Patent Publication Number: US-9849561-B2

Title: Cutting elements including polycrystalline diamond compacts for earth-boring tools

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 13/094,075, filed Apr. 26, 2011, now U.S. Pat. No. 8,839,889, issued Sep. 23, 2014, which application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/328,766, filed Apr. 28, 2010 and entitled “Polycrystalline Diamond Compacts, Cutting Elements and Earth-Boring Tools Including Such Compacts, and Methods of Forming Such Compacts,” the disclosure of each of which is hereby incorporated herein in its entirety by this reference. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present disclosure relate generally to polycrystalline diamond compacts, to cutting elements and earth-boring tools employing such compacts, and to methods of forming such compacts, cutting elements, and earth-boring tools. 
     BACKGROUND 
     Earth-boring tools for forming wellbores in subterranean earth formations generally include a plurality of cutting elements secured to a body. For example, fixed-cutter earth-boring rotary drill bits (also referred to as “drag bits”) include a plurality of cutting elements that are fixedly attached to a bit body of the drill bit. Similarly, roller cone earth-boring rotary drill bits may include cones that are mounted on bearing pins extending from legs of a bit body such that each cone is capable of rotating about the bearing pin on which it is mounted. A plurality of cutting elements may be mounted to each cone of the drill bit. 
     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. Such polycrystalline diamond cutting elements are formed by sintering and bonding together relatively small diamond grains or crystals with diamond-to-diamond bonds under conditions of high temperature and high pressure in the presence of a catalyst (such as, for example, Group VIIIA metals including by way of example cobalt, iron, nickel, or alloys and mixtures thereof) to form a layer or “table” of polycrystalline diamond material on a cutting element substrate. These processes are often referred to as high temperature/high pressure (or “HTHP”) processes. The cutting element substrate may comprise a cermet material (i.e., a ceramic-metal composite material) such as, for example, cobalt-cemented tungsten carbide. In such instances, the cobalt (or other catalyst material) in the cutting element substrate may be swept into the diamond crystals during sintering and serve as the catalyst material for forming the diamond table from the diamond crystals. In other methods, powdered catalyst material may be mixed with the diamond crystals prior to sintering the crystals together in an HTHP process. 
     Upon formation of a diamond table using an HTHP process, catalyst material may remain in interstitial spaces between the crystals of diamond in the resulting polycrystalline diamond table. The presence of the catalyst material in the diamond table may contribute to thermal damage in the diamond table when the cutting element is heated during use due to friction at the contact point between the cutting element and the formation. Accordingly, the polycrystalline diamond cutting element may be formed by leaching the catalyst material (e.g., cobalt) out from interstitial spaces between the diamond crystals in the diamond table using, for example, an acid or combination of acids, e.g., aqua regia. All of the catalyst material may be removed from the diamond table, or catalyst material may be removed from only a portion thereof, for example, from the cutting face, from the side of the diamond table, or both, to a desired depth. 
     PDC cutters are typically cylindrical in shape and have a cutting edge at the periphery of the cutting face for engaging a subterranean formation. Over time, the cutting edge becomes dull. As the cutting edge dulls, the surface area in which the cutting edge of the PDC cutter engages the formation increases due to the formation of a so-called wear flat or wear scar extending into the side wall of the diamond table. As the surface area of the diamond table engaging the formation increases, more friction-induced heat is generated between the formation and the diamond table in the area of the cutting edge. Additionally, as the cutting edge dulls, the downward force or weight on the bit (WOB) must be increased to maintain the same rate of penetration (ROP) as a sharp cutting edge. Consequently, the increase in friction-induced heat and downward force may cause chipping, spalling, cracking, or delamination of the PDC cutter due to a mismatch in coefficient of thermal expansion between the diamond crystals and the catalyst material. In addition, at temperature of about 750° C. and above, presence of the catalyst material may cause so-called back-graphitization of the diamond crystals into elemental carbon. 
     Accordingly, there remains a need in the art for cutting elements that include a polycrystalline diamond table that increase the durability as well as the cutting efficiency of the cutter. 
