Bonding agents for improved sintering of earth-boring tools, methods of forming earth-boring tools and resulting structures

Methods for forming earth-boring tools include providing a metal or metal alloy bonding agent at an interface between a first element and a second element and sintering the first element, the second element, and the boding agent to form a bond between the first element and the second element at the interface. The methods may be used, for example, to bond together portions of a body of an earth-boring tool (which may facilitate, for example, the formation of cutting element pockets) or to bond cutting elements to a body of an earth-boring tool (e.g., a bit body of a fixed-cutter earth-boring drill bit or a cone of a roller cone earth-boring drill bit). At least partially formed earth-boring tools include a metal or metal alloy bonding agent at an interface between two or more elements, at least one of which may comprise a green or brown structure.

FIELD OF THE INVENTION

The present invention relates generally to earth-boring tools and methods of forming earth-boring tools. More particularly, the present invention relates to methods of securing together elements or portions of an earth-boring tool that comprise a particle-matrix composite material.

BACKGROUND OF THE INVENTION

Rotary drill bits are commonly used for drilling bore holes or wells in earth formations. Rotary drill bits include two primary configurations. One configuration is the roller cone bit, which typically includes three roller cones mounted on support legs that extend from a bit body. Each roller cone is configured to spin or rotate on a support leg. Cutting teeth typically are provided on the outer surfaces of each roller cone for cutting rock and other earth formations. The cutting teeth often are composed of steel and coated with an abrasion resistant “hardfacing” material. Such materials often include tungsten carbide particles dispersed throughout a metal alloy matrix material. Alternatively, receptacles are provided on the outer surfaces of each roller cone into which hardmetal inserts are secured to form the cutting elements. The roller cone drill bit may be placed in a bore hole such that the roller cones are adjacent the earth formation to be drilled. As the drill bit is rotated, the roller cones roll across the surface of the formation, the cutting teeth crushing the underlying formation.

A second configuration of a rotary drill bit is the fixed-cutter bit (often referred to as a “drag” bit), which typically includes a plurality of cutting elements secured to a face region of a bit body. Generally, the cutting elements of a fixed-cutter type drill bit have either a disk shape or a substantially cylindrical shape. A hard, super-abrasive material, such as mutually bonded particles of polycrystalline diamond, may be provided on a substantially circular end surface of a supporting substrate of each cutting element to provide a cutting surface. Such cutting elements are often referred to as “polycrystalline diamond compact” (PDC) cutting elements. Typically, the cutting elements are fabricated separately from the bit body and secured within pockets formed in the outer surface of the bit body. A bonding material such as an adhesive or, more typically, a braze alloy may be used to secure the cutting elements by their substrates to the bit body. The fixed-cutter drill bit may be placed in a bore hole such that the cutting elements are adjacent the earth formation to be drilled. As the drill bit is rotated, the cutting elements scrape across and shear away the surface of the underlying formation.

The bit body of a rotary drill bit conventionally is secured to a hardened steel shank having an American Petroleum Institute (API) threaded pin for attaching the drill bit to a drill string. The drill string includes tubular pipe and equipment segments coupled end to end between the drill bit and other drilling equipment at the surface. Equipment such as a rotary table or top drive may be used for rotating the drill string and the drill bit within the bore hole. Alternatively, the shank of the drill bit may be coupled directly to the drive shaft of a down-hole motor, which then may be used to rotate the drill bit.

A conventional earth-boring rotary drill bit10that has a bit body including a particle-matrix composite material is illustrated inFIG. 1. As seen therein, the drill bit10includes a bit body12that is secured to a steel shank20. The bit body12includes a crown14, and a steel blank16that is embedded in the crown14. The crown14includes a particle-matrix composite material15such as, for example, particles of tungsten carbide embedded in a copper alloy matrix material. The bit body12is secured to the steel shank20by way of a threaded connection22and a weld24that extends around the drill bit10on an exterior surface thereof along an interface between the bit body12and the steel shank20. The steel shank20includes an API threaded pin28for attaching the drill bit10to a drill string (not shown).

The bit body12includes wings or blades30, which are separated by junk slots32. Internal fluid passageways (not shown inFIG. 1) extend between the face18of the bit body12and a longitudinal bore40, which extends through the steel shank20and partially through the bit body12. Nozzle inserts (not shown) may be provided at face18of the bit body12within the internal fluid passageways.

