant gas forms a plasma, which plasma forms carbide structures in at least a portion of the PCD pores, wherein the carbide structures are covalently bonded to the cemented carbide substrate. 
     The present disclosure further provides an embodiment B relating to a PDC element including polycrystalline diamond having pores adjacent a cemented carbide substrate and carbide structures in at least a portion of the pores and covalently bonded to the cemented carbide substrate. 
     The disclosure further relates to an embodiment C relating to any PDC element formed using the method of embodiment A. 
     The present disclosure further provides and embodiment D relating to a fixed cutter drill but including a PDC element of embodiments B or C. 
     In addition, embodiments A, B, C and D may be used in conjunction with the following additional elements, which may also be combined with one another unless clearly mutually exclusive, and which method elements may be used to obtain devices and which device elements may result from methods: i) the polycrystalline diamond may include a leached portion in which less than 2% of the volume is occupied by a diamond sintering aid; ii) the carbide-forming metal in gas form may include a metal salt; iii) the plasma may include metal ions; iv) the reactant gas may further include a hydrocarbon gas; v) the plasma may include atomic hydrogen, a proton, or a combination thereof; vi) the reactant gas may further include a hydrocarbon gas; vii) the hydrocarbon gas may include methane, acetone, methanol, or any combinations thereof; viii) the plasma may include methyl, carbon dimmers, or a combination thereof; ix) the temperature may be 1200° C. or less; x) the temperature may be 700° C. or less; xi) the voltage and amperage may be supplied by a continuous direct current or a pulsed direct current; xii) the voltage and amperage may be applied for 20 minutes or less; xiii) the sintering can, polycrystalline diamond, substrate, reactant gas, or any combination thereof may have a rate of temperature increase while the voltage and amperage are applied of least 300° C./minute; xiv) diamond bonds, carbide structures, or both may be formed in at least 25% of the pores of the polycrystalline diamond xv) the PDC element may include diamond bonds, carbide structures, or both in at least 25% of its pores; xvi) the PDC element may be a cutter; xvii) the PDC element may be an erosion resistant element. 
     Although the present disclosure and its advantages have been described in detail, it should be understood that various changes, substitutions and alternations can be made herein without departing from the spirit and scope of the disclosure as defined by the following claims.