Patent Publication Number: US-8535408-B2

Title: High thermal conductivity hardfacing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation in part of U.S. application Ser. No. 12/432,179, filed Apr. 29, 2009, now abandoned, and entitled “High Thermal Conductivity Hardfacing for Drilling Applications,” which is hereby incorporated herein by reference in its entirety. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     BACKGROUND 
     1. Field of the Invention 
     The invention relates generally to hardfacing to enhance resistance to erosion, abrasive wear, and frictional wear. More particularly, the invention relates to high thermally conductive hardfacing for use with drilling equipment and bearings. 
     2. Background of the Technology 
     Oil and gas wells can be formed by rotary drilling processes that involve a drill bit connected onto the lower end of a drill string. The drill bit is rotated downhole by rotating the drill string at the surface, actuation of downhole motors or turbines, or both. With weight applied to the drill string, the rotating drill bit engages the earthen formation and proceeds to form a borehole along a predetermined path toward a target zone. 
     While the bit is rotated, drilling fluid is pumped through the drill string and directed out of the face of the drill bit. The drilling fluid, also referred to as mud, performs several important functions. In particular, the fluid removes formation cuttings from the bit&#39;s cutting structure, removes cut formation materials from the bottom of the hole, and removes heat caused by contact between the bit and the formation. The drilling fluid and cuttings removed from the bit face and from the bottom of the hole are forced from the bottom of the borehole to the surface through the annulus between the drill string and the borehole sidewall. 
     One basic type of drill bit in general use for drilling a wellbore are rotary cone bits, which can also be referred to as rolling cutter bits, milled tooth bits, or rock bits. These generally use one or more rolling cones containing projections called cutting teeth. The cones are rotatably mounted on a drill bit body such that when the drill bit body is rotated and weight is applied, the teeth engage the formation being drilled and the cones rotate, imparting a boring action that forms the wellbore. 
     Another basic type of drill bit in general use is fixed cutter drill bits which can also be referred to as drag bits. A fixed cutter drill bit uses cutting elements that are attached to a drill bit body. When the fixed cutter drill bit is rotated and weight applied, the cutting elements contact the formation being drilled in a shearing action that breaks off pieces of the formation and forms the wellbore. 
     Certain surfaces of both rock bits and drag bits as well as other drilling related tools such as reamers, V-stab and stabilizers can be subject to wear during the drilling process, such as the side surface of a bit body that is contact with the wellbore wall and surface areas between the cutting elements of a drag bit. These surfaces may include a layer of material, often referred to as hardfacing or hardmetal, that is designed to resist wear. 
     Conventional hardmetal materials used to provide wear resistance to the underlying substrate of the drill bit typically comprise carbides. The carbide materials are used to impart properties of wear resistance and fracture resistance to the bit. Conventional hardmetal materials useful for forming a hardfaced layer can also include one or more alloys to provide desired physical properties. 
     Conventional hardfacing is applied onto the underlying bit surface by known welding methods or thermal spray techniques, such as Laser Cladding, Plasma Transferred Arc or Flame Spray techniques. The associated thermal impact of these processes can cause thermal stress and cracking to develop in the hardfacing material microstructure, which may lead to premature chipping, flaking, fracturing, and ultimately failure of the hardfacing layer. In addition, the process of welding the hardmetal materials onto the underlying substrate can make it difficult to provide a hardfaced layer having a consistent coating thickness, which can negatively impact the service life of the bit. 
     Accordingly, there remains a need in the art for a wear and fracture resistant hardfacing and hardmetal compositions that experience reduced stress and associated cracking from thermal loading. Such compositions would be particularly well-received if they offered the potential to improve dimensional consistency and accuracy during deposition. 
     BRIEF SUMMARY OF THE DISCLOSURE 
     These and other needs in the art are addressed in one embodiment by a hardmetal composition. In an embodiment, the hardmetal composition comprises tungsten carbide in an amount greater than 50 weight percent of the hardmetal composition. In addition, the hardmetal composition comprises a binder material consisting of at least 90 weight percent nickel, a binder flux between 3.5 to 10.0 weight percent chosen from the group consisting of boron and silicon, and less than 1.0 weight percent other components. 
     These and other needs in the art are addressed in another embodiment by a bit for drilling a borehole in earthen formations. In an embodiment, the bit comprises a bit body. In addition, the bit comprises a hardfacing composition applied to the bit body. The hardfacing composition comprises tungsten carbide in an amount greater than 50 weight percent of the hardfacing composition. The hardfacing composition further comprises a binder material consisting of at least 90 weight percent nickel and a binder flux of between 3.5 to 10.0 weight percent chosen from the group consisting of boron and silicon. The silicon in the binder flux is 0.5 to 10 weight percent of the binder material and the boron in the binder flux is 0.5 to 14 weight percent of the binder material. 
     These and other needs in the art are addressed in another embodiment by a method for providing a wear resistant hardfacing composition onto an apparatus. In an embodiment, the method comprises providing a hardfacing composition consisting of tungsten carbide in an amount greater than 50 weight percent of the hardfacing composition and a binder material consisting of at least 90 weight percent nickel, a binder flux of between 3.5 to 10.0 weight percent chosen from the group consisting of boron and silicon, and less than 1.0 weight percent other components. In addition, the method comprises depositing the hardfacing composition onto one or more portions of the apparatus. 
     These and other needs in the art are addressed in another embodiment by a hardmetal composition. In an embodiment, the hardmetal composition comprises tungsten carbide in an amount greater than 60 weight percent of the hardmetal composition. The tungsten carbide comprises at least 50 volume percent of spherical tungsten carbide particles. In addition, the hardmetal composition comprises a binder material consisting of nickel and a binder flux consisting of silicon and boron, wherein the silicon in the binder flux is 0.5 to 10 weight percent of the binder material and the boron in the binder flux is 0.5 to 14 weight percent of the binder material. The tungsten carbide content (wt %) in the hardmetal composition ranges from eight to eleven times the binder flux content (wt %) of the binder. 
     Embodiments described herein comprise a combination of features and advantages intended to address various shortcomings associated with certain prior devices, systems, and methods. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a detailed description of the preferred embodiments of the invention, reference will now be made to the accompanying drawings in which: 
         FIG. 1  is a schematic view of a downhole steerable drilling system; 
         FIG. 2  is a perspective view of a drag bit including hardfacing in accordance with the principles described herein; 
         FIG. 3  is an end view of the drill bit of  FIG. 2 ; 
         FIG. 4  is an enlarged partial cross-sectional view of the drill bit of  FIG. 2  illustrating one of the blades; 
         FIG. 5  is a perspective view of a rolling cone bit including hardfacing in accordance with the principles described herein; 
         FIG. 6  is a perspective view of a stabilizer including hardfacing in accordance with the principles described herein; 
         FIG. 7  is a graph illustrating the carbide content versus the binder flux content for various hardfacing compositions; 
         FIG. 8  illustrates enlarged images of the microstructure of embodiments of hardfacing compositions in accordance with the principles described herein; 
         FIG. 9  illustrates enlarged images of the microstructure of prior art hardfacing compositions in accordance with the principles described herein; 
         FIG. 10  is an exploded view of an embodiment of a radial bearing including hardfacing in accordance with the principles described herein; and 
         FIG. 11  is a perspective view of an apparatus for testing hardfacing compositions subjected to radial loads along rolling contacts. 
     