A plurality of PDC cutting elements34are provided on the face18of the bit body12. The PDC cutting elements34may be provided along the blades30within pockets36formed in the face18of the bit body12, and may be supported from behind by buttresses38, which may be integrally formed with the crown14of the bit body12.

The steel blank16shown inFIG. 1is generally cylindrically tubular. Alternatively, the steel blank16may have a fairly complex configuration and may include external protrusions corresponding to blades30or other features extending on the face18of the bit body12.

During drilling operations, the drill bit10is positioned at the bottom of a well bore hole and rotated while drilling fluid is pumped to the face18of the bit body12through the longitudinal bore40and the internal fluid passageways. As the PDC cutting elements34shear or scrape away the underlying earth formation, the formation cuttings and detritus are mixed with and suspended within the drilling fluid, which passes through the junk slots32and the annular space between the well bore hole and the drill string to the surface of the earth formation.

Conventionally, bit bodies that include a particle-matrix composite material, such as the previously described bit body12, have been fabricated by infiltrating hard particles with molten matrix material in graphite molds. In some instances, ceramic molds, cast from rubber masters, have been employed. The cavities of the graphite molds are conventionally machined with a five-axis machine tool. Fine features are then added to the cavity of the graphite mold by hand-held tools. These features are typically present in the rubber master used to cast ceramic molds. Additional clay work also may be required to obtain the desired configuration of some features of the bit body. Where necessary, preform elements or displacements (which may comprise ceramic components, graphite components, or resin-coated sand or other compacted particulate ceramic compact components) may be positioned within the mold and used to define the internal passages, cutting element pockets36, junk slots32, and other external topographic features of the bit body12. The cavity of the mold is filled with hard particulate carbide material (such as tungsten carbide, titanium carbide, tantalum carbide, etc.). The preformed steel blank16may then be positioned in the mold at the appropriate location and orientation. The steel blank16typically is at least partially submerged in the particulate carbide material within the mold.

The mold then may be vibrated or the particles otherwise packed to decrease the amount of space between adjacent particles of the particulate carbide material. A matrix material, such as a copper-based alloy, may be melted, and the particulate carbide material may be infiltrated with the molten matrix material. The mold and bit body12are allowed to cool to solidify the matrix material. The steel blank16is bonded to the particle-matrix composite material, which forms the crown14, upon cooling of the bit body12and solidification of the matrix material. Once the bit body12has cooled, the bit body12is removed from the mold and any displacements are removed from the bit body12. Destruction of the mold typically is required to remove the bit body12.

As previously described, destruction of the mold typically is required to remove the bit body12. After the bit body12has been removed from the mold, the bit body12may be secured to the steel shank20. As the particle-matrix composite material used to form the crown14is relatively hard and not easily machined, the steel blank16is used to secure the bit body12to the steel shank20. Threads may be machined on an exposed surface of the steel blank16to provide the threaded connection22between the bit body12and the steel shank20. The steel shank20may be screwed onto the bit body12, and the weld24then may be provided along the interface between the bit body12and the steel shank20.

The PDC cutting elements34may be bonded to the face18of the bit body12after the bit body12has been cast by, for example, brazing, mechanical affixation, or adhesive affixation. Alternatively, the PDC cutting elements34may be provided within the mold and bonded to the face18of the bit body12during infiltration or furnacing of the bit body12if thermally stable synthetic diamonds, or natural diamonds, are employed.

However, there is a continuing need in the art for methods of forming cutting element pockets on earth-boring rotary drill bits that avoid the tool path interference problems discussed above and that do not require use of additional support elements.

BRIEF SUMMARY OF THE INVENTION

In some embodiments, the present invention includes methods of forming earth-boring tools in which a bonding agent which may comprise a metal or metal alloy material, is provided at an interface between a first element and a second element. The first element, the second element, and the bonding agent may be sintered to form a bond between the first element and the second element. One or both of the first element and the second element may comprise a particle-matrix composite material. The first element and the second element may comprise any element or portion of an earth-boring tool.

In additional embodiments, the present invention includes earth-boring tools that are at least partially formed and include a bonding agent at an interface between a first element and a second element, in which at least one of the first element and the second element comprise a green or brown structure.

