Abstract:
A superhard compact having an improved superabrasive-substrate interface region design for use in drilling bits, cutting tools and wire dies and the like. This compact is designed to provide an interface design to manipulate residual stresses to enhance the working the strength of the compact. The compact is provided with a network on interface features that share common walls to form cavities.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims priority to U.S. Provisional Patent Application No. 60/304,058 filed on Jul. 9, 2001. 

   BACKGROUND OF INVENTION 
   1. Field of the Invention 
   This invention relates to polycrystalline diamond compacts (PDC) used primarily in the oil and gas industry for drilling. More specifically, this invention relates to polycrystalline diamond cutters that utilize a substrate interface design that comprises a network of closed features that extend from the face of the substrate into the superabrasive layer. 
   2. Description of Related Art 
   Polycrystalline diamond compacts (PDC) often form the cutting structure of down hole tools, including drill bits (fixed cutter, roller cone and percussion bits), reamers and stabilizers in the oil and gas industry. A variety of PDC devices, specifically substrate interface designs have been described and are well known in the art. Generally, these devices do not have interface designs that include a network of closed shaped features that share common walls. 
   A polycrystalline diamond compact (PDC) can be manufactured by a number of methods that are well known in the art. The typical process consists of essentially placing a substrate adjacent to a layer of diamond crystals in a refractory metal can. A back can is then positioned over the substrate and is sealed to form a can assembly. The can assembly is then placed into a cell made of an extrudible material such as pyrophyllite or talc. The cell is then subjected to conditions necessary for diamond-to-diamond bonding or sintering in a high pressure/high temperature press. This detail is provided to familiarize the reader with the PDC sintering technology. For more information regarding the manufacture of PDC cutters the reader is referred to U.S. Pat. No. 3,745,623, which is hereby incorporated by reference in its entirety for the material contained therein. 
   There are a variety of U.S. patent documents that are helpful in providing a reader with general background information regarding PDC cutter design and manufacture. The reader is referred to the following U.S. patent documents, each of which is hereby incorporated by reference in its entirety for the material contained therein: U.S. Pat. Nos. 4,527,998, 4,539,018, 4,772,294, 4,941,891, 5,370,717, 5,384,470, 5,469,927, 5,560,754, 5,711,702, 5,871,060, 5,848,348, 5,890,552, 6,011,248, 6,063,333, 6,068,071, and 6,189,634. 
   SUMMARY OF INVENTION 
   Polycrystalline diamond compacts (PDC) are frequently used as the cutting structure on drill bits used to bore through geological formations. It is not unusual for PDC cutters to be subjected to loads down hole that exceed the working mechanical strength of the PDC (also referred to herein as the “insert”) and failures can occur. A most common type of failure is delamination and spallation of the diamond table. This type of failure is typically due to excessive stress loading caused by tool vibration and/or drilling inter-bedded hard formations. Residual stresses in the PDC can also drastically reduce the working load of a PDC, which in turn limits the magnitude of loads that can be applied before failure. Typically, the most harmful residual stresses are located on the outer diameter of the cutter just above the interface to the diamond table. These particular stresses encourage cracks to propagate parallel to the interface and are believed to be the source of most delamination failures. It is desirable to minimize all harmful residual tensile stresses and to maximize the compressive stresses in the diamond table. 
   The geometry of the substrate or interface design can significantly affect the performance of a PDC insert. Through different interface shapes and sizes the residual stresses of a PDC can be controlled. Residual stresses are inherently part of nearly all PDC products and tend to increase with increasing diamond thickness. These stresses arise from the difference in thermal expansion between the diamond layer and the substrate after sintering at extremely high pressures and temperatures. These stresses can be detrimental to the cutter, leading to delamination of the diamond and premature failure. This inherent property of PDC can be beneficial if the stresses are managed properly. Through interface design, residual compressive stresses can be created in the diamond table to increase toughness and diamond attachment strength. With an ever-increasing trend toward thick diamond PDC, it is now more critical than ever to design substrate interfaces that manage residual stresses to minimize premature failure tendencies. 
