Abstract:
A cutting element, insert or compact, is provided for use with drills used in the drilling and boring of subterranean formations. This new insert, in its preferred embodiment, has a “hoop” region of polycrystalline diamond extending around the periphery of the compact to reduce the residual stresses inherent in thick diamond regions of cutters. This compact has improved wear and durability characteristics because it avoids failures due to stresses, delaminations and fractures caused by the differences in thermal expansion coefficient between the diamond and the substrate during sintering. Moreover, this invention may provide multiple polycrystalline diamond edges as the PDC wears. This exposure of multiple polycrystalline diamond edges slows the rate of wear flat surface development and reduces the weight on the bit required for acceptable drill penetration rates.

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. 
     2. Description of Related Art 
     Polycrystalline diamond compacts (PDCs) are used with 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. The current trend in PDC design is toward relatively thick diamond layers. Typically, thick diamond layers bonded to a tungsten carbide substrate suffer from extremely high residual tensile stresses. These stresses arise from the difference in the thermal expansion between the diamond layer and the substrate after sintering at high temperature and high pressure. These stresses tend to increase with increasing diamond layer thickness. This stress contributes to the delamination and fracture of the diamond layer when the compact is used in drilling. 
     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. The components are then enclosed by additional cans. 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 cell is then placed in a high pressure press. The entire assembly is compressed under high pressure and high temperature conditions. This causes the metal binder from the cemented carbide substrate to “sweep” from the substrate face through the diamond crystals and to act as a reactive phase to promote the sintering of the diamond crystals. 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 leeching or 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. 
     While thicker diamond layers are often desirable to increase the wear life of the PDC, as described above, such increases in diamond layer thickness often induce internal stresses at the interface between the diamond and the tungsten carbide substrate interface. Previous approaches to minimize these internal stresses include modifying the geometry of the interface to change the pattern of residual stress. However, usually the change in residual stress is relatively minor because a non-planar interface has little effect on the residual stress distribution in a thick diamond layer. The non-planar features are generally so small as to be regarded as nearly planar in relation to the diamond table thickness on a thick diamond cutter. 
     A number of approaches to the manufacturing process and application of PDCs with thick diamond layers are well established in related art. The applicant includes the following references to related art patents for the reader&#39;s general familiarization with this technology. 
     U.S. Pat. No. 4,539,018 describes a method for fabricating cutter elements for a drill bit. 
     U.S. Pat. No. 4,670,025 describes a thermally stable diamond compact, which has an alloy of liquidus above 700° C. bonded to a surface thereof. 
     U.S. Pat. No. 4,690,691 describes a cutting tool comprised of a polycrystalline layer of diamond or cubic boron nitride which has a cutting edge and at least one straight edge wherein one face of the polycrystalline layer is adhered to a substrate of cemented carbide and wherein a straight edge is adhered to one side of a wall of cemented carbide which is integral with the substrate, the thickness of the polycrystalline layer and the height of the wall being substantially equivalent. 
     U.S. Pat. No. 4,767,050 describes a composite compact having an abrasive particle layer bonded to a support and a substrate bonded to the support by a brazing filler metal having a liquidus substantially above 700° C. disposed there between. 
     U.S. Pat. No. 4,802,895 describes a composite diamond abrasive compact produced from fine diamond particles in the conventional manner except that a thin layer of fine carbide particles is placed between the diamond particles and the cemented carbide support. 
     U.S. Pat. No. 4,861,350 describes a tool component, which comprises an abrasive compact bonded to a cemented carbide support body. The abrasive compact has two zones which are joined by an interlocking, common boundary. 
     U.S. Pat. No. 4,941,891 describes a tool component comprising an abrasive compact bonded to a support which itself is bonded through to an elongated cemented carbide pin. 
     U.S. Pat. No. 4,941,892 describes a tool component, which comprises an abrasive compact bonded to a support which itself is bonded through an alloy to an elongated cemented carbide pin. 
     U.S. Pat. No. 5,111,895 describes a cutting element for a rotary drill bit comprising a thin superhard table of polycrystalline diamond material defining a front cutting face, bonded to a less hard substrate. 
