Patent Publication Number: US-2013247475-A1

Title: Matrix drill bit with dual surface compositions and methods of manufacture

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. provisional application Ser. No. 61/148,665 entitled “Matrix Drill Bit With Dual Surface Compositions And Methods of Manufacture” filed Jan. 30, 2009, the contents of which is hereby incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates in general to matrix drill bits and other well tools with matrix bodies having one or more layers of hard material disposed at selected locations on exterior portions thereof and, more particularly, to forming one or more layers of hard material at selected locations during manufacture of a matrix body or applying one or more layers of hard material at selected locations on exterior portions of a used matrix body. 
     BACKGROUND OF THE DISCLOSURE 
     Rotary drill bits are frequently used to drill oil and gas wells, geothermal wells and water wells. Rotary drill bits may be generally classified as rotary cone or roller cone drill bits and fixed cutter drill bits or drag bits. Fixed cutter drill bits or drag bits may be formed with a matrix bit body having cutting elements or inserts disposed at select locations of exterior portions of the matrix bit body. Fluid flow passageways are typically formed in the matrix bit body to allow communication of drilling fluids from associated surface drilling equipment through a drill string or drill pipe attached to the matrix bit body. Such fixed cutter drill bits or drag bits may sometimes be referred to as “matrix drill bits.” 
     Matrix drill bits are typically formed by placing loose matrix material (sometimes referred to as “matrix powder”) into a mold and infiltrating the matrix material with a hot, liquid binder such as a copper alloy. The mold may be formed by various techniques including, but not limited to, milling a block of material such as graphite to define a mold cavity with features that correspond generally with desired features of the resulting matrix drill bit. Various features of the resulting matrix drill bit such as blades, cutter pockets, and/or fluid flow passageways may be provided by shaping the mold cavity, positioning one or more mold inserts within the mold cavity and/or by positioning temporary displacement materials within the mold cavity. 
     Since machining hard, abrasion, erosion and/or wear resistant materials is generally both difficult and expensive, it is common practice to form some metal parts with a desired configuration and subsequently treat one or more portions of the metal part to provide desired abrasion, erosion and/or wear resistance. Examples may include directly hardening such surfaces (carburizing and/or nitriding) one or more surfaces of a metal part or applying a layer of hard, abrasion, erosion and/or wear resistant material (hardfacing) to one or more surfaces of a metal part depending upon desired amounts of abrasion, erosion and/or wear resistance for such surfaces. For applications when resistance to extreme abrasion, erosion and/or wear of a working surface and/or associated substrate is desired, a layer of hard, abrasion, erosion and/or wear resistant material (hardfacing) be applied to the working surface to protect the associated substrate. Apply hard facing to matrix materials such as a matrix bit body is often more difficult and technically challenging as compared with applying the same hardfacing to a generally uniform, non-matrix metal surface. 
     Hardfacing may be generally defined as a layer of hard, abrasion resistant material applied to a less resistant surface or substrate by plating, welding, spraying or other well known deposition techniques. Hardfacing is frequently used to extend the service life of drill bits and other downhole tools used in the oil and gas industry. Tungsten carbide and various alloys of tungsten carbide are examples of hardfacing materials widely used to protect drill bits and other downhole tools associated with drilling and producing oil and gas wells. 
     A wide variety of hard materials have been applied to exterior portions of rotary drill bits and other downhole tools. Frequently used hard materials include, but are not limited to, sintered tungsten carbide particles in a steel alloy matrix deposit. Tungsten carbide particles may include grains of monotungsten carbide, ditungsten carbide and/or macrocrystalline tungsten carbide. Spherical cast tungsten carbide may typically be formed with no binding material. Examples of binding materials used to form tungsten carbide particles may include, but are not limited to, cobalt, nickel, boron, molybdenum, niobium, chromium, iron and alloys of these elements. 
     SUMMARY 
     The present disclosure provides matrix bit bodies for rotary drill bits or matrix bodies for other downhole tools with one or more layers of hard material disposed at selected locations to provide substantially enhanced resistance to erosion, abrasion, wear, impact and/or fatigue forces as compared with prior matrix bodies without such layers of hard material. In accordance with teachings of the present disclosure, such layers of hard material may include tungsten carbide particles, formed with an optimum amount of binding material, particles of other superabrasive and/or superhard materials. Examples of such hard materials satisfactory for use with the present disclosure may include, but are not limited to, encrusted diamond particles, coated diamond particles, silicon nitride (Si 3 N 4 ), silicon carbide (SiC), boron carbide (B 4 C) and cubic boron nitride (CBN). Such hard materials may also be used to rebuild exterior portions of used drill bits (sometimes referred to as “dull bits”) in accordance with teachings of the present disclosure. 
     One or more layers of hard material may be disposed at selected locations on exterior portions of a matrix bit body associated with a matrix drill bit or at selected locations on other downhole tools in accordance with teachings of the present disclosure during molding of an associated matrix body and/or after molding of the associated matrix body. The resulting matrix body may be described as having a dual phase exterior or dual surface composition. 
     One aspect of the present disclosure may include placing one or more layers of one or more hard materials at selected locations in a mold corresponding generally with respective selected locations on exterior portion of blades, cutter pockets, junk slots and/or other components of an associated matrix bit body. A preformed hollow bit blank or casting mandrel may be disposed in the mold. One or more matrix materials may be added to the mold. The matrix materials may be selected to form a hard, matrix bit body. A binder material may also be added to the mold. During heating of the mold, liquid binder material may flow through the matrix materials and the one or more layers of the hard material. The layer or layers of hard material may provide desired enhancement to resist erosion, abrasion, wear, impact and/or fatigue forces at respective selected locations on exterior portions of the matrix bit body. 
     For some applications, a composite layer of hard material may be disposed at selected locations on exterior portions of a matrix bit body in accordance with teachings of the present disclosure. Each composite layer of hard material may include two, three or more smaller (thinner) layers or sublayers of hard material. Each sublayer of hard material may include a plurality of large hard particles including, but not limited to, low alloy sintered materials in the form of pellets and/or low alloy sintered material in the form of crushed powder. Other forms of low alloy sintered material may also be used to enhance downhole drilling performance and/or associated matrix drill bit life. 
     For some applications, a low percentage of binder material (4% plus or minus 1% Co, Ni, B, Mo, Cr or Se binder or any combination thereof) may be used to bind fine tungsten carbide grains to form generally spherical tungsten carbide particles or pellets. The use of such particles or pellets may provide substantially increased carbide content at one or more selected locations on exterior portions of an associated matrix body as compared to hard materials with twenty to thirty percent (20% to 30%) binder. For some applications, the size of the resulting tungsten carbide particles or pellets may be substantially enlarged such that only one layer of the second hard material is required to provide satisfactory resistance to erosion, abrasion, impact and/or fatigue forces at a selected location. Used matrix drill bits may be repaired by forming one or more layers of hard material at selected locations on exterior portions of an associated matrix bit body. 
