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RELATED APPLICATIONS  
       [0001]     This nonprovisional patent application claims the benefit of co-pending, provisional patent application U.S. Ser. No. 60/737,003, filed on Nov. 15, 2005, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates in general to drill bits for well drilling, and in particular to a metallic hardfacing matrix and method of applying the metallic hardfacing matrix to drill bits.  
         [0004]     2. Background of the Invention  
         [0005]     Rotary well drilling for oil and gas is primarily accomplished through one of two types of bits. In a rotary cutter bit, the bit body has typically three rotatable cones or cutters. The cones rotate on bearing pins and have teeth or tungsten carbide inserts for disintegrating the earth formation. In the fixed cutter or drag bit type, the bit body has a face which contains cutting elements mounted on fixed blades. The cutting elements are typically polycrystalline diamond. The bit body has drilling fluid passages with nozzles for discharging drilling fluid through junk slots that are located between the blades.  
         [0006]     Drag bits are extensively used in directionally drilling, particularly in the technique referred to as steerable drilling. In this method, the drill bit is steered in desired directions for cutting borehole segments as it progresses. A mud motor or turbine is employed with the bit assembly for rotating the drag bit while the drill string remains stationary.  
         [0007]     Hardfacing or wear-resistant materials are typically connected to the outer surfaces of drill bits to help reduce wear and maintain the efficiency of the drill bit. Commonly used hardfacing includes tungsten carbide particles that are welded in place on the outer surface of the drill bit. U.S. Reissue Pat. No. RE 37,127 provides an in depth discussion of hardfacings, and is incorporated herein by reference in its entirety. Even with skilled welders, imperfections can be present due to varying thicknesses of the weld, shape of the drill bit the hardfacing is being welded upon, and the beads associated with welding processes. Machining can be time-consuming and expensive. Moreover, hardfacing was not welded to inner parts due to narrow clearances and expense.  
       SUMMARY OF THE INVENTION  
       [0008]     A method of increasing the durability of a drill bit, which includes the step providing a pliable sheet of a hardfacing matrix material. The pliable sheet of hardfacing material has a nickel and chromium matrix combined with a first element. The first element is selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, and metallic glass. The hardfacing matrix material sheet is placed on a preselected surface of the drill bit. The hardfacing matrix material sheet is then fusion bonded to the drill bit.  
         [0009]     The fusion bonding can be performed by heating the drill bit and hardfacing matrix material sheet in a furnace at about 2100 degrees Fahrenheit. The fusion bonding can also be in a furnace at about 2100 degrees Fahrenheit for a duration of between about five minutes and about ten minutes.  
         [0010]     In step in which the hardfacing matrix material sheet is placed on the preselected surfaced, an adhesive located on a surface of the hardfacing matrix material sheet can secure the hardfacing matrix material sheet in place relative to the preselected surface of the drill bit prior to the fusion bonding step. The preselected surface can comprise an outer gage surface, and a slot surface between a pair of bit blades. The drill bit can be a drag bit or a tri-cone bit.  
         [0011]     The hardfacing matrix material can also comprises a second element, which was not previously selected as the first element. The second element is selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, metallic glass, microcrystalline tungsten carbide and macrocrystalline tungsten carbide. The hardfacing matrix material can further comprise a third element, which was not previously selected as either the first or second elements. The third element is selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, metallic glass, microcrystalline tungsten carbide and macrocrystalline tungsten carbide.  
         [0012]     A method of increasing the durability of a drag bit type of drill bit, when the drag bit has a plurality of blades and a slot formed between each pair of adjacent blades. Each of the blades have a cutting region with cutting elements and a gage surface free of cutting elements. The method includes the step of providing a sheet of a hardfacing matrix material comprising a nickel and chromium matrix combined with a first element selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, and metallic glass. The sheet of a hardfacing matrix material is cut into a pattern corresponding to a preselected surface of the drag bit. The pattern is adhered to the preselected surface of the drag bit. The drill bit, with the pattern adhered thereto is heated in order to bond the pattern to the drag bit.  
         [0013]     The preselected surface can be the gage surface. The preselected surface can be the gage surface and the slot.  
