Patent Publication Number: US-2005129950-A1

Title: Polycrystalline Diamond Partially Depleted of Catalyzing Material

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a divisional of U.S. patent application Ser. No. 10/604,007 filed on Jun. 30, 2003 which is a continuation of U.S. patent application Ser. No. 09/682,042 filed on Jul. 13, 2001 now U.S. Pat. No. 6,592,985, which claims priority from U.S. Provisional Patent Application No. 60/234,075 filed Sep. 20, 2000, and from U.S. Provisional Patent Application No. 60/281,054 filed Apr. 2, 2001, all by Nigel D. Griffin and Peter R. Hughes and all hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to superhard polycrystalline material elements for wear, cutting, drawing, and other applications where engineered superhard surfaces are needed. The invention particularly relates to polycrystalline diamond and polycrystalline diamond-like (collectively called PCD) elements with greatly improved wear resistance and methods of manufacturing them.  
      2. Description of Related Art  
      Polycrystalline diamond and polycrystalline diamond-like elements are known, for the purposes of this specification, as PCD elements. PCD elements are formed from carbon based materials with exceptionally short inter-atomic distances between neighboring atoms. One type of polycrystalline diamond-like material is known as carbonitride (CN) described in U.S. Pat. No. 5,776,615. Another, more commonly used form of PCD is described in more detail below. In general, PCD elements are formed from a mix of materials processed under high-temperature and high-pressure into a polycrystalline matrix of inter-bonded superhard carbon based crystals. A common trait of PCD elements is the use of catalyzing materials during their formation, the residue from which, often imposes a limit upon the maximum useful operating temperature of the element while in service.  
      A well known, manufactured form of PCD element is a two-layer or multi-layer PCD element where a facing table of polycrystalline diamond is integrally bonded to a substrate of less hard material, such as tungsten carbide. The PCD element may be in the form of a circular or part-circular tablet, or may be formed into other shapes, suitable for applications such as hollow dies, heat sinks, friction bearings, valve surfaces, indentors, tool mandrels, etc. PCD elements of this type may be used in almost any application where a hard wear and erosion resistant material is required. The substrate of the PCD element may be brazed to a carrier, often also of cemented tungsten carbide. This is a common configuration for PCD&#39;s used as cutting elements, for example in fixed cutter or rolling cutter earth boring bits when received in a socket of the drill bit, or when fixed to a post in a machine tool for machining. These PCD elements are typically called PDC&#39;s.  
      Another form of PCD element is a unitary PCD element without an integral substrate where a table of polycrystalline diamond is fixed to a tool or wear surface by mechanical means or a bonding process. These PCD elements differ from those above in that diamond particles are present throughout the element. These PCD elements may be held in place mechanically, they may be embedded within a larger PCD element that has a substrate, or, alternately, they may be fabricated with a metallic layer which may be bonded with a brazing or welding process. A plurality of these PCD elements may be made from a single PCD, as shown, for example, in U.S. Pat. Nos. 4,481,016 and 4,525,179 herein incorporated by reference for all they disclose.  
      PCD elements are most often formed by sintering diamond powder with a suitable binder-catalyzing material in a high-pressure, high-temperature press. One particular method of forming this polycrystalline diamond is disclosed in U.S. Pat. No. 3,141,746 herein incorporated by reference for all it discloses. In one common process for manufacturing PCD elements, diamond powder is applied to the surface of a preformed tungsten carbide substrate incorporating cobalt. The assembly is then subjected to very high temperature and pressure in a press. During this process, cobalt migrates from the substrate into the diamond layer and acts as a binder-catalyzing material, causing the diamond particles to bond to one another with diamond-to-diamond bonding, and also causing the diamond layer to bond to the substrate.  
      The completed PCD element has at least one matrix of diamond crystals bonded to each other with many interstices containing a binder-catalyzing material metal as described above. The diamond crystals comprise a first continuous matrix of diamond, and the interstices form a second continuous matrix of interstices containing the binder-catalyzing material. In addition, there are necessarily a relatively few areas where the diamond to diamond growth has encapsulated some of the binder-catalyzing material. These ‘islands’ are not part of the continuous interstitial matrix of binder-catalyzing material.  
      In one common form, the diamond element constitutes 85% to 95% by volume and the binder-catalyzing material the other 5% to 15%. Such an element may be subject to thermal degradation due to differential thermal expansion between the interstitial cobalt binder-catalyzing material and diamond matrix beginning at temperatures of about 400 degrees C. Upon sufficient expansion the diamond-to-diamond bonding may be ruptured and cracks and chips may occur.  
      Also in polycrystalline diamond, the presence of the binder-catalyzing material in the interstitial regions adhering to the diamond crystals of the diamond matrix leads to another form of thermal degradation. Due to the presence of the binder-catalyzing material, the diamond is caused to graphitize as temperature increases, typically limiting the operation temperature to about 750 degrees C.  
      Although cobalt is most commonly used as the binder-catalyzing material, any group VIII element, including cobalt, nickel, iron, and alloys thereof, may be employed.  