   This invention, in its present embodiment, significantly reduces residual tensile stresses on the outer diameter of the cutter, thereby significantly reducing tensile stresses on the outer diameter of the cutter, and therefore, significantly reducing the tendency to delaminate. The present embodiments of the invention have a tungsten carbide substrate that includes multiple closed features that define cavities and protrude into the diamond table. The closed features of one present embodiment illustrated herein share common walls and resemble a honeycomb geometry. This illustrated embodiment having interconnected closed features in its interface works to manipulate the residual stresses to provide the diamond table with reinforcing compressive stresses, while minimizing harmful outer diameter tensile stresses. This invention has many potential embodiments. Each of these embodiments may incorporate one or more of the following objects, however, because of the envisioned many possible embodiments, it is not anticipated that all embodiments will incorporate all of the following objects. Therefore, the limitations of this invention are to be found in the claims and should not include the following or any other potential objects. 
   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 an interface geometry that has a network of protrusions that are closed in form and that defines cavities and that share common walls that favorably manipulates the residual stresses. 
   It is a further object of this invention to provide a PDC that increases the strength and working life of a thick diamond table despite the corresponding increase in external diamond tensile stresses. 
   It is a further object of this invention to provide a PDC that has increased resistance to delamination by providing a mechanical locking device that includes an interface of non-planar networked closed features. 
   It is a further object of this invention to provide a PDC that has increased diamond attachment strength provided by an interface that has in increased surface area for bonding. 
   It is a further object of this invention to provide a PDC that exposes multiple diamond surfaces and new cutting edges, as wear progresses, to maintain a sharp cutting action. 
   It is a further object of this invention to provide a PDC with increased toughness by varying the height of the features across the interface to maintain constant or optimum substrate to diamond volumes. 
   Additional objects, advantages and other novel features of this invention will be set forth in part in the description that follows and in part will be come apparent to those skilled in the art upon examination of the following description or may be learned with the practice of the invention. Still other objects of the present invention will be come readily apparent to those skilled in the art from the following description wherein there is shown and described several preferred embodiments of this invention, simply by way of illustration of several of the various modes of the invention. As it will be realized, this invention is capable of other different embodiments and its several details and specific features are capable of modification in various aspects without departing from the invention. Accordingly, the objects, drawings and descriptions should be regarded as illustrative in nature and not as restrictive. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The accompanying drawings, incorporated in and forming a part of the specification, illustrate present preferred embodiments of the present invention. Some, although not all, alternative embodiments are described in the following description. In the drawings: 
       FIG. 1  depicts a first present interface pattern of a closed network of features, which are hexagonal protrusions with common walls that encompass a hexagonal cavity that resembles a honeycomb. 
       FIGS. 2 ,  3  and  4  depict alternative interface patterns that include various geometric shaped protrusions with common walls defining cavities within. 
       FIG. 5  depicts a top view of a substrate with a network of closed square features. The interface design of this embodiment also includes a peripheral recessed ring. 
       FIGS. 6 ,  7 ,  8 ,  9 ,  10  and  11  depict alternative cross-sectional views of various PDC designs with closed network features that either protrude from or recess into the face of the substrate. 
       FIG. 12  depicts an embodiment of the invention with a large wear flat that exposes a number of diamond surfaces and cutting edges. 
       FIGS. 13 and 14  depict alternative embodiments of the substrate interface design. These designs include hexagonal protrusions that extend out from the face of the substrate and define a peripheral ring. Internal cavity depths decrease as they approach the center of the substrate. The protrusions define a surface that can be flat, concave or convex. 
       FIG. 15  depicts a present embodiment of the substrate interface design. This design includes hexagonal protrusions that extend out from the face of the substrate and define a peripheral ring. The internal depths decrease as they approach the center of the substrate. The protrusions of this embodiment define a surface that is flat. 
   

   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 
   This invention is intended primarily for use as the cutting structure on earth boring devices used in oil and gas exploration, drilling, mining, excavating and the like. The mechanical and thermal properties of polycrystalline diamond make it an ideal material for cutting tools. However, like most hard materials, diamond is brittle and relatively weak under tensile loading. This is why it is so beneficial to make PDC designs that can manage the residual stresses associated with the large thermal expansion mismatch between the diamond layer and the substrate. Designs that minimize tensile stresses and maximize the compressive stresses in diamond are particularly desirable. The presence or absence of either of these residual stresses is a major determinant for significantly improving or weakening the working strength of the PDC. This invention by providing the benefits of increased attachment strength and a plurality of cutting edges is advantageous because it manipulates the residual stresses to a favorable condition to appreciably increase the working life of the cutter. 