    
    
     DETAILED DESCRIPTION 
     The following discussion is directed to various exemplary embodiments. However, one skilled in the art will understand that the examples disclosed herein have broad application, and that the discussion of any embodiment is meant only to be exemplary of that embodiment, and not intended to suggest that the scope of the disclosure, including the claims, is limited to that embodiment. 
     Certain terms are used throughout the following description and claims to refer to particular features or components. As one skilled in the art will appreciate, different persons may refer to the same feature or component by different names. This document does not intend to distinguish between components or features that differ in name but not function. The drawing figures are not necessarily to scale. Certain features and components herein may be shown exaggerated in scale or in somewhat schematic form and some details of conventional elements may not be shown in interest of clarity and conciseness. 
     In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, that connection may be through a direct connection, or through an indirect connection via other devices, components, and connections. In addition, as used herein, the terms “axial” and “axially” generally mean along or parallel to a central axis (e.g., central axis of a body or a port), while the terms “radial” and “radially” generally mean perpendicular to the central axis. For instance, an axial distance refers to a distance measured along or parallel to the central axis, and a radial distance means a distance measured perpendicular to the central axis. Still further, as used herein, the terms “hardmetal,” “hardfacing,” and “hardfaced layer” refer to one or more protective layers of carbide containing material applied to an underlying substrate, such as a drill bit body, a stabilizer, a radial bearing, etc. 
     Referring now to  FIG. 1 , a drilling system for drilling a wellbore  6  into an earthen formation for the ultimate recovery of hydrocarbons is shown. The drilling system includes a drill string  2  suspended by a derrick  4 . A bottom-hole assembly (BHA)  8  is located at the bottom of the drill string  2 . For directional drilling, BHA  8  includes a downhole steerable drilling system  9  and comprises a drill bit  10 . With weight-on-bit (WOB) applied, drill bit  10  is rotated and cuts into the earth allowing the drill string  2  to advance, thus forming the wellbore  6 . In non-directional drilling applications the BHA (e.g., BHA  8 ) may not include a steerable drilling system (e.g., steerable drilling system  9 ) and may simply comprise a drill bit, typically with one or more drill collars, and optionally other tools to improve stability. 
     Referring now to  FIGS. 2-4 , a rotary drag bit  11  that may be used as drill bit  10  in the drilling system of  FIG. 1  is shown. Drag bit  11  has a bit body  12  made of a material such as machined steel. The bit body  12  has a leading face  13  provided with a plurality of protruding, angularly spaced blades  14 . Each blade  14  carries a plurality of cutting elements  16 . A channel  18  is formed between each pair of adjacent blades  14 . As best shown in  FIG. 4 , during drilling, channels  18  are supplied with drilling fluid via a series of passages  20  provided internally of the drill bit body  12 , each passage  20  terminating at a nozzle  22 . The supply of drilling fluid serves to clean and cool the cutting elements  16  while in use and provide a means for circulating cuttings out of the wellbore. Bit body  12  includes a threaded shank  24  that couples drill bit  11  to the lower end of a drill string (e.g., drill string  2 ), thereby enabling bit  11  to be rotated about a central axis of rotation  34 . 
     Referring still to  FIGS. 2-4 , blades  14  extend from the leading face  13  along the bit body  12  to form a gage contact surface  23  that defines the outer diameter of bit  11 . The gage contact surface  23  includes a plurality of wear resistant inserts  25  pressed therein and hardfacing  27  surrounding the wear resistant inserts  25 . During drilling, frictional engagement with the surrounding formation can abrasively wear hardfacing  27 , as well as subject hardfacing  27  to increased temperatures and associated thermal stresses. Accordingly, to enhance resistance to abrasive wear and thermal stresses, hardfacing  27  preferably has a composition in accordance with the principles described in more detail below. 
     Cutting elements  16  may also be disposed within hardfacing  29  on blades  14 , or mounted in pockets in blades  14 , which are surrounded by hardfacing  29 . In other words, hardfacing  29  covers some or all of blades  14  and fills some or all of the area between cutting elements  16 , and thus, may be referred to as “webbing.” During drilling, frictional engagement with the surrounding formation can abrasively wear hardfacing  29 , as well as subject hardfacing  29  to increased temperatures and associated thermal stresses. The incipient hardfacing wear at these locations can lead to cutter damage and/or loss resulting in a catastrophic dull condition referred to as “ringout.” Accordingly, to enhance resistance to abrasive wear and reduce thermal stresses, hardfacing  29  preferably has a composition in accordance with the principles described in more detail below. 
       FIG. 4  is a cross-sectional view of drill bit  11  showing the leading face of one blade  14 , the placement of the cutting elements  16  and wear resistant inserts  25 . Also shown are areas of hardfacing  27  on the gage contact surface  23  and hardfacing  29  webbing between the cutting elements  16 . 
     As best shown in  FIG. 3 , cutters  16  are arranged on the blades  14  in a series of concentric rings  26 ,  28 ,  30 ,  32 . The concentric rings  26 ,  28 ,  30 ,  32  are centered about axis  34 . The areas between the concentric rings  26 ,  28 ,  30 ,  32  are areas where hardfacing  29  webbing between the cutting elements  16  is particularly susceptible to erosion and severe wear damage from tensile stresses due to thermal loading in service. 
     Referring now to  FIG. 5 , a rolling cutter drill bit  50  that may be used as drill bit  10  in the drilling system of  FIG. 1  is shown. Bit  50  includes a body  52  formed from three similar leg portions  54  (only two are shown), each leg portion  54  having an external formation facing surface  56 . Each external surface  56  includes a shirttail region  57  near the bottom of the leg portion  54 . The external surface  56 , including the shirttail region  57 , are covered with hardfacing  56   a . A rolling cutter  58  is rotatably mounted upon each leg portion  54 . Attached to the rolling cutter  58  are cutting inserts  60  which engage the earth to effect a drilling action and cause rotation of the rolling cutter  58 . The exposed surface  62  of the rolling cutter  58  surrounding the cutting inserts  60  is covered with hardfacing  62   a . The portion of the rolling cutter  58  near the leg portion  54  is often referred to as the rolling cutter gage contact surface  64 , and includes hardfacing  64   a . The rolling cutter gage contact surface  64  is a generally conical surface at the heel of a rolling cutter  58  that engages the sidewall of a wellbore as bit  50  rotates. During drilling, frictional engagement with the surrounding formation can abrasively wear hardfacing  56   a ,  62   a ,  64   a  as well as subject hardfacing  56   a ,  62   a ,  64   a  to increased temperatures and associated thermal stresses. Accordingly, to enhance resistance to abrasive wear and thermal stresses, hardfacing  56   a ,  62   a ,  64   a  preferably has a composition in accordance with the principles described in more detail below. 