      To reduce thermal degradation, so-called “thermally stable” polycrystalline diamond components have been produced as preform PCD elements for cutting and/or wear resistant elements, as disclosed in U.S. Pat. No. 4,224,380 herein incorporated by reference for all it discloses. In one type of thermally stable PCD element the cobalt or other binder-catalyzing material in conventional polycrystalline diamond is leached out from the continuous interstitial matrix after formation. While this may increase the temperature resistance of the diamond to about 1200 degrees C., the leaching process also removes the cemented carbide substrate. In addition, because there is no integral substrate or other bondable surface, there are severe difficulties in mounting such material for use in operation.  
      The fabrication methods for this ‘thermally stable’ PCD element typically produce relatively low diamond densities, of the order of 80% or less. This low diamond density enables a thorough leaching process, but the resulting finished part is typically relatively weak in impact strength.  
      In an alternative form of thermally stable polycrystalline diamond, silicon is used as the catalyzing material. The process for making polycrystalline diamond with a silicon catalyzing material is quite similar to that described above, except that at synthesis temperatures and pressures, most of the silicon is reacted to form silicon carbide, which is not an effective catalyzing material. The thermal resistance is somewhat improved, but thermal degradation still occurs due to some residual silicon remaining, generally uniformly distributed in the interstices of the interstitial matrix. Again, there are mounting problems with this type of PCD element because there is no bondable surface.  
      More recently, a further type of PCD has become available in which carbonates, such as powdery carbonates of Mg, Ca, Sr, and Ba are used as the binder-catalyzing material when sintering the diamond powder. PCD of this type typically has greater wear-resistance and hardness than the previous types of PCD elements. However, the material is difficult to produce on a commercial scale since much higher pressures are required for sintering than is the case with conventional and thermally stable polycrystalline diamond. One result of this is that the bodies of polycrystalline diamond produced by this method are smaller than conventional polycrystalline diamond elements. Again, thermal degradation may still occur due to the residual binder-catalyzing material remaining in the interstices. Again, because there is no integral substrate or other bondable surface, there are difficulties in mounting this material to a working surface.  
      Efforts to combine thermally stable PCD&#39;s with mounting systems to put their improved temperature stability to use have not been as successful as hoped due to their low impact strength. For example, various ways of mounting multiple PCD elements are shown in U.S. Pat. Nos. 4,726,718; 5,199,832; 5,025,684; 5,238,074; 6,009,963 herein incorporated by reference for all they disclose. Although many of these designs have had commercial success, the designs have not been particularly successful in combining high wear and/or abrasion resistance while maintaining the level of toughness attainable in non-thermally stable PCD.  
      Other types of diamond or diamond like coatings for surfaces are disclosed in U.S. Pat. Nos. 4,976,324; 5,213,248; 5,337,844; 5,379,853; 5,496,638; 5,523,121; 5,624,068 all herein incorporated by reference for all they disclose. Similar coatings are also disclosed in GB Patent Publication No. 2,268,768, PCT Publication No. 96/34,131, and EPC Publications 500,253; 787,820; 860,515 for highly loaded tool surfaces. In these publications, diamond and/or diamond like coatings are shown applied on surfaces for wear and/or erosion resistance.  
      In many of the above applications physical vapor deposition (PVD) and/or chemical vapor deposition (CVD) processes are used to apply the diamond or diamond like coating. PVD and CVD diamond coating processes are well known and are described for example in U.S. Pat. Nos. 5,439,492; 4,707,384; 4,645,977; 4,504,519; 4,486,286 all herein incorporated by reference.  
      PVD and/or CVD processes to coat surfaces with diamond or diamond like coatings may be used, for example, to provide a closely packed set of epitaxially oriented crystals of diamond or other superhard crystals on a surface. Although these materials have very high diamond densities because they are so closely packed, there is no significant amount of diamond to diamond bonding between adjacent crystals, making them quite weak overall, and subject to fracture when high shear loads are applied. The result is that although these coatings have very high diamond densities, they tend to be mechanically weak, causing very poor impact toughness and abrasion resistance when used in highly loaded applications such as with cutting elements, bearing devices, wear elements, and dies.  
      Some attempts have been made to improve the toughness and wear resistance of these diamond or diamond like coatings by application to a tungsten carbide substrate and subsequently processing in a high-pressure, high-temperature environment as described in U.S. Pat. Nos. 5,264,283; 5,496,638; 5,624,068 herein incorporated by reference for all they contain. Although this type of processing may improve the wear resistance of the diamond layer, the abrupt transition between the high-density diamond layer and the substrate make the diamond layer susceptible to wholesale fracture at the interface at very low strains. This translates to very poor toughness and impact resistance in service.  