     For some applications, one or more layers of the low alloy sintered material may also include matrix materials used to form an associated matrix bit body. Various binding processes including, but not limited to, sintering and/or sinter-hipping may be used to form spherical tungsten carbide particles or pellets in a sintering furnace. For some applications a sintered tungsten carbide pellet may be used in combination with conventional matrix materials to form a matrix drill bit. Such materials may be used to rebuild a matrix bit body in accordance with teachings of the present disclosure. 
     Various techniques may be satisfactorily used to determine the location or locations for forming one or more layers of hard material on exterior portions of an associated matrix body. For example, simulation of fluid flow over exterior portions of a matrix drill bit or other downhole tools having a matrix body in combination with analysis of wear patterns on exterior portions of an associated matrix drill bit and/or other downhole tools may help to identify one or more locations for forming such layers of hard material. Three dimensional (3D) scanning of used drill bits, visual inspection or other techniques may also be used to select locations for forming one or more layers of hard material with enhanced erosion, war, abrasion, impact and/or fatigue resistance on exterior portions of a matrix bit body during manufacture of an associated matrix drill bit. 
     Matrix materials including, but are not limited to, cemented carbides of tungsten, macrocrystalline tungsten carbide, tungsten cast carbide, titanium, tantalum, niobium, chromium, vanadium, molybdenum, hafnium independently or in combination and/or spherical carbides may be used to form one or more layers of hard material at selected locations matrix bodies in accordance with teachings of the present disclosure. However, the present disclosure is not limited to cemented tungsten carbides, spherical carbides, macrocrystalline tungsten carbide and/or cast tungsten carbides or mixtures thereof. 
     Some embodiments one or more layers of hard material may be disposed on exterior portions of a matrix body with at least one layer having both large particles or pellets and small particles or pellets. The ratio of larger pellets to small pellets may vary from approximately one to one or fifty percent large pellets and fifty percent small pellets to approximately three (3) large pellets for every small pellet (3 to 1) or seventy five percent (75%) large pellets and twenty five percent (25%) small pellets. The size of a typical small pellet of hard material may be approximately 20 mesh (850μ) to 30 mesh (600μ). The size of a typical large pellet of hard material may be approximately 16 mesh (1180μ) to 20 mesh (850μ). 
     Additional features, steps, technical advantages and/or benefits of the present disclosure may be discussed in the Detailed Description and/or Claims. The above Summary is not intended to be a comprehensive listing of all features, steps, technical advantages and/or benefits of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages thereof, reference is now made to the following brief descriptions, taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts, in which: 
         FIG. 1  is a schematic drawing showing an isometric view of one example of a matrix drill bit having a matrix bit body with one or more layers of hard material disposed at selected locations on exterior portions of the matrix bit body; 
         FIG. 2A  is a schematic drawing in section with portions broken away showing a mold assembly satisfactory to form a matrix body in accordance with teachings of the present disclosure; 
         FIG. 2B  is a schematic drawing showing multiple layers of hard material or a composite layer of hard material which may be disposed at one or more locations on interior portions of the mold shown in  FIG. 2A ; 
         FIG. 2C  is a schematic drawing in section with portions broken away showing a single layer of hard material which may be disposed at one or more locations on interior portions of the mold shown in  FIG. 2A ; 
         FIG. 3A  is a schematic drawing in elevation with portions broken away showing a welding rod with hard materials disposed therein in accordance with teachings of the present disclosure; 
         FIG. 3B  is an enlarged schematic drawing in section with portions broken away showing tungsten carbide pellets and other hard materials disposed within the welding rod of  FIG. 3A ; 
         FIG. 3C  is an enlarged schematic drawing in section with portions broken away showing tungsten carbide pellets formed with an optimum weight percentage of binding material and bonded to a matrix deposit disposed on and bonded to a substrate or matrix body in accordance with teachings of the present disclosure; 
         FIG. 4A  is a schematic drawing in elevation with portions broken away showing a welding rod with hard materials disposed therein in accordance with teachings of the present disclosure; 
         FIG. 4B  is an enlarged schematic drawing in elevation and in section with portions broken away showing tungsten carbide pellets, encrusted diamond particles and other hard materials disposed within the welding rod of  FIG. 4A ; 
         FIG. 4C  is an enlarged schematic drawing in section with portions broken away showing tungsten carbide pellets formed with an optimum weight percentage of binding material along with encrusted diamond particles and bonded to a matrix deposit disposed on and bonded to a substrate or matrix body in accordance with teachings of the present disclosure; 
         FIG. 5  is a schematic drawing in section with portions broken away showing a mold assembly with mold inserts, matrix materials and other materials disposed therein satisfactory to form a matrix bit body in accordance with teachings of the present disclosure; and 
         FIG. 6  is a schematic drawing in section with portions broken away showing a matrix bit body with recesses formed in exterior portions thereof in accordance with teachings of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     Preferred embodiments and various advantages may be understood by referring in more detail to  FIGS. 1-6  of the drawings, in which like numerals refer to like parts. 
     The terms “matrix bit”, “matrix drill bit” and “matrix rotary drill bit” may be used in this application to refer to “rotary drag bits”, “drag bits”, “fixed cutter drill bits” or any other drill bit incorporating teaching of the present disclosure. Such drill bits may be used to form well bores or boreholes in subterranean formations. 
     Matrix drill bits incorporating teachings of the present disclosure may include a matrix bit body formed by one or more matrix materials. For other embodiments (not expressly shown) a matrix bit body may be formed with at least a first matrix material and a second matrix material. For some applications the first matrix material may have increased toughness or high resistance to fracture and also provide erosion, abrasion and wear resistance. The second matrix material (not expressly shown) with only a limited amount of alloy materials or other contaminates may also be used to form the matrix bit body. The first matrix material may include, but is not limited to, cemented carbides or spherical carbides. The second matrix material may include, but is not limited to, macrocrystalline tungsten carbides and/or cast carbides. One or more layers of hard material may be disposed at selected locations on matrix bodies formed from matrix materials in accordance with teachings of the present disclosure. 
     Various types of binder materials may be used to infiltrate matrix materials disposed in a mold to form a matrix bit body. Binder materials may include, but are not limited to, copper (Cu), nickel (Ni), cobalt (Co), iron (Fe), molybdenum (Mo) individually or alloys based on these metals. The alloying elements may include, but are not limited to, one or more of the following elements—manganese (Mn), nickel (Ni), tin (Sn), zinc (Zn), silicon (Si), molybdenum (Mo), tungsten (W), boron (B) and phosphorous (P). The matrix bit body may be attached to a hollow bit blank or casting mandrel. A generally hollow shank or hollow tool joint with a threaded connection may be attached to the hollow bit blank or casting mandrel for use in releasably engaging the associated matrix drill bit with a drill string, drill pipe, bottom hole assembly or downhole drilling motor (not expressly shown). 