     FIG. 1  shows the present preferred interface pattern  100  of the closed network of features, which in this embodiment are hexagonal protrusions  103   a–e  with common walls  102   a–e  that encompass hexagonal cavities  101   a–e  that together resembles a honeycomb. The cavities  101   a–e  are provided to receive the diamond table to provide a transition from the substrate to the diamond table to soften the stress gradient across the interface. It has been determined that along with residual stresses, the diamond-carbide interface attachment strength is directly related to the dynamic toughness of the PDC. The network of closed features provided by the interface pattern  100  increases the attachment strength of the diamond and thereby increases the toughness of the PDC. These closed features form cavities  101   a–e  to act as mechanical locks to increase the attachment strength of the diamond table to the substrate. Due to the difference in thermal expansion between the substrate and the diamond layer, the substrate will typically contract more than the diamond layer. This causes the closed network of features of the interface pattern  100  to clamp down or pinch the enclosed diamond forming a mechanical lock that increases the attachment strength between the diamond layer and the substrate. This network of closed features of the interface pattern  100  also provides a substantial increase in surface area compared to more traditional planar interface designs. With increased surface area more chemical bonds are formed between the substrate and the diamond layer also increasing the attachment strength. 
   The thickness of walls  102   a–e  of the protrusions can vary depending on the desired stress state. In some embodiments, the wall  102   a–e  thickness can be uniform throughout the pattern  100 , or can vary across the pattern  100  depending on the desired stresses. The wall  102   a–e  thickness of the present embodiment is between 0.015″ and 0.030″ and is uniform throughout the network  100 . 
     FIGS. 2 ,  3  and  4  show a variety of alternative protrusion shapes that can be used in alternative networks of closed features  200 ,  300 ,  400 . 
     FIG. 2  shows a first alternative interface pattern  200  that includes a series of square protrusions  203   a–f  with common walls  202   a–f  defining square cavities  201   a–f  within. 
     FIG. 3  shows a second alternative interface pattern  300  that includes triangular protrusions  303   a–f  with common walls  302   a–f  defining triangular cavities  301   a–f  within. 
     FIG. 4  shows a third alternative interface pattern  400  that includes both diamond shaped protrusions  403   a–e  and triangular protrusions  406   a–d  that share common walls  402   a–e ,  405   a–d  and that define diamond shaped cavities  401   a–e  and triangular cavities  404   a–d  within. 
   Each of these  FIGS. 1–4  are provided to show examples of different geometries. Naturally, a wide variety different geometries are envisioned and can be substituted without departing from the concept of this invention. Such other geometries include, but are not necessarily limited to other polygon shapes, circles, conics, ovals, abstract shapes or combinations thereof. 
     FIG. 5  shows a top view  500  of a substrate  501  with a network of closed square features  502 . The interface design  503  includes a circular portion  504  and peripheral ring  505  that can be varied in width and depth depending on desired stress conditions. The network of closed features  502  can include more than a circular portion  504  and may include polygons, conics, ovals, abstract shapes and combinations thereof. 
     FIG. 6  shows a cross-sectional view  600  of a PDC with a constant depth closed network design  601  that protrudes from the face  602  of the substrate  603 . Protrusions  604  define a peripheral ring  605  of thick diamond  606 . The diamond  606  fills the cavities  607  to provide a transition between the diamond  606  and the substrate  603  to soften the stress gradient across the interface  608  and to increase the attachment strength between the diamond  606  and the substrate  603 . The closed features of the network design  601  are represented to include a draft angled wall  609  for manufacturing ease but are not limited to obtuse angled walls  609  and can include vertical and acute angled walls relative to the substrate center axis  610 . The polycrystalline diamond  606  region is bonded to the substrate  603  typically through a high temperature/high pressure sintering process, although in alternative embodiments bonding can be accomplished by brazing or by chemical vapor deposition or the like. Also, alternatively cubic boron nitride (CBN) or other superabrasive materials can be substituted for the polycrystalline diamond  606  without departing from the concept of this invention. The preferred substrate  603  material is made of tungsten carbide, although in alternative embodiments, such materials as titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof can be used in the substrate  603 . 
     FIG. 7  shows a cross-sectional view  700  of a first alternative PDC design with a variable depth closed network design  701  that protrudes from the face  702  of the substrate  703 . Protrusions  704  extend generally across the face  702  of the substrate  703 . The diamond  706  fills the cavities  707  to provide a transition between the diamond  706  and the substrate  703  to soften the stress gradient across the interface  708  and to increase the attachment strength between the diamond  706  and the substrate  703 . The closed features of the network design  701  are represented to include a draft angled wall  709  for manufacturing ease but are not limited to obtuse angled walls  709  and can include vertical and acute angled walls relative to the substrate center axis  710 . The polycrystalline diamond  706  region is bonded to the substrate  703  typically through a high temperature/high pressure sintering process, although in alternative embodiments bonding can be accomplished by brazing or by chemical vapor deposition or the like. Also, alternatively cubic boron nitride (CBN) or other superabrasive materials can be substituted for the polycrystalline diamond  706  without departing from the concept of this invention. The preferred substrate  703  material is made of tungsten carbide, although in alternative embodiments, such materials as titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof can be used in the substrate  703 . 