      When PCD elements made with a cobalt or other group VIII metal binder-catalyzing material were used against each other as bearing materials, it was found that the coefficient of friction tended to increase with use. As described in European Patent specification number 617,207, it was found that removal (by use of a hydrochloric acid wipe) of the cobalt-rich tribofilm which tended to build up in service from the surface of the PCD bearing element, tended to mitigate this problem. Apparently, during operation, some of the cobalt from the PCD at the surface migrates to the load area of the bearing, causing increased friction when two PCD elements act against each other as bearings. It is now believed that the source of this cobalt may be a residual by-product of the finishing process of the bearing elements, as the acid wipe remedy cannot effectively remove the cobalt to any significant depth below the surface.  
      Because the cobalt is removed only from the surface of the PCD, there is no effective change in the temperatures at which thermal degradation occurs in these bearing elements. Therefore the deleterious effects of the binder-catalyzing material remain, and thermal degradation of the diamond layer due to the presence of the catalyzing material still occurs.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention provides a superhard polycrystalline diamond or diamond-like element with greatly improved resistance to thermal degradation without loss of impact strength. Collectively called PCD elements for the purposes of this specification, these elements are formed with a binder-catalyzing material in a high-temperature, high-pressure process. The PCD element has a plurality of partially bonded diamond or diamond-like crystals forming at least one continuous diamond matrix, and the interstices among the diamond crystals forming at least one continuous interstitial matrix containing a catalyzing material. The element has a working surface and a body, where a portion of the interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.  
      A portion of the working surface on the body of the PCD element may be post-processed so that the interstices among the superhard crystals are substantially free of the catalyzing material. The working surface that is substantially free of the catalyzing material is not subject to the thermal degradation encountered in the other areas of the working surface, resulting in improved resistance to thermal degradation. In cutting elements, the processed working surface may be a portion of the facing table of the body, a portion of the peripheral surface of the body, or portions of all these surfaces.  
      In another embodiment, the catalyzing material is cobalt or other iron group metal, and the method of depleting the catalyzing material is to leach it from the interstices near the surface of a PCD element in an acid etching process. It is anticipated that the method of removing the catalyzing material from the surface may also be by electrical discharge, or other electrical or galvanic process, or by evaporation.  
      In another embodiment, the catalyzing material is subsequently removed from the working surface of a PCD element by combining it chemically with another material such that it no longer acts as a catalyzing material. In this method, a material may remain in the interstices among the diamond crystals, but that material no longer acts as a catalyzing material—effectively removing or depleting the catalyzing material.  
      In still another embodiment, the catalyzing material is removed by causing it to transform into a material that no longer acts as a catalyzing material. This may be accomplished by a crystal structure change, mechanical ‘working’, thermal treatment or other treatment methods. This method may apply to non-metallic or non-reactive catalyzing materials. Again, a material may remain in the interstices among the superhard material crystals, but that material no longer acts as a catalyzing material—effectively removing or depleting the catalyzing material.  
      Disclosed is an element comprising a plurality of partially bonded diamond crystals, a catalyzing material, an interstitial matrix, and a body with a working surface. The interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.  
      Similarly, a PCD element is disclosed having a catalyzing material, an interstitial matrix, and a body with a working surface. The interstitial matrix in the body adjacent to the working surface is substantially free of the catalyzing material, and the remaining interstitial matrix contains the catalyzing material.  
      Also, a PCD element is disclosed having a plurality of superhard crystals, a catalyzing material and a body with a working surface. In this element, a majority of the crystals in the body within at least a 0.1 mm depth from the working surface have a surface which is substantially free of the catalyzing material and the remaining crystals are contacting the catalyzing material.  
      Furthermore, a PCD element is disclosed having a body with a working surface. A first volume of the body remote from the working surface contains a catalyzing material, and a second volume of the body adjacent to the working surface is substantially free of the catalyzing material.  
      Also, an element is disclosed having a plurality of partially bonded diamond crystals, a catalyzing material, and a body with a working surface. The volume of the body adjacent the working surface has a substantially higher diamond density than elsewhere in the body, and the volume is substantially free of the catalyzing material.  
      Also, a PCD element is disclosed having a body with a working surface. The volume of the body adjacent to the working surface has a diamond density substantially higher than elsewhere in the body, and the volume is substantially free of a catalyzing material.  
      In addition, a preform cutting element is disclosed. The element has a facing table of a superhard polycrystalline material having a plurality of partially bonded superhard crystals, a plurality of interstitial regions among the superhard crystals and a catalyzing material. The facing table has a cutting surface and a body. The interstitial regions in at least a portion of the cutting surface are substantially free of the catalyzing material and the remainder of the interstitial regions contain the catalyzing material.  
      The PCD elements of the present invention may be used for wear, cutting, drawing, and other applications where engineered diamond surfaces are needed. Specific applications are as cutting elements in rotary drill bits of both the fixed cutter type and the rolling cutter type, as hollow dies, heat sinks, friction bearings, valve surfaces, indentors, tool mandrels, etc. The PCD element of the present invention may be used to machine abrasive wood products, ferrous and nonferrous materials and also very hard or abrasive engineering materials such as stone and asphalt and the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1A  is a typical PCD element of the present invention.  
       FIG. 1B  is a typical PCD of the present invention shown as a cutting element.  
