Abstract:
A cutting element, insert or compact, is provided for use with drills used in the drilling and boring of subterranean formations or in machining of metal, composites or woodworking. This new insert besides having a superabrasive layer on the surface of a substrate, also may have one or more superabrasive core element sections incorporated in the substrate to provide improved internal residual stress characteristics. By so manipulating residual stresses, this invention provides cutting elements, which are more fracture resistant thereby providing improved work life. Also, by providing additional superabrasive material in the substrate, this invention improves the cutting efficiency of the compact after the compact has undergone significant wear. Another embodiment of this invention employs one or more carbide core regions within a superabrasive region, which covers the majority of the outer surface of the insert.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to devices for drilling and boring through subterranean formations. More specifically, this invention relates to polycrystalline diamond compacts (PDCs), also known as cutting elements or diamond inserts, which are intended to be installed as the cutting element of a drill bit to be used for boring through rock in any application, such as oil, gas, mining, and/or geothermal exploration, requiring drilling through geological formations. Still more specifically, this invention relates to polycrystalline diamond inserts, which have a fully enclosed alternative material structure to minimize high tensile stresses in the diamond compact, minimize crack propagation, and to enhance abrasion resistance. 
     2. Description of Related Art 
     Polycrystalline diamond compacts (PDCs) are used in down hole tools, such as drill bits (including percussion bits; rolling cone bits, also referred to as rock bits; and drag bits, also called fixed cutter bits), reamers, stabilizers and tool joints. A number of different configurations, materials and geometries have been previously suggested to enhance the performance and/or working life of the PDC. Typically, PDCs have uniform internal regions, either being solid diamond, or, more commonly having a relatively thin diamond layer on the top or cutting surface of a solid carbide structure. 
     By way of introduction, a polycrystalline diamond compact (PDC), or cutting element, is typically fabricated by placing a cemented tungsten carbide substrate into a refractory metal container (can) with a layer of diamond crystal powder placed into the can adjacent to one face of the substrate. Additional cans are used to completely enclose the diamond powder and the carbide substrate. A number of such can assemblies are loaded into a high-pressure cell made from a low thermal conductivity extrudable material such as pyrophyllite or talc. The loaded high-pressure cell is then placed in a high-pressure press. The entire assembly is compressed under high pressure and temperature conditions. This causes the metal binder from the cemented carbide substrate to sweep from the substrate face through the diamond grains and to act as a reactive phase to promote the sintering of the diamond grains. The sintering of the diamond grains causes the formation of a polycrystalline diamond structure. As a result the diamond grains become mutually bonded to form a diamond mass over the substrate face. The metal binder may remain in the diamond layer within the pores of the polycrystalline structure or, alternatively, it may be removed via acid leaching and optionally replaced by another material forming so-called thermally stable diamond (TSD). Variations of this general process exist and are described in the related art. This detail is provided so the reader may become familiar with the concept of sintering a diamond layer onto a substrate to form a PDC insert. For more information concerning this process, the reader is directed to U.S. Pat. No. 3,745,623, issued to Wentorf Jr. et al., on Jul. 7, 1973. 
     For general background material, the reader is directed to the following United States Patents, each of which is hereby incorporated by reference in its entirety for the material contained therein. 
     U.S. Pat. No. 4,259,090 describes an improvement in the manufacture of diamond compacts in which a cylindrical mass of polycrystalline diamond is surrounded by and bonded to an outer mass of metal which provides support for the diamond. 
     U.S. Pat. No. 4,380,471 describes a polycrystalline diamond body infiltrated by a silicon atom-containing metal is bonded to a substrate, that comprises cemented carbide with a barrier of refractory material extending between the diamonds cemented together with silicon atom-containing binder and substrate substantially precluding migration of the cemented medium from the carbide substrate into contact with the silicon atom-containing bonding medium in the diamond body. 
     U.S. Pat. No. 4,466,938 describes a process for making compacts containing diamond, which reduces crystal flaws within the diamond. 