         [0014]     The hardfacing matrix material can also include a second element, which was not previously selected as the first element. The second element is selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, metallic glass, microcrystalline tungsten carbide and macrocrystalline tungsten carbide. The hardfacing matrix material can further include a third element, which was not previously selected as either the first or second elements. The third element is selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, metallic glass, microcrystalline tungsten carbide and macrocrystalline tungsten carbide.  
         [0015]     An earth-boring bit includes a bit body with a bit face at its lower end and a nozzle opening to the bit face for discharging drilling fluid from an interior of the bit body. A plurality of blades are formed on and protrude from the bit face. The plurality of blades extend radially outward from a central portion of the bit face to a gage area at the periphery of the bit body. Each blade carries a plurality of cutters thereon. Each pair of blades define a slot extending therebetween for the passage of drilling fluid and cuttings. A layer of hardfacing material is bonded to a surface of the bit body. The hardfacing material is substantially uniform in thickness and free of weldbeads. The hardfacing material includes a nickel and chromium matrix combined with a first element selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, and metallic glass. A bond region is located between the layer of hardfacing material and the surface of the bit body to which the layer of hardfacing material is bonded.  
         [0016]     The bond region can include nickel and chromium from the layer of hardfacing and iron from the bit body, and the bond region can be formed when the layer of hardfacing is bonded to the surface of the bit body with heat. The surface of the bit body to which the layer of hardfacing is bonded can be the gage surface. The surface of the bit body to which the layer of hardfacing is bonded can be the slot. The surface of the bit body to which the layer of hardfacing can be within the nozzle.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a perspective view showing a drag bit assembly without hardfacing.  
         [0018]      FIG. 2  is a vertical sectional view of the drag bit assembly of  FIG. 1 .  
         [0019]      FIG. 3  is perspective view of a hardfacing material matrix sheet constructed in accordance with this invention.  
         [0020]      FIG. 4  is top plan view of the hardfacing material matrix sheet of  FIG. 3 , showing a pattern to be cut therefrom.  
         [0021]      FIG. 5  is a perspective view showing the drag bit assembly of  FIG. 1 , with cutouts from the hardfacing material matrix sheet of  FIG. 3  being attached thereto.  
         [0022]      FIG. 6  is an enlarged sectional view of the interface between the outer surface of the drag bit assembly of  FIG. 1  and the hardfacing material matrix sheet of  FIG. 3  after fusion bonding.  
         [0023]      FIG. 7  are schematic perspective views of various forms of spherical cast tungsten carbide in accordance with this invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]     Referring to  FIG. 1 , bit assembly  11  has a body  13  on a lower end. Body  13  has a face  15  on its lower end. A plurality of blades  17  are formed on and protrude from face  15 , with six blades  17  being shown in the drawings. Blades  17  lead outward from a central portion of face  15  to a gage area at the periphery of body  13 . Blades  17  are separated from each other, defining junk slots  19  between them for the passage of drilling fluid and cuttings. Each blade  17  contains a row of conventional cutters typically polycrystalline diamond (PCD). Nozzles  23  discharge drilling fluid, which flows through junk slots  19  and back up the borehole along with the cuttings. While bit assembly  11  is illustrated as a “drag bit” or steel-bodied bit, it should be readily apparent to those skilled in the art that the teachings herein are also applicable to tri-cone bits, or cast bits, such as those illustrated in FIG. 1 of U.S. Reissue Pat. No. RE 37,127.  
         [0025]     A set of primary gage pads  25  is integrally formed on the sides of bit body  13 . Each primary gage pad  25  is contiguous with and, in the embodiment shown, extends longitudinally from one of the blades  17 . Alternately, primary gage pads  25  could be inclined relative to the axis or curved in a spiral. Each primary gage pad  25  protrudes from body  13 , extending the junk slots  19 . Primary gage pads  25  are dimensioned to have an outer surface  26  at the gage or diameter of the borehole being cut. Outer surface  26  contains wear resistant surfaces, but is smooth and free of any cutting structure. Bit body  13 , along with blades  17  and gage pads  25 , may be formed of a metal matrix composite or steel using a casting or machining process.  
         [0026]     Referring to  FIG. 2 , a steel threaded coupling or blank  27  is joined to an upper end of body  13 . Blank  27  is bonded to body  13  during the casting process. Blank  27  protrudes from the upper end of body  13  and has threads  29  on its exterior. An axial passage  31  extends through blank  27  and joins nozzles  23  for delivering drilling fluid.  