       FIG. 2  is a side view of a fixed cutter rotary drill bit using a PCD element of the present invention.  
       FIG. 3  is a perspective view of a rolling cutter rotary drill bit using a PCD element of the present invention.  
       FIG. 4  is a perspective view of an insert used in machine tools utilizing the PCD element of the present invention.  
       FIG. 5  is a perspective view of a dome shaped PCD element suitable for use in both rolling cutter drill bits and in fixed cutter drill bits.  
       FIG. 6  is a photo-micrograph of the surface of a PCD element of the prior art showing the binder-catalyzing material in the interstitial regions.  
       FIG. 7  is a photo-micrograph of the PCD element of the present invention showing a first portion with a catalyzing material in the interstitial regions and a second portion without the catalyzing material in the interstitial regions.  
       FIG. 8  is a micro-structural representation of a PCD element of the prior art, showing the bonded diamond crystals, with the interstitial regions and the crystallographic orientation of the individual crystals.  
       FIG. 9  is a micro-structural representation of the PCD element of the present invention as shown in  FIG. 7 , indicating the depth of the catalyzing material free region relative to the surface of the PCD element.  
       FIG. 10  is a graph of the relative wear indices of several embodiments of the PCD element of the present invention.  
       FIG. 11A  is a front view of an encapsulated PCD embodiment of the PCD element of the present invention.  
       FIG. 11B  is a section view of another encapsulated PCD embodiment of the PCD element of the present invention.  
       FIG. 11C  is a section view of still another encapsulated PCD embodiment of the PCD element of the present invention.  
       FIG. 12A  is perspective view of a CVD/PVD applied surface for another embodiment of the PCD element of the present invention.  
       FIG. 12B  is an enlarged perspective view of the crystal structure of the embodiment of the PCD element of the present invention shown in  FIG. 12A .  
       FIG. 13  is a section view of a wire drawing die having a PCD element of the present invention.  
       FIG. 14  is perspective view of a heat sink having a PCD element of the present invention.  
       FIG. 15  is perspective view of a bearing having a PCD element of the present invention.  
       FIGS. 16A and 16B  are front views of the mating parts of a valve having a PCD element of the present invention.  
       FIG. 17A  is a side view of an indentor having a PCD element of the present invention.  
       FIG. 17B  is a partial section view of a punch having a PCD element of the present invention.  
       FIG. 18  is perspective view of a measuring device having a PCD element of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT  
      The polycrystalline diamond or diamond-like material (PCD) element  2  of the present invention is shown in  FIG. 1A . The PCD element  2  has a plurality of partially bonded superhard, diamond or diamond-like, crystals  60 , (shown in  FIGS. 7 and 9 ) a catalyzing material  64 , and an interstitial matrix  68  formed by the interstices  62  among the crystals  60 . The element  2  also has one or more working surfaces  4  and the diamond crystals  60  and the interstices  62  form the volume of the body  8  of the PCD element  2 .  
      The working surface  4  is any portion of the PCD body  8  which, in operation, may contact the object to be worked. In this specification, when the working surface  4  is discussed, it is understood that it applies to any portion of the body  8  which may be exposed and/or used as a working surface. Furthermore, any portion of any of the working surface  4  is, in and of itself, a working surface.  
      During manufacture, under conditions of high-temperature and high-pressure, the interstices  62  among the crystals  60  fill with the catalyzing material  64  just as the bonds among the crystals  60  are being formed. In a further step of the manufacture, some of the catalyzing material  64  is selectively depleted from some of the interstices  62 . The result is that a first volume of the body  8  of the PCD element  2  remote from the working surface  4  contains the catalyzing material  64 , and a second volume of the body  8  adjacent to the working surface  4  is substantially free of the catalyzing material  64 . The interstices  62  which are substantially free of the catalyzing material  64  are indicated by numeral  66 .  
      Therefore, the interstitial matrix  68  of the body  8  adjacent to at least a portion of the working surface  4  is substantially free of the catalyzing material  64 , and the remaining interstitial matrix  68  contains the catalyzing material  64 . The PCD element  2  may be bonded to a substrate  6  of less hard material, usually cemented tungsten carbide, but use of a substrate  6  is not required.  
      Because the body adjacent to the working surface  4  is substantially free of the catalyzing material  64 , the deleterious effects of the binder-catalyzing material  64  are substantially decreased, and thermal degradation of the working surface  4  due to the presence of the catalyzing material  64  is effectively eliminated. The result is a new PCD element  2  that has the enhanced thermal properties approximating that of the so called thermally stable PCD elements, while maintaining the toughness, convenience of manufacture, and bonding ability of the traditional PDC elements. This translates to higher wear resistance in cutting applications, higher heat transfer capacity in heat sink applications, higher load capacity in bearing applications, less surface distortion in valve applications, and has advantages in numerous other applications including hollow dies, indentors, tool mandrels, and wear elements. Details of specific applications of the new PCD element  2  will be discussed in more detail later in the specification.  
