Abstract:
An earth-boring drill bit having a bit body with a cutting component formed from a tungsten carbide composite material is disclosed. The composite material includes a binder and tungsten carbide crystals comprising sintered pellets. The composite material may be used as a hardfacing on the body and/or cutting elements, or be used to form portions or all of the body and cutting elements. The pellets may be formed with a single mode or multi-modal size distribution of the crystals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 11/545,914, filed Oct. 11, 2006, now U.S. Pat. No. 7,510,034, issued Mar. 31, 2009, and claims priority to U.S. Provisional Patent Application Ser. No. 60/725,447, filed on Oct. 11, 2005, and to U.S. Provisional Patent Application Ser. No. 60/725,585, filed on Oct. 11, 2005, the disclosure of each of which is incorporated herein in its entirety by this reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to earth-boring bits and, in particular, to an improved system, method, and apparatus for enhancing the durability of earth-boring bits with carbide materials. 
     2. Description of the Related Art 
     Typically, earth boring drill bits include an integral bit body that may be formed from steel or fabricated of a hard matrix material, such as tungsten carbide. In one type of drill bit, a plurality of diamond cutter devices are mounted along the exterior face of the bit body. Each diamond cutter typically has a stud portion which is mounted in a recess in the exterior face of the bit body. Depending upon the design of the bit body and the type of diamonds used, the cutters are either positioned in a mold prior to formation of the bit body or are secured to the bit body after fabrication. 
     The cutting elements are positioned along the leading edges of the bit body, so that as the bit body is rotated in its intended direction of use, the cutting elements engage and drill the earth formation. In use, tremendous forces are exerted on the cutting elements, particularly in the forward to rear direction. Additionally, the bit and cutting elements are subjected to substantial abrasive forces. In some instances, impact, lateral and/or abrasive forces have caused drill bit failure and cutter loss. 
     While steel body bits have toughness and ductility properties, which render them resistant to cracking and failure due to impact forces generated during drilling, steel is subject to rapid erosion due to abrasive forces, such as high velocity drilling fluids, during drilling. Generally, steel body bits are hardfaced with a more erosion-resistant material containing tungsten carbide to improve their erosion resistance. However, tungsten carbide and other erosion-resistant materials are brittle. During use, the relatively thin hardfacing deposit may crack and peel, revealing the softer steel body, which is then rapidly eroded. This leads to cutter loss, as the area around the cutter is eroded away, and eventual failure of the bit. 
     Tungsten carbide or other hard metal matrix bits have the advantage of high erosion resistance. The matrix bit is generally formed by packing a graphite mold with tungsten carbide powder and then infiltrating the powder with a molten copper alloy binder. A steel blank is present in the mold and becomes secured to the matrix. The end of the blank can then be welded or otherwise secured to an upper threaded body portion of the bit. 
     Such tungsten carbide or other hard metal matrix bits, however, are brittle and can crack upon being subjected to impact forces encountered during drilling. Additionally, thermal stresses from the heat generated during fabrication of the bit or during drilling may cause cracks to form. Typically, such cracks occur where the cutter elements have been secured to the matrix body. If the cutter elements are sheared from the drill bit body, the expensive diamonds on the cutter elements are lost, and the bit may cease to drill. Additionally, tungsten carbide is very expensive in comparison with steel as a material of fabrication. 
     Accordingly, there is a need for a drill bit that has the toughness, ductility, and impact strength of steel and the hardness and erosion resistance of tungsten carbide or other hard metal on the exterior surface, but without the problems of prior art steel body and hard metal matrix body bits. There is also a need for an erosion-resistant bit with a lower total cost. 
     SUMMARY OF THE INVENTION 
     One embodiment of a system, method, and apparatus for enhancing the durability of earth-boring bits with carbide materials is disclosed. Drill bits having a drill bit body with a cutting component include a composite material formed from a binder and tungsten carbide crystals. In one embodiment, the crystals have a generally spheroidal shape, and a mean grain size range of about 0.5 to 8 microns. In one embodiment, the distribution of grain size is characterized by a Gaussian distribution having a standard deviation on the order of about 0.25 to 0.50 micron. The composite material may be used as a component of hardfacing on the drill bit body, or be used to form portions or all of the drill bit and/or its components. 
     In one embodiment, the tungsten carbide composite material comprises sintered spheroidal pellets. The pellets may be formed with a single mode or multi-modal size distribution of the crystals. The invention is well suited for many different types of drill bits including, for example, drill bit bodies with PCD cutters having substrates formed from the composite material, drill bit bodies with matrix heads, rolling cone drill bits, and drill bits with milled teeth. 