     U.S. Pat. No. 4,592,433 describes a cutting blank, preferably for use on a drill bit for cutting through earth formations, that comprises a substrate formed of a hard material and includes a cutting surface, with a plurality of shallow grooves, with strips of diamond disposed in the grooves. 
     U.S. Pat. No. 4,714,120 describes an earth boring bit that has a body with one end connected to a drill string member for rotation and has an opposite end with a matrix formed thereon. A plurality of cutting elements are mounted on the matrix for dislodging geological formations. 
     U.S. Pat. No. 4,984,642 describes a composite tool that comprises a sintered metal carbide support and a polycrystalline diamond active part having an inner surface of metallurgical connection to the support and an outwardly facing working surface. 
     U.S. Pat. No. 5,007,493 describes a cutting element retention system for a diamond drill bit. 
     U.S. Pat. No. 5,011,515 describes a compact blank for use in operations that require very high impact strength and abrasion resistance. 
     U.S. Pat. Nos. 5,045,092 and 5,158,148 describe cemented tungsten carbide rock bit inserts that has diamond particles dispersed therein for enhanced hardness and wear resistance. 
     U.S. Pat. No. 5,119,714 describes an earth boring bit of the type having one or more rotatable cones secured to bearing shafts, a cutting structure having diamond compacts used as wear resistant inserts. 
     U.S. Pat. No. 5,159,857 describes a single piece earth boring bit of the type having a body that includes a solid bit face on one end and a shank on the opposite end for connection in a drill string, and a cutting structure having diamond compacts used as wear resistant inserts. 
     U.S. Pat. No. 5,173,090 describes a method for manufacturing a diamond compact of the type used as a cutting insert. 
     U.S. Pat. No. 5,195,403 describes a method of producing a composite cutting insert for a twist drill that includes the steps of cutting an intermediate blank from a composite diamond compact. 
     U.S. Pat. No. 5,248,006 describes an earth boring bit of the type having one or more rotatable cones secured to bearing shafts, an improved cutting structure having diamond compacts used as wear resistant inserts. 
     U.S. Pat. No. 5,273,125 describes a single piece earth boring bit of the type having a body that includes a solid bit face on one end and a shank on the opposite end for connection in a drill string, an improved cutting structure having diamond compacts used as wear resistant inserts. 
     U.S. Pat. No. 5,310,512 describes a method and apparatus for producing a non-planar synthetic diamond structure of predetermined shape. 
     U.S. Pat. No. 5,441,817 describes a method for making diamond and CBN composites, under HP/HT conditions. 
     U.S. Pat. No. 5,451,430 describes a stress relieved CVD diamond that is produced by annealing said CVD diamond at a temperature above about 1100 to about 2200 degrees Centigrade in an non-oxidizing atmosphere at a low pressure or vacuum and for a suitable short period of time, which decreases with increasing annealing temperature so as to prevent graphitization of said diamond. 
     U.S. Pat. No. 5,469,927 describes a preform cutting element, particularly for a drag-type rotary drill bit, comprises a thin cutting table of polycrystalline diamond, a substrate of cemented tungsten carbide, and a transition layer between the cutting table and substrate, cutting table, transition layer, and substrate having been bonded together in a high pressure, high temperature press. 
     U.S. Pat. No. 5,484,330 describes an abrasive tool insert that comprises a cemented metallic substrate and a polycrystalline diamond layer formed thereon by high pressure, high temperature processing. 
     U.S. Pat. No. 5,486,137 describes an abrasive tool insert having an abrasive particle layer having an upper surface, an outer periphery, and a lower surface integrally formed on a substrate, which defines an interface therebetween. 
     U.S. Pat. No. 5,494,477 describes an abrasive tool insert that comprises a cemented substrate and a polycrystalline diamond layer formed thereon by high pressure, high temperature processing. 
     U.S. Pat. No. 5,501,909 describes a diamond substrate having a smooth surface, including a polycrystalline diamond film having a surface with a pit, and an insulating material other than diamond, which occupies the pit. 
     U.S. Pat. Nos. 5,510,193 and 5,603,070 describe a metal carbide supported polycrystalline diamond (PCD) compacts that have improved shear strength and impact resistance properties, and a method for making the same under high temperature/high pressure (HT/HP) processing conditions. 