     Although  FIG. 5  and the discussion herein references a rolling cutter bit having cutting inserts, embodiments described herein are not limited to the same and include other rolling cutter bit designs such as mill tooth bits, which have teeth protruding from the cones rather than inserts. For mill tooth bits, the hardfacing can be applied on the external surface, shirttail region webbing between the teeth, as well as on the surface of the teeth themselves. 
     Referring now to  FIG. 6 , a stabilizer  70  is shown comprising a generally cylindrical body  72  with a screw-threaded recesses  74  at one end configured to mate with an adjacent components of the drill string (e.g., drill string  2 ) or BHA (e.g., BHA  8 ). The radially outer wall  76  of body  72  is provided with a plurality of upstanding blades  78 , each blade  78  having a substantially uniform height along its length, other than at its ends  78   a  where it tapers to the diameter of the body  72 . In addition, blades  78  are substantially equally circumferentially spaced about body  72 , and in this case, oriented in a generally spiral form. One or more bridging regions  80  interconnect each pair of adjacent blades  78 . The surface  82  of the blades  78  and bridging regions  80  have hardfacing  85  applied, and may optionally include wear resistant inserts. During drilling, frictional engagement with the surrounding formation can abrasively wear hardfacing  85 , as well as subject hardfacing  85  to increased temperatures and associated thermal stresses. Accordingly, to enhance resistance to abrasive wear and thermal stresses, hardfacing  85  preferably has a composition in accordance with the principles described in more detail below. 
     Embodiments of hardware (e.g., bearings), downhole tools and equipment (e.g., stabilizers, collars, etc.), drill bits (e.g., fixed cutter bits, roller cone bits, percussion bits, etc.), and devices described herein include surfaces formed from the application of engineered hardfacing that offers the potential to improve wear and fracture resistance as compared to conventional hardfacing. As will be described in more detail below, embodiments of hardfacing disclosed herein preferably (a) comprise relatively high thermal conductivity materials that reduce the potential for the introduction of detrimental thermal effects inherent with welding or thermal spray application techniques, and (b) have relatively good fluid flow properties during application to reduce the potential for dimensional inconsistencies. The hardfacing is disposed on an underlying metal or metal alloy substrate using any suitable application method including, without limitation, a thermal spray technique, such as laser cladding, plasma transferred arc welding (PTAW), flame spray, or oxyacetylene welding deposition. The applied hardfacing preferably has a surface layer thickness in the range of 0.1 to 10 mm, more preferably in the range of 0.5 to 8 mm, and still more preferably in the range of 1.0 to 5 mm. It is to be understood that the exact surface layer thickness may vary within these preferred ranges depending on the specific composition of the hardfacing, the underlying substrate, and the anticipated use of the tool or device to which the hardfacing is applied. 
     For drill bits, it is generally desirable to provide as much wear resistance as possible on the portions of the bit that contact the formation, as well as the portions of the bit susceptible to high erosion or other high wear conditions. The effective life of the bit is enhanced as the wear resistance of the bit is increased. As wear occurs, the drill bit may be replaced when the rate of penetration decreases to an unacceptable level. Thus, it is desirable to minimize wear so that the footage drilled by each bit is maximized. This not only decreases direct cost, but also decreases the frequency of having to “trip” a drill string to replace a worn bit with a new bit. Moreover, as gage contact surfaces of a bit wear, the diameter of the hole drilled by the bit decreases, sometimes causing drilling problems or requiring “reaming” of the hole by the next bit used. Thus, advances in drill bit wear resistance is desirable to increase the duration which a hole diameter (or gage) can be maintained, to enhance the footage a drill bit can drill before needing to be replaced, and to enhance the rate of penetration of such drill bits. Such improvements generally translate into reduction of drilling expense. 
     Embodiments of wear and fracture resistant hardfacing described herein have a composition comprising tungsten carbide disposed throughout a binder material. The tungsten carbide may be in the form of WC and/or W 2 C, and provides hardness and toughness to the composition. The thermal conductivity of WC and W 2 C are not substantially different, and thus, the selection of tungsten carbide in the form of WC and/or W 2 C has a very small, if any, effect on the overall thermal conductivity of the composition. Moreover, any one or more of three different tungsten carbides can be used—Spherical Cast WC/W 2 C, Cast and Crushed WC/W 2 C, Macro-crystalline WC, or combinations thereof. With regard to hardness, Spherical Cast WC/W 2 C has a greater hardness than Cast and Crushed WC/W 2 C, which in turn has greater hardness than Macro-crystalline WC. For toughness properties the Spherical Cast WC/W 2 C has greater toughness than Macro-crystalline WC, which in turn has greater toughness than Cast and Crushed WC/W 2 C. Therefore, to optimize the hardness and toughness properties of the hardfacing composition, Spherical Cast WC/W 2 C is preferred. Accordingly, at least half of the total tungsten carbide (vol %) is preferably Spherical Cast WC/W 2 C. In some embodiments the Spherical Cast WC/W 2 C provides at least 60 percent (vol %) of the total tungsten carbide, optionally at least 70 percent (vol %) of the total tungsten carbide and optionally at least 80 percent (vol %) of the total tungsten carbide. 
     Embodiments of wear and fracture resistant hardfacing compositions described herein preferably have a relatively high thermal conductivity. This is in stark contrast to conventional wisdom as exemplified by U.S. Pat. No. 6,521,353 to Majagi et al., which teaches that a low thermal conductivity is a preferred property of a hardfacing composition. 
     As previously described, the thermal conductivity of WC and W 2 C are not substantially different, and thus, the selection of tungsten carbide in the form of WC and/or W 2 C has a very small, if any, effect on the overall thermal conductivity of the composition. Consequently, the thermal conductivity of the hardfacing composition is primarily driven by the selection of the binder material. Observations of the application of hardfacing to drill bits and analysis of drill bit performance in the field have shown that hardfacing including binder materials with relatively high thermal conductivities experience reduced cracking during the application process, good wear resistance, and greater resistance to thermal stress when used in drilling applications as compared to conventional hardfacing including binder materials with relatively low thermal conductivities. In addition, a high thermal conductivity binder material reduces micro and macro thermal gradients in the hardfacing during application and/or when subjected to thermal loads in service, thereby offering the potential to reduce the propensity for thermal damage. 
     A comparison of the thermal conductivities of various compounds that may be included in the hardfacing binder material are listed in Table 1 below, the data coming from the Handbook of Refractory Compounds by G. V. Samsonov and I. M. Vinitskii, IFI/PLENUM Data Company, 1980. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Thermal Conductivity 
                 Thermal Conductivity 
               