      Referring now to the photo-micrograph of a prior art PCD element in  FIG. 6 , and also the microstructural representation of a PCD element of the prior art in  FIG. 8 , it is well known that there is a random crystallographic orientation of the diamond or diamond-like crystals  60  as shown by the parallel lines representing the cleavage planes of each crystal  60 . As can be seen, adjacent crystals  60  have bonded together with interstitial spaces  62  among them. Because the cleavage planes are oriented in different directions on adjacent crystals  60  there is generally no straight path available for diamond fracture. This structure allows PCD materials to perform well in extreme loading environments where high impact loads are common.  
      In the process of bonding the crystals  60  in a high-temperature, high-pressure press, the interstitial spaces  62  among the crystals  60  become filled with a binder-catalyzing material  64 . It is this catalyzing material  64  that allows the bonds to be formed between adjacent diamond crystals  60  at the relatively low pressures and temperatures present in the press.  
      The prior art PCD element has at least one continuous matrix of crystals  60  bonded to each other with the many interstices  62  containing a binder-catalyzing material  64 , typically cobalt or other group VIII element. The crystals  60  comprise a first continuous matrix of diamond, and the interstices  62  form a second continuous matrix of interstices  62  known as the interstitial matrix  68 , containing the binder-catalyzing material. In addition, there are necessarily a relatively few areas where the diamond to diamond growth has encapsulated some of the binder-catalyzing material. These ‘islands’ are not part of the continuous interstitial matrix  68  of binder-catalyzing material  64 .  
      Referring now to  FIGS. 7 and 9 , shown is a cross section of the PCD element  2  of the present invention. The PCD element  2  may be formed in the same manner as the prior art PCD elements described above. In a preferred embodiment, after a preliminary cleanup operation or at any time thereafter in the process of manufacturing, the working surface  4 ,  70 ,  72  of the PCD element  2  is processed in a manner which removes a portion of the binder-catalyzing material from the adjacent body. The result is that the interstices  62  among the diamond crystals  60  adjacent to the working surface are substantially free of the catalyzing material  64  indicated by numeral  66 . The portion of the working surface  4 ,  70 ,  72  that is free of the catalyzing material  64  is not subject to the thermal degradation encountered in the other areas of the PCD, resulting in improved thermal characteristics.  
      There are many methods for removing or depleting the catalyzing material  64  from the interstices  62 . In one method, the catalyzing material  64  is cobalt or other iron group material, and the method of removing the catalyzing material  64  is to leach it from the interstices  62  near the working surface  4 ,  70 ,  72  of a PCD element  2  in an acid etching process to a depth of greater than about 0.2 mm. It is also possible that the method of removing the catalyzing material  64  from near the surface may be by electrical discharge, or other electrical or galvanic process or by evaporation.  
      In another method for depleting the catalyzing material  64  from the interstices  62 , the catalyzing material  64  is depleted by combining it chemically, such as alloying, with another material such that it no longer acts as a catalyzing material. In this method, a material may remain in the interstices among the diamond crystals  60 , but that material no longer acts as a catalyzing material  64 —effectively removing it.  
      In still another method for depleting the catalyzing material  64  from the interstices  62 , the catalyzing material  64  is removed by causing it to transform into a material that no longer acts as a catalyzing material. This may be accomplished by a crystal structure change, phase change, mechanical ‘working’, thermal treatment or other treatment methods. This method may apply to non-metallic or non-reactive catalyzing materials. Again, a material may remain in the interstices  62  among the diamond crystals, but that material no longer acts as a catalyzing material  64 —effectively removing the catalyzing material.  
      Once the catalyzing material  64  adjacent to the working surface  4 ,  70 ,  72  has been rendered ineffective, the PCD element  2  of the present invention is no longer susceptible to the type of thermal degradation known to occur in the prior art PCD elements. As previously described, there are two modes of thermal degradation known to be caused by the catalyzing material  64 . The first mode of thermal degradation begins at temperatures as low as about 400 degrees C. and is due to differential thermal expansion between the catalyzing material  64  in the interstices  62  and the crystals  60 . Upon sufficient expansion the diamond-to-diamond bonding may be ruptured and cracks and chips may occur.  
      The second mode of thermal degradation begins at temperatures of about 750 degrees C. This mode is caused by the catalyzing ability of the binder-catalyzing material  64  contacting the crystals  60 , and causing the crystals  60  to graphitize as the temperature nears 750 degrees C. As the crystals  60  graphitize, they undergo a huge volume increase resulting in cracking and dis-bond from the body  4 . Even a thickness of a few microns of the catalyzing material  64  on the surfaces of the diamond crystals  60  can enable this mode of thermal degradation.  
      It would therefore be appreciated by those skilled in the art that for maximum benefit, the catalyzing material  64  must be removed both from the interstices  62  among the diamond crystals  60  and from the surfaces of the diamond crystals  60  as well. If the catalyzing material  64  is removed from both the surfaces of the diamond crystals  60  and from the interstices  62  the onset of thermal degradation for the diamond crystals  60  in that region would approach 1200° C.  