     U.S. Pat. No. 5,524,719 describes an insert for drill bits that is formed with an elongate body, typically having a cylindrical cross section terminating at an exposed outer end, which is covered with a polycrystalline disc. The polycrystalline disk is reinforced with an insert, which is wholly captured in the polycrystalline material. 
     U.S. Pat. No. 5,560,754 describes a polycrystalline diamond and cubic boron nitride (CBN) composite compact and a method for making the same under high temperature/high pressure (HT/HP) processing. 
     U.S. Pat. No. 5,590,729 describes a cutting element for a rotary drill bit that includes a substantially planar table of superhard material having a cutting face and a cutting edge. The table may be reinforced against bending with one or more strut portions extending from the rear of the substrate and at least partially across the cutting element. 
     U.S. Pat. No. 5,662,720 describes a cutting element that comprises a diamond layer and metal carbide substrate. The diamond layer and the metal carbide substrate form an egg-carton shaped interface. 
     U.S. Pat. No. 5,669,271 describes a preform cutting element for a drag-type rotary drill bit that includes a facing table of polycrystalline diamond bonded to a less hard substrate, such as cemented tungsten carbide. 
     U.S. Pat. No. 5,672,395 describes a method for treating as as-grown chemical vapor deposited (CVD) starting diamond film having stresses and containing voids. 
     U.S. Pat. No. 5,743,346 describes an abrasive cutting element comprised of an abrasive cutting layer and a metal substrate wherein the interface therebetween has a tangential chamfer, the plane of which forms an angle of about 5 degrees to about 85 degrees with the plane of the surface of the cylindrical part of the metal substrate. 
     U.S. Pat. No. 5,804,321 describes a unitary article that is solid at a temperature in excess of about 1100 degrees Centigrade, which includes a diamond, a metal, and a brazing material brazing the diamond and the metal. 
     U.S. Pat. No. 5,819,862 describes downhole components for use in subsurface drilling. 
     U.S. Pat. No. 5,820,985 describes a polycrystalline diamond layer attached to a cemented metal carbide structure used as a cutter wherein the cutter has improved toughness or fracture resistance during use through the boron, beryllium or the like therein. 
     SUMMARY OF THE INVENTION 
     In drill bits, which are used to bore through subterranean geologic formations, it is often desirable to provide a compact that avoids high tensile stresses in the diamond layer, while providing diamond compression to minimize diamond crack propagation. Moreover, it is desirable to provide a polycrystalline diamond cutter that has an additional diamond region, which will be exposed after the cutter has worn sufficiently to erode the carbide wall. 
     Therefore, it is an object of this invention to provide a PDC with an internal diamond core in the substrate, to provide additional diamond for exposure when the substrate is sufficiently eroded. 
     It is a further object of this invention to provide a PDC with an internal carbide core, which is entirely enclosed by the diamond region of the PDC cutter, to avoid high tensile stresses in the diamond region. 
     It is a further object of this invention to provide a PDC with increased diamond mass for abrasion resistance. 
     It is a further object of this invention to provide a PDC with improved internal stress characteristics. 
     It is a further object of this invention to provide a PDC, with reduced crack propagation in the diamond portion of the PDC. 
     These and other objectives, features and advantages of this invention, which will be readily apparent to those of ordinary skill in the art upon review of the following drawings, specification, and claims, are achieved by the invention as described in this application. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts a section view of a preferred PDC having a diamond region completely enclosed within the carbide substrate. 
     FIGS. 2 a-m  depict section views of alternative substrates with enclosed diamond regions of this invention. 
     FIGS. 3 a-k  depict section views of preferred PDC embodiments having an entirely diamond outer surface, which encloses a metal substrate. 
     FIGS. 4 a, b  and  c  depict section views of preferred PDC embodiments having a diamond outer surface as well as enclosed diamond regions within the substrate. 