         [0027]     A shank  33  is secured to blank  27 . Shank  33  is also formed of steel, rather than of a carbide matrix. Shank  33  is a cylindrical member that may have a length longer than the axial dimension of body  13 . Shank  33  has a threaded receptacle  35  which engages threads  29  of blank  27 . A chamfer or bevel  37  is formed on the lower end of shank  33 . Similarly, a bevel  39  is formed on the upper end of body  13 . The opposed bevels  37 ,  39  create a V-shaped annular cavity. This cavity is filled with a weld material  41 , the welding permanently joining shank  33  to bit body  13 . Shank  33  has an axial passage  43  which registers with passage  31  for delivering drilling fluid. Shank  33  has a threaded pin  45  on its upper end. Pin  45  is dimensioned for securing to a lower end of a drill string.  
         [0028]     Bit assembly  11  operates in a manner that is conventional with other steerable drag bit assemblies. It is normally secured to a turbine or mud motor which is at the lower end of drill string. Drilling fluid pumped down the drill string drives the mud motor, which in turn causes rotation of bit  11 . The spaced apart gage pads  25  stabilize bit  11  to condition the borehole wall, preventing ledging and other irregularities.  
         [0029]     The hardfacing on outer surfaces and leading and trailing edges typically comprises a tungsten carbide material that is welded into place. Depending on the skill of the welder, welding such hardfacing can create imperfections and high stress zones along the weld bead lines or in the hardfacing deposit that can lead to the hardfacing chipping off or disengaging from the surface it is meant to protect with its wear-resistant properties. Even for skilled welders, the process of welding hardfacing can be time consuming, difficult, and tedious due to the geometry of the surfaces to which the hardfacing material is being applied. Some surfaces, like internal surfaces that engage each other, are simply not available for welded hardfacing.  
         [0030]     A hardfacing metal matrix has been used on the internal surfaces of bearings. The hardfacing metal matrix typically comes in the form of a pliable sheet. A desired shape of the hardfacing surface is cut out of the pliable sheet and then fusion bonded onto the target surface, or the surface to be hardfaced. Previous pliable hardfacing sheets comprised a metal matrix that typically included mostly either microcrystalline tungsten carbide or macrocrystalline tungsten carbide with lesser amounts of nickel and chromium.  
         [0031]     Referring to  FIG. 3 , a hardfacing matrix sheet  101  is shown in its pliable state. Hardfacing matrix sheet  101  comprises a hardfacing material matrix  103  and an adhesive surface  105  along one surface. Adhesive surface  105  helps to hold hardfacing matrix sheet  101  against the target surface prior to fusion bonding.  
         [0032]     Hardfacing material matrix  103  preferably comprises spherical sintered tungsten carbide, spherical cast tungsten carbide, or a nanosteel composite also known as “metallic glass.” U.S. Pat. Nos. 6,689,234 and 6,767,419 provide a discussion of metallic glass and disclose various methods of applying metallic glass to a substrate. U.S. Pat. Nos. 6,689,234 and 6,767,419 are incorporated herein by reference in their entireties. Matrix  103  can also comprise a combination of at least two of spherical sintered tungsten carbide, spherical cast tungsten carbide, and metallic glass. Microcrystalline and macrocrystalline tungsten carbide can also be added to matrix  103  having spherical sintered tungsten carbide, spherical cast tungsten carbide, or metallic glass, alone or in combination. Crushed cast tungsten carbide and crushed sintered tungsten carbide may also be added to matrix  103  having spherical sintered tungsten carbide, spherical cast tungsten carbide, or metallic glass, alone or in combination.  