DETAILED DESCRIPTION OF THE INVENTION

The illustrations presented herein are, in some instances, not actual views of any particular cutting element insert, cutting element, or drill bit, but are merely idealized representations which are employed to describe the present invention. Additionally, elements common between figures may retain the same numerical designation.

The term “green” as used herein means unsintered.

The term “green bit body” as used herein means an unsintered structure comprising a plurality of discrete particles held together by a binder material, the structure having a size and shape allowing the formation of a bit body suitable for use in an earth-boring drill bit from the structure by subsequent manufacturing processes including, but not limited to, machining and densification.

The term “brown” as used herein means partially sintered.

The term “brown bit body” as used herein means a partially sintered structure comprising a plurality of particles, at least some of which have partially grown together to provide at least partial bonding between adjacent particles, the structure having a size and shape allowing the formation of a bit body suitable for use in an earth-boring drill bit from the structure by subsequent manufacturing processes including, but not limited to, machining and further densification. Brown bit bodies may be formed by, for example, partially sintering a green bit body.

The term “sintering” as used herein means densification of a particulate component involving removal of at least a portion of the pores between the starting particles (accompanied by shrinkage) combined with coalescence and bonding between adjacent particles.

As used herein, the term “[metal] material” (where [metal] is any metal) means commercially pure [metal] in addition to metal alloys or mixtures wherein the weight percentage of [metal] in the alloy or mixture is greater than the weight percentage of any other component of the alloy or mixture.

As used herein, the term “material composition” means the chemical composition and microstructure of a material. In other words, materials having the same chemical composition but a different microstructure are considered to have different material compositions.

As used herein, the term “tungsten carbide” means any material composition that contains chemical compounds of tungsten and carbon, such as, for example, WC, W2C, and combinations of WC and W2C. Tungsten carbide includes, for example, cast tungsten carbide, sintered tungsten carbide, and macrocrystalline tungsten carbide.

Recently, new methods of forming rotary drill bits having bit bodies comprising particle-matrix composite materials have been developed in an effort to improve the performance and durability of earth-boring rotary drill bits. Such methods are disclosed in U.S. patent application Ser. No. 11/271,153 (which is entitled “Earth-Boring Rotary Drill Bits And Methods Of Manufacturing Earth-Boring Rotary Drill Bits Having Particle-Matrix Composite Bit Bodies,” was filed Nov. 10, 2005, now U.S. Pat. No. 7,802,409, issued Sep. 28, 2010, and is assigned to the same assignee of the present invention) and U.S. patent application Ser. No. 11/272,439 (which is entitled “Earth-Boring Rotary Drill Bits And Methods Of Forming Earth-Boring Rotary Drill Bits,” was filed Nov. 10, 2005, now U.S. Pat. No. 7,776,256, issued Aug 17, 2010, and is assigned to the same assignee of the present invention), the disclosure of each of which application is incorporated herein in its entirety by this reference.

In contrast to conventional infiltration methods (in which hard particles (e.g., tungsten carbide) are infiltrated by a molten liquid metal matrix material (e.g., a copper-based alloy) within a refractory mold), these new methods generally involve pressing a powder mixture to form a green powder compact, and sintering the green powder compact to form a bit body. The green powder compact may be machined or modified as necessary or desired prior to sintering using conventional machining and shaping techniques like those used to form steel bit bodies. Furthermore, additional machining or shaping processes may be performed after sintering the green powder compact to a partially sintered brown state, or after sintering the green powder compact to a desired final density.

During the fabrication of a bit body of a rotary drill bit using such methods, it may be necessary or desirable to bond at least one green or brown element to another green, brown, or fully sintered element during a sintering process. By way of example and not limitation, two or more elements, each comprising a portion of a bit body, may be bonded together during a sintering process to form a unitary bit body, as described with reference toFIGS. 2A and 2Bbelow.

FIG. 2Ais a cross-sectional side view of a partially formed bit body50. The bit body50includes a first element52forming a first region of the bit body50and a second element54forming a second region of the bit body50.FIG. 2Bis a cross-sectional view of the partially formed bit body50shown inFIG. 2Ataken along section line2B-2B shown therein.