     U.S. Pat. No. 5,120,327 describes a composite for cutting in subterranean formations, which comprises a cemented carbide substrate and a diamond layer adhered to a surface of the substrate. 
     U.S. Pat. No. 5,176,720 describes a method of producing a composite abrasive compact. 
     U.S. Pat. No. 5,370,717 describes a tool insert, which comprises an abrasive compact layer having a working surface and an opposite surface bonded to a cemented carbide substrate along an interface. At least one cemented carbide projection extends through the compact layer from the compact/substrate interface to the working surface in which it presents a matching surface. 
     U.S. Pat. No. 5,469,927 describes a preform cutting element, which comprises a thin cutting table of polycrystalline diamond, a substrate of cemented tungsten carbide, and a transition layer between the cutting table and substrate. The interface between the cutting table and the transition layer is configured and non-planar to reduce the risk of spalling and delamination of the cutting table. 
     U.S. Pat. No. 5,472,376 describes a tool component, which comprises an abrasive compact layer bonded to a cemented carbide substrate along an interface. The abrasive compact layer has a working surface, on a side opposite to the interface, that is flat and presents a cutting edge or point around its periphery. A recess, having a side wall and a base both of which are located entirely within the carbide substrate, extends into the substrate from the interface. 
     U.S. Pat. No. 5,560,754 describes a method of making polycrystalline diamond and cubic boron nitride composite compacts, having reduced abrasive layer stresses, under high temperature and high pressure processing conditions. 
     U.S. Pat. No. 5,566,779 describes a drag bit formed of an elongate tooth made of tungsten carbide and having an elongate right cylinder construction. The end face is circular at the end of a conic taper. The tapered surface is truncated with two 180° spaced flat faces at 15° to about 45° with respect to the axis of the body. A PDC layer caps the end. 
     U.S. Pat. No. 5,590,727 describes a tool component comprising an abrasive compact, having a flat working surface which presents a cutting edge and an opposite surface bonded to a surface of cemented carbide substrate to define an interface having at least two steps. 
     U.S. Pat. No. 5,590,728 describes a preform cutting element for a drag-type drill bit that includes a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to a substrate which is less hard than the superhard material. The rear surface of the facing table is integrally formed with a plurality of ribs which project into the substrate and extend in directions outwardly away from an inner area of the facing table towards the peripheral surface thereof. 
     U.S. Pat. No. 5,647,449 describes a crowned insert. The end of the insert is crowned with a PDC layer integrally cast and bonded thereto so that the enlargement is fully surrounded by the PDC crown. 
     U.S. Pat. No. 5,667,028 describes a polycrystalline diamond composite cutter having a single or plurality of secondary PDC cutting surfaces in addition to a primary PDC cutting surface, where at least two of the cutting surfaces are non-abutting , resulting in enhanced cutter efficiency and useful life. The primary PDC cutting surface is a PDC layer on one end face of the cutter. The secondary PDC cutting surfaces are formed by sintering and compacting polycrystalline diamond in grooves formed on the cutter body outer surface. The secondary cutting surfaces can have different shapes such as circles, triangles, rectangles, crosses, finger-like shapes, or rings. 
     U.S. Pat. No. 5,685,769 describes a tool compact comprising an abrasive compact layer bonded to a cemented carbide substrate along an interface, with a recess provided that extends into the substrate from the interface. The recess has a shape of at least two stripes which intersect. 
     U.S. Pat. No. 5,706,906 describes a cutting element for use in drilling subterranean formations. 
     U.S. Pat. No. 5,711,702 describes a cutting compact having a superhard abrasive layer bonded to a substrate layer, where the configuration of the interface between the abrasive and the substrate layers is a non-planar, or three dimensional to increase the surface area between the layers available for bonding. 
     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 there between has a tangential chamfer the plane of which forms an angle of about 5° to about 85° with the plane of the surface of the cylindrical part of the metal substrate. 
     U.S. Pat. No. 5,766,394 describes a method for forming a polycrystalline layer of ultra hard material where the particles of diamond have become rounded instead of angular in a multiple roller process. 
     Each of the aforementioned patents and elements of related art is hereby incorporated by reference in its entirety for the material disclosed therein. 