     BRIEF SUMMARY 
     Embodiments of the present disclosure relate to methods of forming polycrystalline diamond compact (PDC) elements, such as cutting elements suitable for use in subterranean drilling, exhibiting enhanced cutting ability and thermal stability, and the resulting PDC elements formed thereby. 
     In some embodiments, the present disclosure includes methods of forming PDC cutting elements for earth-boring tools. A diamond table is formed that comprises a polycrystalline diamond material and a first material disposed in interstitial spaces between inter-bonded diamond crystals of the polycrystalline diamond material. The first material is at least substantially removed from the interstitial spaces in a portion of the polycrystalline diamond material, and a second material is then provided in the interstitial spaces between the inter-bonded diamond crystals in the portion of the polycrystalline diamond material in a peripheral portion of the diamond table. The second material is selected to promote a higher rate of degradation of the diamond crystals under elevated temperature conditions than a rate of degradation of the diamond material having the first material at least substantially removed from the interstitial spaces under substantially equivalent elevated temperature conditions. Removing the first material from the interstitial spaces in a portion of the polycrystalline diamond material may include at least substantially removing the first material from the interstitial spaces in an annular region of the diamond table substantially circumscribing an outer side peripheral surface of the diamond table. 
     In some embodiments, the present disclosure includes methods of forming PDC cutting elements for earth-boring tools. A diamond table is formed that comprises a polycrystalline diamond material and a first material disposed in interstitial spaces between inter-bonded diamond crystals of the polycrystalline diamond material. The first material is at least substantially removed from the interstitial spaces in a portion of the polycrystalline diamond material, and a second material is then introduced into the interstitial spaces between the inter-bonded diamond crystals. The second material may be selected to promote a higher rate of degradation of the polycrystalline diamond material responsive to exposure to an elevated temperature than a rate of degradation of the first material under a substantially equivalent elevated temperature. 
     In additional embodiments, the present disclosure includes methods of drilling. At least one cutting element is engaged with a formation, the at least one cutting element including a diamond table having a first region of polycrystalline diamond material comprising a first material in interstitial spaces between inter-bonded diamond crystals in the first region of polycrystalline diamond material and a second region of polycrystalline diamond material comprising a second material in interstitial spaces between diamond crystals in the second region of polycrystalline diamond material. The second material inducing a higher rate of degradation of the polycrystalline diamond material than the first material under approximately equal elevated temperatures. The second region of polycrystalline diamond material wears faster than the first region of polycrystalline diamond material as friction from engagement of the at least one cutter increases the temperature of the first region and the second region. 
     Further embodiments include PDC cutting elements for use in earth-boring tools. The cutting elements include a first region of polycrystalline diamond material comprising a first material in interstitial spaces between inter-bonded diamond crystals in the first region of polycrystalline diamond material, and a second region of polycrystalline diamond material comprising a second material in interstitial spaces between diamond crystals in the second region of polycrystalline diamond material. The second material may be selected to induce a higher rate of degradation of the polycrystalline diamond material than the first material under approximately the same elevated temperature. 
     In yet additional embodiments, the present disclosure includes earth-boring tools having a body and at least one PDC cutting element attached to the body. The at least one PDC cutting element comprises a diamond table on a surface of a substrate. The diamond table includes a first region of polycrystalline diamond material disposed adjacent a surface of the substrate, the first region comprising a first material in interstitial spaces between inter-bonded diamond crystals in the first region of polycrystalline diamond material, and a second region of polycrystalline diamond material located in a recess in a side of the first region of polycrystalline diamond material, the second region comprising a second material in interstitial spaces between inter-bonded diamond crystals in the second region of polycrystalline diamond material. The second material promoting a higher rate of degradation of the polycrystalline diamond material than the first material under substantially equivalent elevated temperatures. 