    
    
     Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention is intended for use in cutting tools, most typically roller cone bits, drag bits or fixed-cutter bits, percussion bits, and/or metal machining or woodworking tools. A typical bit or tool has a plurality of PDCs mounted on its cutting surface. When the bit is rotated, the leading edge of one or more PDCs comes into contact with the rock or work surface. During a drilling or machining operation, the stresses and pressures imposed on each PDC require that the PDC be capable of sustaining high stresses and that the diamond layer of the PDC be strong. Moreover, as the PDC comes into repeated contact with the work surface, residual stresses internal to the PDC can significantly diminish the working life of the PDC. This invention directly addresses the problem of PDC failure due to residual stresses by providing a PDC with a core having different material properties from the surrounding region. Such a PDC can provide tailored structural support and/or compressibility. The manipulation of the residual stress can thereby increase the working life of the PDC. Two general embodiments of this invention are presented in this disclosure. The first is a PDC having a carbide substrate and a superabrasive face region, which also has an integral diamond (or other superabrasive material) core within the substrate. The second embodiment is a PDC having a predominantly superabrasive outer surface, with at least one internal carbide core. The two embodiments may also be employed jointly to further provide the advantages described above. A number of exemplary specific embodiments of each general embodiment are also described to provide the reader with an idea of the types of core geometry which are compatible and contemplated in this invention. For the purposes of this disclosure the term diamond shall be defined to mean polycrystalline diamond, polycrystalline cubic boron nitride or other superabrasive materials, which can be substituted for polycrystalline diamond in the manufacture of compacts or cutters for drilling, machining, woodworking, or the like. Also, for the purposes of this disclosure the term carbide shall be defined to be a material selected from one or more of the following materials: tungsten carbide, boron tetracarbide, tantalum carbide, titanium carbide, vandium carbide, niobium carbide, halfnium carbide, zirconium carbide, or the like. 
     FIG. 1 shows the section view of a preferred embodiment of a PDC  100 . This PDC  100  has a carbide substrate  101  into which a cavity  105  is provided. Within the cavity  105  a diamond core  103  is sintered in place. Atop the diamond core  103  a carbide region  104  provides a cover for the diamond core  103  and acts as a buffer region for the diamond surface region  102  sintered to form the top cutting surface  106  of the PDC  100 . In this preferred embodiment  100  of the invention the carbide regions  101 ,  104  completely surround the diamond core  103 . Although, as the PDC  100  wears in use both the diamond surface region  102  and the carbide  101 ,  104  may wear away exposing the diamond core  103  and providing additional cutting life of the PDC  100 . The diamond core  103  may or may not be the same material composition as the diamond surface region  102  and the carbide substrate  101  may or may not necessarily be the same material composition as the carbide region  104 . 
     FIGS. 2 a-m  show a variety of different embodiments of this invention having a carbide substrate with enclosed diamond regions. These figures are intended to be examples of the variety of embodiments of PDCs of this invention and are not intended to be exhaustive or limiting. 
     FIG. 2 a  shows the cross section of an alternative embodiment of the PDC  200  of this invention. A carbide substrate  201  is provided with a cavity  206 , within which a diamond core  203  is sintered in place. A carbide region  204  provides a cover for the diamond core  203  and provides a carbide buffer for the diamond surface region  202 , which is sintered to the carbide substrate  201  and the carbide region  204  to provide the cutting surface  207 . This embodiment  200  of the invention is provided with a ring  205  of diamond extending from the diamond surface region  202  into the carbide substrate  201  to provide improved adhesion properties. Again, in this embodiment  200  of the invention the carbide regions  201 ,  204  completely surround the diamond core  203 . Although, as the PDC  200  wears both the diamond surface region  202  and the carbide  201 ,  204  may wear away exposing the diamond core  203  and providing additional cutting life of the PDC  200 . The diamond core  203  may or may not be the same material composition as the diamond surface region  202  and the carbide substrate  201  may or may not necessarily be the same material composition as the carbide region  204 . 