     FIG. 8  shows a cross-sectional view  800  of a second alternative PDC design with an alternative variable depth closed network design  801  that recesses into the face  802  of the substrate  803 . The recesses  804  extend generally across the face  802  of the substrate  803  and in this embodiment the depth of the recesses  804  decrease at they  804  approach the center axis  810  of the substrate  803 . The diamond  806  fills the recesses  804  to provide a transition between the diamond  806  and the substrate  803  to soften the stress gradient across the interface  808  and to increase the attachment strength between the diamond  806  and the substrate  803 . Although in this shown embodiment  800 , the recess  804  bottom geometry is depicted as constant throughout the network  801  while the recess  804  opening size increases with depth, in alternative embodiments straight walled recesses  804  can be substituted so that both the recess  804  bottom and opening can remain constant. The closed features of the network design  801  are represented to include a draft angled wall  809  for manufacturing ease but are not limited to obtuse angled walls  809  and can include vertical and acute angled walls relative to the substrate center axis  810 . The polycrystalline diamond  806  region is bonded to the substrate  803  typically through a high temperature/high pressure sintering process, although in alternative embodiments bonding can be accomplished by brazing or by chemical vapor deposition or the like. Also, alternatively cubic boron nitride (CBN) or other superabrasive materials can be substituted for the polycrystalline diamond  806  without departing from the concept of this invention. The preferred substrate  803  material is made of tungsten carbide, although in alternative embodiments, such materials as titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof can be used in the substrate  803 . 
     FIG. 9  shows a cross-sectional view  900  of a third alternative PDC with an alternative variable depth closed network design  901  that protrudes from the face  902  of the substrate  903 . Protrusions  904  define a peripheral ring  905  of thick diamond  906 . The diamond  906  fills the cavities  907  to provide a transition between the diamond  906  and the substrate  903  to soften the stress gradient across the interface  908  and to increase the attachment strength between the diamond  906  and the substrate  903 . The closed features of the network design  901  are represented to have a top surface  911  that is generally concave and the protrusions include a draft angled walls  909  for manufacturing ease but are not limited to obtuse angled walls  909  and can include vertical and acute angled walls relative to the substrate center axis  910 . Alternatively, it is envisioned that the top surface  911  can be flat, convex or combinations thereof. The polycrystalline diamond  906  region is bonded to the substrate  903  typically through a high temperature/high pressure sintering process, although in alternative embodiments bonding can be accomplished by brazing or by chemical vapor deposition or the like. Also, alternatively cubic boron nitride (CBN) or other superabrasive materials can be substituted for the polycrystalline diamond  906  without departing from the concept of this invention. The preferred substrate  903  material is made of tungsten carbide, although in alternative embodiments, such materials as titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof can be used in the substrate  903 . 
     FIG. 10  shows a cross-sectional view  1000  of a fourth alternative PDC with a variable depth closed network design  1001  that recesses  1004  into the face  1002  of the substrate  1003 . The recesses  1004  define a peripheral ring  1005  of thick diamond  1006 . The diamond  1006  also fills the recesses  1007  to provide a transition between the diamond  1006  and the substrate  1003  to soften the stress gradient across the interface  1008  and to increase the attachment strength between the diamond  1006  and the substrate  1003 . The closed features of the network design  1001  are represented to include a draft angled wall  1009  for manufacturing ease but are not limited to obtuse angled walls  1009  and can include vertical and acute angled walls relative to the substrate center axis  1010 . The polycrystalline diamond  1006  region is bonded to the substrate  1003  typically through a high temperature/high pressure sintering process, although in alternative embodiments bonding can be accomplished by brazing or by chemical vapor deposition or the like. Also, alternatively cubic boron nitride (CBN) or other superabrasive materials can be substituted for the polycrystalline diamond  1006  without departing from the concept of this invention. The preferred substrate  1003  material is made of tungsten carbide, although in alternative embodiments, such materials as titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof can be used in the substrate  1003 . 