     Other features and advantages 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 SEVERAL VIEWS OF THE DRAWINGS 
       While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this disclosure may be more readily ascertained from the description of embodiments of the disclosure when read in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an enlarged cross-sectional view of one embodiment of a cutting element having a multi-portion diamond table of the present disclosure; 
         FIG. 2  illustrates an enlarged cross-sectional view of another embodiment of a cutting element having a multi-portion diamond table of the present disclosure; 
         FIG. 3A  is a simplified figure illustrating how a microstructure of the multi-portion diamond table of the cutting element shown in  FIG. 1  and  FIG. 2  may appear under magnification; 
         FIG. 3B  is a simplified figure illustrating how a microstructure of another region of the multi-portion diamond table of the cutting element shown in  FIG. 1  may appear under magnification; 
         FIGS. 4A through 4C  depict one embodiment of forming the cutting element having the multi-portion diamond table of the  FIG. 1 ; 
         FIGS. 5A through 5C  depict one embodiment of forming the cutting element having the multi-portion diamond table of  FIG. 2 ; 
         FIG. 6  is a perspective view of an embodiment of an earth-boring tool of the present disclosure that includes a plurality of cutting elements formed in accordance with embodiments of the present disclosure; and 
         FIGS. 7A and 7B  are enlarged cross-sectional views of a cutting element of an embodiment of the present disclosure having a multi-portion diamond table as depicted in  FIG. 1  and  FIG. 2  engaging a formation. 
     
    
    
     DETAILED DESCRIPTION 
     Some of the illustrations presented herein are not meant to be actual views of any particular material or device, but are merely idealized representations, which are employed to describe the present disclosure. Additionally, elements common between figures may retain the same numerical designation. 
     Embodiments of the present disclosure include methods for fabricating cutting elements that include a multi-portion diamond table comprising polycrystalline diamond material. In some embodiments, the methods employ the use of a catalyst material to form a portion of the diamond table. 
     As used herein, the term “drill bit” means and includes any type of bit or tool used for drilling during the formation or enlargement of a wellbore in a subterranean formation and includes, for example, rotary drill bits, percussion bits, core bits, eccentric bits, bicenter bits, reamers, mills, drag bits, roller cone bits, hybrid bits and other drilling bits and tools known in the art. 
     As used herein, the term “polycrystalline compact” means and includes any structure comprising a polycrystalline material formed by a process that involves application of pressure (e.g., compaction) to the precursor material or materials used to form the polycrystalline material. 
     As used herein, the term “inter-granular bond” means and includes any direct atomic bond (e.g., covalent, metallic, etc.) between atoms in adjacent grains of material. 
     As used herein, the “catalyst material” refers to any material that is capable of substantially catalyzing the formation of inter-granular bonds between grains of hard material during an HTHP but at least contributes to the degradation of the inter-granular bonds and granular material under elevated temperatures, pressures, and other conditions that may be encountered in a drilling operation for forming a wellbore in a subterranean formation. For example, catalyst materials for diamond include cobalt, iron, nickel, other elements from Group VIIIA of the Periodic Table of the Elements, and alloys thereof. 
       FIG. 1  is a simplified enlarged cross-sectional view of an embodiment of a polycrystalline diamond compact (PDC) cutting element  100  of the present disclosure. The PDC cutting element  100  includes a multi-portion diamond table  102  that is provided on (e.g., formed on or attached to) a supporting substrate  104 . In additional embodiments, the multi-portion diamond table  102  of the present disclosure may be formed without a supporting substrate  104 , and/or may be employed without a supporting substrate  104 . The multi-portion diamond table  102  may be formed on the supporting substrate  104 , or the multi-portion diamond table  102  and the supporting substrate  104  may be separately faulted and subsequently attached together. The multi-portion diamond table  102  includes a cutting face  117  opposite the supporting substrate  104 . The multi-portion diamond table  102  may also, optionally, have a chamfered edge  118  at a periphery of the cutting face  117 . The chamfered edge  118  of the PDC cutting element  100  shown in  FIG. 1  has a single chamfer surface, although the chamfered edge  118  also may have additional chamfer surfaces, and such chamfer surfaces may be oriented at chamfer angles that differ from the chamfer angle of the chamfer edge  118 , as known in the art. Further, in lieu of a chamfered edge  118 , the edge may be rounded or comprise a combination of one or more chamfer and one or more arcuate surfaces. 
     The supporting substrate  104  may have a generally cylindrical shape as shown in  FIG. 1 . The supporting substrate  104  may have a first end surface  110 , a second end surface  112 , and a generally cylindrical lateral side surface  114  extending between the first end surface  110  and the second end surface  112 . 