     The terms “cemented carbide” and “cemented carbides” may be used within this application to include WC, MoC, TiC, TaC, NbC, Cr 3 C 2 , VC and solid solutions of mixed carbides such as WC—TiC, WC—TiC—TaC, WC—TiC−(Ta,Nb)C in a metallic binder (matrix) phase. Typically, Co, Ni, Fe, Mo and/or their alloys may be used to form the metallic binder. Cemented carbides may sometimes be referred to as “composite” carbides or sintered carbides. Some cemented carbides may also be referred to as spherical carbides. However, cemented carbides may have many configurations and shapes other than spherical. 
     Cemented carbides may be generally described as powdered refractory carbides which have been united by compression and heat with binder materials such as powdered cobalt, iron, nickel, molybdenum and/or their alloys. Cemented carbides may also be sintered, crushed, screened and/or further processed as appropriate. Cemented carbide pellets may be used to form a matrix bit body. The binder material may provide ductility and toughness which often results in greater resistance to fracture (toughness) of cemented carbide pellets, spheres or other configurations as compared to cast carbides, macrocrystalline tungsten carbide and/or formulates thereof. 
     Binder materials used to form cemented carbides may sometimes be referred to as “bonding materials” in this Application to help distinguish between binder materials used to form cemented carbides and binder materials used to form a matrix drill bit. 
     The terms “computational fluid dynamics” and/or “CFD” may be used in this application to include various commercially available computer programs and algorithms used to simulate and evaluate complex fluid interactions. Such simulations may include calculating mass transfer, turbulence, velocity changes and other characteristics associated with multiphase, complex fluid flow associated with a matrix drill bit forming a wellbore. Such fluids may often be a mixture of liquids, solids and/or gases with varying concentrations depending on associated downhole drilling conditions. Simulations using CFD programs may be used to determine optimum locations for forming one or more layers of hard material on exterior portions of a matrix body based on anticipated fluid flow for the type/size of pump used on an associated drilling rig (not expressly shown), size of associated drill string (not expressly shown), size and configuration of an associated matrix drill bit or other downhole tool and/or anticipated downhole drilling conditions. 
     The term “digital scanning” may be used to describe a wide variety of equipment and techniques satisfactory for measuring exterior dimensions of a matrix drill bit and other downhole tools with a very high degree of accuracy and to create a three dimensional image of exterior portions of such well tools. The results of digital scanning may be used with other computer programs such as “computational fluid dynamics” or CFD programs to evaluate fluid flow characteristics over exterior portions of matrix drill bits and other downhole tools. 
     Some examples of digital scanning equipment and techniques are discussed in U.S. Patent Application Ser. No. 60/992,392; Filing Date: Dec. 5, 2007, entitled “Method and Apparatus to Improve Design, Manufacture, Performance and/or Use of Well Tools” now U.S. patent Ser. No. ______. CFD programs are available from various vendors. One example of a CFD program satisfactory for use with the present invention is FLUENT, available from ANSYS, Inc. located in Canonsburg, Pa. 
     Various computer programs and computer models may be used to design blades, cutting elements, fluid flow paths and/or associated rotary drill bits. Examples of such methods and systems which may be used to design and evaluate performance of cutting elements and rotary drill bits are shown in U.S. Patent Applications entitled “Methods and Systems for Designing and/or Selecting Drilling Equipment Using Predictions of Rotary Drill Bit Walk,” application Ser. No. 11/462,898, filing date Aug. 7, 2006, (now U.S. patent Ser. No. ______); U.S. patent application entitled “Methods and Systems of Rotary Drill Bit Steerability Prediction, Rotary Drill Bit Design and Operation,” application Ser. No. 11/462,918, filed Aug. 7, 2006, (now U.S. patent Ser. No. ______) and U.S. Patent Application entitled “Methods and Systems for Design and/or Selection of Drilling Equipment Based on Wellbore Simulations,” application Ser. No. 11/462,929, filing date Aug. 7, 2006, (now U.S. patent Ser. No. ______). 
     The terms “dual surface compositions”, “dual exterior composition”, dual phase surface” and/or “dual phase exterior” may be used to describe a matrix body having one or more layers of hard material disposed at selected locations on exterior portions of the matrix body. The matrix body may be formed from one or more matrix materials. Hard materials forming the layer or layers at the selected locations on exterior portions of the matrix body may generally have a hardness greater than the hardness of matrix materials used to form the associated matrix body. 
     The term “gage pad” as used in this application may include a gage, gage segment or gage portion disposed on exterior portion of a blade. Gage pads may often contact adjacent portions of a wellbore formed by an associated rotary drill bit. Exterior portions of blades and/or associated gage pads may be disposed at various angles, either positive or negative and/or parallel, relative to adjacent portions of a straight wellbore. A gage pad may include one or more layers of material formed in accordance with teachings of the present disclosure. One or more gage pads may be disposed on a blade. 
     The terms “matrix deposit” and/or “metallic matrix deposit” may refer to a layer or layers of hard material disposed at selected exterior portions of a matrix body and/or substrate to protect the matrix body and/or the substrate at the selected locations from abrasion, erosion, wear, impact and/or fatigue forces. A matrix deposit may also sometimes be referred to as “metallic alloy material” or as a “deposit matrix.” Various binders and/or binding materials such as cobalt, nickel, copper, iron and alloys thereof may be used to form a matrix deposit with hard, abrasion resistant materials and/or particles dispersed therein and bonded thereto. Nickel based alloys with increased ductility may be used at locations subject to erosion and/or abrasion. 
     Various types of tungsten carbide particles and/or pellets having an optimum size and/or optimum weight percentage of binder or binding material may be included as part of a matrix deposit or layer of hard material incorporating teachings of the present disclosure. One or more layers of hard material may be formed on a matrix body from a wide range of hard metal alloys and other hard materials. 
     The term “tungsten carbide” may include monotungsten carbide (WC), ditungsten carbide (W 2 C), macrocrystalline tungsten carbide. 
     The terms “tungsten carbide pellet,” “WC pellet,” “tungsten carbide pellets” and “WC pellets” may refer to nuggets, spheres and/or particles of tungsten carbide formed with an optimum size and/or weight percentage of binding material in accordance with the teachings of the present disclosure. The terms “binder”, “binding material” and/or “binder materials” may be used interchangeably in this Application. 
       FIG. 1  is a schematic drawing showing one example of a fixed cutter drill bit or matrix drill bit having one or more layers of hard material disposed on exterior portion thereof in accordance with teachings of the present disclosure. Matrix drill bit  20  as shown in  FIG. 1  may sometimes be referred to as a “rotary drill bit,” “fixed cutter drill bit” or “drag bit”. Matrix drill bit  20  may include matrix bit body  50  having a plurality of blades  54  extending radially therefrom. Respective fluid flow paths (sometimes referred to as “junk slots”)  56  may be disposed between adjacent blades  54 . Each blade  54  may include respective leading surface  51  and trailing surface  52 . Arrow  24  indicates the general direction of rotation of rotary drill bit  20  relative to an associated bit rotational axis (not expressly shown) during formation of a wellbore (not expressly shown). 
