Patent Description:
PDCs have found particular utility as superabrasive cutting elements in rotary drill bits, such as roller-cone drill bits and fixed-cutter drill bits. A PDC cutting element typically includes a superabrasive diamond layer commonly known as a diamond table. The diamond table is formed and bonded to a substrate using a high-pressure/high-temperature ("HPHT") process. The PDC cutting element may be brazed directly into a preformed pocket, socket, or other receptacle formed in a bit body. The substrate may often be brazed or otherwise joined to an attachment member, such as a cylindrical backing. A rotary drill bit typically includes a number of PDC cutting elements affixed to the bit body. It is also known that a stud carrying the PDC may be used as a PDC cutting element when mounted to a bit body of a rotary drill bit by press-fitting, brazing, or otherwise securing the stud into a receptacle formed in the bit body.

Conventional PDCs are normally fabricated by placing a cemented carbide substrate into a container with a volume of diamond particles positioned on a surface of the cemented carbide substrate. A number of such containers may be loaded into an HPHT press. The substrate(s) and volume(s) of diamond particles are then processed under HPHT conditions in the presence of a catalyst material that causes the diamond particles to bond to one another to form a matrix of bonded diamond grains defining a polycrystalline diamond ("PCD") table. The catalyst material is often a metal-solvent catalyst (e.g., cobalt, nickel, iron, or alloys thereof) that is used for promoting intergrowth of the diamond particles.

In one conventional approach, a constituent of the cemented carbide substrate, such as cobalt from a cobalt-cemented tungsten carbide substrate, liquefies and sweeps from a region adjacent to the volume of diamond particles into interstitial regions between the diamond particles during the HPHT process. The cobalt acts as a metal-solvent catalyst to promote intergrowth between the diamond particles, which results in formation of a matrix of bonded diamond grains having diamond-to-diamond bonding therebetween. Interstitial regions between the bonded diamond grains are occupied by the metal-solvent catalyst.

Known embodiments relate to PDCs and methods of manufacturing such PDCs are disclosed in <CIT>, <CIT> or <CIT>.

Despite the availability of a number of different PDCs, manufacturers and users of PDCs continue to seek PDCs with improved mechanical properties.

The present invention relates to a PDC according to claim <NUM>,.

The present invention moreover relates to a method for fabricating a PDC according to claim <NUM>.

Other embodiments include applications utilizing the claimed PDCs in various articles and apparatuses.

Features from any of the disclosed embodiments may be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings.

The drawings illustrate several embodiments of the invention, wherein identical reference numerals refer to identical or similar elements or features in different views or embodiments shown in the drawings.

Embodiments of the invention relate to PDCs including a PCD table in which at least one Group VIII metal is alloyed with at least one alloying element to improve the thermal stability of the PCD table. The disclosed PDCs may be used in a variety of applications, such as rotary drill bits, machining equipment, and other articles and apparatuses.

<FIG> are isometric and cross-sectional views, respectively, of an embodiment of a PDC <NUM>. The PDC <NUM> includes a PCD table <NUM> having an interfacial surface <NUM>, and a substrate <NUM> having an interfacial surface <NUM> that is bonded to the interfacial surface <NUM> of the PCD table <NUM>. The substrate <NUM> may comprise, for example, a cemented carbide substrate, such as tungsten carbide, tantalum carbide, vanadium carbide, niobium carbide, chromium carbide, titanium carbide, or combinations of the foregoing carbides cemented with iron, nickel, cobalt, or alloys thereof. In an embodiment, the cemented carbide substrate comprises a cobalt-cemented tungsten carbide substrate. While the PDC <NUM> is illustrated as being generally cylindrical, the PDC <NUM> may exhibit any other suitable geometry and may be non-cylindrical. Additionally, while the interfacial surfaces <NUM> and <NUM> are illustrated as being substantially planar, the interfacial surfaces <NUM> and <NUM> may exhibit complementary non-planar configurations.

The PCD table <NUM> is integrally formed with the substrate <NUM>. For example, the PCD table <NUM> may be integrally formed with the substrate <NUM> in an HPHT process by sintering of diamond particles on the substrate <NUM>. The PCD table <NUM> further includes a plurality of directly bonded-together diamond grains exhibiting diamond-to-diamond bonding (e.g., sp<NUM> bonding) therebetween. The plurality of directly bonded-together diamond grains define a plurality of interstitial regions. For example, the diamond grains of the PCD table <NUM> may exhibit an average grain size of about less than <NUM>, about less than <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM> (e.g., about <NUM> to about <NUM>). The PCD table <NUM> defines the working upper surface <NUM>, at least one side surface <NUM>, and an optional peripherally-extending chamfer <NUM> that extends between the at least one side surface <NUM> and the working upper surface <NUM>.

A metallic interstitial constituent is disposed in at least a portion of the interstitial regions of the PCD table <NUM>. In an embodiment, the metallic interstitial constituent includes and/or is formed from an alloy that is chosen to exhibit a selected melting temperature or melting temperature range and bulk modulus that are sufficiently low so that it does not break diamond-to-diamond bonds between bonded diamond grains during heating experienced during use, such as cutting operations. During cutting operations using the PCD table <NUM>, the relatively deformable metallic interstitial constituent may potentially extrude out of the PCD table <NUM>. However, before, during, and after the cutting operations, the PCD table <NUM> still includes the metallic interstitial constituent distributed substantially entirely throughout the PCD table <NUM>.