At least one of the first element52and the second element54may be less than fully sintered. The first element52and the second element54may be assembled together, as shown inFIGS. 2A and 2B, and the resulting assembly may be sintered in a subsequent process to secure the first element52and the second element54together to form a fully sintered bit body50. In some embodiments, the first element52and the second element54each may comprise a green structure or a brown structure. In additional embodiments, one of the first element52and the second element54may comprise a green structure, and the other of the first element52and the second element54may comprise a brown structure. In yet further embodiments, one of the first element52and the second element54may comprise a fully sintered structure, and the other of the first element52and the second element54may comprise a green structure or a brown structure.

During such a sintering process, any structure that is less than fully dense (e.g., a green structure or a brown structure) may undergo shrinkage. Such shrinkage may cause a surface of the less than fully dense structure to pull or shark away from an opposing surface of an adjacent structure in such a manner as to prevent the opposing surfaces from bonding together during the sintering process. Explaining further, as a non-limiting example, each of the first element52and the second element54may comprise green structures. During a sintering process used to bond the first element52and the second element54together, the first element52may undergo shrinkage, which may cause the surfaces53that are vertically oriented inFIG. 2Ato retract or pull away from the opposing surfaces55of the second element54. Similarly, the second element54may undergo shrinkage, which may cause the surfaces55that are vertically oriented inFIG. 2Ato retract or pull away from the opposing surfaces53of the first element52. As a result upon sintering, there may be one or more regions at the interface between the first element52and the second element54at which the first element52and the second element54are not bonded together. In other words, there may be one or more voids at the interface between the first element52and the second element54after sintering.

In embodiments of the present invention, a metal material may be provided at the interface between the first element52and the second element54prior to sintering the first element52and the second element54to enhance the formation of a bond therebetween during sintering. Such a metal or metal alloy is referred to herein as a “bonding agent.” By way of example and not limitation, a foil60may be provided over or along at least a portion of the interface between the first element52and the second element54, as shown inFIGS. 2A and 2B. The foil60may comprise a metal or metal alloy bonding agent having a melting point below a temperature at which the first element52and the second element54are to be sintered. The bonding agent may be wettable to at least one material of the first element52and the second element54, such that, upon melting of the foil60during sintering, surface tension causes the molten bonding agent of the foil60to form a fluid bridge between the exposed, opposing surfaces53,55of the first element52and the second element54at the interface therebetween, which may facilitate the formation of an enhanced bond or joint between the first element52and the second element54.

The metal or metal alloy of the bonding agent may be chemically compatible with the materials of the first element52and the second element54, such that materials (e.g., intermetallic compounds) exhibiting undesirable physical properties (e.g., brittleness) are not formed at the interface between the first element52and the second element54during the sintering process. In some embodiments, the metal or metal alloy bonding agent may be substantially identical to a material of one or both of the first element52and the second element54. For example, each of the first element52and the second element54may comprise a particle matrix composite material, each comprising a plurality of hard particles and a matrix material, as discussed in further detail below. In such embodiments, the metal or metal alloy bonding agent may be substantially identical to the matrix material of one or both of the first element52and the second element54.

By way of example and not limitation, the foil60may have a thickness of between about five microns (5 μm) and about five hundred and fifty microns (550 μm). The foil60may be applied to one or both of the first element52and the second element54prior to assembling together the first element52and the second element54. Furthermore, the foil60may be applied to at least a portion of one or more surfaces of the first element52, to at least a portion of one or more surfaces of the second element54, or to at least a portion of one or more surfaces of both the first element52and the second element54.

In some embodiments, the foil60may be formed as a substantially planar sheet, and the foil60may be caused to conform to the surfaces of the first element52and/or the second element54merely by pressing the foil60against the surfaces and causing the foil60to deform so as to conform to the surfaces of the first element52and/or the second element54. In additional embodiments, the foil60may be preformed (e.g., stamped, cast, etc.) to have a conformal shape to that of the surfaces of the first element52and/or the second element54to which the foil60is to be applied.