         [0033]     Referring to  FIG. 7 , spherical cast tungsten carbide  117  can comprise numerous shapes. Preferably, spherical cast tungsten carbide  117  for use in matrix  103  will be substantially shaped like a sphere or spherical-shaped  117   a . However, spherical cast tungsten carbide  117 , but it can also be shaped like a sphere that has been stretched from its upper and lower surfaces, or prolate-shaped  117   b . Alternatively, spherical cast tungsten carbide  117  can be shaped like a sphere that has been compressed from its upper and lower surfaces, or oblate-shaped  117   c . Spherical-, prolate-, and oblate-shaped  117   a ,  117   b ,  117   c  shapes of spherical cast tungsten carbide  117  are due to the manufacturing methods of spherical cast tungsten carbide  117  and are useful to illustrate that the name spherical cast tungsten carbide should not limit matrix  103  to only spherical-shaped  117   a  rather than including prolate- and oblate-shaped  117   b ,  117   c  matrixes of cast tungsten carbide.  
         [0034]     Referring to  FIG. 4 , hardfacing matrix sheet  101  is cut along pattern  107  to form a desired shape. As shown in  FIG. 5 , pattern  107  preferably corresponds to a surface on bit assembly  11 . Pattern  107  shown in  FIG. 4 , corresponds to outer surface  57 . However, as shown in  FIG. 5 , various patterns  107   a ,  107   b  can be cut from hardfacing matrix sheet  101  to correspond with desired surfaces on bit assembly. For example, pattern  107   a  corresponds with outer surface  26 , and pattern  107   b , corresponds with body  13  between blades  17 . Moreover, hardfacing matrix sheet  101  can also be cut with patterns to correspond to interior surfaces of bit assembly  11 .  
         [0035]     Patterns  107   a ,  107   b  are placed on the desired surfaces of bit assembly  11 .  FIG. 5 , illustrates bit assembly  11  with patterns  107   a ,  107   b  being placed onto various desired surfaces. Adhesive  105  initially secures patterns  107   a ,  107   b  to the desired surfaces of bit assembly  11 . Bit assembly  11  with the secured patterns  107   a ,  107   b  attached thereto is placed into a furnace. In the preferred embodiment, bit assembly  11  with patterns  107   a ,  107   b  is placed in the furnace for about five to ten minutes at about 2100 degrees Fahrenheit to fusion bond the hardfacing matrix on patterns  107   a ,  107   b  onto the desired outer surfaces of bit assembly  11 . As will be readily appreciated by those skilled in the art, the exact length of time and exact temperature can vary depending upon the composition of hardfacing material matrix  103  in accordance with the variations described above herein. After fusion bonding patterns  107   a ,  107   b  into place, hardfacing material matrix  103  can be machined from a rough surface to a smoother surface as desired.  
         [0036]     Referring to  FIG. 6 , a microscopic representation of the interface between hardfacing material matrix  103  on patterns  107   a ,  107   b  and the desired outer surfaces bit assembly  11  following fusion bonding is shown. Cladding region  109  comprises hardfacing material matrix  103  with the hardfacing material being densely packed substantially uniformly throughout. As discussed above herein, the particular hardfacing material can be in a nickel and chromium matrix including spherical sintered tungsten carbide, spherical cast tungsten carbide, or metallic glass individually, in combination with each other, or in combination with microcrystalline or macrocrystalline tungsten carbide. Bond region  111  is a true metallurgical bond region located between hardfacing material matrix  103  and the desired outer surfaces of bit assembly  11  due to the fusion bonding process. Bond region  111  has high interparticle bond strength and helps to reduce chipping, flaking and cracking. Diffusion zone region  113  results from the fusion bonding process. Bond region  111  comprises nickel and chromium from patterns  107   a ,  107   b  and iron from the substrate or bit assembly  11 . Typically, the substrate or bit assembly  11  uniformly retains most of its mechanical properties. Heat treatable region  115  includes the remainder of the substrate of bit assembly  11 . Region  115  can be heat treated, if necessary, to restore any mechanical properties of bit assembly  11  that may have deteriorated to the fusion bonding process.  
         [0037]     While the invention has been shown in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, bit assembly can also be a tri-cone bit, or cast bit.

Summary:
An earth-boring bit, and a method of increasing the durability of the same, which includes the step providing a pliable sheet of a hardfacing matrix material. The pliable sheet of hardfacing material has a nickel and chromium matrix combined with a first element. The first element is selected from a group consisting of spherical sintered tungsten carbide, spherical cast tungsten carbide, and metallic glass. The hardfacing matrix material sheet is placed on a preselected surface of the drill bit. The hardfacing matrix material sheet is then fusion bonded to the drill bit.