According to various embodiments, the alloy comprises at least one Group VIII metal including cobalt, iron, nickel, or alloys thereof and at least one alloying element selected from silver, gold, aluminum, antimony, boron, carbon, cerium, chromium, copper, dysprosium, erbium, iron, gallium, germanium, gadolinium, hafnium, holmium, indium, lanthanum, magnesium, manganese, molybdenum, niobium, neodymium, nickel, praseodymium, platinum, ruthenium, sulfur, antimony, scandium, selenium, silicon, samarium, tin, tantalum, terbium, tellurium, thorium, titanium, vanadium, tungsten, yttrium, zinc, zirconium, and any combination thereof. For example, a more specific group for the alloying element includes boron, copper, gallium, germanium, gadolinium, silicon, tin, zinc, zirconium, and combinations thereof. The alloying element may be present with the at least one Group VIII metal in an amount at a eutectic composition, hypo-eutectic composition, or hyper-eutectic composition for the at least one Group VIII-alloying element chemical system if the at least one Group VIII-alloying element has a eutectic composition. The alloying element may lower a melting temperature of the at least one Group VIII metal, a bulk modulus of the at least one Group VIII metal, a coefficient of thermal expansion of the at least one Group VIII metal, or any combination thereof.

The at least one Group VIII metal may be infiltrated from the cementing constituent of the substrate <NUM> (e.g., cobalt from a cobalt-cemented tungsten carbide substrate) and alloyed with the alloying element provided from a source other than the substrate <NUM>. In such an embodiment, a depletion region of the at least one Group VIII metal in the substrate <NUM> in which the concentration of the at least one Group VIII metal is less than the concentration prior to being bonded to the PCD table <NUM> may be present at and near the interfacial surface <NUM>. In such an embodiment, the at least one Group VIII metal may form and/or carry tungsten and/or tungsten carbide with it during infiltration into the diamond particles being sintered that, ultimately, forms the PCD table <NUM>.

Depending on the alloy system, in some embodiments, the alloy disposed interstitially in the PCD table <NUM> comprises one or more solid solution alloy phases of the at least one Group VIII metal and the alloying element, one or more intermediate compound phases (e.g., one or more intermetallic compounds) between the alloying element and the at least one Group VIII metal and/or other metal (e.g., tungsten) to form one or more binary or greater intermediate compound phases, one or more carbide phases between the alloying element, carbon, and optionally other metal(s), or combinations thereof. In some embodiments, when the one or more intermediate compounds are present in the alloy, the one or more intermediate compounds are present in an amount less than about <NUM> weight % of the alloy, such as less than about <NUM> weight %, about <NUM> weight % to about <NUM> weight %, about <NUM> weight % to about <NUM> weight %, or about <NUM> weight % to about <NUM> weight %, with the balance being the one or more solid solution phases and/or one or more carbide phases. In other embodiments, when the one or more intermediate compounds are present in the alloy, the one or more intermediate compounds are present in the alloy in an amount greater than about <NUM> weight % of the alloy, such as about <NUM> weight % to about <NUM> weight %, about <NUM> weight % to about <NUM> weight %, about <NUM> weight % to about <NUM> weight %, about <NUM> weight % to about <NUM> weight %, about <NUM> weight % to about <NUM> weight %, or about <NUM> weight % (i.e., substantially all of the alloy). That is, the alloy is a multi-phase alloy that may include one or more solid solution alloy phases, one or more intermediate compound phases, one or more carbide phases, or combinations thereof. The inventors currently believe that the presence of the one or more intermediate compounds may enhance the thermal stability of the PCD table <NUM> due to the relatively lower coefficient of thermal expansion of the one or more intermediate compounds compared to a pure Group VIII metal, such as cobalt. Additionally, the inventors currently believe that the presence of the solid solution alloy of the at least one Group VIII metal may enhance the thermal stability of the PCD table <NUM> due to lowering of the melting temperature and/or bulk modulus of the at least one Group VIII metal.