     SUMMARY OF THE INVENTION 
     In drill bits, which are used to bore through subterranean geologic formations, it is desirable to manipulate the harmful stresses created at the superabrasive—substrate interface, the superabrasive surface, and/or at the location of cutter contact with the formation. When present such stresses can reduce the working life of the PDC by causing premature failure of the superabrasive layer. It is also desirable to have PDCs with increasingly thick diamond or cBN superabrasive layers. However, such thick diamond or cBN layers exacerbate the problem of residual stresses. In general, the most damaging tensile stress regions are located on the outer diameter of the cutter in the superabrasive diamond layer just above the diamond—carbide interface. High tensile stress regions may also be found on the cutting face. These stresses increase with increasing diamond layer thickness. On standard cutters, the relatively thin diamond table will be in compression near the center of the diamond face. This invention provides a geometry that manipulates the residual stresses and provides the increased strength and working life of thick diamond layers, by, in its preferred embodiment, providing a polycrystalline diamond layer that extends across the top and down the side of the PDC. A “hoop” of diamond is created about the perimeter of the cutter, which serves to significantly reduce the harmful residual stresses while producing a cutter having improved working life and cutting performance. Additionally, this “hoop” has been found to counteract the bending stress at the diamond—carbide interface. Moreover, the “hoop” induces compressive forces on the top surface and inner diameter of the diamond layer. These compressive forces serve as a barrier to crack propagation, thereby providing a considerable improvement in fracture toughness of the PDC. An additional benefit of the present invention is the creation of two cutting edges as the PDC wears. Typically, thick diamond cutters have large wear flats which tend to behave as bearing surfaces, requiring excessive weight on the bit for reasonable penetration rates. This invention addresses this issue because, although it behaves as a typical PDC cutter during initial wear, as the wear increases the wear flat becomes comprised of a carbide center portion surrounded by diamond, thereby creating two cutting edges. The second cutting edge slows the rate of wear flat development and reduces the weight requirement on the bit for acceptable bit penetration rates. 
     Therefore, it is an object of this invention to provide a PDC with an enhanced residual stress distribution. 
     It is a further object of this invention to provide a PDC with a “hoop” geometry that favorably manipulates the residual stresses associated with the differences in thermal expansion between the diamond and the substrate. 
     It is a further object of this invention to provide a PDC that provides the increased strength and working life of thick diamond layers without the associated increase in external diamond surface tensile stresses. 
     It is a further object of this invention to provide a PDC with a “hoop” region that counteracts the bending stresses at the diamond—carbide interface. 
     It is a further object of this invention to provide a PDC with a “hoop” region that provides compressive forces, which serve as a barrier to crack propagation, on the top surface and the inner diameter of the diamond layer of the cutter. 
     It is a further object of this invention to provide a PDC with a “hoop” region that exposes a plurality of cutting edges during normal wear of the cutter. 
     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 perspective view of the preferred embodiment of this invention. 
     FIG. 2 depicts a cross-section view of the preferred embodiment of the invention. 
     FIGS. 3 a  and  3   b  depict representative views of the preferred embodiment of the invention while in use. FIG. 3 a  shows the preferred PDC of this invention at initial wear conditions. FIG. 3 b  shows the preferred PDC of this invention at extended wear conditions. 
     FIGS. 4 a-l  show top and cross section views of a variety of alternative embodiments of the invention. 
     FIG. 5 shows the perspective view of an additional embodiment of the invention. 
     FIGS. 6 a-f  show cross-sectional views of a variety of alternative embodiments of the invention presented in FIG.  5 . 
     FIGS. 7 a-p  show top and cross-sectional views of additional alternative embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This invention is intended for use in cutting tools, most typically drag bits, roller cone bits and percussion bits used in oil and gas exploration, drilling, mining, excavating and the like. Typically the bit has a plurality of PDCs mounted on the bit&#39;s cutting surface. When the drill bit is rotated, the leading edge of one or more PDCs comes into contact with the rock surface. During the drilling operation, the stresses and pressures imposed on each PDC require that the PDC be capable of sustaining high internal stresses and that the diamond layer of the PDC be strong. The present invention is, in its preferred embodiment, a polycrystalline diamond compact (PDC) cutter with a polycrystalline diamond layer that extends fully across the top and around a portion of the sides of the PDC. The portion of the polycrystalline diamond layer that extends around some or all of the side of the PDC is referred to as a “hoop” region. The preferred thickness of the diamond layer down the side may or may not be the same as the thickness of the top surface of the diamond layer. The thickness selection is made based on the desired stress characteristics. For the purposes of this disclosure, thickness of the top surface of the polycrystalline diamond layer is defined as the distance from the top surface to the nearest carbide region. The thickness of the “hoop” portion of the polycrystalline diamond layer is defined as the distance from the outer edge of the side of the polycrystalline diamond layer to the nearest carbide region. The stress mitigation is controlled mainly by the hoop width  208  and the top layer thickness  207 . The diamond height on the outer diameter  210  is unimportant as long as the width  208  and the thickness  207  are appropriate. 