     FIG. 2 b  shows the cross section of an alternative embodiment  208  of the PDC of this invention. A carbide substrate  209  is provided having a recesses  213   a-c , within which diamond cores  210   a-c  are sintered in place. A outer diamond region  211  is provided on the top surface  212   a  of the substrate  209 . In this embodiment  208  the diamond cores  210   a-c  and the diamond surface region  211  are separate diamond regions, having intervening carbide layers. The top surface  212   b  of the diamond surface region  211  provides the cutting surface of the PDC  208 . 
     FIG. 2 c  shows the cross section of an alternative embodiment  214  of the PDC of this invention. A carbide substrate  215   a  is provided having a deep recess  218 , within which a diamond core  216  is sintered in place along with a second carbide region  215   b.  In this embodiment  214  the diamond core  216  and the diamond surface region  217  are separate bodies of diamond material, with an intervening carbide layer  215   b.  The top surface  219  of the diamond surface region  217  provides the cutting surface of the PDC  214 . 
     FIG. 2 d  shows the cross section of an alternative embodiment  220  of the PDC of this invention. A carbide substrate  221  is provided having an internal cavity  224 , within which a diamond core  222  is sintered in place. A second carbide region  242  is provided to enclose the diamond core  222 . In this embodiment  220 , the carbide substrate  221  and the second carbide region  242  fully enclose the diamond core  222 . Sintered to the top surface  225  of the carbide substrate  221  is a diamond surface region  223 , the top surface  226  of which provides the cutting surface of the PDC  220 . In this embodiment  220  of this invention, the diamond core  222  may or may not necessarily be composed of the same material composition as the diamond surface region  223 . 
     FIG. 2 e  shows the cross section of an alternative embodiment  227  of the PDC of this invention. A carbide substrate  228   a  is provided having an internal channel  229  running essentially completely from the top  233  to the bottom  234 , through essentially the center  235 , of the substrate  228 . Within this channel  229  a diamond core  230  is sintered and two carbide segments  228   b,c  provide carbide layers to the diamond core  230  and the diamond surface region  231 . In this embodiment  227  of the invention, the diamond core  230  and the diamond surface region  231  are separate diamond regions, with an intervening carbide layer  228   b.  The top surface  232  of the diamond surface region  231  provides the cutting surface of the PDC  227 . 
     FIG. 2 f  shows the cross section of an alternative embodiment  236  of the PDC of this invention. A carbide substrate  237  is provided with a top surface  239   a  which has been ground or otherwise evacuated in order to provide a diamond surface region  239   b  that is separated from the diamond surface region  238  by an intervening carbide region  241 . This intervening carbide region  241  extends beyond the substrate  237  into the diamond surface region  238 . The top surface  240  of the diamond surface region  238  provides the cutting surface of the PDC  236 . 
     FIG. 2 g  shows the cross section of an alternative embodiment  244  of the PDC of this invention. A carbide substrate  245  is provided having multiple diamond regions  246  interspersed throughout. In this embodiment  244  the carbide substrate  245  completely encloses each diamond region  246 . Sintered to the top surface  249  of the carbide substrate  245  is a diamond surface region  247 , the top surface  248  of which provides the cutting surface of the PDC  244 . In this embodiment  244  of the invention, the diamond regions  246  may or may not be composed of the same material composition as the diamond surface region  247 . 
     FIG. 2 h  shows the cross section of an alternative embodiment  250  of the PDC of this invention. A carbide substrate  251  is provided with a diamond core  252  and diamond layer  253 , extending from the core  252 , sintered to the substrate  251  top surface  258 . A carbide ring  251   a  surrounds the periphery of the diamond region  252  ensuring that the diamond core  252  does not extend to the exterior sidewall  265  of the PDC. A second carbide region  254  is sintered to the diamond core  252  and diamond layer  253 , providing a buffer between the diamond core  252  and the diamond surface region  256 , which is sintered to the top surface  255  of the second carbide region  254 . The top surface  257  of the diamond surface region  256  provides the cutting surface of the PDC. In this embodiment  250  of the invention it is not necessary that the diamond surface region  256 , the diamond core  252 , or the diamond layer  253  be composed of the same material composition. Similarly, it is not necessary that the carbide substrate  251  and the second carbide region  254  be the same carbide material. 