     First end or downhole end  21  of matrix drill bit  20  may include a plurality of cutting elements  60  operable to engage downhole formation materials and remove such materials to form a wellbore. Each cutting element  60  may be disposed in respective pocket  62  formed on exterior portion  58  of respective blade  54 . Each cutting element  60  may include respective cutting surface  64  formed from hard materials satisfactory for engaging and removing adjacent downhole formation materials (not expressly shown). 
     Cutting elements  60  may scrape and gouge formation materials from the bottom and sides of a wellbore (not expressly shown) during rotation of matrix drill bit  20 . For some applications, various types of polycrystalline diamond compact (PDC) cutters may be satisfactorily used as cutting elements  60 . A matrix drill bit having PDC cutters may sometimes be referred to as a “PDC bit”. 
     Second end  22  of matrix drill bit  20  may include shank or tool joint  30  operable to releasably engage matrix drill bit  20  with a drill string (not expressly shown), bottom hole assembly (not expressly shown) and/or a downhole drilling motor (not expressly shown) to rotate matrix drill bit  20  during formation of a wellbore. Shank  30  and associated bit blank  36  may be described as having respective generally hollow cylindrical configurations defined in part by a fluid flow passageway extending therethrough. See, for example fluid flow passageway  32  in  FIG. 6 . Various types of threaded connections such as American Petroleum Institute (API) drill pipe connection or threaded pin  34  may be formed on shank  30  proximate second end  22  of matrix drill bit  20 . Shank  30  may also include bit breaker slots  35 . 
     Various techniques may be used to securely engage generally hollow shank  30  with portions of bit blank  36  extending from matrix bit body  50 . See for example  FIGS. 1 and 6 . For example, weld  39  may be formed in groove  38  disposed between and extending around the perimeter of shank  30  and bit blank  36 . 
     For some applications each blade  54  may include respective recess  70  formed in exterior portion  58  of each blade  54 . The location and dimensions of each recess  70  may be selected to correspond generally with a selected location for forming a gage pad on associated blade  54 .  FIGS. 5 and 6  show one example of techniques which may be satisfactorily used to form respective recess  70  at selected locations on exterior portion  58  of each blade  54 . One or more layers of hard material may be disposed within each recess  70  in accordance with teachings of the present disclosure. 
       FIGS. 3A and 3B  and  FIGS. 4A and 4B  show examples of welding rods  71  and  71   a  which may be used to form one or more layers of hard material in recess  70  in accordance with teachings of the present disclosure. Welding rods  71  and  71   a  may also be used to repair or rebuild a used matrix drill bit or matrix body in accordance with teachings of the present disclosure. 
     One or more nozzle openings  66  may be formed in exterior portions of matrix bit body  50 . Respective nozzle  68  may be disposed in each nozzle opening  66 . Various types of drilling fluid may be pumped from surface drilling equipment (not expressly shown) through an associated drill string (not expressly shown) attached to threaded connection  34  of shank or tool joint  30  to fluid flow passageway  32  disposed within matrix bit body  50 . One or more fluid flow paths may be formed in matrix bit body  50  to communicate drilling fluid and/or other fluids to associated nozzle  68 . See for example fluid passageways  72  and  74  in  FIG. 6 . For some embodiments, one or more layers  101  of hard material may be disposed on exterior portions of matrix bit body  50  adjacent to nozzle opening  66 . See for example  FIG. 1 . 
     One or more layers of hard material  102  may be disposed on exterior portions of one or more blades  54  proximate a transition or junction between adjacent junk slot  56  and associated leading surface  51 . One or more layers  103  of hard material may be disposed on trailing surface  52  of one or more blades  54 . In a similar manner, one or more layers  104  of hard material may be disposed on exterior portion  58  of each blade  54  proximate associated pockets  62  and/or cutting elements  60 . One or more layers  105  of hard material may be disposed exterior portions of selected pockets  62 . Respective locations, dimensions and configurations for layers  101 ,  102 ,  103 ,  104  and  105  and associated hard materials on new matrix drill bits and/or used matrix drill bits may be selected using CFD analysis, digital scanning, visual scanning and drill bit design techniques in accordance with teachings of the present disclosure. 
     U.S. Pat. No. 6,296,069 entitled Bladed Drill Bit with Centrally Distributed Diamond Cutters and U.S. Pat. No. 6,302,224 entitled Drag-Bit Drilling with Multiaxial Tooth Inserts show various examples of blades and/or cutting elements which may be used with a matrix bit body incorporating teachings of the present disclosure. It will be apparent to persons having ordinary skill in the art that a wide variety of fixed cutter drill bits, drag bits and other drill bits may be satisfactorily formed with a matrix bit body incorporating teachings of the present disclosure. The present disclosure is not limited to matrix drill bit  20  or any specific features as shown in  FIGS. 1-6 . 
     A wide variety of molds may be satisfactorily used to form a matrix bit body and associated matrix drill bit in accordance with teachings of the present disclosure. Mold assembly  200  shown in  FIG. 2A  and mold assembly  200   a  shown in  FIG. 5  represents only two examples of mold assemblies satisfactory for use in forming a matrix bit body incorporating teachings of the present disclosure. U.S. Pat. No. 5,373,907 entitled Method And Apparatus For Manufacturing And Inspecting The Quality Of A Matrix Body Drill Bit shows additional details concerning mold assemblies and conventional matrix bit bodies. 
     Layers  101 ,  102 ,  103 ,  104  and  105  of various hard materials may be placed in mold assembly  200  at locations  101   a ,  102   a ,  103   a ,  104   a  and  105   a  corresponding generally with selected locations for forming corresponding layers of hard material on exterior portions of matrix drill bit  20 . One or more layers  101 - 105  of hard material may be disposed at each location in accordance with teachings of the present disclosure. For some applications a composite layer or multiple layers of hard material may be disposed at each location in mold assembly  200 . See for example  FIG. 2B . For other applications a single layer of hard material may be disposed at each location in mold assembly  200 . See for example  FIG. 2C . 
     Mold assemblies  200  and  200   a  as shown in  FIGS. 2A ,  5  and  6  represent only two examples of molds and/or mold assemblies which may be satisfactorily used to form a matrix body incorporating teachings of the present disclosure. Mold assemblies  200  and  200   a  may be generally described as having cylindrical configurations defined in part by respective first, opened end  201  and second, closed end  202  with respective mold cavity  252  and  252   a  disposed there between. Mold cavities  252  and  252   a  may be generally described as negative images or inverse images of a matrix bit body formed by the respective mold assemblies  200  and  200   a.    
     For some embodiments, interior portions of mold cavities  252  and/or  252   a  may be coated with a mold wash to prevent gasses, produced by heating and/or cooling of associated mold assemblies  200  and  200   a , from entering into matrix materials disposed within respective mold cavities  252  and  252   a . Various commercially available mold washes may be satisfactorily used. Mold assemblies  200  and/or  200   a  may also be placed within a container (not expressly shown). Interior portions of such containers may be designed to receive exterior portions of mold assemblies  200  and/or  200   a . Such containers may sometimes be referred to as a “housing”, “crucible” and/or “bucket”. 