     FIG. 1 shows the perspective view of the preferred embodiment of this invention. This view depicts the exterior of the preferred PDC  100 . The polycrystalline diamond region  101  is shown fixed to a carbide substrate region  102 . The preferred bond  103  between the diamond region  101  and the carbide region  102  is accomplished using a sintering process although alternatively a brazing or chemical vapor phase deposition of the polycrystalline diamond can be used. The polycrystalline diamond region  101  is formed of diamond crystals bound together by a high pressure/high temperature process that forms the diamond crystals together into a solid diamond mass. Alternatively, a cubic boron nitride (cBN) or other superabrasive material layer can be substituted for the polycrystalline diamond layer  101 . The preferred substrate region  102  is composed of tungsten carbide, although alternative materials, including titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof, can be used for the substrate  102  material. Such superabrasive materials and substrate materials suitable for use in PDC are well known in the art. 
     FIG. 2 shows the cross-section view of the preferred embodiment of the invention. This view shows the “hoop”  201  region of the polycrystalline diamond layer  101  being bounded by a substrate  102  shelf  204  and a substrate  102  center region  203  side wall  206 . In this depiction of the preferred embodiment of the invention  100 , the top surface  202  and the sidewall  206  of the center region  203  are shown as being generally flat. Alternatively, irregularities, including but not limited to indentations, protrusions, grooves, channels, posts and the like may be imposed on the surface of the top surface  202  and/or the side wall  206 . Similarly, the shelf  204  is shown to be generally flat, although alternatively irregularities including but not limited to indentations, protrusions, grooves, channels, posts and the like may be imposed on the surface of the shelf  204 . Such alternative imposed surface features when used along with the “hoop”  201  of this invention should be considered within the scope of the invention. The thickness dimension  208  of the “hoop”  201  region may be either greater than, less than or equal to the thickness  207  of the top surface of the polycrystalline diamond layer  101 . 
     FIGS. 3 a  and  3   b  show representative views of the preferred embodiment of the invention under use. FIG. 3 a  shows the preferred PDC of this invention at initial wear conditions. This view provides a simplified diagram of the preferred PDC of this invention  100  being used to cut a surface  301 . A contact point  302  is shown in contact with the surface  301 . This view shows very little wear on the PDC  100 . An expanded view of the contact point, or wear flat  302  is shown  307 . This expanded view  307  shows the wear point  302  as exposing only polycrystalline diamond  308  of the polycrystalline diamond layer  101 . This is the typical wear flat  302  during the initial wear stage. FIG. 3 b  shows the preferred PDC of this invention at extended wear conditions. This view also provides a simplified diagram of the preferred PDC of this invention  100  being used to cut a surface  301 . A contact point  303  is shown in contact with the surface  301 . This view shows a significant amount of wear on the PDC  100 . An expanded view of the contact point, or wear flat  303  is shown  308 . This expanded view  308  shows the wear point  303  as exposing both the substrate  306 , material of the substrate  102 , and one or more polycrystalline cutting surfaces  304 ,  305  of the polycrystalline diamond layer  101 . This is the typical wear flat  303  during the extended wear stage of the preferred PDC  100 . 