     Although the first end surface  110  shown in  FIG. 1  is at least substantially planar, it is well known in the art to employ non-planar interface geometries between substrates and diamond tables formed thereon, and additional embodiments of the present disclosure may employ such non-planar interface geometries at the interface between the supporting substrate  104  and the multi-portion diamond table  102 . Additionally, although cutting element substrates commonly have a cylindrical shape, like the supporting substrate  104 , other shapes of cutting element substrates are also known in the art, and embodiments of the present disclosure include cutting elements having shapes other than a generally cylindrical shape. 
     The supporting substrate  104  may be formed from a material that is relatively hard and resistant to wear. For example, the supporting substrate  104  may be formed from and include a ceramic-metal composite material (which are often referred to as “cermet” materials). The supporting substrate  104  may include a cemented carbide material, such as a cemented tungsten carbide material, in which tungsten carbide particles are cemented together in a metallic binder material. The metallic binder material may include, for example, a catalyst material such as cobalt, nickel, iron, or alloys and mixtures thereof. 
     With continued reference to  FIG. 1 , the multi-portion diamond table  102  may be disposed on or over the first end surface  110  of the supporting substrate  104 . The multi-portion diamond table  102  may comprise a first portion  106 , a second portion  108 , and a third portion  109  as discussed in further detail below. The multi-portion diamond table  102  is primarily comprised of polycrystalline diamond material. In other words, diamond material may comprise at least about seventy percent (70%) by volume of the multi-portion diamond table  102 . In additional embodiments, diamond material may comprise at least about eighty percent (80%) by volume of the multi-portion diamond table  102 , and in yet further embodiments, diamond material may comprise at least about ninety percent (90%) by volume of the multi-portion diamond table  102 . The polycrystalline diamond material include grains or crystals of diamond that are bonded together to form the diamond table. Interstitial regions or spaces between the diamond grains may be filled with additional materials or they may be at least substantially free of additional materials, as discussed below. Although the embodiments described herein comprise a multi-portion diamond table  102 , in other embodiments, a different hard polycrystalline material may be used to form a polycrystalline compact, such as polycrystalline cubic boron nitride. 
     In one embodiment, the multi-portion diamond table  102  includes at least the first portion  106 , the second portion  108 , and the third portion  109 . As shown in  FIG. 1 , the second portion  108  of the multi-portion diamond table  102  comprises an annular region extending around a periphery of the multi-portion diamond table  102 . While the second portion  108  of the multi-portion diamond table  102  is illustrated as having at least substantially planar, mutually perpendicular sidewalls  116 , it is understood that the second portion  108  may have other shapes. For example, a cross section of the second portion  108  may have an arcuate, a triangular, or a trapezoidal shape. 
     The second portion  108  may extend along a sidewall  120  of the multi-portion diamond table  102  from the supporting substrate  104  to the chamfered edge  118 . The second portion  108  is separated from the cutting face  117  so that the third portion  109  includes the entire cutting face  117 . In some embodiments, a segment  122  of the first portion  106  may be located between the second portion  108  and the supporting substrate  104 . Having a segment  122  of the first portion  106  located between the second portion  108  and the supporting substrate  104  may help maintain the bond security of the multi-portion table  102  to the supporting substrate  104  during use of the cutting element  100 . The second portion  108  may have a thickness T extending inward of sidewall  120  of about 50 microns to about 400 microns. 
     The third portion  109  may be located between the second portion  108  and the cutting face  117  of the diamond table  102 . In some embodiments, the third portion  109  may also be located between the first portion  106  and the cutting face  117  of the diamond table  102 . While the third portion  109  is illustrated in  FIG. 1  as extending into the diamond table  102  from the cutting face  117  to about a depth of the second portion  108 , in additional embodiments, the third portion  109  may extend farther downward from the cutting face  117  toward the supporting substrate  104 . 
     In another embodiment, as shown in  FIG. 2 , the multi-portion diamond table  102  may include only the first portion  106  and the second portion  108 . The second portion  108  may extend from the supporting substrate  104  to the cutting face  117 . 