For example, when the at least one Group VIII element is cobalt and the at least one alloying element is boron, the alloy may include WC phase, CoAWBBc (e.g., Co<NUM>W<NUM>B<NUM>) phase, CoDBE (e.g., Co<NUM>B or BCo<NUM>) phase, and Co phase (e.g., substantially pure cobalt or a cobalt solid solution phase) in various amounts. According to one or more embodiments, the WC phase may be present in the alloy in an amount less than <NUM> weight %, or less than <NUM> weight %; the CoAWBBc (e.g., Co<NUM>W<NUM>B<NUM>) phase may be present in the alloy in an amount less than <NUM> weight %, about <NUM> weight % to about <NUM> weight %, more than <NUM> weight %, about <NUM> weight % to about <NUM> weight %, or more than <NUM> weight %;, the CoDBE (e.g., Co<NUM>B or BCo<NUM>) phase may be present in the alloy in an amount greater than about <NUM> weight %, greater than about <NUM> weight %, or about <NUM> weight % to about <NUM> weight %; and the Co phase (e.g., substantially pure cobalt or a cobalt solid solution phase) may be present in the alloy in an amount less than <NUM> weight %, or less than <NUM> weight %. Any combination of the recited concentrations for the foregoing phases may be present in the alloy. In some embodiments, the maximum concentration of the Co<NUM>W<NUM>B<NUM> may occur at an intermediate depth below the working upper surface <NUM> of the PCD table <NUM>, such as about <NUM> inches to about <NUM> inches, about <NUM> inches to about <NUM> inches, or about <NUM> inches to about <NUM> inches (e.g., about <NUM> inches) below the working upper surface <NUM> of the PCD table. In the region of the PCD table <NUM> that has the maximum concentration of the Co<NUM>W<NUM>B<NUM> phase, the diamond content of the PCD table may be less that <NUM> weight %, such as about <NUM> weight % to about <NUM> weight %, or about <NUM> weight % to about <NUM> weight % (e.g., about <NUM> weight %).

Table I below lists various different embodiments for the alloy of the interstitial constituent. For some of the alloying elements, the eutectic composition with cobalt and the corresponding eutectic temperature at <NUM> atmosphere is also listed. As previously noted, in such alloys, in some embodiments, the alloying element may be present at a eutectic composition, hypo-eutectic composition, or hyper-eutectic composition for the cobalt-alloying element chemical system.

In a more specific embodiment, the alloy includes cobalt for the at least one Group VIII metal and zinc for the alloying element. For example, the alloy of cobalt and zinc may include a cobalt solid solution phase of cobalt and zinc and/or a cobalt-zinc intermetallic phase. In another embodiment, the alloy includes cobalt for the at least one Group VIII metal and zirconium for the alloying element. In a further embodiment, the alloy includes cobalt for the at least one Group VIII metal and copper for the alloying element. In some embodiments, the alloying element is a carbide former, such as aluminum, niobium, silicon, tantalum, or titanium. In some embodiments, the alloying element may be a non-carbon metallic alloying element, such as any of the metals listed in the table above. In other embodiments, the alloying element may not be a carbide former or may not be a strong carbide former compared to tungsten. For example, copper and zinc are examples of the alloying element that are not strong carbide formers. For example, in another embodiment, the alloy includes cobalt for the at least one Group VIII metal and boron for the alloying element. In such an embodiment, the metallic interstitial constituent may include a number of different intermediate compounds, such as BCo, W<NUM>B<NUM>, B<NUM>CoW<NUM>, Co<NUM>B, WC, Co<NUM>W<NUM>B<NUM>, Co<NUM>W<NUM>C, CoB<NUM>, CoW<NUM>B<NUM>, CoWB, combinations thereof, along with some pure cobalt. It should be noted that despite the presence of boron in the alloy, the alloy may be substantially free of boron carbide in some embodiments but include tungsten carbide with the tungsten provided from the substrate <NUM> during the sweep through of the at least one Group VIII metal into the PCD table <NUM> during formation thereof.

The composition of the alloy disposed in the interstitial regions of the PCD table <NUM> exhibits a gradient in which the concentration of the alloying element decreases with distance away from the working upper surface <NUM> of the PCD table <NUM> toward the substrate <NUM>. In such an embodiment, if present at all, the alloy may exhibit a decreasing concentration of any intermediate compounds with distance away from the working upper surface <NUM> of the PCD table <NUM>.

The alloy of the PCD table <NUM> may be selected from a number of different alloys exhibiting a melting temperature of about <NUM> or less and a bulk modulus at <NUM> of about <NUM> GPa or less. As used herein, melting temperature refers to the lowest temperature at which melting of a material begins at standard pressure conditions (i.e., <NUM> kPa). For example, depending upon the composition of the alloy, the alloy may melt over a temperature range such as occurs when the alloy has a hypereutectic composition or a hypoeutectic composition where melting begins at the solidus temperature and is substantially complete at the liquidus temperature. In other cases, the alloy may have a single melting temperature as occurs in a substantially pure metal or a eutectic alloy.

In one or more embodiments, the alloy exhibits a coefficient of thermal expansion of about <NUM> × <NUM>-<NUM> per °C to about <NUM> x <NUM>-<NUM> per °C, a melting temperature of about <NUM> to about <NUM>, and a bulk modulus at <NUM> of about <NUM> GPa to about <NUM> GPa; a coefficient of thermal expansion of about <NUM> x <NUM>-<NUM> per °C to about <NUM> x <NUM>-<NUM> per °C, a melting temperature of about <NUM> to about <NUM>, and a bulk modulus at <NUM> of about <NUM> GPa to about <NUM> GPa; a coefficient of thermal expansion of about <NUM> x <NUM>-<NUM> per °C to about <NUM> x <NUM>-<NUM> per °C, a melting temperature of about <NUM> to about <NUM> (e.g., <NUM>), and a bulk modulus at <NUM> of about <NUM> GPa to about <NUM> GPa (e.g., about <NUM> GPa); or a coefficient of thermal expansion of about <NUM> x <NUM>-<NUM> per °C to about <NUM> x <NUM>-<NUM> per °C, a melting temperature of about <NUM> to about <NUM> (e.g., about <NUM>), and a bulk modulus at <NUM> of about <NUM> GPa to about <NUM> GPa (e.g., about <NUM> GPa). For example, the alloy may exhibit a melting temperature of less than about <NUM> (e.g., less than about <NUM>) and a bulk modulus at <NUM> of less than about <NUM> GPa (e.g., less than about <NUM> GPa). For example, the alloy may exhibit a melting temperature of less than about <NUM> (e.g., less than <NUM>), and a bulk modulus at <NUM> of less than about <NUM> GPa.