In additional embodiments of the present invention, the metal or metal alloy bonding agent provided at the interface between the first element52and the second element54may not comprise a foil (like the foil60), and may comprise a powder, a paste, a film, a coating, or any other form of material. As non-limiting examples, a powder comprising relatively fine particles of the metal or metal alloy bonding agent may be applied to the complementary surfaces of the first element52and/or the second element54. Additionally, a coating of the bonding agent may be applied to the complementary surfaces of the first element52and/or the second element54by one or more of a flame spraying process, an electroplating process, an electroless plating process, or a vapor deposition process (e.g., physical vapor deposition (PVD) or chemical vapor deposition (CVD)). In yet additional methods, the first element52and the second element54may be assembled together, and the metal or metal alloy bonding agent may be brazed into the interface between the first element52and the second element54. In other words, the first element52and the second element54may be assembled together, and the bonding agent may be melted and applied along an exposed edge of the interface between the first element52and the second element54in the molten state. Surface tension between the molten bonding agent and each of the first element52and the second element54may cause the molten bonding agent to be drawn into and along the interface therebetween. Optionally, the first element52and the second element54may be heated to an elevated temperature to prevent the molten bonding agent from prematurely solidifying, which may prevent the interface between the first element52and the second element54from being sufficiently filled with the molten bonding agent.

As previously mentioned, the first element52and the second element54each may comprise a green, brown, or fully sintered structure formed by mixing hard particles with particles comprising a matrix material (together with any necessary or desirable organic binders, lubricants, adhesives, etc.) to form a powder mixture, and pressing the powder mixture to form a powder compact. If either the first element52or the second element54comprises a brown or fully sintered structure, the powder compact may be sintered to the desired state. Methods of forming such powder compacts, as well as methods for sintering such powder compacts, are more fully described in, for example, the aforementioned U.S. patent application Ser. No. 11/271,153, filed Nov. 10, 2005, and U.S. patent application Ser. No. 11/272,439, also filed Nov. 10, 2005.

By way of example and not limitation, the hard particles used to form the first element52and the second element54may comprise a hard material such as diamond, boron carbide, boron nitride, aluminum nitride, and carbides or borides of the group consisting of W, Ti, Mo, Nb, V, Hf, Zr, Si, Ta, and Cr, and the particles comprising the matrix material may comprise a cobalt-based alloy, an iron-based alloy, a nickel-based alloy, a cobalt and nickel-based alloy, an iron and nickel-based alloy, an iron and cobalt-based alloy, an aluminum-based alloy, a copper-based alloy, a magnesium-based alloy, or a titanium-based alloy.

As one particular non-limiting example, the hard particles may comprise tungsten carbide, and the matrix material may comprise a metal alloy predominantly comprised of one or both of nickel and cobalt. In other words, the matrix material may comprise greater than about fifty atomic percent (50 at %) of one or both of nickel and cobalt. Furthermore, the matrix material may exhibit a melting point of between about one thousand and fifty degrees Celsius (1050° C.) and about one thousand, three hundred, and fifty degrees Celsius (1350° C.). In such an embodiment, the metal or metal alloy bonding agent applied to the interface between the first element52and the second element54may have a melting point that is between about sixty percent (60%) and one hundred percent (100%) of the melting point of the matrix material, may be wettable to both tungsten carbide and the matrix material. As one particular non-limiting example, the metal or metal alloy bonding agent also may be predominantly comprised of nickel, a nickel-based alloy, cobalt, a cobalt-based alloy, silver, or a silver-based alloy. The bonding agent may further comprise at least one constituent, the identity and concentration of which is selected to reduce the melting point of the bonding agent to a selected temperature that is lower than that of the matrix material or materials of the first element52and the second element54.

In additional embodiments, the first element52and the second element54may comprise portions of a bit body other than those illustrated inFIGS. 2A and 2B, and each may comprise any other portion of a bit body. As another non-limiting example, one or both of the first element52and the second element54may comprise a portion of a bit body adjacent a cutting element pocket. As described in, for example, U.S. patent application Ser. No. 11/717,905, filed Mar. 13, 2007 (which is entitled “Earth-Boring Tools Having Pockets For Receiving Cutting Elements Therein And Methods Of Forming Such Pockets And Earth-Boring Tools,” was filed Mar. 13, 2007, and is assigned to the same assignee of the present invention), it can be difficult to form cutting element pockets having a desired size, shape, and orientation in a bit body of a drill bit due to mechanical interference between tools used to form the cutting element pocket and other portions of the drill bit. Therefore, it may be necessary or desirable to remove (e.g., machine) a relatively larger portion of the drill bit than is required to form the cutting element pocket, and to subsequently re-form a portion of the bit body around the cutting element pocket to replace the excess material removed.