     The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the invention, as well as others which will become apparent are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only an embodiment of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a schematic drawing of one embodiment of a single carbide crystal constructed in accordance with the present invention; 
         FIG. 2  is a schematic side view of one embodiment of a pellet formed from the carbide crystals of  FIG. 1  and is constructed in accordance with the present invention; 
         FIG. 3  is a schematic side view of one embodiment of a bi-modal pellet formed from different sizes of the carbide crystals of  FIG. 1  and is constructed in accordance with the present invention; 
         FIG. 4  is a schematic side view of one embodiment of a tri-modal pellet formed from different sizes of the carbide crystals of  FIG. 1  and is constructed in accordance with the present invention; 
         FIG. 5  is a plot of size distributions for samples of various embodiments of carbide crystals constructed in accordance with the present invention, compared to a sample of conventional crystals; 
         FIG. 6  is a plot of wear resistance and toughness for samples of various embodiments of composite materials constructed in accordance with the present invention compared to a sample of conventional composite material; 
         FIG. 7  is a schematic side view of one embodiment of an irregularly shaped particle formed from a bulk crushed and sintered, carbide crystal-based composite material and is constructed in accordance with the present invention; 
         FIG. 8  is a partially sectioned side view of one embodiment of a drill bit polycrystalline diamond (PCD) cutter incorporating carbide crystals constructed in accordance with the present invention; 
         FIG. 9  is a partially sectioned side view of one embodiment of a drill bit having a matrix head incorporating carbide crystals constructed in accordance with the present invention; 
         FIG. 10  is an isometric view of one embodiment of a rolling cone drill bit incorporating carbide crystals constructed in accordance with the present invention; 
         FIG. 11  is an isometric view of one embodiment of a polycrystalline diamond (PCD) drill bit incorporating carbide crystals constructed in accordance with the present invention; 
         FIG. 12  is a micrograph of conventional composite material; 
         FIG. 13  is a micrograph of one embodiment of a composite material constructed in accordance with the present invention; and 
         FIG. 14  is an isometric view of another embodiment of a drill bit incorporating a composite material constructed in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , one embodiment of a carbide crystal  21  constructed in accordance with the present invention is depicted in a simplified rounded form. In the embodiment shown, crystal  21  is formed from tungsten carbide (WC) and has a mean grain size range of about 0.5 to 8 microns, depending on the application. The term “mean grain size” refers to an average diameter of the particle, which may be somewhat irregularly shaped. 
     Referring now to  FIG. 2 , one embodiment of the crystals  21  are shown formed in a sintered spheroidal pellet  41 . Neither crystals  21  nor pellets  41  are drawn to scale and they are illustrated in a simplified manner for reference purposes only. The invention should not be construed or limited because of these representations. For example, other possible shapes include elongated or oblong rounded structures, etc. 
     Pellet  41  is suitable for use in, for example, a hardfacing for drill bits. The pellet  41  is formed by a plurality of the crystals  21  in a binder  43 , such as an alloy binder, a transition element binder, and other types of binders such as those known in the art. In one embodiment, cobalt may be used and comprises about 6% to 8% of the total composition of the binder for hardfacing applications. In other embodiments, about 4% to 10% cobalt is more suitable for some applications. In other applications, such as using the composite material of the invention for the formation of structural components of the drill bit (e.g., bit body, cutting structure, etc.), the range of cobalt may comprise, for example, 15% to 30% cobalt. 
     Alternative embodiments of the invention include multi-modal distributions of the crystals. For example,  FIG. 3  depicts a bi-modal pellet  51  that incorporates a spheroidal carbide aggregate of crystals  21  having two distinct and different sizes (i.e., large crystals  21   a  and small crystals  21   b ) in a binder  43 . In one embodiment, the crystals  21   a ,  21   b  have a size ratio of about 7:1, and provide pellet  51  with a carbide content of about 88%. For example, the large crystals  21   a  may have a mean size of ≦8 microns, and the small crystals  21   b  may have a mean size of about 1 micron. Both crystals  21   a ,  21   b  exhibit the same properties and characteristics described herein for crystal  21 . This design allows for a reduction in binder content without sacrificing fracture toughness. 