               
                   
                 Phase 
                 W/(m · K) 
                 cal/(cm · sec · ° C.) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Cr 4 B 
                 10.97 
                 0.0262 
               
               
                   
                 Cr 4 B 
                 10.89 
                 0.026 
               
               
                   
                 CrB 
                 20.10 
                 0.048 
               
               
                   
                 Cr 2 B 5   
                 18.00 
                 0.043 
               
               
                   
                 Fe 2 B 
                 30.14 
                 0.072 
               
               
                   
                 Co 3 B 
                 17.00 
                 0.0406 
               
               
                   
                 Co 2 B 
                 13.98 
                 0.0334 
               
               
                   
                 CoB 
                 17.00 
                 0.0406 
               
               
                   
                 Ni 3 B 
                 41.87 
                 0.1 
               
               
                   
                 Ni 2 B 
                 54.85 
                 0.131 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1 above, cobalt, iron, or chromium based binder materials, which form iron boride, cobalt boride and chromium boride after hardfacing deposition, respectively, have significantly lower thermal conductivities than nickel based binder materials that form nickel boride compounds. Consequently, in many conventional hardfacing compositions that preferred low thermal conductivities, cobalt, iron, chromium, or combinations thereof were often included in the binder material. To the contrary, in embodiments described herein, a binder with a relatively high thermal conductivity is preferred, and thus, the hardfacing composition preferably comprises a nickel based binder material (e.g., nickel-silicon-boron binder material). 
     The binder material also includes silicon (Si) and boron (B). As used herein, the phrase “binder flux” refers to the boron and silicon in the binder material of the hardfacing composition. During the deposition of the hardfacing composition, part of the silicon in the binder material may gather oxygen to form SiO 2  as a slag on the top of the surface of the hardfacing. Silicon in the form of slag on the surface can be removed and is not considered as a part of the hardfacing composition. Although NiSi 3  may form during deposition and coexist with NiB 3 , no NiSi 3  phase was observed in the hardfacing compositions described in the examples below. 
     As previously described, binder materials that include cobalt, iron, or chromium have lower thermal conductivities. Accordingly, in embodiments described herein, the binder material preferably contains less than 1.0 wt % of elements other than nickel, boron and silicon, more preferably contain less than 0.75 wt % of elements other than nickel, boron and silicon, more preferably less than 0.5 wt % of elements other than nickel, boron and silicon, and still more preferably less than 0.25 wt % of elements other than nickel, boron and silicon. In particular, embodiments of hardfacing compositions described herein are preferably completely free or at least substantially free (only trace quantities, if any) of chromium, cobalt or iron. 
     The quality of hardfacing deposited on an underlying metal substrate can be dependent on the fluidity of the hardfacing material during the application. In general, a good fluidity during deposition results in better bonding between the hardfacing and the substrate, a more even distribution of the hardfacing, and a more uniform hardfacing thickness. A number of samples of hardfacing having various binder compositions and various tungsten carbide loadings were applied to observe the fluidity characteristics. Table 2 shows the results of these tests. Herein, binder material compositions are noted with an “X-a Y-b Z” nomenclature, where “X”, “Y”, and “Z” represent the elements in the binder material, “a” represents the wt % of element “Y” in the binder material composition, and “b” represents the wt % of element “Z” in the binder material composition. Element “X” does not include a wt % as it represents the balance of the binder material composition. For example, the hardfacing composition of Sample 1 shown below comprises 70 wt % WC/W 2 C and 30 wt % binder material. The binder material of Sample 1 includes nickel, silicon, and boron, with the silicon content of the binder material being 3.39 wt %, the boron content of the binder material being 1.78 wt %, and nickel being the balance of the binder material. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 WC/W 2 C Content of 
                 Binder Material Content of 
                 Binder Material 
                   
                 Binder Flux (Si + B) 
                   
               
               
                   
                 Hardfacing Composition 
                 Hardfacing Composition 
                 Composition 
                 WC/W 2 C 
                 Content 
                   
               
               
                 Sample 
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 Shape 
                 (wt %) 
                 Fluidity 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 1 
                 70 
                 30 
                 Ni-3.39 Si-1.78 B 
                 spherical 
                 5.17 
                 poor 
               