       FIG. 3A  is an enlarged view illustrating how a microstructure of the first portion  106  of the multi-portion diamond table  102 , shown in  FIG. 1  and  FIG. 2 , may appear under magnification.  FIG. 3B  is an enlarged view illustrating how a microstructure of the second portion  108  of the multi-portion diamond table  102 , shown in  FIG. 1  and  FIG. 2 , may appear under magnification. Referring now to  FIG. 3A , the first portion  106  includes diamond crystals  202  that are bonded together by inter-granular diamond-to-diamond bonds. The diamond crystals  202  may comprise natural diamond, synthetic diamond, or a mixture thereof, and may be formed using diamond grit of different crystal sizes (i.e., from multiple layers of diamond grit, each layer having a different average crystal size or by using a diamond grit having a multi-modal crystal size distribution). 
     A first material  204  may be disposed in interstitial regions or spaces between the diamond crystals  202  of first portion  106 . In one embodiment, the first material  204  may comprise a catalyst material that catalyzes the formation of the inter-granular diamond-to-diamond bonds during formation of the multi-portion diamond table  102 , and will promote degradation to the first portion  106  of multi-portion diamond table  102  when the PDC cutting element  100  is used for drilling. In additional embodiments, the first material  204  may have no effect on the diamond crystals  202  but rather, will be an at least substantially inert material. 
     In some embodiments, the first material  204  ( FIG. 3A ) may be removed from a portion of the diamond table  102  to a depth from the cutting face  117  toward supporting substrate  104 , and inward of second portion  108  to form the third portion  109  ( FIG. 1 ). The third portion  109  of the multi-portion diamond table  102  may be at least substantially free of the first material  204  and a second material  206 . 
     Referring now to  FIG. 3B , the second portion  108  includes a second material  206  disposed in interstitial regions or spaces between the diamond crystals  202 . In some embodiments, the second material  206  is selected to cause a higher rate of degradation of the diamond crystals  202  than diamond crystals having the first material at least substantially removed from the interstitial regions between diamond crystals when the cutting element  101  is used for drilling. In additional embodiments, the second material  206  is selected to cause a higher rate of degradation of the diamond crystals  202  than the first material  204  when the cutting element  101  is used for drilling. As used herein, the phrase “rate of degradation” refers to a material that causes at least one of graphitization of the diamond crystals and weakening of the inter-granular diamond-to-diamond bonds at temperatures and pressures common in drilling. In other words, the second material  206  is selected to preferentially weaken the polycrystalline diamond structure of the second portion  108  relative to that of at least one of the third portion  109  or the first portion  106  during drilling as described in greater detail below. 
     The first material  204  and the second material  206  may each comprise a catalyst material known in the art for catalyzing the formation of inter-granular diamond-to-diamond bonds in the polycrystalline diamond materials. For example, the first material  204  and the second material  206  may each comprise a Group VIII element or an alloy thereof such as Co, Ni, Fe, 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. The combination of the first material  204  and the second material  206  may be selected by one of ordinary skill in the art so long as the second material  206  promotes a higher rate of degradation of the diamond crystals  202  than the first material  204 . For example, iron has a higher reactivity, and thus promotes a higher rate of degradation of diamond crystals  202  than cobalt under substantially equivalent elevated temperatures, as known in the art. Accordingly, in one embodiment, the first material  204  may comprise cobalt and the second material  206  may comprise iron. In another embodiment, the first material  204  may be at least substantially removed from the third portion  109  of the multi-portion diamond table  102  adjacent the cutting face  117  and the chamfer  118 , and the second material  206  may comprise any of the aforementioned catalysts. For example, the second material  206  may comprise iron as iron has a higher reactivity, and thus promotes a higher rate of degradation of diamond crystals  202  than diamond crystals  202  having at least substantially void regions between the diamond crystals  202 . In yet another embodiment, the first material  204  may be removed from a majority of the diamond table  102  to a substantial depth from the cutting face toward supporting substrate  104 , and inward of second portion  108 . The second material  206  may also comprise a combination of more than one material. For example, the second material  206  may be formed as a gradient of more than one material such that the rate of degradation of the second material  206  near the sidewall  120  of the multi-portion diamond table  102  is higher than the rate of degradation of the second material  206  near an interior of the multi-portion diamond table  102 . 