     FIGS. 4 a-l  show top and cross section views of a variety of alternative embodiments of the invention. Referring to FIGS. 4 a  and  4   b , which are the top view and cross section view of an alternative embodiment  400  of the invention. FIG. 4 a  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  408  center region  432  bounded by a “hoop”  439  region of polycrystalline diamond  414 , as shown in a perspective drawing in FIG. 1. A shelf  426  is provided on which the “hoop”  439  region is attached to the substrate  408 . The intersection of the substrate  408  shelf  426  and substrate  408  center region  432  side wall  420  is rounded in this embodiment  400 . Similarly, the intersection of the top surface  445  and the side wall  420  of the center region  432  are rounded. This embodiment  400  of the invention also provides a polycrystalline diamond layer  414 , which covers the entire top surface  445  of the substrate  408 . 
     Referring to FIGS. 4 c  and  4   d , which are the top view and cross section view of a second alternative embodiment  401  of the invention. FIG. 4 c  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  409  center region  433  bounded by a “hoop”  440  region of polycrystalline diamond  415 , as shown in a perspective drawing in FIG. 1. A shelf  427  is provided on which the “hoop”  440  region is attached to the substrate  409 . The intersection of the substrate  409  shelf  427  and substrate  409  center region  433  side wall  421  is extremely rounded in this embodiment  401 . Similarly, the intersection of the top surface  446  and the side wall  421  of the center region  433  are extremely rounded. This embodiment  401  of the invention also provides a polycrystalline diamond layer  415 , which covers the entire top surface  446  of the substrate  409 . 
     Referring to FIGS. 4 e  and  4   f , which are the top view and cross section view of a third alternative embodiment  402  of the invention. FIG. 4 e  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  410  center region  434  bounded by a “hoop”  441  region of polycrystalline diamond  416 , as shown in a perspective drawing in FIG. 1. A shelf  428  is provided on which the “hoop”  441  region is attached to the substrate  410 . The intersection of the substrate  410  shelf  428  and substrate  410  center region  434  side wall  422  slopes upward and toward the center region  434  in this embodiment  402 . The intersection of the top surface  447  and the side wall  422  of the center region  434  forms an obtuse angle. This embodiment  402  of the invention also provides a polycrystalline diamond layer  416 , which covers the entire top surface  447  of the substrate  410 . 
     Referring to FIGS. 4 g  and  4   h , which are the top view and cross section view of a fourth alternative embodiment  403  of the invention. FIG. 4 g  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  411  center region  435  bounded by a “hoop”  442  region of polycrystalline diamond  417 , as shown in a perspective drawing in FIG. 1. A shelf  429  is provided on which the “hoop”  442  region is attached to the substrate  411 . The intersection of the substrate  411  shelf  429  and substrate  411  center region  435  side wall  423  slopes upward and away from the center region  435  in this embodiment  403 . The intersection of the top surface  448  and the side wall  423  of the center region  435  forms an acute angle. This embodiment  403  of the invention also provides a polycrystalline diamond layer  417 , which covers the entire top surface  448  of the substrate  411 . 
     Referring to FIGS. 4 i  and  4   j , which are the top view and cross section view of a fifth alternative embodiment  404  of the invention. FIG. 4 i  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  412  center region  436  bounded by a “hoop”  443  region of polycrystalline diamond  418 , as shown in a perspective drawing in FIG. 1. A shelf  430  is provided on which the “hoop”  443  region is attached to the substrate  412 . The intersection of the substrate  412  shelf  430  and substrate  412  center region  436  side wall  424  slopes upward and away from the center region  436  in this embodiment  404 . The intersection of the top surface  449 , which in this embodiment  404  is the apex of a near parabolic substrate  412  surface, and the side wall  424  of the center region  436  is continuously curved. This embodiment  404  of the invention also provides a polycrystalline diamond layer  418 , which covers the entire top surface  449  of the substrate  412 . 
     Referring to FIGS. 4 k  and  4   l , which are the top view and cross section view of a sixth alternative embodiment  405  of the invention. FIG. 4 k  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  413  center region  438  bounded by a “hoop”  444  region of polycrystalline diamond  419 , as shown in a perspective drawing in FIG. 1. A shelf  431  is provided on which the “hoop”  444  region is attached to the substrate  413 . The intersection of the substrate  413  shelf  431  and substrate  413  center region  438  side wall  425  slopes upward and away from the center region  438  in this embodiment  405 . The intersection of the top surface  450  and the side wall  425  of the center region  438  is curved. This embodiment  405  of the invention also provides a polycrystalline diamond layer  419 , which covers the entire top surface  450  of the substrate  413 . 