When the HPHT sintering pressure is greater than about <NUM> GPa cell pressure, optionally in combination with the average diamond grain size being less than about <NUM>, any portion of the PCD table <NUM> (prior to being leached) defined collectively by the bonded diamond grains and the alloy may exhibit a coercivity of about <NUM> Aim (<NUM> Oe) or more and the alloy content in the PCD table <NUM> may be less than about <NUM>% by weight as indicated by a specific magnetic saturation of about <NUM>·cm<NUM>/g or less. In another embodiment, the coercivity may be about <NUM> Aim (<NUM> Oe) to about <NUM> Aim (<NUM> Oe) and the specific magnetic saturation of the PCD table <NUM> (prior to being leached) may be greater than <NUM>·cm<NUM>/g to about <NUM>·cm<NUM>/g. In another embodiment, the coercivity may be about <NUM> Aim (<NUM> Oe) to about <NUM> Aim (<NUM> Oe) and the specific magnetic saturation of the PCD may be about <NUM>·cm<NUM>/g to about <NUM>·cm<NUM>/g. In yet another embodiment, the coercivity of the PCD table (prior to being leached) may be about <NUM> Aim (<NUM> Oe) to about <NUM> Aim (<NUM> Oe) and the specific magnetic saturation of the first region <NUM> may be about <NUM>·cm<NUM>/g to about <NUM>·cm<NUM>/g. The specific permeability (i.e., the ratio of specific magnetic saturation to coercivity) of the PCD table <NUM> may be about <NUM>·cm<NUM>/g·Oe or less, such as about <NUM>·cm<NUM>/g·Oe to about <NUM>·cm<NUM>/g·Oe. In some embodiments, the average grain size of the bonded diamond grains may be less than about <NUM> and the alloy content in the le <NUM> (prior to being leached) may be less than about <NUM>% by weight (e.g., about <NUM>% to about <NUM>% by weight, about <NUM>% to about <NUM>% by weight, or about <NUM>% to about <NUM>% by weight). Additionally details about magnetic properties that the PCD table <NUM> may exhibit is disclosed in <CIT>. Referring specifically to the cross-sectional view of <FIG>, in an embodiment, the PCD table <NUM> may be leached to improve the thermal stability thereof. The PCD table <NUM> includes a first region <NUM> adjacent to the interfacial surface <NUM> of the substrate <NUM>. The metallic interstitial constituent occupies at least a portion of the interstitial regions of the first region <NUM> of the PCD table <NUM>. For example, the metallic interstitial constituent may be any of the alloys discussed herein. The PCD table <NUM> also includes a leached second region <NUM> remote from the substrate <NUM> that includes the upper surface <NUM>, the chamfer <NUM>, and a portion of the at least one side surface <NUM>. The leached second region <NUM> extends inwardly to a selected depth or depths from the upper surface <NUM>, the chamfer <NUM>, and a portion of the at least one side surface <NUM>.

The leached second region <NUM> has been leached to deplete the metallic interstitial constituent therefrom that previously occupied the interstitial regions between the bonded diamond grains of the leached second region <NUM>. The leaching may be performed in a suitable acid (e.g., aqua regia, nitric acid, hydrofluoric acid, or combinations thereof) so that the leached second region <NUM> is substantially free of the metallic interstitial constituent. As a result of the metallic interstitial constituent (e.g., cobalt) being depleted from the leached second region <NUM>, the leached second region <NUM> is relatively more thermally stable than the underlying first region <NUM>.

Generally, a maximum leach depth <NUM> may be greater than <NUM>. For example, the maximum leach depth <NUM> for the leached second region <NUM> may be about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>. The maximum leach depth <NUM> may be measured inwardly from at least one of the upper surface <NUM>, the chamfer <NUM>, or the at least one side surface <NUM>.

<FIG> is a schematic diagram at different stages during a comparative method for the fabrication of the PDC <NUM> shown in <FIG> Referring to <FIG>, an assembly <NUM> including a mass of diamond particles <NUM> is positioned between the interfacial surface <NUM> of the substrate <NUM> and at least one material <NUM> that includes any of the alloying elements disclosed herein (e.g., at least one alloying element that lowers a temperature at which melting of at least one Group VIII metal begins and exhibits a melting temperature greater than that of the melting temperature of the at least one Group VIII metal). For example, the at least one material <NUM> may be in the form of particles of the alloying element(s), a thin disc of the alloying element(s), a green body of particles of the alloying elements(s), at least one material of the alloying element(s), or combinations thereof. In some embodiments, the at least one alloying element may even comprise carbon in the form of at least one of graphite, graphene, fullerenes, or other sp<NUM>-carbon-containing particles. As previously discussed, the substrate <NUM> may include a metal-solvent catalyst as a cementing constituent comprising at least one Group VIII metal, such as cobalt, iron, nickel, or alloys thereof. For example, the substrate <NUM> may comprise a cobalt-cemented tungsten carbide substrate in which cobalt is the at least one Group VIII metal that serves as the cementing constituent.