       FIGS. 4A through 4C  illustrate one embodiment of a method of forming the multi-portion diamond table  102  of  FIG. 1 . As shown in  FIG. 4A , a diamond table  302  comprising the first material  204  ( FIG. 3A ) is formed on the supporting substrate  104 . The diamond table  302  may be formed using a high temperature/high pressure (HTHP) process. Such processes, and systems for carrying out such processes, are generally known in the art and described by way of non-limiting example, in U.S. Pat. No. 3,745,623 to Wentorf et al. (issued Jul. 17, 1973), and U.S. Pat. No. 5,127,923 Bunting et al. (issued Jul. 7, 1992), the disclosure of each of which patents is incorporated herein in its entirety by this reference. In some embodiments, the first material  204  ( FIG. 3A ) may be supplied from the supporting substrate  104  during an HTHP process used to form the diamond table  302 . For example, the supporting substrate  104  may comprise a cobalt-cemented tungsten carbide material. The cobalt of the cobalt-cemented tungsten carbide may serve as the first material  204  during the HTHP process. 
     To form the diamond table  302  in an HTHP process, a particulate mixture comprising diamond granules or particles may be subjected to elevated temperatures (e.g., temperatures greater than about one thousand degrees Celsius (1,000° C.)) and elevated pressures (e.g., pressures greater than about five gigapascals (5.0 GPa)) to form inter-granular bonds between the diamond granules or particles. 
     Once formed, the diamond table  302  ( FIG. 4A ) may be masked (not shown), as known in the art, so that the cutting face  117  and a portion of the sidewall  120  of the diamond table  203  are exposed. The unmasked portions of the diamond table  302  are then leached using a leaching agent to remove the first material  204  ( FIG. 3A ) forming a leached portion  304  of the diamond table  302  ( FIG. 4B ). The portion of the diamond table  302  that is not leached at least substantially corresponds to the first portion  106  ( FIG. 1 ). The leached portion  304  at least substantially corresponds to the area of the second portion  108  and the third portion  109  ( FIG. 1 ). Such leaching agents are known in the art and described more fully in, for example, U.S. Pat. No. 5,127,923 to Bunting et al. (issued Jul. 7, 1992), and U.S. Pat. No. 4,224,380 to Bovenkerk et al. (issued Sep. 23, 1980), the disclosure of each of which is incorporated herein in its entirety by this reference. Specifically, aqua regia (a mixture of concentrated nitric acid (HNO 3 ) and concentrated hydrochloric acid (HCl)) may be used to at least substantially remove the first material  204  ( FIG. 3A ) from the interstitial voids between the diamond crystals  202  in the first portion  106  ( FIG. 1 ). It is also known to use boiling hydrochloric acid (HCl) and boiling hydrofluoric acid (HF) as leaching agents. One particularly suitable leaching agent is hydrochloric acid (HCl) at a temperature of above 110° C., which may be provided in contact with unmasked portion of the diamond table  302  for a period of about 30 minutes to about 60 hours, depending upon the desired thickness T ( FIG. 1 ) of the leached portion  304 . The supporting substrate  104  and a portion of the diamond table  302  at least substantially corresponding to the area of the first portion  106  ( FIG. 1 ) of the multi-portion diamond table  102  may be precluded from contact with the leaching agent by encasing the supporting substrate  104  and a portion of the diamond table  302  in a plastic resin or masking material (not shown). In another embodiment, only the supporting substrate  104  may be precluded from contact with the leaching agent, and a substantial depth of diamond table  302  may be leached downward from the cutting face  117  ( FIG. 1 ) toward the supporting substrate  104 , as known in the art. As known in the art, it is desirable that the first material  204  remain within the diamond table  302  to some thickness proximate the interface with supporting substrate  104  to maintain mechanical strength and impact resistance of diamond table  302 . 