               
                 2 
                 75 
                 25 
                 Ni-4.56 Si-3.27 B 
                 spherical 
                 7.83 
                 good 
               
               
                 3 
                 80 
                 20 
                 Ni-4.56 Si-3.27 B 
                 spherical 
                 7.83 
                 good 
               
               
                 4 
                 70 
                 30 
                 Ni-3.98 Si-2.53 B 
                 spherical 
                 6.51 
                 good 
               
               
                 5 
                 70 
                 30 
                 Ni-1.0 Cr-3.3 Si-1.6 B-0.75 Fe 
                 spherical 
                 4.90 
                 poor 
               
               
                 6 
                 70 
                 30 
                 Ni-3.39 Si-1.78 B 
                 angular 
                 5.17 
                 poor 
               
               
                 7 
                 55 
                 45 
                 Ni-3.51 Si-1.93 B 
                 spherical 
                 5.44 
                 good 
               
               
                 8 
                 58 
                 42 
                 Ni-3.51 Si-1.93 B 
                 spherical 
                 5.44 
                 good 
               
               
                 9 
                 70 
                 30 
                 Ni-4.56 Si-3.27 B 
                 spherical 
                 7.83 
                 good 
               
               
                 10 
                 65 
                 35 
                 Ni-4.56 Si-3.27 B 
                 spherical 
                 7.83 
                 good 
               
               
                 11 
                 65 
                 35 
                 Ni-3.98 Si-2.53 B 
                 spherical 
                 6.51 
                 good 
               
               
                 12 
                 60 
                 40 
                 Ni-3.98 Si-2.53 B 
                 spherical 
                 6.51 
                 good 
               
               
                 13 
                 60 
                 40 
                 Ni-3.39 Si-1.78 B 
                 spherical 
                 5.17 
                 poor 
               
               
                 14 
                 60 
                 40 
                 Ni-3.51 Si-1.93 B 
                 spherical 
                 5.44 
                 poor 
               
               
                 15 
                 68 
                 32 
                 Ni-9.5 Cr-3 Fe-3 Si-1.6 B-0.3 C 
                 spherical 
                 4.8 
                 poor 
               
               
                 16 
                 60 
                 40 
                 Ni-9.5 Cr-3 Fe-3 Si-1.6 B-0.3 C 
                 spherical 
                 4.8 
                 poor 
               
               
                   
               
            
           
         
       
     