     Mold assembly  200  as shown in  FIG. 2A  may include a plurality of displacements  208  disposed on interior portions of mold cavity  252 . The configuration and dimensions associated with each displacement  208  may be selected to generally correspond with blades  54  and fluid flow paths  56  formed on exterior portions of matrix bit body  50 . 
     Depending on the type of materials used to form mold assembly  200  and/or heating and cooling cycles associated with forming matrix bit body  50 , out gassing may occur. For such applications, a plurality of internal flow paths (not expressly shown) may be formed within mold assembly  200 . Such fluid flow paths may communicate gasses associated with heating and cooling of mold assembly  200  through fluid flow channels  206  and/or exterior portions of mold assembly  200 . 
     Mold cavity  252  as shown in  FIG. 2A  may be formed with a plurality of negative blade profiles  210  disposed between respective displacements  208 . For some applications, mold assembly  200  and associated components may be formed using a 3D printer in combination with 3D design data. A plurality of negative pocket recesses or pocket profiles  262  may be formed within each negative blade profile  210 . Negative pocket recesses  262  may have complex configurations and/or orientations as desired for respective pocket  62  and associated cutting element  60 . 
     Locations  101   a - 105   a  within mold assembly  200  may be selected to correspond generally with locations on exterior portions of associated matrix drill bit  20  where high erosion, abrasion, wear, impact and/or fatigued forces may be applied. For example, one or more layers of hard material may be disposed at location  101   a  to minimize erosion from fluid flowing from associated nozzle  68 . One or more layers of hard material may be disposed at locations  102   a  and  103   a  to minimize abrasion and/or wear associated with fluid flowing through associated flow path or junk slot  56 . One or more layers of a second hard material may be disposed at locations  104   a  to minimize erosion, abrasion, wear, impact and/or fatigue forces applied to exterior portions  58  of associated blade  54  during engagement of associated cutting elements  60  with adjacent downhole formation materials. One or more layers of hard material may be disposed at location  105   a  on exterior portions of associated pocket  62  to minimize erosion, abrasion, wear, impact and/or fatigue forces resulting from respective cutting element  60  engaging and removing downhole formation materials. 
       FIGS. 2B and 2C  show examples of layers of hard materials which may be disposed at one or more locations  101   a - 105   a  in accordance with teachings of the present disclosure.  FIG. 2B  shows first layer or sublayer  111 , second layer or sublayer  112  and third layer or sublayer  113  disposed at location  101   a  in mold assembly  200 . The resulting configuration of layers or sublayers  111 ,  112  and  113  may sometimes be referred to as “composite layer”  101 . Each sublayer  111 ,  112  and  113  may have approximately the same general configuration and dimensions including thickness. Each layer  111 ,  112  and  113  may include a plurality of large pellets  130  and/or  140 . Also, a plurality of smaller pellets and matrix material  131  used to form associated matrix drill bit  20  may also be disposed within layers  111 ,  112  and/or  113 . 
     For embodiments such as shown in  FIG. 2B , first layer  111  may start with a layer of glue disposed at location  101   a . Various types of glue and/or adhesive materials including, but not limited to, aerosol adhesives such as Super 77 Multipurpose Adhesive available from 3M Company located in St. Paul, Minn. may be satisfactorily used. Hard particles or hard pellets  130  as shown in  FIGS. 2B and 3C  and/or hard pellets  140  as shown in  FIGS. 4B and 4C  may then be disbursed within the glue of first layer  111 . Matrix material  131  may also be disbursed within first layer  111 . The ratio of hard pellets or hard particles with respect to matrix material may be selected to provide desired uniformity of the resulting first layer  111  and desired hardness. 
     A second layer of glue may be disposed on first layer  110  at location  101   a . Additional hard pellets  130  and/or  140  may then be distributed within the glue at second layer  112 . Matrix material  131  may be disbursed within the glue at second layer  112 . Similar procedures may be used to form third layer  113  and additional layers of glue, hard pellets and/or matrix material as desired for each selected location on exterior portions of matrix drill bit  20 . 
     The dimensions and configuration of each layer of glue may be selected to correspond with desired dimensions and configuration of corresponding layers  101 - 105  of hard material disposed at selected locations on exterior portions of matrix drill bit  20 . For some applications, the total thickness of the hard material disposed at respective locations  101   a - 105   a  may be between approximately 0.25 inches and 0.5 inches. 
       FIG. 2C  is a schematic drawing showing single layer  114  and hard materials which may also be disposed at location  101   a  or any other desired location in mold assembly  200 . The overall configuration and dimensions of layer  114  in  FIG. 2C  may be approximately the same as composite layer  101  in  FIG. 2B . For some applications, pellets  130  and/or  140  as shown in  FIG. 2C  may be larger than corresponding pellets  130  and/or  140  as shown in  FIG. 2B . For some applications increasing the size of the pellets may accommodate forming layer  114  in  FIG. 2C  in a “single pass” of adhesive material and a “single pass” to disperse hard materials therein as compared with composite layer  101  formed by using three separate layers or sublayers  111 ,  112  and  113  of glue and respective distribution of hard materials within each layer or sublayer. 
     The types of hard materials used to form layers  111 ,  112 ,  113  and  114  may be selected to be compatible with infiltration of binder material therethrough during infiltration of matrix materials  131  and  132  to form matrix bit body  50 . Some examples of hard materials which may be satisfactory used to form one or more layers of hard material disposed on exterior portions of a matrix drill bit in accordance with teachings of the present disclosure are shown in  FIGS. 3B ,  3 C,  4 B and  4 D. 
       FIGS. 3C and 4C  are schematic representations of respective layers of hard material disposed on matrix material  131  in accordance with teachings of the present disclosure. For purposes of explanation, surface  122  as shown in  FIGS. 3C and 4C  may be representative of respective exterior surfaces  122  associated with layers  101 - 105  of hard material disposed at selected locations on exterior portions of matrix drill bit  50 . See  FIG. 1 . Respective surfaces  122  of layers  101 - 105  may conform with and be tightly bonded to adjacent matrix materials used to form matrix bit body  50 . The cross sections of a layer of hard material disposed on matrix material as shown in  FIGS. 3C and 4C  may also be representative of one or more layers of hard material disposed in recesses  70  to form a gage pad (not expressly shown) on respective blades  54 . 
     Layer  103  as shown in  FIG. 3C  may include tungsten carbide particles or pellets  130  disposed in matrix  146  in accordance with teachings of the present disclosure. Other hard materials and/or hard particles selected from a wide variety of metals, metal alloys, ceramic alloys and/or cermets may also be used to form one or more layers  103  of hard material. As a result of using tungsten carbide particles  130  having an optimum weight percentage of binder material, layer  103  may enhance erosion, abrasion, wear, impact and/or fatigue resistance as compared with exterior portions of matrix bit body  50  which do not include such layers of hard material. 