      This dual degradation mode, however, provides some unexpected benefits. For example, in many applications it is desirable to engineer the wear rate of the working surface. In the present invention, this may be accomplished by changing the treatment process such that in areas requiring maximum wear resistance, the catalyzing material is depleted from both the interstices  62  and the surfaces of the diamond crystals  60 . In areas where less wear resistance is desired, for example in a self sharpening tool, those areas would be treated so as to deplete the catalyzing material  64  primarily from the interstices  62 , but allowing some, if not all, of the diamond crystals  60  to remain in contact with the catalyzing material.  
      It should also be apparent, that it is more difficult to remove the catalyzing material  64  from the surfaces of the diamond crystals  60  than from the interstices  62 . For this reason, depending upon the manner in which the catalyzing material is depleted, to be effective in reducing thermal degradation, the depth of depletion of the catalyzing material  64  from the working surface  4  may vary depending upon the method used for depleting the catalyzing material  64 .  
      In some applications, improvement of the thermal threshold to above 400 C but less than 750 C is adequate, and therefore a less intense catalyzing material  64  depletion process is permissible. As a consequence, it would be appreciated that there are numerous combinations of catalyzing material  64  depletion methods which could be applied to achieve the level of catalyzing material  64  depletion required for a specific application.  
      In this specification, when the term ‘substantially free’ is used referring to catalyzing material  64  in the interstices  62 , the interstitial matrix  68 , or in a volume of the body  8 , it should be understood that many, if not all, the surfaces of the adjacent diamond crystals  60  may still have a coating of the catalyzing material  64 . Likewise, when the term ‘substantially free’ is used referring to catalyzing material  64  on the surfaces of the diamond crystals  60 , there may still be catalyzing material  64  present in the adjacent interstices  62 .  
      With the catalyzing material  64  removed or depleted, two major mechanisms for thermal degradation are no longer present. However, it has been found that the catalyzing material  64  has to be removed at a depth sufficient to allow the bonded crystals  60  to conduct away the heat generated by a thermal event to below the degradation temperature of the crystals  60  where the catalyzing material  64  is present.  
      In one set of laboratory tests, heat was input into a PCD element  2  configured as a cutting element  10 . Since this test was designed as a standard wear test for these cutting elements, it provided a reasonable comparison of cutting elements  10  with various depths of the catalyzing material  64  removal. In these tests, care was taken to assure the depletion process removed the catalyzing material  64  from both the interstices  62  and from the surfaces of the diamond crystals  60 . The test was designed such that a repeatable input of heat was applied to the cutting edge of the PCD cutting element  10  for a known period of time.  
      Once the test was complete, a wear index was calculated. The higher the wear index, the better the wear resistance. Due to the nature of the test, it is assumed that an increased wear index number indicates increased resistance to thermal degradation of the working surface  70 ,  72  of the cutting element  10 .  
      As can be seen in curve A in the graph of  FIG. 10  there is a dramatic increase in the wear index result for cutting elements  10  when the catalyzing material  64  depletion depth approaches 0.1 mm. Therefore, for the types of heat input common in cutting elements  10 , a 0.1 mm depth is the critical depletion depth from the working surface  4 ,  70 ,  72  when the catalyzing material  64  is removed from both interstices  62  and from the surfaces of the diamond crystals  60 .  
      In other tests, on cutting elements  10  made with a more economical process for removing the catalyzing material  64 , the wear versus depth of depletion is believed to approximate that shown in curve ‘B’ of  FIG. 10 . The catalyzing material  64  depletion process used in these cutters was not as effective for removing the catalyzing material  64  from the surfaces of the diamond crystals  60  as the process of curve ‘A’. Therefore, it was not until most of the catalyzing material  64  was removed from the interstices  62  to a depth of about 0.2 mm that the wear rate improved to that of curve ‘A’.  
      It is believed that thermal degradation relating to wear rates as shown in curve ‘C’ of  FIG. 10  can be engineered into PCD elements  2  where it is beneficial. For example, it may be desirable to have edges of curved cutting elements  10  remote from the center of contact to wear more quickly than the center point. This would tend to preserve the curved shape of the cutting element, rather than having it become a flat surface.  
      Improved thermal degradation resistance improves wear rates because diamond is an extremely good thermal conductor. If a friction event at working surface  4 ,  70 ,  72  caused a sudden, extreme heat input, the bonded diamond crystals would conduct the heat in all directions away from the event. This would permit an extremely high temperature gradient through the material, possibly 1000 C per mm or higher. A gradient this steep would enable the working surface  4 ,  70 ,  72  to reach 950 C, and not cause significant thermal degradation if interstices  62  and the surfaces of the diamond crystals  62  adjacent to the working surface are substantially free of the catalyzing material  64  to a depth of just 0.2 mm from the source of the heat.  