     As shown in  FIG. 4C , a mask  306  may be formed over the cutting face  117  and a portion of the sidewalls  120  of the diamond table  302 . The exposed portions of the leached portion  304  on the sidewalls  120  may then be filled with the second material  206  ( FIG. 3B ) to form the second portion  108  ( FIG. 1 ). The diamond table  302  may then be subjected to a second HTHP process causing the second material  206  to infiltrate the leached portion  304  forming the second portion  108  of the multi-portion diamond table  102  ( FIG. 1 ). In other embodiments, the second material  206  may be deposited into the leached portion  304  using a physical vapor deposition (PVD) process or chemical vapor deposition (CVD) process such as a plasma-enhanced chemical vapor deposition process (PECVD), as known in the art. PVD includes, but is not limited to, sputtering, evaporation, or ionized PVD. Such deposition techniques are known in the art and, therefore, are not described in detail herein. Where a major portion of the diamond table  302  has been leached downward from cutting face  117  toward supporting substrate  104  so that the portion of diamond table  302  interior of region  304  is substantially free of first material  204 , the thickness T of the second portion  108  ( FIG. 1 ) may be achieved by controlling the time of the deposition process, as known in the art. Once the second portions  108  are filled with the second material  206  ( FIG. 3B ), the mask  306  may be removed exposing the third portion  109  ( FIG. 1 ). 
       FIGS. 5A through 5C  illustrate one embodiment of a method of forming the multi-portion diamond table  102  of  FIG. 2 .  FIG. 5A  illustrates a diamond table  302  comprising the first material  204  ( FIG. 3A ) formed on the supporting substrate  104 , which is a substantial duplication of  FIG. 4A  and may be formed as described above regarding  FIG. 4A . 
     Once formed, the diamond table  302  ( FIG. 5A ) may be masked (not shown), as known in the art, so that only portions of the diamond table  302  intended to become the second portion  108  ( FIG. 2 ) are exposed. The unmasked portions of the diamond table  302  are then leached using a leaching agent to remove the first material  204  ( FIG. 3A ) forming a leached portion  304  of the diamond table  302  ( FIG. 5B ). The leached portion  304  at least substantially corresponds to the area of the second portion  108  ( FIG. 2 ). The leached portion  304  may be formed using a leaching agent as previously discussed regarding  FIG. 4B . The supporting substrate  104  and a portion of the diamond table  302  at least substantially corresponding to the area of the first portion  106  ( FIG. 2 ) of the multi-portion diamond table  102  may be precluded from contact with the leaching agent by encasing the supporting substrate  104  and a portion of the diamond table  302  in a plastic resin or masking material (not shown). In another embodiment, only the supporting substrate  104  may be precluded from contact with the leaching agent, and a substantial depth of diamond table  302  may be leached downward from the cutting face  117  ( FIG. 2 ) toward the supporting substrate  104 , as known in the art. As known in the art, it is desirable that that the first material  204  remain within the diamond table  302  to some thickness proximate the interface with supporting substrate  104  to maintain mechanical strength and impact resistance of diamond table  302 . 
     If only a portion of the diamond table  302  is leached, for example an annular portion adjacent the sidewall  120 , the second material  206  ( FIG. 3B ) may then be deposited into the leached portion  304  to form the second portion  108  of the multi-portion diamond table  102  ( FIG. 2 ). In one embodiment, as shown in  FIG. 5C , a powder comprising the second material  206  may be placed on the leached portion  304 . The supporting substrate  104  and the portion of the diamond table  302  at least substantially corresponding to the first portion  106  ( FIG. 2 ) may remain masked so as not to contact the second material  206 , or a new mask may be formed on the supporting substrate  104  and the portion of the diamond table  302  at least substantially corresponding to the first portion  106 . Alternatively, if a major portion of the diamond table  302  is leached downward from the cutting face  117  toward supporting substrate  104 , the portion of the diamond table  302  at least substantially corresponding to the first portion  106  ( FIG. 2 ) is masked on the cutting face  117 , the chamfer  118  and portions of the sidewall  120  above and below region  304  so as not to be contacted by the second material  206 . The exposed portions of the leached portion  304  on the sidewalls  120  may be filled with the second material  206  ( FIG. 3B ) using a second HTHP process, a PVD process, or a CVD process as previously discussed regarding  FIG. 4C . 