     Layer  104  as shown in  FIG. 4C  may include tungsten carbide particles or pellets  130  and encapsulated diamond particles  140 . In accordance with teachings of the present disclosure. Other hard materials and/or hard particles selected from a wide variety of metals, metal alloys, ceramic alloys and/or cermets may also be used to form one or more layers  104  of hard material. By including both a combination of tungsten carbide pellets  130  and diamond encrusted particles or pellets  140 , layer  104  may have enhanced erosion, abrasion, wear, impact and/or fatigues resistance as compared with exterior portions of matrix bit body  50  which do not include such layers of hard material. 
       FIGS. 3A and 4A  shows examples of welding rods which may be satisfactory used to form one or more layers of hard material on exterior portions of matrix bit body  50  such as respective recesses  70  formed on blades  54  following removal of matrix bit body  50  from as associated mold assembly. The welding rods  71  and  71   a  may also be used to form one or more layers of hard material to repair a used matrix drill bit in accordance with teachings of the present disclosure. 
     For some applications both new matrix bit bodies and used matrix drill bits may be heated to a desired temperature such as approximately seven hundred degrees Fahrenheit (700° F.) and allowed to “soak” prior to forming one or more layers of hard material on exterior portions thereof using welding rods  71  or  71   a . The desired temperature may vary depending on materials used to form an associated matrix bit body and hard particles used to form the layers of hard material. 
     Heating a matrix bit body to an appropriate, relatively uniform temperature may minimize potential cracking or damage to the matrix bit body during welding. After one or more layers of hard material have been disposed at selected locations on the associated matrix bit body, the matrix bit body may be slowly cooled at a desired rate to ambient temperature. The cooling rate may be selected to prevent cracking or damage to the matrix bit body and/or layers of hard material. 
     Welding rod  71  as shown in  FIGS. 3A and 3B  may be used to form a layer of hard material with characteristics similar to layer  103  as shown in  FIG. 3C . Welding rod  71   a  as shown in  FIGS. 4A and 4B  may be used to form a layer of hard material with characteristics similar to layer  104   a  shown in  FIG. 4C . Welding rods  71  and  71   a  may include respective hollow steel tube  76  which may be closed at both ends with filler  78  and hard particles  130  and/or  140  or other hard materials disposed therein. 
     For some applications tungsten carbide pellets may have generally spherical configurations (see  FIGS. 3C and 4C ) with a weight percentage of binder between approximately four percent (4%) plus or minus one percent (1%) of the total weight of each tungsten carbide pellet in accordance with teachings of the present disclosure. Tungsten carbide pellets may also be formed with an optimum weight percentage of binder and various non-spherical or partially spherical configurations (not expressly shown). For some applications crushed tungsten carbide pellets may also be used. 
     Spherical tungsten carbide pellets formed with no binding material or substantially 0% binder may tend to crack and/or fracture during formation of a matrix deposit or hardfacing layer containing such pellets. Tungsten carbide pellets formed with no binding material or substantially 0% binder may also fracture or crack when exposed to thermal stress and/or impact stress. Spherical tungsten carbide pellets formed with relatively high percentages (5% or greater) by weight of binding material or binder may tend to break down or dissolve into solution during formation of an associated matrix deposit or hardfacing layer. As a result, such spherical tungsten carbide pellets and associated matrix deposit or hardfacing layer may have less abrasion, erosion, wear, impact, and/or fatigue resistance than desired. Spherical tungsten carbide pellets with more than 5% binder may crack when exposed to thermal stress and/or impact stress. 
     Tungsten carbide pellets formed with an optimum percentage of binding material or binder may neither crack nor dissolve into solution in associated matrix material during formation of one or more layers of hard material. Spherical tungsten carbide pellets formed with an optimum percentage of binding material and/or binder may also neither crack nor fracture when exposed to thermal stress and/or impact stress. Forming tungsten carbide pellets with an optimum weight percentage of binding material in accordance with teachings of the present disclosure may improve weldability of the tungsten carbide pellets and may substantially improve temperature stress resistance and/or impact stress resistance of the tungsten carbide pellets to fracturing and/or cracking. 
     For some applications layers of hard material formed with spherical tungsten carbide particles having an optimum weight percentage of binder have shown improved wear properties during testing of associated layers and/or matrix deposits. For some applications improvement in wear properties may increase approximately forty-five percent (45%) during wear testing in accordance with ASTM B611 as compared with a matrix deposits or layers of hard material having spherical tungsten carbide particles with binding material representing five percent (5%) or greater the total weight of each tungsten carbide particle. 
     Layers of hard material may be formed with tungsten carbide pellets having an optimum weight percentage of binding material in a wide range of mesh sizes. For some applications the size of such tungsten carbide pellets may vary between approximately 12 U.S. mesh and 100 U.S. mesh. The ability to use a wide range of mesh sizes may substantially reduce costs of manufacturing such tungsten carbide pellets and costs associated with forming a deposit matrix or hardfacing with such tungsten carbide pellets. For example, tungsten carbide pellets  130  as shown in  FIG. 3C  or  4 C may have a size range from approximately 12 to 100 U.S. Mesh. 
     Depending upon selected locations for depositing one or more layers of hard material on a matrix bit body, tungsten carbide pellets  130  may be selected within a more limited size range such as 40 U.S. Mesh to 80 U.S. Mesh. For other applications, tungsten carbide pellets  130  may be selected from two or more different size ranges such as 30 to 60 mesh and 80 to 100 mesh. Tungsten carbide pellets  130  may have approximately the same general spherical configuration. However, by including tungsten carbide pellets  130  or other hard particles with different configurations and/or mesh ranges, wear, erosion, abrasion, impact, and/or fatigue resistance of resulting layers of hard material may be modified to accommodate specific downhole operating environments for an associated matrix drill bit. By increasing the size of tungsten carbide pellets  130 , a single layer of hard material having optimum thickness may be deposited within mold assembly  200  with a single pass. For some applications the optimum size for tungsten carbide pellets may be approximately sixteen (16) mesh to thirty (30) mesh. 
     Tungsten carbide pellets may be formed by cementing, sintering, and/or HIP-sintering (sometimes referred to as “sinter-hipping”) fine grains of tungsten carbide with an optimum weight percentage of binding material. Sintered tungsten carbide pellets may be made from a mixture of tungsten carbide and binding material such as cobalt powder. Other examples of binding materials include, but are not limited to cobalt, nickel, boron, molybdenum, niobium, chromium, iron, and alloys of these elements. Various alloys of such binding materials may also be used to form tungsten carbide pellets in accordance with teachings of the present disclosure. The weight percentage of the binding material may be approximately four percent (4%) plus or minus one percent (1%) of the total weight of each tungsten carbide pellet. 
     A mixture of tungsten carbide and binding material may be used to form green pellets. The green pellets may then be sintered or HIP-sintered at temperatures near the melting point of cobalt to form either sintered or HIP-sintered tungsten carbide pellets with an optimum weight percentage of binding material. HIP-sintering may sometimes be referred to as “over pressure sintering” or as “sinter-hipping.” 