For example,FIGS. 3A and 3Billustrate a portion of a bit body61of an earth-boring rotary drill bit that includes a cutting element34secured within a cutting element pocket36. The cutting element pocket36shown inFIG. 1, as well as the manner in which the cutting element pocket36may be formed, is described in further detail in the aforementioned pending U.S. patent application Ser. No. 11/717,905. As described therein, the cutting element pocket36may be formed by machining one or more recesses into the bit body61, and subsequently filling at least a portion of the recesses with preformed elements. As a non-limiting example, a first preformed element62may be used to fill at least a portion of a first recess71in the bit body61, as shown inFIG. 3A. A second preformed element64may be used to fill at least a portion of a second recess73at the rotationally forward end of the cutter pocket, as also shown inFIG. 3A. Furthermore, one or more additional preformed elements66may be used to fill at least a portion of the second recess73in a region over (i.e., radially outward from a longitudinal axis of the drill bit (not shown)) the cutting element34to be positioned in the cutting element pocket36. The first preformed element62, the second preformed element64, and the one or more preformed elements66may be bonded to the bit body61before securing a cutting element34within the cutting element pocket36, after securing a cutting element34within the cutting element pocket36(so long as the cutting element will not be degraded or harmed by the sintering process), or at substantially the same time the cutting element34is secured within the cutting element pocket36.

In additional embodiments, preformed elements may be used to form other portions of the bit body61adjacent the cutting element pocket including, for example, the regions of the bit body61rotationally behind, and/or laterally to the side of, the cutting element pocket.

Each of the bit body61, the first preformed element62, the second preformed element64, and the one or more preformed elements66may comprise a green, brown, or fully sintered structure, and may be bonded together in a sintering process in a manner substantially similar to that previously described in relation to the first element52and the second element54with reference toFIGS. 2A and 2B. Displacement members may be used as necessary during such a sintering process to assure that the various components coalesce in such a manner as to provide a desired geometry. For example, displacement members such as those described in U.S. patent application Ser. No. 11/635,432, filed Dec. 7, 2006 and entitled “Displacement Members and Methods of Using Such Displacement Members To Form Bit Bodies Of Earth-Boring Rotary Drill Bits,” the disclosure of which is incorporated herein in its entirety by this reference, may be used to assure that the resulting sintered structure has a desired geometry. Furthermore, a metal or metal alloy bonding agent, as previously described herein, may be used to enhance the degree of bonding between the bit body61and each of the first preformed element62, the second preformed element64, and the one or more additional preformed elements66. By way of example and not limitation, a foil60, as previously described herein, may be provided between the bit body61and each of the first preformed element62, the second preformed element64, and the one or more additional preformed elements66prior to sintering the assembly and bonding the first preformed element62, the second preformed element64, and the one or more additional preformed elements66to the bit body61.

In yet additional embodiments of the present invention, cutting elements or portions of cutting elements may be bonded to another portion of an earth-boring tool, such as, for example, a bit body of a fixed-cutter earth-boring rotary drill bit or the body of a cone of a roller cone earth-boring rotary drill bit.

For example,FIG. 4illustrates a cross-sectional view of a cone70of a roller cone earth-boring rotary drill bit (not shown). The cone70shown inFIG. 4, methods for forming the cone70, and an earth-boring rotary drill bit including such a cone70, are described in further detail in U.S. patent application Ser. No. 11/710,091 (which is entitled “Earth-Boring Tools And Cutter Assemblies Having A Cutting Element Co-Sintered With A Cone Structure, Methods Of Using The Same,” was filed Feb. 23, 2007, and is assigned to the same assignee of the present invention), the entire disclosure of which is incorporated herein in its entirety by this reference.

As described in the aforementioned U.S. patent application Ser. No. 11/710,091, cone70may be predominantly comprised of a particle-matrix composite material, and cutting inserts72that also comprise a particle-matrix composite material may be co-sintered with the cone70to form a bond between the cone70and the cutting inserts72. Furthermore, bearing structures74may be co-sintered with the cone70to form a bond between the cone70and the bearing structures74.