The diamond particles may exhibit one or more selected sizes. The one or more selected sizes may be determined, for example, by passing the diamond particles through one or more sizing sieves or by any other method. In an embodiment, the plurality of diamond particles may include a relatively larger size and at least one relatively smaller size. As used herein, the phrases "relatively larger" and "relatively smaller" refer to particle sizes determined by any suitable method, which differ by at least a factor of two (e.g., <NUM> and <NUM>). In various embodiments, the plurality of diamond particles may include a portion exhibiting a relatively larger size (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) and another portion exhibiting at least one relatively smaller size (e.g., <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, less than <NUM>, <NUM>, less than <NUM>). In an embodiment, the plurality of diamond particles may include a portion exhibiting a relatively larger size between about <NUM> and about <NUM> and another portion exhibiting a relatively smaller size between about <NUM> and <NUM>. Of course, the diamond particles may also include three or more different sizes (e.g., one relatively larger size and two or more relatively smaller sizes), without limitation.

The assembly <NUM> may be placed in a pressure transmitting medium, such as a refractory metal can embedded in pyrophyllite or other pressure transmitting medium, and subjected to a first stage HPHT process. For example, the first stage HPHT process may be performed using an ultra-high pressure press to create temperature and pressure conditions at which diamond is stable. The temperature of the first stage HPHT process may be at least about <NUM> (e.g., about <NUM> to about <NUM>) and the pressure of the HPHT process may be at least <NUM> GPa (e.g., about <NUM> GPa to about <NUM> GPa or about <NUM> GPa to about <NUM> GPa) for a time sufficient to sinter the diamond particles to form a PCD table. For example, the pressure of the first stage HPHT process may be about <NUM> GPa to about <NUM> GPa and the temperature of the HPHT process may be about <NUM> to about <NUM> (e.g., about <NUM> to about <NUM>). The foregoing pressure values employed in the HPHT process refer to the cell pressure in the pressure transmitting medium that transfers the pressure from the ultra-high pressure press to the assembly.

In an embodiment, during the first stage HPHT process, the at least one Group VIII metal from the substrate <NUM> or another source (e.g., metal-solvent catalyst mixed with the diamond particles) liquefies and infiltrates into the mass of diamond particles <NUM> and sinters the diamond particles together to form a PCD table having diamond grains exhibiting diamond-to-diamond bonding (e.g., sp<NUM> bonding) therebetween with the at least one Group VIII metal disposed in the interstitial regions between the diamond grains. In an embodiment, the alloying element from the at least one material <NUM> does not melt during the first stage HPHT process. Thus, in this embodiment, the at least one alloying element has a melting temperature greater than the at least one Group VIII metal (e.g., cobalt) that is used. For example, if the substrate <NUM> is a cobalt-cemented tungsten carbide substrate, cobalt from the substrate <NUM> may be liquefied and infiltrate the mass of diamond particles <NUM> to catalyze formation of the PCD table, and the cobalt may subsequently be cooled to below its melting point or range.

After sintering the diamond particles to form the PCD table in the first stage HPHT process, in a second stage HPHT process, the temperature is increased from the temperature employed in the first stage HPHT process, while still maintaining application of the same, less, or higher cell pressure to maintain diamond-stable conditions. The temperature of the second stage HPHT process is chosen to partially or completely diffuse/melt the alloying element of the at least one material <NUM>, which then alloys with the at least one Group VIII metal interstitially disposed in the PCD table and forms the final PCD table <NUM> having the alloy disposed interstitially between at least some of the diamond grains. Optionally, the temperature of the second stage HPHT process may be controlled so that the at least one Group VIII metal is still liquid or partially liquid so that the alloying with the at least one alloying element occurs in the liquid phase, which typically speeds diffusion.

Before or after alloying, the PDC may be subjected to finishing processing to, for example, chamfer the PCD table and/or planarize the upper surface thereof. The temperature of the second stage HPHT process may be about <NUM> to about <NUM>, and the temperature of the first stage HPHT process may be about <NUM> to about <NUM>. After and/or during cooling from the second stage HPHT process, the PCD table <NUM> bonds to the substrate <NUM>. As discussed above, the alloying of the at least one Group VIII metal with the at least one alloying element lowers a melting temperature of the at least one Group VIII metal and at least one of a bulk modulus or coefficient of thermal expansion of the at least one Group VIII metal.