     FIG. 5 shows the perspective view of an additional embodiment of this invention. This view depicts the exterior of the alternative PDC  500 . The polycrystalline diamond region  502  is shown fixed to a carbide substrate region  501 . The preferred bond  504  between the diamond region  502  and the carbide region  501  is accomplished using a sintering process, although alternatively a brazing or chemical vapor phase deposition of the polycrystalline diamond can be used. The polycrystalline diamond region  502  is formed of diamond crystals bound together by a high pressure/high temperature process that forms the diamond crystals together into a solid diamond mass. Alternatively, a cubic boron nitride (cBN) or other superabrasive material layer can be substituted for the polycrystalline diamond layer  502 . The preferred substrate region  501  is composed of tungsten carbide, although alternative materials, including titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof, can be used for the substrate  501  material. Such superabrasive materials and substrate materials suitable for use in PDC are well known in the art. This alternative embodiment  500  also provides for an exposed center  503  carbide region. In sum, this embodiment  500  and the embodiments shows in FIGS. 6 a-f  provide a polycrystalline diamond “hoop” region  502  without a top polycrystalline diamond layer covering the entire substrate surface. 
     Referring to FIG. 6 a , which is the cross section view of a first alternative embodiment  600  of the invention having only a polycrystalline diamond “hoop” region  612 . Residual stress mitigation is provided by the substrate  606  center region  624  bounded by a “hoop”  612  region of polycrystalline diamond, as shown in the perspective drawing of FIG. 5. A shelf  630  is provided on which the “hoop”  612  region is attached to the substrate  606 . The intersection of the substrate  606  shelf  630  and substrate  606  center region  624  side wall  636  meets at an approximate right angle  618  in this embodiment  600 . 
     Referring to FIG. 6 b , which is the cross section view of a second alternative embodiment  601  of the invention having only a polycrystalline diamond “hoop” region  613 . Residual stress mitigation is provided by the substrate  607  center region  625  bounded by a “hoop”  613  region of polycrystalline diamond, as shown in the perspective drawing of FIG. 5. A shelf  631  is provided on which the “hoop”  613  region is attached to the substrate  607 . The intersection of the substrate  607  shelf  631  and substrate  607  center region  625  side wall  637  meets at an obtuse angle  619  in this embodiment  601 . 
     Referring to FIG. 6 c , which is the cross section view of a third alternative embodiment  602  of the invention having only a polycrystalline diamond “hoop” region  614 . Residual stress mitigation is provided by the substrate  608  center region  626  bounded by a “hoop”  614  region of polycrystalline diamond, as shown in the perspective drawing of FIG. 5. A shelf  632  is provided on which the “hoop”  614  region is attached to the substrate  608 . The intersection of the substrate  608  shelf  632  and substrate  608  center region  626  side wall  638  meets at an acute angle  620  in this embodiment  602 . 
     Referring to FIG. 6 d , which is the cross section view of a fourth alternative embodiment  603  of the invention having only a polycrystalline diamond “hoop” region  615 . Residual stress mitigation is provided by the substrate  609  center region  627  bounded by a “hoop”  615  region of polycrystalline diamond, as shown in the perspective drawing of FIG. 5. A shelf  633  is provided on which the “hoop”  615  region is attached to the substrate  609 . The intersection of the substrate  609  shelf  633  and substrate  609  center region  627  side wall  639  meets at a curved corner  621  with the side wall  639  generally parallel to the side  642  of this embodiment  603  of the PDC. Although being generally parallel to the side  642  the side wall  639  may include a typical manufacturing draft angle. 
     Referring to FIG. 6 e , which is the cross section view of a fifth alternative embodiment  604  of the invention having only a polycrystalline diamond “hoop” region  616 . Residual stress mitigation is provided by the substrate  610  center region  628  bounded by a “hoop”  616  region of polycrystalline diamond, as shown in the perspective drawing of FIG. 5. A shelf  634  is provided on which the “hoop”  616  region is attached to the substrate  610 . The intersection of the substrate  610  shelf  634  and substrate  610  center region  628  side wall  640  meets at a curved corner  622  with the side wall  640  sloping generally upwards and towards the center region  628  of this embodiment  604  of the PDC. 