     FIG. 2 i  shows the cross section of an alternative embodiment  259  of this invention. A carbide substrate  260  is provided having a number of recesses  264 , within which a number diamond core protrusions  261  are sintered in place. In this embodiment  259  the diamond core protrusions  261  and the diamond surface region  262  are portions of the same diamond material, without an intervening carbide layer. The top surface  263  of the diamond surface region  262  provides the cutting surface of the PDC  259 . In alternative embodiments of this  259  configuration of the invention, the protrusions  261  are not of the same diamond material as the diamond surface region  262 . It is also envisioned that a carbide gap may be used between the diamond surface region  262  and one or more of the protrusions  261 . 
     FIG. 2 j  shows the cross section of another alternative embodiment  261  of the invention. A carbide substrate  265  is provided which has a cavity  264  within which polycrystalline diamond  289  is sintered in place. This embodiment  261  has a generally hemispherical top surface  262 , which is covered with polycrystalline diamond  263 . A carbide region  266  and the carbide substrate  265  surround the internal diamond region  264   b.  The diamond surface  262  and the internal diamond region  264   b  may or may not necessarily be the same diamond material. 
     FIG. 2 k  shows the cross section of another alternative embodiment  267  of the invention. This embodiment  267 , like that of FIG. 2 j ,  261 , has a cavity  271  within the carbide substrate  272 , within which a polycrystalline diamond region  292  is sintered. The internal cavity  271  and internal polycrystalline diamond region  292  of this embodiment  267  has a convex upper surface  291  and a concave lower surface  290 . This embodiment  267  has a generally hemispherical top surface  268  that is covered by polycrystalline diamond  269 . Carbide regions  270 ,  272  surround the internal diamond region  292 . The diamond surface  269  and the internal diamond region  292  may or may not necessarily be the same diamond material. 
     FIG. 2 l  shows the cross section of another alternative embodiment  273  of the invention. A carbide substrate  278  is provided which has a cavity  293  within which polycrystalline diamond  277  is sintered in place. This embodiment  273  has a generally conical top surface  274 , which is covered with polycrystalline diamond  275 . A carbide region  276  and the carbide substrate  278  surround the internal diamond region  277 . The diamond surface  275  and the internal diamond region  277  may or may not necessarily be the same diamond material. 
     FIG. 2 m  shows the cross section of another alternative embodiment  279  of the invention. A carbide substrate  288  is provided which has three cavities  294 ,  295 ,  296  within each of which are polycrystalline diamond regions  283 ,  285 ,  287  sintered in place. This embodiment  279  has a generally conical top surface  280  which is covered with polycrystalline diamond  281 . The internal diamond regions  283 ,  285 ,  287  are surrounded by a carbide regions  282 ,  284 ,  286  and the carbide substrate  288 . The diamond surface  281  and the internal diamond regions  283 ,  28 ,  287  may or may not necessarily be the same diamond material. 
     While the FIGS. 2 a-m  show multiple regions of carbide and diamond, the reader should be aware that after the sintering process step the carbide components are sintered into one apparent carbide mass. Similarly, after sintering adjacent polycrystalline diamond regions are sintered together, forming a single diamond region. 
     FIGS. 3 a-k  show a variety of different embodiments of this invention having one or more carbide cores surrounded by diamond regions. These embodiments are intended to be examples of the variety of different embodiments of PDCs of this invention and are not intended to be either exhaustive or limiting. Moreover, these embodiments may, but are not required to, work in combination with a carbide substrate. In each of these, below illustrated embodiments, the carbide cores are typically sintered within the diamond regions, using a process that forms the diamond region and bonds the carbide region during the sintering process step or steps. 
     FIG. 3 a  shows the cross section of a first embodiment  300  of the diamond region of a PDC. In this embodiment  300 , diamond  305  completely surrounds an internal carbide core  310 . The carbide core  310  of this embodiment  300  has a cylindrical shape and is positioned generally in the center of the diamond region  305 . 