For example, in an embodiment, the at least one material <NUM> may comprise boron particles, such as boron particles mixed with aluminum oxide particles. In another embodiment, the at least one material <NUM> may comprise copper or a copper alloy in powder or foil form. In such embodiments, the pressure of the second stage HPHT process may be about <NUM> GPa to about <NUM> GPa cell pressure and the temperature of the second stage HPHT process may be about <NUM> to about <NUM> (e.g., <NUM>), which is maintained for about <NUM> minutes to about <NUM> minutes (e.g., about <NUM> minutes to about <NUM> minutes, about <NUM> minutes to about <NUM> minutes, about <NUM> to about <NUM> minutes, about <NUM> to about <NUM> minutes, or about <NUM> to about <NUM> minutes).

In an embodiment, a second stage HPHT process is not needed. Particularly, alloying may be possible in a single HPHT process. In an example, when the at least one alloying element is copper or a copper alloy, the copper or copper alloy may not always infiltrate the un-sintered diamond particles under certain conditions. For example, after the at least one Group VIII metal has infiltrated (or as it infiltrates the diamond powder) and at least begins to sinter the diamond particles, copper may be able and/or begin to alloy with the at least one Group VIII metal. Such a process may allow materials that would not typically infiltrate diamond powder to do so during or after infiltration by a catalyst.

<FIG> is a cross-sectional view of a precursor PDC assembly <NUM> during the fabrication of the PDC <NUM> shown in <FIG> according to the method.

In this method, a precursor PDC <NUM>' is provided that has already been fabricated and includes a PCD table <NUM>' integrally formed with substrate <NUM>. For example, the precursor PDC <NUM>' may be fabricated using the same HPHT process conditions as the first stage HPHT process discussed above. Additionally, details about fabricating a precursor PDC <NUM>' according to known techniques is disclosed in <CIT>. Thus, the PCD table <NUM>' includes bonded diamond grains exhibiting diamond-to-diamond bonding (e.g., sp<NUM> bonding) therebetween, with at least one Group VIII metal (e.g., cobalt) disposed interstitially between the bonded diamond grains.

At least one material <NUM>' of any of the at least one alloying elements (or mixtures or combinations thereof) disclosed herein may be positioned adjacent to an upper surface <NUM>' of the PCD table <NUM>' to form the precursor PDC assembly <NUM>. For example, the at least one material <NUM>' may be in the form of particles of the alloying element(s), a thin disc of the alloying element(s), a green body of particles of the alloying elements(s), or combinations thereof. Although the PCD table <NUM>' is illustrated as being chamfered with a chamfer <NUM>' extending between the upper surface <NUM>' and at least one side surface <NUM>', in some embodiments, the PCD table <NUM>' may not have a chamfer. As the PCD table <NUM>' is already formed, any of the at least one alloying elements disclosed herein may be used, regardless of its melting temperature. The precursor PDC assembly <NUM> may be subjected to an HPHT process using the same or similar HPHT conditions as the second stage HPHT process discussed above or even lower temperatures for certain low-melting at least one alloying elements, such as bismuth. For example, the temperature may be about <NUM> to about <NUM> for such embodiments. During the HPHT process, the at least one alloying element partially or completely melts/diffuses and alloys with the at least one Group VIII metal of the PCD table <NUM>' which may or may not be liquid or partially liquid depending on the temperature and pressure.

For example, in an embodiment, the at least one material <NUM>' may comprise boron particles. In another embodiment, the at least one material <NUM> may comprise copper or a copper alloy in powder or foil form. In such embodiments, the pressure of the second stage HPHT process may be about <NUM> GPa to about <NUM> GPa cell pressure and the temperature of the second stage HPHT process may be about <NUM> to about <NUM> (e.g., <NUM>), which is maintained for about <NUM> minutes to about <NUM> minutes (e.g., about <NUM> to about <NUM> minutes, about <NUM> to about <NUM> minutes, or about <NUM> to about <NUM> minutes).

In some embodiments, the at least one material <NUM>' of the alloying element may be non-homogenous. For example, the at least one material <NUM>' may include a layer of a first alloying element having a first melting temperature encased/enclosed in a layer of a second alloying element having a second melting temperature greater than the first melting temperature. For example, the first one of the at least one alloying element may be silicon or a silicon alloy and the second one of the at least one alloying element may be zirconium or a zirconium alloy. During the melting of the at least one material <NUM>' (e.g., during the second stage HPHT process), once the second alloying element is completely melted and alloys the at least one Group VIII metal, the first alloying element may escape and further alloy the at least one Group VIII metal of the PCD table. In other embodiments, the first alloying element may diffuse through the layer of the second alloying element via solid state or liquid diffusion to alloy the at least one Group VIII metal.

In other embodiments, a second stage HPHT process may be performed without the use of the alloying element from the at least one material <NUM>'. Such a second stage HPHT process may increase the thermal stability and/or wear resistance of the PCD table even in the absence of the alloying element.

Referring to <FIG>, in another embodiment, the at least one material <NUM>' may be in the form of an annular body so that the at least one alloying element diffuses into the at least one Group VIII metal in selected location(s) of the PCD table <NUM>'. <FIG> illustrates another embodiment for diffusing the at least one alloying element into the at least one Group VIII metal in selected location(s) of the PCD table <NUM>'. For example, one or more grooves <NUM> may be machined in the PCD table <NUM>' such as by laser machining. The at least one material <NUM>' may be preplaced in the one or more grooves <NUM>. <FIG> illustrates the resultant structure of the PCD table <NUM>' after the at least one alloying element of the at least one material <NUM>' diffuses into the PCD table <NUM>' to form peripheral region <NUM> in which the at least one Group VIII metal thereof is alloyed with the at least one alloying element.