     In another embodiment ( FIG. 4 ), a tri-modal pellet  61  incorporates crystals  21  of three different sizes (i.e., large crystals  21   a , intermediate crystals  21   b , and small crystals  21   c ) in a binder  43 . In one version, the crystals  21   a ,  21   b ,  21   c  have a size ratio of about 35:7:1, and provide pellet  61  with a carbide content of greater than 90%. For example, the large crystals  21   a  may have a mean size of ≦8 microns, the intermediate crystals  21   b  may have a mean size of about 1 micron, and the small crystals  21   c  may have a mean size of about 0.03 micron. All crystals  21   a ,  21   b , and  21   c  exhibit the same properties and characteristics described herein for the other embodiments. Again, the drawings depicted in  FIGS. 1-4  are merely illustrative and are greatly simplified for ease of reference and understanding. These depictions are not intended to be drawn to scale, to show the actual geometry, or otherwise illustrate any specific features of the invention. 
     In still another embodiment, the invention comprises a hardfacing material having hard phase components (e.g., cast tungsten carbide, cemented tungsten carbide pellets, etc.) that are held together by a metal matrix, such as iron or nickel. The hard phase components include at least some of the crystals of tungsten carbide and binder that are described herein. 
     Referring now to  FIG. 7 , another embodiment of the present invention is shown as a particle  71 . Like the previous embodiments, particle  71  includes a plurality of the crystals  21  in a binder  43 . However, particle  71  is generated by forming a large bulk quantity (e.g., a billet) of the crystal  21  and binder  43  composite (any embodiment), sintering the bulk composite, and then crushing the bulk composite to form particles  71 . As shown in  FIG. 7 , the crushed particles  71  contain a plurality of crystals  21 , have irregular shapes, and are non-uniform. The particles  71  are then sorted by size for selected applications such as those described herein. 
     Comparing the composite materials of  FIGS. 2-4  and  13  (collectively referred to with numeral  22  in  FIG. 13 ) with the conventional composite material  23  having carbide crystals depicted in  FIG. 12 , composite material  22  in  FIG. 13  is generally spheroidal, having a profile that is more rounded without angular structures such as sharp corners or edges. In contrast, the conventional composite material  23  of  FIG. 12  is much less rounded and has many more sharp and/or jagged corners and edges. 
     In addition, the composite material  22  of  FIG. 13  is formed in batches with a much tighter size distribution than that of the conventional composite material  23  in  FIG. 12 . Thus, composite material  22  is much more uniform in size than conventional composite material  23 . As shown in  FIG. 5 , a plot of a typical distribution  25  of crystals  21  may be characterized as a relatively narrow Gaussian distribution, whereas a plot of a typical distribution  27  of conventional crystals may be characterized as log-normal (i.e., a normal distribution when plotted on a logarithmic scale). For example, for a mean target grain size of 5 microns, the standard deviation for crystals  21  is on the order of about 0.25 to 0.50 micron. In contrast, for a mean target grain size of 5 microns, the standard deviation for conventional crystals is about 2 to 3 microns. 
     A composite material of the present invention that incorporates crystals  21  has significantly improved performance over conventional materials. For example, the composite material is both harder (e.g., wear resistant) and tougher than prior art materials. As shown in  FIG. 6 , plot  31  for the composite material of the present invention depicts a greater hardness for a given toughness, and vice versa, compared to plot  33  for conventional composite materials. In one embodiment, the composite material of the present invention has 70% more wear resistance for an equivalent toughness of conventional carbide materials, and 50% more fracture toughness for an equivalent hardness of conventional carbide materials. 
     There are many applications for the present invention, each of which may use any of the embodiments described herein. For example,  FIG. 8  depicts a drill bit polycrystalline diamond (PCD) cutter  81  that incorporates a substrate  83  formed from the previously described composite material of the present invention with a diamond layer  85  formed thereon. Cutters  81  may be mounted to, for example, a drill bit body  115  ( FIG. 11 ) of the drill bit  111 . Alternatively or in combination, the PCD drill bit  111  may incorporate the composite material of the present invention as either hardfacing  113  on bit  111 , or as the material used to form portions of or the entire bit body  115 , such as the cutting structures. In another alternate embodiment ( FIG. 14 ), portions or all of the cutting structures  116  (e.g., teeth, cones, etc.) may incorporate the composite material of the present invention. 
     In still another embodiment,  FIG. 9  illustrates a drill bit  91  having a matrix head  93  that incorporates the composite material of the present invention.  FIG. 10  depicts a rolling cone drill bit  101  incorporating the composite material of the present invention as hardfacing  103  on portions of the bit body  105  or cutting structure (e.g., inserts  106 ), on the entire bit body  105  or cutting structure (including, e.g., the cone support  108 ), or as the material used to form portions of or the entire bit body  105  or cutting structure. Bits with milled teeth are also suitable applications for the present invention. For example, such applications may incorporate hardfaced teeth, bit body portions, or complete bit body structures fabricated with the composite material of the present invention. 
     While the invention has been shown or described 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.