     As shown in Table 2, samples having a greater binder flux (silicon plus boron) content (wt %) in the binder material exhibited better fluidity than comparable compositions having a lower binder flux (silicon plus boron) content (wt %) in the binder material. Both Samples 4 and 5 had hardfacing compositions of 70 wt % tungsten carbide and 30 wt % of a nickel based binder material. Sample 4 had a non-Ni binder material content of 6.51 wt % made up exclusively of Si and B, and exhibited good fluidity properties. Sample 5 had a non-Ni binder material content of 6.65 wt %, of which 1.0 wt % was Cr, 0.75 wt % was Fe, and 4.90 wt % was binder flux (Si and B), and exhibited poor fluidity properties. The 1.75 wt Cr and Fe content in binder material of Sample 5 changed the binder material characteristic from one of good fluidity to one of poor fluidity. For this reason, as well as the impact on thermal conductivity described above, in embodiments of hardfacing compositions described herein, the binder material preferably contains less than 1.0 wt % of elements other than nickel, boron and silicon; more preferably contain less than 0.75 wt % of elements other than nickel, boron and silicon; more preferably less than 0.5 wt % of elements other than nickel, boron and silicon; and still more preferably less than 0.25 wt % of elements other than nickel, boron and silicon. In particular, embodiments of hardfacing compositions described herein are preferably completely free or at least substantially free (only trace quantities, if any) of chromium, cobalt or iron. 
     Samples 1 and 6 are identical other than Sample 1 is composed of spherical tungsten carbide while Sample 6 is composed of angular (non-spherical) tungsten carbide. Both Samples 1 and 6 exhibited poor fluidity. 
     Samples 15 and 16 were commercially available hardmetal compositions and are available from Technogenia S.A. under the names Technosphere® GG and LaserCarb®. Both samples 15 and 16 exhibited poor deposition fluidity. 
       FIG. 7  is a graph of the data from Table 2 illustrating the effect of the content of the binder flux (boron and silicon) (wt %) in the binder material and the content of the carbide (wt %) in the hardfacing composition on the deposition fluidity. In general, as the binder flux content in the binder material increases, the carbide (hardphase) content in the hardfacing composition can be increased while maintaining good fluidity. For example, carbide contents of 65 wt % and 70 wt % in the hardfacing composition are achieved while maintaining good deposition fluidity at a binder flux content above 6 wt % in the binder material. At binder flux content above 7 wt % in the binder material, good deposition fluidity is maintained with carbide contents of greater than 70 wt % in the hardfacing composition. 
     As shown in  FIG. 7 , good deposition fluidity was observed for hardfacing compositions having a carbide content (wt %) in the hardfacing composition up to eleven times the binder flux content (wt %) in the binder material. The upper dashed line on the graph in  FIG. 7  indicates a ratio of 11:1 of the carbide content (wt %) in the hardfacing composition to the binder flux content (wt %) in the binder material; and the lower dashed line on the graph in  FIG. 7  indicates a ratio of 8:1 of the carbide content (wt %) in the hardfacing composition to the binder flux content (wt %) in the binder material. Good fluid depositions were observed in hardfacing composition samples having carbide content (wt %) in the hardfacing composition to the binder flux content (wt %) in the binder material ratios between 8:1 and 11:1 (i.e., between the dashed lines on  FIG. 7 ). Thus, embodiments of hardfacing compositions described herein, the carbide content (wt %) in the hardfacing composition is preferably between eight to eleven times the binder flux content (wt %) in the binder material, and more preferably between nine to eleven times the binder flux content (wt %) in the binder material. 
     Samples 15 and 16, the commercially available hardfacing compositions, are designated by triangles in  FIG. 7 . Both Samples 15 and 16 have a ration of carbide content (wt %) in the hardfacing composition to the binder flux content (wt %) in the binder material greater than 11:1 (i.e., above the upper dashed line on  FIG. 7 ), and thus, are located in the poor deposition fluidity region of  FIG. 7 . 
     A binder material having a relatively high thermal conductivity and good deposition fluidity has been found to reduce the propensity for undesirable thermal stress cracking in the hardfacing material layer in the application process as well as during use. Improvements in deposition fluidity also enable a thicker layer of the hardfacing material to be applied to the underlying substrate, thereby providing added wear resistance and extending the life of the associated hardware. 
     Due to the improved thermal properties, tests of hardfacing compositions described herein have been air cooled without cracking, and without the use of insulation to manage post-deposition cooling rates. Many conventional hardfacing compositions require the use of insulation during the cooling process to reduce hardfacing cracking and spalling. 
     Hardware (e.g., bearings), downhole tools and equipment (e.g., stabilizers, collars, etc.), drill bits (e.g., fixed cutter bits, roller cone bits, percussion bits, etc.), and other devices having wear and fracture resistant surfaces formed from the hardfacing compositions and/or binder materials described herein offer the potential for a more consistent hardfacing microstructure with a reduction of the detrimental effects of thermal applications (e.g., the introduction of unwanted thermal stress-related cracks into the material microstructure) as compared to conventional hardfacing compositions. In addition, they can provide a surface layer or surface feature with enhanced resistance to wear, thermal stress and material loss, as well as an ability to achieve a reproducible and dimensionally consistent hardfacing layer thickness. As a result, embodiments of hardfacing compositions described herein offer the potential to enhance the service life of the underlying hardware (e.g., bearing, drill bit, etc.). 
     Two samples of a hardmetal composition according to the principles described herein, Samples A and B, and two conventional commercially available hardfacing compositions, Samples D and E, were tested for low stress abrasion resistance according to the ASTM G65 standards and high stress abrasion resistance according to the ASTM B611 standards. Sample A had a composition of 70 wt % WC/W 2 C and 30 wt % binder material (Ni-4.56 Si-3.27 B), and Sample B had a composition of 55 wt % WC/W 2 C and 45 wt % binder material (Ni-3.39 Si-1.78 B). Sample D is a conventional hardfacing having a composition of 55 wt % angular WC/W 2 C and a 45 wt % binder material (Ni-7.5Cr-3Fe-3.5Si-1.5B-0.3C) commercial available as Eutectic 8913 from Eutectic Corporation of Menomonee Falls, Wis., and Sample E is a conventional hardfacing having 68 wt % spherical WC/W 2 C and a 32 wt % binder (Ni-9.5 Cr-3 Fe-3 Si-1.6 B-0.6 C) commercially available as Technosphere GG from Technogenia S.A. of Conroe, Tex. In addition, a material composition used to make the matrix bodies of drill bits, Sample C, was also tested according to the ASTM G65 testing standards and ASTM B611 standards, and used as a comparative sample. Sample C was a tungsten carbide matrix body bit material manufactured by infiltrating tungsten carbide particles, macrocrystalline WC or chill-cast and crushed WC/W 2 C, or a mixture thereof, with a Cu—Ni—Mn—Zn alloy, comprising a 66 vol % WC content in a Cu based alloy (Cu-15 Ni-24 Mn-8 Zn). The material of Sample C is commercially available from Kennametal, Inc. of Latrobe, Pa. 
     Microstructure images of embodiments described herein applied by various thermal spray techniques are shown in  FIG. 8 , and illustrate a crack-free and relatively dense structure with uniform distribution of spherical WC/W 2 C particles throughout the hardfacing layer thickness. In particular, the upper image shown in  FIG. 8  is the microstructure of Sample A in Table 3 and the lower image shown in  FIG. 8  is the microstructure of Sample B in Table 3. Microstructure images of comparative Samples D and E are shown in  FIG. 9 , and illustrate pores and micro-cracks throughout the hardfacing layer thickness. 
     The test results indicated that Sample A applied via flame spray application process resulted in better abrasion resistance as compared to the commercially available hardfacing compositions (Samples D and E), while Sample B applied via laser cladding application process, and containing lower content of WC/W 2 C than Sample A, had an abrasion resistance comparable to Samples D and E. The abrasion resistance test data are shown in Table 3 below. 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Low Stress Abrasion 
                 High Stress Abrasion 
               
               
                   
                 ASTM G65 
                 ASTM B611 
               
               
                 Sample 
                 (mm 3 /1000 revolutions) 
                 (mm 3 /1000 revolutions) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
            
               
                 A (flame spray) 
                 0.78 
                 0.36 
               
               
                 B (laser clad) 
                 1.50 
                 0.52 
               
               
                 C (comparative 
                 1.67 
                 1.23 
               
               
                 matrix bit material) 
                   
                   
               
               
                 D (conventional 
                 3.38 
                 0.75 
               
               
                 hardfacing) 
                   
                   
               
               
                 E (conventional 
                 1.33 
                 0.42 
               
               
                 hardfacing) 
               
               
                   
               
            
           
         
       
     