     Referring to FIG. 6 f , which is the cross section view of a sixth alternative embodiment  605  of the invention having only a polycrystalline diamond “hoop” region  617 . Residual stress mitigation is provided by the substrate  611  center region  629  bounded by a “hoop”  617  region of polycrystalline diamond, as shown in the perspective drawing of FIG. 5. A shelf  635  is provided on which the “hoop”  617  region is attached to the substrate  611 . The intersection of the substrate  611  shelf  635  and substrate  611  center region  629  side wall  641  meets at a curved corner  623  with the side wall  641  sloping generally upwards and away from the center region  629  of this embodiment  605  of the PDC. 
     FIGS. 7 a-p  show top and cross section views of a variety of alternative embodiments of the invention which employ different substrate to polycrystalline diamond interface geometries for the purposes of enhancing the strength and/or the manufacturability of the PDC. Each of these embodiments also incorporates a polycrystalline diamond “hoop” fixed to a substrate shelf. Specific detail concerning these embodiments is provided as follows. Referring to FIGS. 7 a  and  7   b , which are the top view and cross section view of an alternative embodiment  700  of the invention. FIG. 7 a  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  708  center ring  724  bounded by a “hoop”  740  region of polycrystalline diamond  716 , as shown in a perspective drawing in FIG. 1. A shelf  732  is provided on which the “hoop”  740  region is attached to the substrate  708 . The intersection of the substrate  708  shelf  732  and substrate  708  center ring  724  side wall  748  is formed in an angle of approximately 90 degrees (although a draft angle may be included for manufacturability), in this embodiment  700 . Similarly, the intersection of the top surface  756  and the side wall  748  of the center ring  724  is formed in an approximately 90 degrees. This embodiment  700  of the invention also provides a polycrystalline diamond layer  716 , which covers the entire top surface  756  of the substrate  708 . 
     Referring to FIGS. 7 c  and  7   d , which are the top view and cross section view of an alternative embodiment  701  of the invention. FIG. 7 c  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  709  center region  725  bounded by a “hoop”  741  region of polycrystalline diamond  717 , as shown in a perspective drawing in FIG. 1. A shelf  733  is provided on which the “hoop”  741  region is attached to the substrate  709 . The intersection of the substrate  709  shelf  733  and substrate  709  center region  725  side wall  749  is formed in an angle of approximately 90 degrees, in this embodiment  701 . Similarly, the intersection of the top surface  757  and the side wall  749  of the center region  725  is formed in an approximately 90 degrees. This embodiment  701  of the invention also provides a polycrystalline diamond layer  717 , which covers the entire top surface  757  of the substrate  709 . 
     Referring to FIGS. 7 e  and  7   f , which are the top view and cross section view of an alternative embodiment  702  of the invention. FIG. 7 e  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  710  center ring  726  bounded by a “hoop”  742  region of polycrystalline diamond  718 , as shown in a perspective drawing in FIG. 1. A shelf  734  is provided on which the “hoop”  742  region is attached to the substrate  710 . The intersection of the substrate  710  shelf  734  and substrate  710  center ring  726  side wall  750  curves upwardly and toward the center  764  of the PDC, in this embodiment  702 . The geometry of the substrate  710  to polycrystalline diamond region  718 , of this embodiment  702  is provided with a substrate  710  concavity  766  positioned approximately at the center  764  of the PDC. This embodiment  702  of the invention also provides a polycrystalline diamond layer  718 , which covers the entire top surface  758  and  734  of the substrate  710 . 
     Referring to FIGS. 7 g  and  7   h , which are the top view and cross section view of an alternative embodiment  703  of the invention. FIG. 7 g  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  711  center ring  727  bounded by a “hoop”  743  region of polycrystalline diamond  719 , as shown in a perspective drawing in FIG. 1. A shelf  735  is provided on which the “hoop”  743  region is attached to the substrate  711 . The intersection of the substrate  711  shelf  735  and substrate  711  center ring  727  side wall  751  curves upwardly and toward the center  765  of the PDC, in this embodiment  703 . The geometry of the substrate  711  to polycrystalline diamond region  719 , of this embodiment  703  is provided with a substrate  711  protrusion  767  extending from the substrate  711  into the polycrystalline diamond region  719  and positioned approximately at the center  765  of the PDC. This embodiment  703  of the invention also provides a polycrystalline diamond layer  719 , which covers the entire top surface  759  and  735  of the substrate  711 . 