      It should be apparent that the temperature gradient will vary depending upon the crystal  60  size and the amount of inter-crystal bonding. However, in field tests of cutting elements  10  for earth boring bits, removal of substantially all of the catalyzing material  64  from the interstices  62  to a distance D of about 0.2 mm to about 0.3 mm from a working surface  4 ,  70 ,  72  produced dramatic improvements in wear resistance, with a combination of a 40% increase in rate of penetration and a 40% improvement in wear resistance. The improvement in wear resistance indicates that the attrition of the diamond crystals  60  due to catalyzing material  64  induced thermal degradation was dramatically reduced. The rate of penetration increase is believed to be due to the ability of the cutter to remain ‘sharper’ longer due to the increased wear resistance.  
      There are other possible constructions of PCD elements that benefit from depletion or removal of the catalyzing material  64  as described above. As shown in  FIGS. 11A, 11B  and  11 C another embodiment of the present invention is a compound PCD element  102 . The PCD element  102  has a body  108  with a group VIII binder-catalyzing material with a second preformed PCD element  110  embedded within it. The embedded PCD element  110  may be flush with the working surface  104  of the encapsulating PCD element  120  as shown in  FIG. 11A , or it may be embedded wholly within the encapsulating PCD element  120  as shown in  FIG. 11B . This embedded PCD element  110  is made in a process using powdery carbonates of Mg, Ca, Sr, and Ba as the binder-catalyzing material, and is formed into a compound PCD element as described in the commonly assigned co-pending U.S. patent application Ser. No. 09/390,074 herein incorporated by reference.  
      In this embodiment, since the embedded preformed PCD element  110  is formed at higher pressures, the diamond density may be made higher than that of the encapsulating PCD element  120 . In this construction since the embedded PCD element  110  has a catalyzing material with a higher activation temperature, it may for example, be beneficial to deplete the catalyzing material only in the working surface of the encapsulating PCD element  120 . Furthermore, the embedded PCD element  110  may be positioned within the encapsulating PCD element  120  to take advantage of the higher impact resistance of the embedded PCD element  110  combined with the improved wear resistance of the encapsulating element  120 .  
      As shown in  FIGS. 9, 11A ,  11 B, and  11 C, the element  102  has a plurality of partially bonded diamond crystals  60 , a catalyzing material  64  and a body  108  with a working surface  104 . The volume  112  of the body adjacent the working surface  104  has a substantially higher diamond density than elsewhere  114  in the body  108 , and the volume  112  is substantially free of the catalyzing material  64 .  
      Several embedded PCD elements  110  may be arranged in the compound element  100 , as shown in  FIG. 11C , in a manner where the best of both impact resistance and improved wear resistance may be realized.  
      It may be desirable to deplete the catalyzing material in the embedded PCD element  110  as well as the catalyzing material of the encapsulating PDC element  120 . This combination would provide an element with the highest possible impact strength combined with the highest possible wear resistance available in diamond elements for commercial use.  
      In  FIGS. 12A and 12B  another embodiment of the PCD element  202  of the present invention is shown. In this embodiment, the PCD element  202  is first formed in the manner of the prior art. After a surface has been prepared, a CVD or PVD process is used to provide a closely packed set of epitaxially oriented crystals of diamond  260  deposited upon a future working surface  204  on a portion  210  of the PCD element  202 . The assembly is then subjected to a high-pressure high-temperature process whereby the deposited diamond crystals  260  form diamond to diamond bonds with each other, and to the diamond crystals in the parent PCD. This diamond-to-diamond bonding is possible due to the presence of the catalyzing material  64  infusing from the surface of parent PCD element  202 .  
      After cleanup, a portion of the working surface  204  is treated to deplete the catalyzing material  64  from the CVD or PVD deposited layer. The final product is a PCD element having one portion of a working surface  204  with a volume  214  much higher in diamond density than that of the other surfaces  280  of the PCD element  202 . This region  214  of high diamond density is subsequently depleted of the catalyzing material  64 . Portions of the other surfaces  280  of the PCD element  202  may be depleted of the binder catalyzing material as well.  
      In general the elements  102 ,  202  shown in  FIGS. 11A, 11B ,  11 C,  12 A, and  12 B may be characterized as PCD element  102 ,  102  having a body  108 ,  208  with a working surface  104 ,  204 . The diamond density adjacent the working surface  104 ,  204  is substantially higher than elsewhere in the body  108 ,  208 , and is substantially free of the catalyzing material  64 .  
      One particularly useful application for the PCD element  2  of the present invention is as cutting elements  10 ,  50 ,  52  as shown in  FIGS. 1B, 4  and  5 . The working surface of the PCD cutting elements  10 ,  50 ,  52  may be a top working surface  70  and/or a peripheral working surface  72 . The PCD cutting element  10  of  FIG. 1B  is one that may be typically used in fixed cutter type rotary drill bits  12 , or for gauge protection in other types of downhole tools. The PCD cutting element  50  shown in  FIG. 5  may be shaped as a dome  39 . This type of PCD cutting element  50  has an extended base  51  for insertion into sockets in a rolling cutter drill bit  38  or in the body of both types of rotary drill bits,  12 ,  38  as will be described in detail.  