     Sintering a green pellet generally includes heating the green pellet to a desired temperature at approximately atmospheric pressure in a furnace with no force or pressure applied to the green pellet. HIP-sintering a green pellet generally includes heating the green pellet to a desired temperature in a vacuum furnace with pressure or force applied to the green pellet. 
     A hot isostatic press (HIP) sintering vacuum furnace generally uses higher pressures and lower temperatures as compared to a conventional sintering vacuum furnace. For example, a sinter-HIP vacuum furnace may operate at approximately 1400° C. with a pressure or force of approximately 800 μsi applied to one or more hot tungsten carbide pellets. Construction and operation of sinter-HIP vacuum furnaces are well known. The melting point of binding material used to form tungsten carbide pellets may generally decrease with increased pressure. Furnaces associated with sintering and HIP-sintering are typically able to finely control temperature during formation of tungsten carbide pellets. 
     Layers of hard material disposed at selected locations on exterior portions of a matrix body may include tungsten carbide particles or pellets  130  having an optimum weight percentage of binding material in accordance with teachings of the present disclosure. Other hard materials and/or hard particles selected from a wide variety of metals, metal alloys, ceramic alloys, and cermets may be used to form layers  101 - 105  of hard material. As a result of using tungsten carbide particles  130  having an optimum weight percentage of binding material, layers  101 - 105  of hard material may have significantly enhanced abrasion, erosion, wear, impact, and/or fatigue resistance. 
     A plurality of tungsten carbide pellets  130  having an optimum weight percentage of binding material in accordance with teachings of the present disclosure may be dispersed within filler  78 . A plurality of coated diamond particles  140  may also be dispersed within filler  78  of welding rod  71   a . Conventional tungsten carbide particles or pellets (not expressly shown) which do not have an optimum weight percentage of binder material may sometimes be included as part of filler  78 . For some applications, filler  78  may include a deoxidizer and a temporary resin binder. Examples of deoxidizers satisfactory for use with the present disclosure may include various alloys of iron, manganese, and silicon. 
     For some applications, the weight of welding rods  71  and/or  71   a  may be approximately fifty-five percent to eighty percent filler  78  and twenty to thirty percent or more steel tube  76 . Layers of hard material formed by welding rods with less than approximately fifty-five percent by weight of filler  78  may not provide sufficient wear resistance. Welding rods with more than approximately eighty percent by weight of filler  78  may be difficult to use to form layers of hard material with desired dimensions including thickness and/or desired configurations. 
     Loose material such as powders of hard material selected from the group consisting of tungsten, niobium, vanadium, molybdenum, silicon, titanium, tantalum, zirconium, chromium, yttrium, boron, carbon and carbides, nitrides, oxides, or silicides of these materials may be included as part of filler  78 . The loose material may also include a powdered mixture selected from the group consisting of copper, nickel, iron, cobalt, and alloys of these elements to form matrix bit body  50 . Powders of materials selected from the group consisting of metal borides, metal carbides, metal oxides, metal nitrides, and other superhard or superabrasive alloys may be included within filler  78 . The specific compounds and elements selected for filler  78  will generally depend upon intended applications for the resulting matrix drill bit and selected welding technique. 
     When tungsten carbide pellets  130  are mixed with other hard particles, such as coated diamond particles  140 , both types of hard particles may have approximately the same density. One of the technical benefits of the present disclosure may include varying the percentage of binding materials associated with tungsten carbide pellets  130  and thus the density of tungsten carbide pellets  130  to ensure compatibility with coated diamond particles  140  and/or matrix portion  146  of layers  101 - 105  of hard material. 
     Tungsten carbide pellets  130  with or without coated diamond particles  140  and selected loose materials may be included as part of a continuous welding rod (not expressly shown), composite welding rod (not expressly shown), core wire (not expressly shown) and/or welding rope (not expressly shown). For some applications flexible, hard facing ropes may be satisfactorily used to form one or more layers of hard material at selected locations on exterior portions of a new matrix drill bit or a used (dull) matrix drill bit. Flexible welding rope or hard facing rope may be available from several vendors including, but not limited to, Technogenia, Inc. having offices in Conroe, Tex. and Atlanta, Ga. Some welding ropes may include a central small diameter nickel wire coated with a thick layer of hard particles and matrix material such shown in  FIGS. 3B and 4B . 
     Oxyacetylene welding, atomic hydrogen welding techniques, tungsten inert gas (TIG-GTA), stick welding, SMAW and/or GMAW welding techniques may be satisfactorily used to form layers of hard material at selected locations on used matrix drill bit or new matrix bit bodies using welding rods, welding rope, etc. 
     For some applications, a mixture of tungsten carbide pellets  130  and coated diamond particles  140  may be blended and thermally sprayed onto select portions of a matrix body of a matrix body using techniques well known in the art. A laser may then be used to densify and fuse the resulting powdered mixture at selected locations on exterior portions of the matrix body. U.S. Pat. No. 4,781,770 entitled “A process For Laser Hardfacing Drill Bit Cones Having Hard Cutter Inserts” shows one process satisfactory for use with the present disclosure. 
     Layers of hard material  103  and  104  as shown in  FIG. 3C  and  FIG. 4C  may include a plurality of tungsten carbide particles  130  embedded or encapsulated in matrix portions  146  and  146   a . Various materials including cobalt, copper, nickel, iron, and alloys of these elements may be used to form matrix portions  146  and  146   a . For some applications matrix portions  146  and  146   a  may be similar to and operable to bond with adjacent portion of matrix  131 . 
     Coated diamond particles or encrusted diamond particles  140  may be formed using various techniques such as those described in U.S. Pat. No. 4,770,907 entitled “Method for Forming Metal-Coated Abrasive Grain Granules” and U.S. Pat. No. 5,405,573 entitled “Diamond Pellets and Saw Blade Segments Made Therewith.” 
     Coated diamond particles  140  may include diamond  144  with coating  142  disposed thereon. Materials used to form coating  142  may be metallurgically and chemically compatible with materials used to form both matrix portion  146   a  and binder for tungsten carbide pellets  130 . For many applications, the same material or materials used to form coating  142  will also be used to form matrix portion  146   a  and associated matrix bit body. 
     Metallurgical bonds may be formed between coating  142  of each coated diamond particle  140  and matrix portion  146   a . As a result of such metallurgical or chemical bonds coated diamond particles  140  may remain fixed within layers of hard material  101 - 105  until the adjacent tungsten carbide pellets  130  and/or other hard materials in matrix portion  146   a  have been worn away. Coated diamond particles  140  may provide high levels of abrasion, erosion and wear resistance to protect an associated matrix body as compared with hardfacing formed from only matrix portion  146   a  and tungsten carbide pellets  130 . High abrasion, erosion, wear, impact, and/or fatigue resistance of the newly exposed tungsten carbide pellets  130  and/or coated diamond particles  140  may increase overall abrasion, erosion, wear, impact, and/or fatigue resistance of layers of hard material  101 - 105 . As surrounding matrix portion  146   a  continues to be worn away, additional tungsten carbide pellets  130  and/or coated diamond particles  140  may be exposed to provide continued protection and increased useful life of an associated matrix drill bit. 