<FIG> is an isometric view and <FIG> is a top elevation view of an embodiment of a rotary drill bit <NUM> that includes at least one PDC configured according to any of the disclosed PDC embodiments. The rotary drill bit <NUM> comprises a bit body <NUM> that includes radially and longitudinally extending blades <NUM> having leading faces <NUM>, and a threaded pin connection <NUM> for connecting the bit body <NUM> to a drilling string. The bit body <NUM> defines a leading end structure for drilling into a subterranean formation by rotation about a longitudinal axis <NUM> and application of weight-on-bit. At least one PDC, configured according to any of the disclosed PDC embodiments, may be affixed to the bit body <NUM>. With reference to <FIG>, each of a plurality of PDCs <NUM> is secured to the blades <NUM> of the bit body <NUM> (<FIG>). For example, each PDC <NUM> may include a PCD table <NUM> bonded to a substrate <NUM>. More generally, the PDCs <NUM> may comprise any PDC disclosed herein, without limitation. In addition, if desired, in some embodiments, a number of the PDCs <NUM> may be conventional in construction. Also, circumferentially adjacent blades <NUM> define so-called junk slots <NUM> therebetween. Additionally, the rotary drill bit <NUM> includes a plurality of nozzle cavities <NUM> for communicating drilling fluid from the interior of the rotary drill bit <NUM> to the PDCs <NUM>.

<FIG> and <FIG> merely depict one embodiment of a rotary drill bit that employs at least one PDC fabricated and structured in accordance with the disclosed embodiments, without limitation. The rotary drill bit <NUM> is used to represent any number of earth-boring tools or drilling tools, including, for example, core bits, roller-cone bits, fixed-cutter bits, eccentric bits, bi-center bits, reamers, reamer wings, or any other downhole tool including superabrasive compacts, without limitation.

The PDCs disclosed herein (e.g., PDC <NUM> of <FIG>) may also be utilized in applications other than cutting technology. For example, the disclosed PDC embodiments may be used in wire dies, bearings, artificial joints, inserts, cutting elements, and heat sinks. Thus, any of the PDCs disclosed herein may be employed in an article of manufacture including at least one superabrasive element or compact.

Thus, the embodiments of PDCs disclosed herein may be used in any apparatus or structure in which at least one conventional PDC is typically used. In one embodiment, a rotor and a stator, assembled to form a thrust-bearing apparatus, may each include one or more PDCs (e.g., PDC <NUM> of <FIG>) configured according to any of the embodiments disclosed herein and may be operably assembled to a downhole drilling assembly. <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>; by this reference, disclose subterranean drilling systems within which bearing apparatuses utilizing PDCs disclosed herein may be incorporated. The embodiments of PDCs disclosed herein may also form all or part of heat sinks, wire dies, bearing elements, cutting elements, cutting inserts (e.g., on a roller-cone-type drill bit), machining inserts, or any other article of manufacture as known in the art. Other examples of articles of manufacture that may use any of the PDCs disclosed herein are disclosed in <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; <CIT>; and <CIT>.

The following working examples provide further detail in connection with the specific embodiments described above. Comparative working examples <NUM> and <NUM> are compared with working examples <NUM>-<NUM> fabricated according to specific embodiments of the invention.

Several PDCs were formed according to the following process. A first layer of diamond particles having an average particle size of about <NUM> was disposed on a cobalt-cemented tungsten carbide substrate. The diamond particles and the cobalt-cemented tungsten carbide substrate were HPHT processed in a high-pressure cubic press at a temperature of about <NUM> and a cell pressure of about <NUM> GPa to form a PDC comprising a PCD table integrally formed and bonded to the cobalt-cemented tungsten carbide substrate. Cobalt infiltrated from the cobalt-cemented tungsten carbide substrate occupied interstitial regions between bonded diamond grains of the PCD table.

Several PDCs were formed according to the process of comparative working example <NUM>. The PCD table was then leached in an acid to substantially remove cobalt therefrom to a depth of greater than <NUM> from an upper surface of the PCD table.

Several PDCs were formed according to the process of comparative working example <NUM>. Each PDC was then placed in a canister with boron powder positioned adjacent to an upper surface and side surface of the PCD table. The canister and the contents therein were subjected to a second HPHT process at a cell pressure of about <NUM> GPa and a temperature of about <NUM> for about <NUM> minutes to alloy the cobalt in the PCD table with boron. The alloyed PCD table was not leached.

One of the PDCs was destructively analyzed using x-ray diffraction ("XRD") to determine the phases present at various depths in the PCD table. The PCD table was subjected to XRD to determine the phases present at a given depth, the PCD table was then ground, and then the grounded PCD table was subjected to XRD to determine the phases present at the different depth. This process was repeated. Table II below shows the approximate depth and the corresponding phases determined via XRD. The XRD data indicated that boron forms several different intermediate compounds with both cobalt, tungsten, and cobalt and tungsten. The concentration of boron decreased with distance from the upper surface of the PCD table. It is notable that despite the presence of boron, that only tungsten carbide was detected and no boron carbide was detected.