     FIG. 3 b  shows the cross section of a second embodiment  301  of the diamond region of a PDC. This embodiment has two or more carbide cores  311   a,b  arranged generally at the same depth within the diamond  306  portion of the PDC, with diamond interspaced there between. Alternatively, the carbide core  311  of this invention could also be a carbide ring—providing the same cross-sectional appearance. 
     FIG. 3 c  shows the cross section of a third embodiment  302  of the diamond region of a PDC. This embodiment has two carbide cores  312   a,b  arranged at different depths in the diamond portion  307  of the PDC, with diamond interspaced there between. 
     FIG. 3 d  shows the cross section of a fourth embodiment  303  of the diamond region of a PDC. This embodiment has a single carbide core  313 , which has a roughness imposed both on the top  315  and the bottom  316  of the carbide core  313  to enhance the adhesion properties of the carbide-diamond interface during wear of the PDC. In alternative embodiments of this invention any number of interface geometry&#39;s may be employed to enhance the attachment properties of the carbide-diamond interface. 
     FIG. 3 e  shows the cross section of a fifth embodiment  304  of the diamond region of a PDC. This embodiment has a single carbide core  314  with large protruding features  317  extending into the surrounding diamond region  309  to provide local compression at the diamond surface. 
     FIG. 3 f  shows the cross section of a sixth embodiment  318  of the diamond region of a PDC. This embodiment has a carbide core  320  and a relatively large surrounding diamond layer  319 . 
     FIG. 3 g  shows the cross section of a seventh embodiment  321  of the diamond region of a PDC. This embodiment has a carbide core  323  and has a relatively thin surrounding diamond layer  322 . 
     FIG. 3 h  shows the cross section of an alternative embodiment  324  of the diamond region of a PDC. In this embodiment  324 , diamond  326  completely surrounds an internal carbide core  327 . The carbide core  327  of this embodiment  324  has a generally cylindrical shape and is positioned generally in the center of the diamond region  326 . In this embodiment  324 , a generally hemispherical top shape  325  is imposed on the top surfaces  342 ,  343  of both the diamond layer  326  and the carbide core  327 . 
     FIG. 3 i  shows the cross section of a still further alternative embodiment  328  of the diamond region of a PDC. In this embodiment  328 , diamond  330  completely surrounds an internal carbide core  331 . The carbide core  331  of this embodiment  328  has a cylindrical shape with irregularities  340 ,  341  on the top surface  344  and the bottom surface  343  of the carbide core  331  and is positioned generally in the center of the diamond region  330 . The diamond region  330  is provided with a generally hemispheric top surface  329 . 
     FIG. 3 j  shows the cross section of an alternative embodiment  332  of the diamond region of a PDC. In this embodiment  332 , diamond  334  completely surrounds an internal carbide core  335 . The carbide core  335  of this embodiment  332  has a generally cylindrical shape and is positioned generally in the center of the diamond region  305 . In this embodiment  332  both the diamond region  334  and the carbide region  335  have a generally conic shaped top surfaces  333 ,  345 . 
     FIG. 3 k  shows the cross section of another alternative embodiment  336  of the diamond region of a PDC. In this embodiment  336 , diamond  338  completely surrounds an internal carbide core  339 . The carbide core  339  of this embodiment  336  has an irregular shape and is positioned generally in the center of the diamond region  338 . This embodiment  336  has a generally conic shaped top surface  337  to the diamond region  338   
     FIGS. 4 a, b  and  c  show a cross-sections of embodiments  401 ,  406 ,  415  of the invention employing features of both FIG.  1  and FIGS. 3 a-g,  by having carbide cores  405 ,  410 ,  421  surrounded by a relatively thin surrounding diamond layer  402 ,  407 ,  416 . Internal to the carbide cores  405 ,  410 ,  421  are a plurality of diamond regions  403 ,  404 ,  409 ,  411 ,  413 ,  418 ,  420 ,  422 ,  423 . In FIG. 4 b  the top surface  425  of the diamond layer  407  has a generally hemispherical shape and in FIG. 4 c  the top surface  426  of the diamond layer  416  has a generally conic shape. The internal diamond regions  409 ,  411 ,  413  and the diamond layer  407  of FIG. 4 b  are separated by intervening carbide regions  408 ,  410 ,  412 ,  414 . The internal diamond regions  418 ,  420 ,  422 ,  423  and the diamond layer  416  of FIG. 4 c  are separated by intervening carbide regions  417 ,  419 ,  421 ,  427 ,  424 . 