     Additional information about coated or encrusted diamond particles and other hard particles may be found in U.S. Pat. No. 6,469,278 entitled “Hardfacing Having Coated Ceramic Particles Or Coated Particles Of Other Hard Materials;” U.S. Pat. No. 6,170,583 entitled “Inserts And Compacts Having Coated Or Encrusted Cubic Boron Nitride Particles;” U.S. Pat. No. 6,138,779 entitled “Hardfacing Having Coated Ceramic Particles Or Coated Particles Of Other Hard Materials Placed On A Rotary Cone Cutter” and U.S. Pat. No. 6,102,140 entitled “Inserts And Compacts Having Coated Or Encrusted Diamond Particles.” 
     The ratio of coated diamond particles  140  or other hard particles with respect to tungsten carbide pellets  130  disposed within layers of hard material  101 - 105  may be varied to provide desired erosion, abrasion, wear, impact, and fatigue resistance for an associated matrix bit body depending upon anticipated downhole operating environment. For some extremely harsh environments, the ratio of coated diamond particles  140  to tungsten carbide particles  130  may be 10:1. For other downhole drilling environments, the ratio may be substantially reversed. 
     Tube rod welding with an oxyacetylene torch (not shown) may be satisfactorily used to form metallurgical bonds between layers of hard material and adjacent portions of matrix bit body  50  and metallurgical and/or mechanical bonds between matrix portion  146  and tungsten carbide pellets  130 . For other applications, laser welding techniques may be used to form layers of hard material on exterior portions of a matrix body. 
     Mold assembly  200   a  as shown in  FIG. 5  may include several components such as mold  203   a , gauge ring or connector ring  204   a , and funnel  220   a . Mold  203   a , gauge ring  204   a , and funnel  220   a  may be formed from graphite or other suitable materials. Various techniques may be used including, but not limited to, machining a graphite blank to form mold cavity  252   a  having a negative profile or a reverse profile of desired exterior features for a resulting fixed cutter drill bit. For example mold cavity  204   a  may have a negative profile which corresponds with the exterior profile or configuration of blades  54  and junk slots  56  as shown in  FIG. 1 . 
     Various types of temporary displacement materials and mold insert may be satisfactorily installed within mold cavity  252   a  depending on the desired configuration of a resulting matrix drill bit. For example mold inserts  70   a  may be formed from various materials such as consolidated sand and/or graphite may be disposed within mold cavity  104 . Various resins may be satisfactorily used to form consolidated sand. Mold inserts  70   a  may have configurations and dimensions corresponding with desired features of matrix bit body  50  such as recess  70  formed in exterior portion  58  of blades  54 . The dimensions and configuration of mold inserts  70   a  and associated recesses  70  may be selected to correspond with desired dimensions and configuration for resulting gage pads (not expressly shown) on respective blades  54 . 
     Matrix bit body  50  may include relatively large fluid cavity or chamber  32  with multiple fluid flow passageways  72  and  74  extending therefrom. See  FIG. 6 . As shown in  FIG. 5 , displacement materials such as consolidated sand may be installed within mold assembly  200   a  at desired locations to form portions of cavity  32  and fluid flow passages  72  and  74  extending therefrom. The orientation and configuration of consolidated sand legs  172  and  174  may be selected to correspond with desired locations and configurations of associated fluid flow passageways  72  and  74  communicating from cavity  32  to respective nozzles  68 . 
     A relatively large, generally cylindrically shaped consolidated sand core  150  may be placed on the legs  172  and  174 . The number of legs extending from sand core  150  will depend upon the desired number of nozzle openings in a resulting matrix bit body. 
     After desired displacement materials, including core  150  and legs  172  and  174 , have been installed within mold assembly  200   a , matrix material  131  having desired characteristics for matrix bit body  50  may be placed within mold assembly  200   a . The present disclosure allows the use of matrix materials having characteristics of toughness and wear resistance for forming a fix cutter drill bit or drag bit. 
     A generally hollow, cylindrical bit blank  36  may then be placed within mold assembly  200   a . Bit blank  36  preferably includes inside diameter  37  which is larger than the outside diameter of sand core  150 . Various fixtures (not expressly shown) may be used to position bit blank  36  within mold assembly  200   a  at a desired location spaced from first matrix material  131 . 
     For some applications second matrix material  132  such as tungsten powder may then be placed in mold assembly  200   a  between exterior portions of bit blank  36  and adjacent interior portions of funnel  220   a . Second matrix material  132  may be a relatively soft powder which forms a matrix that may subsequently be machined to provide a desired exterior configuration and transition between matrix bit body  50  and bit blank  36 . See  FIG. 6 . Second matrix material  132  may sometimes be described as an “infiltrated machinable powder.” 
     Matrix material  131  may be cemented carbides and/or spherical carbides as previously discussed. Alloys of cobalt, iron, and/or nickel may be used to form cemented carbides and/or spherical carbides. For some matrix drill bit designs an alloy concentration of approximately six percent in the first matrix material may provide optimum results. Alloy concentrations between three percent and six percent and between approximately six percent and fifteen percent may also be satisfactory for some matrix drill bit designs. However, alloy concentrations greater than approximately fifteen percent and alloy concentrations less than approximately three percent may result in less than optimum characteristics of a resulting matrix bit body. 
     A typical infiltration process for forming matrix bit body  50  may begin by forming mold assembly  200   a . Gage ring  204   a  may be threaded onto the top of mold  203   a . Funnel  220   a  may be threaded onto the top of gage ring  204   a  to extend mold assembly  200   a  to a desired height to hold previously described matrix materials and binder material. Displacement materials such as, but not limited to, mold inserts  70   a , legs  172  and  174 , and sand core  150  may then be loaded into mold assembly  200   a  if not previously placed in mold cavity  252   a . Matrix materials  131  and  132  and bit blank  36  may be loaded into mold assembly  200   a  as previously described. 
     As mold assemblies  200  or  200   a  are being filled with matrix materials, a series of vibration cycles may be induced in each mold assembly  200  or  200   a  to assist desired distribution of each layer or zone of matrix materials  131  and  132 . Vibrations help to ensure consistent density of each layer of matrix materials  131  and  132  within respective ranges required to achieve desired characteristics for matrix bit body  50 . 
     Binder material  160  may be placed on top of layer  132 , bit blank  36  and core  150 . Binder material  160  may be covered with a flux layer (not expressly shown). A cover or lid (not expressly shown) may be placed over mold assembly  200   a . Mold assembly  200   a  and materials disposed therein may be preheated and then placed in a furnace (not expressly shown). When the furnace temperature reaches the melting point of binder material  160 , liquid binder material  160  may infiltrate matrix materials  131  and  132  and layer  101 - 105  of hard material. See  FIG. 2A . 
     Mold assembly  200   a  may then be removed from the furnace and cooled at a controlled rate. Once cooled, mold assembly  200   a  may be broken away to expose matrix bit body  50 . See for example  FIG. 6 . 
     Although the present disclosure has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the present appended claims.