Several PDCs were formed according to the process of comparative working example <NUM>. Each PDC was then placed in a canister with a copper foil positioned adjacent to an upper surface of the PCD table. The canister and the contents therein were subjected to a second HPHT process at a cell pressure of about <NUM> GPa and a temperature of about <NUM> for a about <NUM> minutes to alloy the cobalt in the PCD table with copper. The alloyed PCD table was not leached.

Copper was detected to a depth of about <NUM> inches from the upper surface of the PCD table using XRD. The inventors currently believe that longer soak times at high temperature will enable more copper to diffuse into cobalt of the PCD table to a greater depth.

Thermal stability testing was performed on the PDCs of working examples <NUM>-<NUM>. <FIG> are graphs of probability to failure of a PDC versus distance to failure for the PDC. The results of the thermal stability testing are shown in <FIG> compared the thermal stability of comparative working examples <NUM> and <NUM> with working example <NUM> of the invention. <FIG> compared the thermal stability of comparative working examples <NUM> and <NUM> with working example <NUM> of the invention. The thermal stability was evaluated in a mill test in which a PDC is used to cut a Barre granite workpiece. The test parameters used were an in-feed for the PDC of about <NUM>/min, a width of cut for the PDC of about <NUM>, a depth of cut for the PDC of about <NUM>, a rotary speed of the workpiece to be cut of about <NUM> RPM, and an indexing in the Y direction across the workpiece of about <NUM>. Failure is considered when the PDC can no longer cut the workpiece.

As shown in <FIG>, working example <NUM>, which was unleached, exhibited a greater thermal stability than even the deep leached PDC of comparative working example <NUM>. The characteristic distance to failure for the non-leached PDC of comparative working example <NUM> is <NUM> inches (<NUM> inches- <NUM> inches, n=<NUM>, <NUM>%). The characteristic distance to failure for the deep-leached PDC of comparative working example <NUM> is <NUM> inches (<NUM> inches-<NUM> inches, n=<NUM>, <NUM>%). The characteristic distance to failure for the boron diffused non-leached PDC of working example <NUM> is <NUM> inches (<NUM> inches-<NUM> inches, n=<NUM>, <NUM>%). As shown in <FIG>, the thermal stability of the PDC of working example <NUM> was better than the PDC of comparative working example <NUM>, but not as good as the deep leached PDC of comparative working example <NUM>. The inventors currently believe that longer soak times at high temperature will enable more copper atoms to diffuse into cobalt of the PCD table to a greater depth and improve thermal stability to be comparable to that of the PDC of comparative working example <NUM>. The characteristic distance to failure for a non-leached PDC of comparative working example <NUM> is <NUM> inches (<NUM> inches-<NUM> inches, n=<NUM>, <NUM>%). The characteristic distance to failure for a deep-leached PDC of comparative working example <NUM> is <NUM> inches (<NUM> inches-<NUM> inches, n=<NUM>, <NUM>%). The characteristic distance to failure for the copper diffused non-leached PDC of working example <NUM> is <NUM> inches (<NUM> inches-<NUM> inches, n=<NUM>, <NUM>%).

A PDC was formed according process of working example <NUM>. The PDC was destructively analyzed using Rietveld XRD analysis to determine the phases present at various depths in the PCD table and the relative weight % of the phases in the PCD table. The PCD table was subjected to Rietveld XRD analysis to determine the phases present at the upper surface of the PCD table and their relative weight %, and the PCD table was then ground at <NUM> inch intervals up to <NUM> inch, and then the ground PCD table was subjected to Rietveld XRD analysis to determine the phases present at the different depths. Table III below shows the approximate depth, and the corresponding phases and relative weight % determined via Rietveld XRD analysis. The Rietveld XRD analysis data indicated that boron forms several different intermediate compounds with both cobalt, tungsten, and cobalt and tungsten. Near the upper surface at a depth <NUM> inch and <NUM> inch, there was a relatively low concentration pure cobalt phase detected. The concentration of boron decreased with distance from the upper surface of the PCD table. It is notable that despite the presence of boron, that only tungsten carbide was detected and no boron carbide was detected with this test sample too.

Claim 1:
A polycrystalline diamond compact, comprising:
a substrate; and
a polycrystalline diamond table including an upper surface spaced from an interfacial surface that is bonded to and integrally formed with the substrate, the polycrystalline diamond table including a plurality of diamond grains defining a plurality of interstitial regions, the polycrystalline diamond table further including an alloy comprising at least one Group VIII metal and at least one alloying element, which is a metallic element or an element selected from the group of boron, sulfur, selenium, silicon, tellurium, the alloy including one or more solid solution phases comprising the at least one Group VIII metal and the at least one alloying element and one or more intermediate compounds comprising the at least one Group VIII metal and the at least one alloying element, the alloy being disposed in at least a portion of the plurality of interstitial regions, characterized in that the alloy exhibiting a decreasing concentration of the at least one alloying element with distance away from the upper surface, the alloy present at the upper surface.