Each of the cone70, the cutting inserts72, and the bearing structures74may comprise a green, brown, or fully sintered structure, and may be bonded together in a sintering process in a manner substantially similar to that previously described in relation to the first element52and the second element54with reference toFIGS. 2A and 2B. Furthermore, a metal or metal alloy bonding agent, as previously described herein, may be used to enhance the degree of bonding between the cone70and each of the cutting inserts72and the bearing structures74. By way of example and not limitation, a foil60, as previously described herein, may be provided between the cone70and each of the cutting inserts72and the bearing structures74prior to sintering the assembly and bonding the cutting inserts72and the bearing structures74to the cone70.

FIG. 5illustrates a portion of another cone80that includes a cutting tooth structure82. For example, the cone80may be similar to a so-called “milled-tooth” cone. The cutting tooth structure82includes a tooth base structure84and a tooth cap structure86that is bonded to the tooth base structure84. The cone80shown inFIG. 5, methods for forming the cone80, and an earth-boring rotary drill bit including such a cone80, are described in further detail in the aforementioned pending U.S. patent application Ser. No. 11/710,091. As described in the aforementioned pending U.S. patent application Ser. No. 11/710,091, the tooth base structure84and the tooth cap structure86of the cutting teeth82of the cone80may comprise a particle-matrix composite material, and may be co-sintered to form a bond between the tooth base structure84and the tooth cap structure86. Each of the tooth base structure84and the tooth cap structure86may comprise a green, brown, or fully sintered structure, and may be bonded together in a sintering process in a manner substantially similar to that previously described in relation to the first element52and the second element54with reference toFIGS. 2A and 2B. The tooth base structure84may be machined or otherwise formed on and/or in the surface of the cone80when the cone80is in the green, brown, or fully sintered state. The tooth cap structure86may be formed separately and attached to the tooth base structure84during the sintering process.

Furthermore, a metal or metal alloy bonding agent, as previously described herein, may be used to enhance the degree of bonding between the tooth base structure84and the tooth cap structure86. By way of example and not limitation, a foil60, as previously described herein, may be provided between the tooth base structure84and the tooth cap structure86prior to sintering the assembly and bonding the tooth cap structure86to the tooth base structure84.

FIG. 6illustrates a portion of another cone90that includes another cutting tooth structure92that is generally similar to the cutting tooth structure82. The cutting tooth structure92includes a tooth base structure94and a tooth plug structure96that is bonded within a recess in the tooth base structure94. The cone90shown inFIG. 6, methods for forming the cone90, and an earth-boring rotary drill bit including such a cone90, are described in further detail in the aforementioned pending U.S. patent application Ser. No. 11/710,091. As described therein, the tooth base structure94and the tooth plug structure96of the cutting teeth92of the cone90may comprise a particle-matrix composite material, and may be co-sintered to form a bond between the tooth base structure94and the tooth plug structure96. Each of the tooth base structure94and the tooth plug structure96may comprise a green, brown, or fully sintered structure, and may be bonded together in a sintering process in a manner substantially similar to that previously described in relation to the first element52and the second element54with reference toFIGS. 2A and 2B. Furthermore, a metal or metal alloy bonding agent, as previously described herein, may be used to enhance the degree of bonding between the tooth base structure94and the tooth plug structure96. By way of example and not limitation, a foil60, as previously described herein, may be provided between the tooth base structure94and the tooth plug structure96prior to sintering the assembly and bonding the tooth plug structure96to the tooth base structure94.

Providing a bonding agent between elements prior to sintering the elements to form a bond therebetween, as previously described herein, may enable improved bonding between the elements during the sintering process. For example, using a bonding agent as described herein may reduce or prevent the formation of voids or recesses at the interface between the elements that would otherwise form during a sintering process. Accordingly, earth-boring tools and methods for forming at least portions of such earth-boring tools may be improved according to embodiments of the present invention.

While the present invention has been described herein with respect to certain preferred embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Rather, many additions, deletions and modifications to the preferred embodiments may be made without departing from the scope of the invention as hereinafter claimed. In addition, features from one embodiment may be combined with features of another embodiment while still being encompassed within the scope of the invention as contemplated by the inventors. Further, the invention has utility with different and various bit profiles as well as cutting element types and configurations.