      The PCD cutting element  52  of  FIG. 4  is adapted for use in a machining process. Although the configuration of the cutting element  52  in  FIG. 4  is rectangular, it would be appreciated by those skilled in the art that this element could be triangular, quadrilateral or many other shapes suitable for machining highly abrasive products that are difficult to machine with conventional tools.  
      The PCD cutting element  10  may be a preform cutting element  10  of a fixed cutter rotary drill bit  12  (as shown in  FIG. 2 ). The bit body  14  of the drill bit is formed with a plurality of blades  16  extending generally outwardly away from the central longitudinal axis of rotation  18  of the drill bit. Spaced apart side-by-side along the leading face  20  of each blade is a plurality of the PCD cutting elements  10  of the present invention.  
      Typically, the PCD cutting element  10  has a body in the form of a circular tablet having a thin front facing table  30  of diamond or diamond-like (PCD) material, bonded in a high-pressure high-temperature press to a substrate  32  of less hard material such as cemented tungsten carbide. The cutting element  10  is preformed and then typically bonded on a generally cylindrical carrier  34  which is also formed from cemented tungsten carbide, or may alternatively be attached directly to the blade. The PCD cutting element  10  has working surfaces  70  and  72 .  
      The cylindrical carrier  34  is received within a correspondingly shaped socket or recess in the blade  16 . The carrier  34  will usually be brazed or shrink fit in the socket. In operation the fixed cutter drill bit  12  is rotated and weight is applied. This forces the cutting elements  10  into the earth being drilled, effecting a cutting and/or drilling action.  
      The PCD cutting elements  10  may also be applied to the gauge region  36  of the bit  12  to provide a gauge reaming action as well as protecting the bit  12  from excessive wear in the gauge region  36 . In order to space these cutting elements  10  as closely as possible, it may be desirable to cut the elements into shapes, such as the rectangular shape shown, which more readily fit into the gauge region  36 .  
      In a second embodiment, the cutting element  50  (as shown in  FIG. 5 ) of the present invention is on a rolling cutter type drill bit  38 , shown in  FIG. 3 . A rolling cutter drill bit  38  typically has one or more truncated rolling cone cutters  40 ,  41 ,  42  assembled on a bearing spindle on the leg  44  of the bit body  46 . The cutting elements  50  may be mounted as one or more of a plurality of cutting inserts arranged in rows on rolling cutters  40 ,  41 ,  42 , or alternatively the PCD cutting elements  50  may be arranged along the leg  44  of the bit  38 . The PCD cutting element  50  has a body in the form of a facing table  35  of diamond or diamond like material bonded to a less hard substrate  37 . The facing table  35  in this embodiment of the present invention is in the form of a domed surface  39  and has working surfaces  70  and  72 . Accordingly, there are often a number of transitional layers between the facing table  35  and the substrate  37  to help more evenly distribute the stresses generated during fabrication, as is well known to those skilled in the art.  
      In operation the rolling cutter drill bit  38  is rotated and weight is applied. This forces the cutting inserts  50  in the rows of the rolling cone cutters  40 ,  41 ,  42  into the earth, and as the bit  36  is rotated the rolling cutters  40 ,  41 ,  42  turn, effecting a drilling action.  
      In another embodiment, the PCD cutting element  52  of the present invention is in the form of a triangular, rectangular or other shaped material for use as a cutting insert in machining operations. In this embodiment, the cutting element  52  has a body in the form of a facing table  54  of diamond or diamond like material bonded to a less hard substrate  56  with working surfaces  70  and  72 . Typically, the cutting element  52  would then be cut into a plurality of smaller pieces which are subsequently attached to an insert  58  that is mounted in the tool holder of a machine tool. The cutting element  52  may be attached to the insert by brazing, adhesives, welding, or clamping. It is also possible to finish form the cutting element  52  in the shape of the insert in a high-temperature high-pressure manufacturing process.  
      As shown in  FIGS. 13-18 , PCD elements  2 ,  102 ,  202  of the present invention may also be used for other applications such as hollow dies, shown for example as a wire drawing die,  300  of  FIG. 13  utilizing a PCD element  302  of the present invention. It may also be desirable to utilize the excellent heat transfer capabilities of the PCD element  2 ,  102 ,  202  along with its electrical insulation properties as a heat sink  310  with a PCD element  312  of the present invention.  
      Other applications include friction bearings  320  with a PCD bearing element  322  shown in  FIG. 15  and the mating parts of a valve  340 ,  344  with surfaces  342  having a PCD element  342  of the present invention as shown in  FIGS. 16A and 16B . In addition, indentors  360  for scribes, hardness testers, surface roughening, etc. may have PCD elements  362  of the present invention as shown in  FIG. 17A . Punches  370  may have either or both dies  372 ,  374  made of the PCD material of the present invention, as shown in  FIG. 17B . Also, tool mandrels  382  and other types of wear elements for measuring devices  380 , shown in  FIG. 18  may be made of PCD elements of the present inventions. It should be understood that almost every application for polycrystalline diamond would benefit from the catalyzing material depleted PCD elements of the present invention.  
      Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.