     FIG. 11  shows a cross-sectional view  1100  of a fifth alternative PDC with a variable depth closed network design  1101  that protrudes from the face  1102  of the substrate  1103 . Protrusions  1104  define a peripheral ring  1105  of thick diamond  1106 . The diamond  1106  fills the cavities  1107  to provide a transition between the diamond  1106  and the substrate  1103  to soften the stress gradient across the interface  1108  and to increase the attachment strength between the diamond  1106  and the substrate  1103 . The closed features of the network design  1101  are represented to include a draft angled wall  1109  for manufacturing ease but are not limited to obtuse angled walls  1109  and can include vertical and acute angled walls relative to the substrate center axis  1110 . The polycrystalline diamond  1106  region is bonded to the substrate  1103  typically through a high temperature/high pressure sintering process, although in alternative embodiments bonding can be accomplished by brazing or by chemical vapor deposition or the like. Also, alternatively cubic boron nitride (CBN) or other superabrasive materials can be substituted for the polycrystalline diamond  1106  without departing from the concept of this invention. The preferred substrate  1103  material is made of tungsten carbide, although in alternative embodiments, such materials as titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof can be used in the substrate  1103 . 
     FIG. 12  shows an embodiment of this invention  1200  with a large wear flat  1201  in both the diamond layer  1205  and the substrate  1201  that has exposed a plurality of diamond surfaces  1202  and cutting edges  1203 . This  FIG. 12  is representative of a typical extended wear flat that can be seen on typical used PDC inserts. Generally, as extended wear flats  1201  are produced the drilling efficiency of a PDC insert drops dramatically. Instead of a sharp edge to bite and shear the formation, an extended wear flat acts as a bearing surface that will not engage the formation to be cut unless increased force is applied to the drilling assembly. Maintaining a sharp cutter or edge is preferred for efficient drilling. With this embodiment of the invention, as wear progresses into the network cavities, new diamond surfaces  1202  and cutting edges  1203  are exposed, further enhancing drilling efficiency. 
     FIGS. 13 and 14  depict alternative embodiments  1300 ,  1400  of the substrate interface design  1301 ,  1401 . As can be seen, these design  1301 ,  1401  also have hexagonal protrusions  1302 ,  1402  that extend out from the face  1303 ,  1403  of the substrate  1304 ,  1404  and define a peripheral ring  1305 ,  1405 . The internal cavity  1306 ,  1406  depths decrease as they approach the center  1307 ,  1407  of the substrate  1304 ,  1404 . The protrusions  1302  in  FIG. 13  provide a generally concave interface surface  1308 , while the protrusions  1402  in  FIG. 14  provide a generally convex interface surface  1408 . In alternative embodiments, the interface surface could be flat or a combination of flat, concave and convex. 
     FIGS. 15   a, b, c, d, e  and  f  show several views of the present substrate interface design of this invention. Hexagonal protrusions  1501  extend out from the face  1502  of the substrate  1507  and define a peripheral ring  1503 . The protrusions  1501  define a surface  1513  that is flat. The internal cavity  1504  depths decrease as they approach the center  1505  of the substrate  1507 . The cavity&#39;s  1504  bottom hole shape  1506  follows the profile  1509  of a dome that protrudes from the surface  1508  of the substrate  1507 . This domed profile  1509  allows the diamond volume to gradually increase as it moves toward the perimeter  1510  of the PDC  1500 . The closed features of the hexagonal protrusions  1501  include a draft angle  1511  for conventional powdered metallurgy pressing techniques. Polycrystalline diamond  1512  is bonded to the substrate  1507  typically through a high temperature/high pressure sintering process. Polycrystalline diamond, although the preferred material for the superhard surface, may alternatively be substituted with cubic boron nitride (CBN) or any other appropriate superhard material. The preferred substrate  1507  is composed of tungsten carbide, although alterative materials such as titanium carbide, tantalum carbide, vanadium carbide, niobium carbide, hafnium carbide, zirconium carbide, or alloys thereof can be substituted without departing from the concept of this invention. 
   The described preferred and alternative embodiments of this disclosure are to be considered in all respects only as illustrative of the current best modes of the invention known to the inventors and not as restrictive. Alternative embodiments of the invention, including a combination of one or more of the features of the foregoing PDC devices should be considered within the scope of this invention. The appended claims define the scope of this invention. All processes and devices that come within the meaning and range of equivalency of the claims are to be considered as being within the scope of this patent.