     In general, the lower the volume of material removed/lost by abrasive wear (mm 3 /1000 revolutions), the better the abrasion wear resistance per low-stress and high-stress abrasion test. As shown in Table 3, Sample A had a low stress abrasion of 0.78 mm 3 /1000 revolutions and a high stress abrasion of 0.36 mm 3 /1000 revolutions, and Sample B had a low stress abrasion of 1.50 mm 3 /1000 revolutions and a high stress abrasion of 0.52 mm 3 /1000 revolutions. Thus, Samples A and B each had a low stress abrasion of less than or equal to 1.50 mm 3 /1000 revolutions, and a high stress abrasion less than or equal to 0.52 mm 3 /1000 revolutions. For embodiments of hardfacing compositions described herein, the low stress abrasion is preferably equal to or less than 2.0 mm 3 /1000 revolutions, more preferably equal to or less than 1.7 mm 3 /1000 revolutions, more preferably equal to or less than 1.5 mm 3 /1000 revolutions, more preferably equal to or less than 1.3 mm 3 /1000 revolutions, and still more preferably equal to or less than 1.0 mm 3 /1000 revolutions or less. Further, for embodiments of hardfacing compositions described herein, the high stress abrasion is preferably equal to or less than 1.0 mm 3 /1000 revolutions, more preferably equal to or less than 0.75 mm 3 /1000 revolutions, more preferably equal to or less than 0.6 mm 3 /1000 revolutions, and still more preferably equal to or less than 0.5 mm 3 /1000 revolutions. 
       FIGS. 2-4 ,  5 , and  6  previously described illustrate exemplary devices to which embodiments of hardfacing compositions described herein can be applied to enhance wear resistance, reduce thermal stress induced cracking, and generally enhance service durability. However, it should be appreciated that embodiments of hardfacing compositions described herein may also be applied to a multitude of other devices for which wear resistant hardfacing is beneficial such as drilling equipment (e.g., reamers, under-reamers, V-stabs, centralizers, and the like), drill collars, percussion drill bits, and bearings (e.g., radial bearings, needle bearings, thrust bearings, ball bearings, roller bearings, etc.) Moreover, although  FIGS. 2-4 ,  5 , and  6  disclose the application of hardfacing compositions on outer surfaces of exemplary devices, embodiments of hardfacing described herein may also be applied to radially inner surfaces. 
     Referring now to  FIG. 10 , a radial bearing  90  for supporting radial loads while allowing relative rotation between two components is shown. Radial bearing  90  is a roller bearing having a central axis  95  and including an outer race  91 , an inner race  92  disposed within outer race  91 , and a plurality of circumferentially spaced roller elements  93  radially positioned between races  91 ,  92 . Race  91  is a ring including an annular recess or groove  91   a  on its inner surface, and race  92  is a ring including an annular recess or groove  92   a  on its outer surface. Roller elements  93  are seated in recesses  91   a ,  92   a , which restrict roller elements  93  from moving axially relative to races  91 ,  92 . A cage  94  is provided between races  91 ,  92  to maintain the circumferential spacing of roller elements  93 . 
     In operation, races  91 ,  92  rotate about axis  95  relative to each other, and roller elements  93  roll in recesses  91   a ,  92   a . Roller elements  93  support radial loads while allowing races  91 ,  92  to roll with very little rolling resistance and sliding. Contact between races  91 ,  92  and roller elements  93  under radial load over time can wear and/or dent races  91 ,  92  and roller elements  93 , as well as increase the temperature of races  91 ,  92  and roller elements  93 . Thus, to enhance resistance to wear and thermal stresses, hardfacing  96  in accordance with the principles described herein is applied to races  91 ,  92  in grooves  91   a ,  92   a , respectively, and applied to the outer surfaces of roller elements  93 . Although radial bearing  90  is a cylindrical roller bearing, hardfacing  96  may also be applied to contact surfaces between races and roller elements in other types of bearings such as radial ball bearings, thrust bearings, tapered roller bearings, etc. 
     Cracks in hardfacing employed on radial bearings are particularly detrimental due to the relatively high heat generated along the contact surfaces of radial bearings. In particular, spalling, delamination, and separation of the hardfacing from the underlying substrate due to thermal stresses typically initiates at original crack sites, and can lead to catastrophic failure. 
     A variety of hardfacing compositions were tested for use with radial bearings such as radial bearing  90  previously described.  FIG. 11  shows the testing apparatus  100  used to test the hardfacing compositions. Apparatus  100  includes a stand  110 , a shaft  120  rotatably coupled to the stand, a bearing wheel  121  mounted to shaft  120 , a lever arm  130  pivotally coupled to stand  110 , and a wear wheel  131  rotatably coupled to lever arm  130 . Bearing wheel  121  is coaxially aligned with and fixably attached to shaft  120 , and thus, wheel  121  and shaft  120  rotate about the central axis  125  of shaft  120 . Rotation of shaft  120 , and hence wheel  121 , is driven by a motor  140 . Lever arm  130  pivots relative to stand  110  about an axis  135  oriented parallel to axis  125 , and wear wheel  131  rotates relative to lever arm  130  about an axis parallel to axes  125 ,  135 . By applying a load L to the end of lever arm  130  distal axis  135  and wheel  131 , wear wheel  131  is pressed into rolling engagement with bearing wheel  121 . By varying load L, the compressive forces between wheels  121 ,  131  can be controlled and varied. 
     Three different samples of hardfacing compositions were tested using apparatus  100 . For testing, a plurality of bearing wheels  121  and wear wheels  131  were machined from AISI 4130 steel. Each wear wheel  131  had a diameter of 38 mm and an axial length of 12.7 mm, and each bearing wheel  121  had a diameter of 105 mm and an axial length of 95 mm. The different hardfacing compositions to be tested were then applied to the radially outer surfaces contact surfaces of wheels  121 ,  131  by laser cladding or plasma transferred arc welding (PTAW). One hardfacing composition was tested in each test. Further, for each given test, the same hardfacing composition was applied to both wheels  121 ,  131 . To test the applied hardfacing compositions in a radially compressive rolling environment as would be experienced in a radial bearing, a downward load L of 80 lbf. was applied to lever arm  130  to press wheel  131  into wheel  121 , and wheels  121 ,  131  were rotated at 60 RPM and 150 RPM, respectively. After 480 minutes of continuous rolling contact under load L, wheels  121 ,  131  were removed from apparatus  100  and analyzed. In particular, the radial depth of wear in each wheel  121 ,  131  was calculated by comparing the measured outer diameter of each wheel  121 ,  131  before testing and the measured outer diameter of each wheel  121 ,  131  along the wear track after testing. The radial bearing wear simulation test data are shown in Table 4 below. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                 Binder 
                   
                 Radial 
                 Radial 
               
               
                   
                   
                 WC/W 2 C Content 
                 Material Content 
                   
                 Depth of 
                 Depth of 
               
               
                   
                 Hardfacing 
                 of Hardfacing 
                 of Hardfacing 
                 Binder Material 
                 Wear in 
                 Wear in 
               
               
                   
                 Application 
                 Composition 
                 Composition 
                 Composition 
                 Bearing 
                 Wear Wheel 
               
               
                 Sample 
                 Process 
                 (wt %) 
                 (wt %) 
                 (wt %) 
                 Wheel (mm) 
                 (mm) 
               
               
                   
               
             
            
               
                 A′ 
                 Laser 
                 60 
                 40 
                 Ni-4.0 Si-2.5 B 
                 0.28 
                 0.20 
               
               
                   
                 cladding 
                   
                   
                   
                   
                   
               
               