     Referring to FIGS. 7 i  and  7   j , which are the top view and cross section view of an alternative embodiment  704  of the invention. FIG. 7 i  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  712  center region  728  bounded by a “hoop”  744  region of polycrystalline diamond  720 , as shown in a perspective drawing in FIG. 1. A shelf  736  is provided on which the “hoop”  744  region is attached to the substrate  712 . The intersection of the substrate  712  shelf  736  and substrate  712  center region  728  side wall  752  is formed in an angle of approximately 90 degrees, in this embodiment  704 . Similarly, the intersection of the top surface  760  and the side wall  752  of the center region  728  is formed in an approximately 90 degrees. This embodiment  701  of the invention also provides a polycrystalline diamond layer  720 , which covers the entire top surface  760  of the substrate  712 . 
     Referring to FIGS. 7 k  and  7   l , which are the top view and cross section view of an alternative embodiment  705  of the invention. FIG. 7 k  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  713  center region  768  bounded by a “hoop”  745  region of polycrystalline diamond  721 , as shown in a perspective drawing in FIG.  1 . A shelf  737  is provided on which the “hoop”  745  region is attached to the substrate  713 . Protruding from the substrate  713  are a plurality of generally cylindrical knobs or protrusions  729 . The intersection of the substrate  713  shelf  737  and substrate  713  protrusions  729  side walls  753  are formed in an angle of approximately 90 degrees (although a draft angle may be included for manufacturability), in this embodiment  705 . Similarly, the intersection of the top surface  761  of the protrusions  729  and the side wall  753  of the protrusions  729  are formed in an angle of approximately 90 degrees. This embodiment  705  of the invention also provides a polycrystalline diamond layer  721 , which covers the entire top surface  737  and  761  of the substrate  713 . 
     Referring to FIGS. 7 m  and  7   n , which are the top view and cross section view of an alternative embodiment  706  of the invention. FIG. 7 m  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  714  center region  730  bounded by a “hoop”  746  region of polycrystalline diamond  722 , as shown in a perspective drawing in FIG. 1. A shelf  738  is provided on which the “hoop”  746  region is attached to the substrate  714 . The intersection of the substrate  714  shelf  738  and substrate  714  center region  730  side wall  754  is formed in an angle of approximately 90 degrees, in this embodiment  706 . Similarly, the intersection of the top surface  762  and the side wall  754  of the center region  730  is formed in an approximately 90 degrees. This embodiment  706  of the invention also provides a polycrystalline diamond layer  722 , which covers the entire top surface  762  of the substrate  714 . 
     Referring to FIGS. 7 o  and  7   p , which are the top view and cross section view of an alternative embodiment  707  of the invention. FIG. 7 o  shows the top of the substrate without the polycrystalline diamond region to better show the surface topography of the substrate. Residual stress mitigation is provided by the substrate  715  center region  769  bounded by a “hoop”  747  region of polycrystalline diamond  723 , as shown in a perspective drawing in FIG. 1. A shelf  739  is provided on which the “hoop”  747  region is attached to the substrate  715 . Protruding from the substrate  715  are a plurality of generally cylindrical knobs or protrusions  731 . In this embodiment  707  of the invention the knobs  731  generally form a circle within the periphery of the top surface of the substrate  715 . The intersection of the substrate  715  shelf  739  and substrate  715  protrusions  731  side walls  755  are formed in an angle of approximately 90 degrees, in this embodiment  707 . Similarly, the intersection of the top surface  763  of the protrusions  731  and the side wall  755  of the protrusions  731  are formed in an angle of approximately 90 degrees. This embodiment  707  of the invention also provides a polycrystalline diamond layer  723 , which covers the entire top surface  739  and  763  of the substrate  715 . 
     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 a number of alternative embodiments of the invention are provided above, these embodiments are provided only as illustrative and not as exhaustive of potential alternative embodiments of the invention. 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.