     The embodiments of the present invention are shown with a generally flat diamond surface and typically would be standard cylindrical PDCs, although, alternatively, oval, triangular, square, rectangular or other shaped PDCs are contemplated, as are diamond top surfaces with complex surface features including ribs, protrusions, recesses, buttons, channels, hemispherical, conic, convex and other cutting surface shapes. Also, it is contemplated that the periphery of the cutting surface would have a chamfer. Again, although the interfaces between the carbide regions are generally shown as smooth, it would also be possible to include in the interface a variety of mechanical modifications (e.g., ridges, protrusions, depressions, grooves, undulations or dimples, or chemical modifications) to enhance both the adhesion between the diamond and carbide, as well as the manipulation of stress between the materials employed. 
     The PDCs of this invention, as shown in FIGS. 1 and 2 a-m,  are typically and preferably fabricated by placing a carbide substrate, having a provided cavity, in a can assembly. Diamond crystals or grains are placed into the cavity in the carbide substrate. Additional carbide is placed in the cavity over the diamond. Next, additional diamond is placed over the finished substrate with the enclosed diamond core. The can assembly is then completed by placing additional cans around the carbide and diamond regions. High Pressure and High Temperature are applied, in a manner well known in the art, which allows the cobalt from the tungsten carbide to sweep through the diamond, thereby causing the sintering of the carbide diamond regions into the desired PDC structure. A number of such can assemblies can be loaded into a high-pressure press simultaneously. The result of the High Pressure/High Temperature press causes the metal binder from the substrate body and carbide core or layer to be swept to the diamond regions through the diamond crystals and to act as a reactive phase to thereby promote the sintering of the diamond grains to form a polycrystalline diamond structure bonded to a carbide substrate. As a result, the diamond grains become mutually bonded together forming one or more diamond masses. The heat and pressure is removed, after which, the PDC is removed from the can. The diamond is subsequently lapped to smooth and flatten the top diamond surface, if desired. A centerless grinding (“CG”) of the PDC is performed to bring the PDC to its final diameter and to remove the can material from the PDC. The PDC is next sized typically using a surface grinding operation, to finalize the length of the PDC. The typical final processing step is chamfering of the periphery of the top diamond surface and the carbide back surface. 
     The preferred processing method of the cutter elements shown in FIGS. 3 a-k  and  4   a-c  are typically manufactured by placing diamond into a can, onto which a carbide core is placed on the diamond surface. Additional diamond is added around the carbide core, completely enclosing it. The can assembly is completed prior to HP/HT pressing-sintering as described above. 
     The metal binder may remain in the diamond layer within the pores existing between the diamond grains or may be removed and optionally replaced by another material, as known in the art, to form a so-called thermally stable diamond. Where the binder is removed by leaching the diamond pores may be back-filled with silicon, or alternatively another material having a coefficient of thermal expansion similar to that of diamond. Variations of this general process exist in the art, but this detail is provided so that the reader will understand the general concept of sintering a diamond layer onto a substrate in order to form a cutter or insert. 
     Typically, the desired surface shape of the diamond layer is achieved by utilizing preformed cans. Alternatively, the surface shape can be formed by grinding or even through the use of etching, electrical discharge machining (“EDM”) or electrical discharge grinding (“EDG”), etc. 
     The described embodiments are to be considered in all respects only as illustrative of the current best mode of the invention known to the inventor at the time of filing the patent application, and not as restrictive. Although several of the embodiments shown here include particular diamond and/or carbide core geometry, these are intended to be examples of the best mode only and is not intended to be limiting. The scope of this invention is, therefore, indicated by the appended claims rather than by the foregoing description. All devices that come within the meaning and range of equivalency of the claims are to be embraced as within the scope of this patent.