                 B′ 
                 Laser 
                 60 
                 40 
                 Ni-3.1 Si-1.7 B-9.5 Cr-3 Fe-0.3 C 
                 0.51 
                 0.66 
               
               
                   
                 cladding 
                   
                   
                   
                   
                   
               
               
                 C′ 
                 PTAW 
                 65 
                 35 
                 Ni-3.8 Si-3.3 B-16.5 Cr-0.8-1.0 W-0.8 to 1.0 C 
                 0.36 
                 1.55 
               
               
                   
               
            
           
         
       
     
     The type of WC/W 2 C employed in each sample tested was the 80-210 μm diameter spherical WC/W 2 C particles manufactured by Technogenia S.A. of Conroe, Tex. Thus, the primary difference between the samples was the composition of the binder material, and more specifically, the alloying elements in the Ni-alloy. Sample A′ was a hardfacing composition in accordance with the principles described herein, including only nickel, silicon, and boron in the binder material, whereas Samples B′ and C′ were conventional hardfacing compositions having a binder material that included iron and/or chromium. 
     As shown in Table 4, Sample A′ provided greater wear resistance on both the bearing wheel and the wear wheel than Samples B′ and C′. Without being limited by this or any particular theory, it is believed that the performance differences between the three hardfacing compositions was primarily due to differences in the thermal conductivity of the binder materials. The primary phase in the binder material of Sample A′ was Ni 3 B, whereas the primary phase in the binder material in Samples B′ and C′ was CrB. 
     To assess the impact of the addition of chromium, iron, aluminum, or combinations thereof in the binder material on hardfacing thermal conductivity, four cylinders were fabricated by Spark Plasma Sintering (SPS). Each cylinder had a composition identical to powdered mixtures of hardfacing. In particular, to form each cylinder, a premix of 60 wt %, 80-210 μm diameter spherical WC/W 2 C particles and 40 wt % Ni-alloy powder were placed in a graphite sleeve and then positioned between two graphite plungers in a vacuum chamber. A different Ni-alloy composition was used for each of the four cylinders, as shown in Table 5 below. The chamber was then evacuated to ˜7 Pa, electrical power was supplied through the graphite sleeve to heat the powered mixture, and uniaxial force was gradually increased on one of the plungers. Sintering was carried out under a uniaxial force of 59 MPa in a vacuum of 20 Pa at 1213K. At least 99.9% theoretical density was achieved in each sintered material. Disk-shaped samples having a diameter of 12.7 mm and axial length of 2 mm were machined from the SPS sintered cylinders, and then subjected to thermal diffusivity and specific heat measurements at 300K and 810K using a Holometrix Thermalflash 2200 instrument available from Holometrix Inc, of Cambridge, Mass. according to STM E1461-92 “Standard Test Method for Thermal Diffusivity of Solids by the Flash Method.” Using the thermal diffusivity and specific heat measurements, the thermal conductivity was calculated according to the following equation:
 
κ= D·Cp·ρ 
     where κ is the thermal conductivity, D is the measured diffusivity, Cp is the measured specific heat, and ρis the density of the test material.   

     
       
         
           
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 WC/W 2 C Content of 
                 Binder Material Content 
                 Thermal 
                 Thermal 
               
               
                   
                 Hardfacing Material 
                 of Hardfacing Material 
                 Conductivity 
                 Conductivity 
               
               
                 Sample 
                 (wt %) 
                 (wt %) 
                 (300K) 
                 (810K) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 A″ 
                 60 
                 40 (Ni-4.0 Si-2.5 B) 
                 26.2 
                 32.1 
               
               
                 B″ 
                 60 
                 40 (Ni-3.5 Si-1.9 B) 
                 24.9 
                 31.3 
               
               
                 C″ 
                 60 
                 40 (Ni-3.5 Si-1.9 B-0.75 Al) 
                 22.5 
                 29.1 
               
               
                 D″ 
                 60 
                 40 (Ni-4.5 Si-3.1 B-7 Cr-2 Fe) 
                 16.2 
                 23.8 
               
               
                   
               
            
           
         
       
     
     As shown in Table 5, Sample A″ had the same composition as Sample A′ previously described. In addition, Samples A″ and B″, each had a binder material consisting exclusively of nickel, silicon, and boron. Sample C″ was the same to Sample B″ with the exception that Sample C″ included small quantities of aluminum in the binder material. Sample D″ had a conventional hardfacing composition including chromium and iron. Samples A″ and B″ exhibited a significantly higher thermal conductivity at 300K and 810K than the Sample D″. Since Sample C′ had the same composition as Sample B′ with the sole exception that aluminum was added to the binder material, Sample C′ provided insight as to the detrimental effect of an elemental addition to the binder material on thermal conductivity. In particular, a 0.75 wt % addition of aluminum in the Ni, 3.5 Si, 1.9 B binder material degraded thermal conductivity by 9.6% and 7% at 300K and 810K, respectively. Further, as shown by the Sample D″, additions of chromium and iron in the binder material drastically reduced thermal conductivity, thereby confirming that a hardfacing composition having a binder material comprising chromium and iron lowers its thermal conductivity. 
     Embodiments of hardfacing compositions described herein preferably have a thermal conductivity greater than 22.0 W/(m·K) or 0.053 cal/(cm·sec·° C.) at 300K, and more preferably a thermal conductivity of greater than 25.0 W/(m·K) or 0.060 cal/(cm·sec·° C.). To achieve the relatively high thermal conductivity, as well as good deposition fluidity discussed above, the binder material preferably comprises 0.5 to 10 wt % silicon and 0.5 to 14 wt % boron, with the balance of the binder material being nickel. 
     While preferred embodiments have been shown and described, modifications thereof can be made by one skilled in the art without departing from the scope or teachings herein. The embodiments described herein are exemplary only and are not limiting. Many variations and modifications of the systems, apparatus, and processes described herein are possible and are within the scope of the invention. For example, the relative dimensions of various parts, the materials from which the various parts are made, and other parameters can be varied. Accordingly, the scope of protection is not limited to the embodiments described herein, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims. Unless expressly stated otherwise, the steps in a method claim may be performed in any order. The recitation of identifiers such as (a), (b), (c) or (1), (2), (3) before steps in a method claim are not intended to and do not specify a particular order to the steps, but rather are used to simply subsequent reference to such steps.