     Embodiments of PDC cutting elements  100  of the present disclosure that include a multi-portion diamond table  102  as illustrated in  FIG. 1  and  FIG. 2 , may be formed and secured to an earth-boring tool such as, for example, a rotary drill bit, a percussion bit, a coring bit, an eccentric bit, a reamer tool, a milling tool, etc., for use in forming wellbores in subterranean formations. As a non-limiting example,  FIG. 6  illustrates a fixed cutter type earth-boring rotary drill bit  400  that includes a plurality of cutting elements  100 , at least some of which comprise a multi-portion diamond table  102  as previously described herein. The rotary drill bit  400  includes a bit body  402 , and the cutting elements  100 , at least some of which include multi-portion diamond tables  102 , are bonded to the bit body  402 . The cutting elements  100  may be brazed (or otherwise secured) within pockets formed in the outer surface of the bit body  402 . 
       FIGS. 7A and 7B  show the PDC cutting element  100  of  FIG. 1 or 2  as it engages with a subterranean formation  500 , such as when the cutting element  100  is secured to the earth-boring rotary drill bit  400  of  FIG. 6 .  FIG. 7A  shows the PDC cutting element  100  as it first engages the formation  500 . The PDC cutting element  100  includes a bearing surface  502  between the cutting element  100  and the formation  500 .  FIG. 7B  shows a dulled PDC cutting element  100 ′ after engaging the formation  500 . As shown in  FIG. 7B , the bearing surface  502  of  FIG. 7A  has been worn to form a bearing surface  502 ′. Because the second portion  108  includes the second material  206  ( FIG. 2B ), which promotes a higher rate of degradation of the polycrystalline diamond than the third portion  109  ( FIG. 1 ) having the first material  204  at least substantially removed therefrom, the polycrystalline material in second portion  108  degrades or wears faster than the third portion  109  due to frictional temperature-induced back-graphitization of the diamond-to-elemental carbon as the PDC cutting element  100  engages the formation  500 . Alternatively, the second portion  108  includes the second material  206  ( FIG. 2B ), which promotes a higher rate of degradation than the first portion  106  ( FIG. 2 ) having the first material  204  ( FIG. 2A ), which causes the polycrystalline material in the second portion  108  to degrade or wear faster than the first portion  106  due to frictional temperature-induced back graphitization of the diamond-to-elemental carbon as the PDC cutting element  100  engages the formation. As the second portion  108  degrades or wears, a groove  504  forms around a portion of the sidewall  120  of multi-portion diamond table  102  in the area of second portion  108 . A lip structure or abutment  506  is formed in the third portion  109  ( FIG. 1 ) or the first portion  106  ( FIG. 2 ) under the cutting edge  117  due to the undercut in the side wall provided by degradation of the diamond in second portion  108 . Cutting elements having a preformed abutment  506  are known in the art and described in detail in U.S. Publication No. 2006/0201712, now U.S. Pat. No. 7,861,808, issued Jan. 4, 2011, to Zhang et al. (filed Mar. 1, 2006) the entire disclosure of which is incorporated herein by this reference. 
     As the abutment  506  is worn away, the area of bearing surface  502 ′ between the dulled cutting element  100 ′ and the formation  500  remains at least substantially uniform. As a result, the area of bearing surface  502 ′ is smaller than a bearing surface of a conventional cutter, which includes a substantial wear scar. For example, as illustrated in  FIG. 5B , the bearing surface  502 ′ of the dulled cutting element  100 ′ has a length L 1  while a bearing surface of a conventional cutter, which does not include the abutment  506 , would have a length of L 2 . Thus, the area of bearing surface  502 ′ of the dulled cutting element  100 ′ may be at least about 20% smaller than the bearing surface of a dulled conventional cutting element. 
     As a result of a smaller area of bearing surface  502 ′ of the dulled cutting element  100 ′, less WOB is required to maintain a desired ROP. Additionally, the durability and efficiency of the dulled cutting element  100 ′ may be improved. Because the smaller bearing surface  502 ′ of the dulled cutting element  100 ′ has a sharper edge than a conventional cutter, a more efficient cutting action results, and when the region of the diamond table  102  adjacent the cutting face  117  and chamfer  118  and between second portion  108  and cutting face  117  has been leached of the first material  204 , the dulled cutting element  100 ′ is less likely to experience mechanical or thermal breakdown, or spall or crack. 
     While the present invention has been described herein with respect to certain embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions and modifications to the embodiments described herein may be made without departing from the scope of the invention as hereinafter claimed. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventor.