Abstract:
A polycrystalline diamond composite including a generally circular sintered polycrystalline cutting disc and a refractory substrate operationally connected to the polycrystalline cutting disc. The polycrystalline cutting disc further includes a plurality of coarse diamond grains and a plurality of fine diamond grains. The plurality fine diamond grains are concentrated in an annulus positioned to define an outer edge of the polycrystalline cutting disc.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims priority to co-pending U.S. patent application Ser. No. 14/248,717, filed on Apr. 9, 2014, which was a continuation of co-pending U.S. patent application Ser. No. 13/072,203, filed on Mar. 25, 2011, and also claims priority to co-pending U.S. provisional patent application Ser. No. 61/887,221, filed on Oct. 4, 2013. 
     
    
     TECHNICAL FIELD 
       [0002]    The present novel technology relates to a polycrystalline diamond composite and a method to attach polycrystalline diamond cutting surfaces to substrates. 
       BACKGROUND 
       [0003]    The conventional method to manufacture Polycrystalline Diamond Composite (PDC) is to start with diamond grains which are placed inside an enclosure. The enclosure usually used is made up of a refractory metals or materials, as shown in  FIG. 1 . The diamond grains are sintered together by the formation of carbon-to-carbon bonds between carbon atoms in adjacent diamond grains. In order to facilitate this binding process, a catalyst metal, typically cobalt, is used; however, metals selected from Group VIII of the periodic table, such as nickel, iron, cobalt and alloys thereof, have been used successfully as catalysts to facilitate the formation of carbon-to-carbon sp 3  bonds between diamond grains within the PDC body during sintering. During the sintering process, diamond grains are subjected to a pressure of around 55 Kbar or higher along with a temperature around 1500° C. In this temperature-pressure regime, and especially in the presence of a catalyzing metal, sp 3  type bonds between carbon atoms in adjacent diamond grains are formed rendering the collection of diamond grains into a solid body known as a polycrystalline diamond composite or PDC. 
         [0004]    To facilitate the use of this solid PDC in wear resistant and/or impact resistant applications, it is typical to attach a solid PDC layer to a solid tungsten carbide matrix or like support substrate. The tungsten carbide substrate typically contains cobalt metal as a binder matrix. Attachment of PDC to the tungsten carbide substrate is usually done under high pressure and high temperature (HPHT), more typically during the sintering process. Under the high pressures and high temperatures achieved during the sintering process, cobalt metal within the substrate melts and infiltrates the interstices between diamond grains acting as the catalyst during sintering. The end product is a two layered structure, as shown in  FIG. 1 , with the majority of the top part of the structure being composed of sintered diamond (the sintered diamond body is typically composed of 90% or higher of diamond by volume); the diamond is infiltrated with cobalt and/or tungsten and/or alloys of cobalt and tungsten and carbon. 
         [0005]    Another method of making PDCs is to start with a sintered diamond layer of PDC and then attach the sintered PDC to a substrate. The solid PDC layer typically contains cobalt and/or cobalt tungsten alloys within the interstitial spaces located between diamond grains. These interstitial spaces are generally interconnected to define open pore structures. Prior to attaching the solid PDC to a solid tungsten carbide or like substrate, the cobalt and/or cobalt-tungsten alloys within the interstitial spaces within the solid PDC are removed by introducing the PDC to an acid to leach out the metals from the solid PDC. Leaching the catalyst metal involves exposing the PDC to a typically heated strong acid or a combination of acids, such as nitric acid, hydrofluoric acid, hydrochloric acid, perchloric acid, and combinations thereof. 
         [0006]    Once the catalyst metal is removed from the PDC layer, the remaining sintered PCD layer is often referred to as a Thermally Stable Polycrystalline diamond or TSP. Attaching the TSP to a substrate is typically done under HPHT conditions. The TSP and substrate are placed in contact with each other and are subjected to the HPHT conditions, similar to the sintering conditions. Once the substrate is sufficiently heated, the metal binder within the substrate melts and penetrates the TSP. Upon cooling, the liquid metal solidifies and acts as a glue attaching TSP to substrate ( FIG. 2 ). However, preparing the TSP as described above presents many challenges. Principal among these is coaxing molten cobalt and/or cobalt tungsten alloy to fully penetrate the open porosity of the TSP to fill the interstitial spaces. Such penetration is necessary in order to allow pressure transmission within the body of the TSP. The TSP volume is composed of diamond grains bound together by SP 3  type bonds and interstitial spaces that have been cleared of catalyst metal. 
         [0007]    In order to protect the diamond grains during the HPHT carbide substrate/TSP attachment process, the diamond grains are typically maintained under elevated pressure at the elevated HPHT temperatures, which may reach 1500 C. The diamond grains are typically maintained within the temperature-pressure regime of the carbon phase diagram in which diamond is the stable form of carbon. The TSP surfaces are exposed to elevated pressure in HPHT to keep the diamond grains in the diamond stable pressure-temperature region. However, the grains within the body of the TSP may still be exposed to lower pressure and without a medium to transmit pressure into the interstitial spaces within the TSP body, diamond grains within the TSP body will convert to graphite since the prevailing pressure within the TSP is less than that required to maintain the diamond within the diamond stable region. 
         [0008]    The molten cobalt and cobalt alloys that penetrate within the interstitial spaces within the TSP body act as a pressure transmission medium, since liquids act as isobaric pressure transmitters. Therefore during HPHT the molten cobalt and cobalt alloys penetrate the TSP body and fill the void interstitial spaces to protect diamond grains by maintaining sufficient pressure to keep them from converting to graphite. 
         [0009]    The size of the interstitials spaces is determined by the diamond grain size and diamond grains shape. The larger diamond grains result in larger interstitial spaces. Also, smaller grain sizes result in a larger overall surface area within the TSP that the molten cobalt and/or cobalt alloy will need to wet in order to fill the interstitial spaces, more surface area the molten metal has to flow over presents more friction resistance to the molten metal flow. When comparing a TSP composed of larger diamond grains to one composed on smaller grain size, the pore structure of the TSP composed of larger diamond grains is likewise larger. Thus, it is more difficult to fill the interstitial spaces within the TSP composed of smaller grains since these spaces tend to be narrower and harder to fill with liquid metal, in part due to the surface tension of the liquid metal. This results in lower yield and more defects when attaching TSP&#39;s of smaller grains compared to more desirable yield and defect rates of TSP composed of larger grains. 
         [0010]    The smaller the diamond grains used to make the TSP the more difficult it is to attach the TSP to a carbide substrate in HPHT. However, TSP&#39;s composed of smaller grains are desired in applications that require abrasion resistance. A TSP composed of small diamond grains has a larger density of diamond-to-diamond SP 3  bonds. Thus, PDC&#39;s characterized by finer grain sizes tend to be harder, but are more difficult to make due to the smaller interstitial spaces that need to be filled with liquid metal and, consequently, present higher resistance to metal infiltration due to the increased interior surface area of the pore structure that the metal has to wet while filling the smaller spaces. Thus, there is a need of a TSP body having the abrasion resistance associated with fine diamond grain size but with the substrate attachment ability associated with a coarser diamond grain size. The present novel technology addresses this need. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an illustration of a conventional prior art PDC. 
           [0012]      FIG. 2  is an illustration of a two-layered sintered prior art PDC. 
           [0013]      FIG. 3A  is a first plan view illustration of a first embodiment of the novel technology PDC. 
           [0014]      FIG. 3B  is a side elevation view of  FIG. 3A . 
           [0015]      FIG. 4A  is an exploded side elevation illustration of one embodiment of the novel method for manufacturing the novel PDC. 
           [0016]      FIG. 4B  is an exploded perspective view of  FIG. 4A . 
           [0017]      FIG. 5A  is a top plan illustration of the regions of a polycrystalline layer. 
           [0018]      FIG. 5B  is a side elevation cutaway view of  FIG. 5A . 
           [0019]      FIG. 5C  is a partial exploded view of the outer ring of  FIG. 5B . 
           [0020]      FIG. 5D  is a partial exploded view of the inner ring of  FIG. 5B . 
           [0021]      FIG. 6A  is a partial top plan view of a polycrystalline layer according to one embodiment of the present novel technology. 
           [0022]      FIG. 6B  is a cross-sectional view of  FIG. 6A . 
           [0023]      FIG. 6C  is a partial top plan view of a polycrystalline layer according to another embodiment of the present novel technology. 
           [0024]      FIG. 6D  is a cross-sectional view of  FIG. 6B . 
           [0025]      FIG. 6E  is a partial exploded view of  FIG. 6D . 
           [0026]      FIG. 7  is a carbon phase diagram. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    For the purposes of promoting an understanding of the principles of the claimed technology and presenting its currently understood best mode of operation, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the claimed technology is thereby intended, with such alterations and further modifications in the illustrated device and such further applications of the principles of the claimed technology as illustrated therein being contemplated as would typically occur to one skilled in the art to which the claimed technology relates. 
         [0028]    The novel polycrystalline diamond layer structure may vary for several reasons. In some embodiments, the structure is a single layer of diamond where the properties of the diamond grains within this layer are homogeneous or similar throughout the layer. In other embodiments, the PDC layer may be made of multiple sub-layers stacked on top of each other, each sub-layer having properties different from adjacent layers, wherein the change in properties from layer to layer may be gradual or may be abrupt, as desired. Different sub-layers within the PDC layer may also contain constituents other than diamond. Commonly used constituents are tungsten carbide grains, other metal carbides, compounds, and/or elements used to provide the PDC layer with desired physical and/or chemical properties. 
         [0029]    One embodiment of the present novel technology is the PDC layer  10  shown in  FIG. 3 . In this embodiment, the PDC layer  10  is formed having an annulus portion  15  of fine diamond grains  20  surrounding the remainder or core portion  25  of the PDC layer  10 , which is formed from coarse diamond grains  30 . The finer diamond particles  20  are typically between the sizes of 1 to 30 micron in diameter, although larger particle sizes may be elected as long as the diamond particle size in the core portion  25  and the rest of the PDC body  10  is relatively coarser. The coarser diamond particles  30  are typically between the sizes of 12 to 100 micron in diameter, but may likewise fall outside this range, as long as the relatively coarser diamond particles  30  in one region are larger than the relatively finer diamond grains  20  in the annulus region  15 . Particle size typically refers to average or mean sizes. Typically, the closer the mean sizes are, the easier it is to make a defect-free PDC body. The farther apart the mean sizes are, the more attention will have to be paid to compaction and fill quality or density distribution of the grains  20 ,  30 . When the size ratio is more than 1½ times between coarse grains  30  and fine grains  20 , the sintering quality of the fine diamond grains  20  may be adversely affected, all other factors being equal. 
         [0030]    In this embodiment, it is easier to sweep and sinter the PDC layer  10 , which produces a PDC with a high density of spa type bonds. Sintered bodies with a fine grain diamond microstructure may offer improved abrasion resistance over those having a coarser grain diamond microstructure. Since the outer edge  35  of the polycrystalline diamond layer  10  does most of the cutting and experiences most of the abrasion wear, the outer edge  35  is typically formed from fine grained diamond precursors  20  oriented as an outer annulus  15 . Since coarse grain diamond microstructures may offer better impact resistance over fine grain diamond microstructures, a PDC layer  10  having coarser grains  30  in the majority of its volume may provide the PDC composite body  40  with improved impact resistance. 
         [0031]    The annulus  15  portion is typically not as thick as the PDC disc  10 . In other words, the PCD disc  10  typically has a thickness defined as the distance between the top disc face and the bottom, parallel disc face. The annulus  15  typically extends from the top disc face towards the bottom disc face, but typically does not reach the bottom disc face. 
         [0032]    In some embodiments, a PDC layer  10  may need to be attached or re-attached to a substrate  45 . In one embodiment, a pre-sintered, metal-free PDC layer  50 , or TSP, may be attached or re-attached to a tungsten carbide substrate  45 . The pre-sintered metal-free PDC layer  50  may be placed into a refractory metal cup  55  and the carbide substrate  45  may be placed in contact with one side of the PDC layer  50  to define a bilayer  60 , as illustrated in  FIG. 4 . The sintered polycrystalline diamond layer-substrate combination  60  may be subjected to temperatures of approximately 1500° C. and pressures of approximately 55 Kbar, the pressure applied in the re-attachment may be similar to the original pressure and heat conditions used to make a conventional PDC. Typical pressure range to sinter PDC is 55 to 85 Kbar, however, pressures of 125 Kbar in laboratory environments have been used successfully to sinter diamond, temperatures needed to sinter diamond are the temperatures required to melt the metal catalyst and maintain carbon in the diamond stable region. Cobalt catalyst is typically used and has a melting temperature of 1495° C., although lower melting cobalt alloys of around with melting points around 1200° C. may be used. Temperatures of 1800° C. with higher corresponding pressures from the in the diamond stable region may be used to sinter diamond. Similar HPHT conditions that are used for diamond sintering may be used to re-attach the TSP However, any pressure and temperature sufficient to partially or completely melt the substrate  45  to facilitate penetration of the polycrystalline diamond layer  50  may be used. At elevated temperatures cobalt metal, cobalt-tungsten carbon alloy, or the like used to bind the tungsten carbide substrate  45  may melt. The high pressure environment surrounding the assembly  60 , while increasing the melting point of the cobalt, can force the molten cobalt  65 , molten cobalt alloy  65 , or the like to penetrate through the TSP  50 . The penetrating molten metal  65  catalyst binds the tungsten carbide substrate  45  to the pre-sintered PDC  50 . 
         [0033]    According to one method of manufacturing a PDC  10  having an annulus  15  of fine diamond grains  20  surrounding the core portion  25  of the PDC layer  10  as is formed from coarse diamond grains  30 , a TSP  50  is produced as shown in  FIGS. 4 &amp; 5  by first acid leaching metal from the pre-sintered PDC  50 . Such a TSP  50  is typically easier to attach to a carbide or like substrate  45  than a TSP  50  that is made from one layer composed solely of fine diamond grains  20 , or diamond grains all falling into a relatively narrow PSD. Typically, at least about 50% by volume of such a TSP  50  is composed of coarse grains  30  which give rise to larger intergranular pores  70  presenting less resistance to being filled with molten cobalt and cobalt tungsten alloys  65 . This improves the yield and reduces defects of the product. 
         [0034]    In an alternate embodiment, the starting material may be metal free, pre-sintered PDC  50 . However, various PDC layer designs may be used, such as single layer, multiple layer, and, the like. In this embodiment, a PDC layer  50  composed of two regions, as shown in  FIG. 5 , may be used to make the re-attached PDC. The PDC layer may be include an annulus  15  of fine grain diamond encircling a core portion  25  made of coarse grained diamond  30 .  FIG. 6  shows a variation of the aforementioned PDC structure, in addition to an annulus  15  of fine grain diamond  20 , another fine grained region may be formed by one, and more typically two, channels or bands  80 . The two channels  80  are typically oriented perpendicular to each other, and more typically cross the each other at the center of the PDC layer  50 . In other words, the channels  80  are typically perpendicular to each other and both channels  80  bisect the PDC disc  50 , with a first band  80  extending from a first point on the outer edge  35  of the polycrystalline cutting disc  10  to a second, spaced point on the outer edge  35  of the polycrystalline cutting disc, and a second band  80  extending from a third, spaced point on the outer edge  35  of the polycrystalline cutting disc  10  to a fourth, spaced point on the outer edge  35  of the polycrystalline cutting disc  10 . 
         [0035]    The addition of the intersecting channels  80  may reduce the residual stress within the PDC layer  50 . The novel technology allows for the coarse diamond grains  30  to present less resistance to catalyst penetration into the metal free PDC layer  50 . The coarse grains  30  are more resistant to being crushed when subjected to high sintering pressure during the re-attachment process. Thus, fine grains  20  may present a challenge in re-attachment process. In one embodiment, the PDC layer  10  offers the more attractive properties of a fine diamond grain microstructure on the cutting edge  35  while employing coarser-grained microstructure regions to reduce the chance of crushing the diamond grains. 
         [0036]    In some embodiments, before re-attachment may occur metal-free PDC  50  may be prepared. PDC layers  10  may be soaked in acid while heat is applied, with or without applied pressure, to leach metal from the PDC layer  50 . 
         [0037]    In some embodiments, during the PDC reattachment process heat may not be evenly distributed throughout the PDC layer. For example, the PDC portion close to the outside diameter is typically hotter than the rest of the PDC. With the proposed PDC layer design in this novel technology, the higher temperature refractory metal close to the PDC layer  50  may aid penetration through the fine grained diamond regions  15 ,  80 . 
         [0038]    In operation, a polycrystalline diamond portion  10 ,  50  may be attached to substrate  45  by first positioning at least one polycrystalline diamond layer  10  in mechanical communication with a substrate  45  to define a bilayer  60 . Then, the bilayer  60  is heated to a temperature sufficient to at least partially melt the substrate  45  to yield molten substrate material  65 , and sufficient pressure is applied to the bilayer  60  to urge penetration of molten substrate material  65  into the polycrystalline diamond layer  10 ,  50 . The polycrystalline diamond layer  10 ,  50  is bonded to the substrate  45  as the molten metal  60  cools and solidifies. Typically, the substrate  45  is tungsten carbide. More typically, the bilayer  60  is heated to about 1500° C. under a pressure of about 55 Kbar, which may be applied sequentially or simultaneously. Typically, the molten substrate material  65  contains cobalt. The substrate  45  may be monolayered or multilayered, and the PDC layer  10 ,  50  may be a non-uniform mixture of a coarse diamond grains  30  and fine diamond grains  20 . 
         [0039]    While the claimed technology has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. It is understood that the embodiments have been shown and described in the foregoing specification in satisfaction of the best mode and enablement requirements. It is understood that one of ordinary skill in the art could readily make a nigh-infinite number of insubstantial changes and modifications to the above-described embodiments and that it would be impractical to attempt to describe all such embodiment variations in the present specification. Accordingly, it is understood that all changes and modifications that come within the spirit of the claimed technology are desired to be protected.