Erosion resistant fluid passageways and flow tubes for earth-boring tools, methods of forming the same and earth-boring tools including the same

Flow tubes for earth-boring tools include hardfacing material for protecting the tubes from erosion due to the flow of fluid through a fluid passageway extending therethrough. Earth-boring tools include an erosion-resistant material covering a surface of a body of the tools for protecting the bodies from erosion due to the flow of fluid through a fluid passageway extending therethrough. Methods of forming earth-boring tools include forming a body having a fluid passageway extending therethrough and covering a surface of the body with a hardfacing material. The surface of the body may be located in a region susceptible to erosion when fluid is caused to flow through the fluid passageway.

FIELD OF THE INVENTION

The present invention relates generally to earth-boring tools, components of earth-boring tools, and methods of forming earth-boring tools and components thereof. More particularly, the present invention relates to earth-boring tools and components thereof that are relatively resistant to erosion caused by the flow of fluid through fluid passageways extending through the earth-boring tools and components thereof, to methods of forming such earth-boring tools and components, and methods of improving the erosion resistance of such tools and components.

BACKGROUND OF THE INVENTION

Earth-boring rotary drill bits have two primary configurations. One configuration is the roller cone bit, which typically includes three cones mounted on supporting bit legs that extend from a bit body, which may be formed from, for example, three bit head sections that are welded together to form the bit body. Each bit leg may depend from one bit head section. Each roller cone is configured to spin or rotate on a bearing shaft that extends from a bit leg in a radially inward and downward direction from the bit leg. The cones are typically formed from steel, but they also may be formed from a particle-matrix composite material (e.g., a cement composite such as cemented tungsten carbide). Cutting teeth for cutting rock and other earth formations may be machined or otherwise formed in or on the outer surfaces of each cone. Alternatively, receptacles are formed in outer surfaces of each cone, and inserts formed of hard, wear resistant material are secured within the receptacles to form the cutting elements of the cones.

The roller cone drill bit may be placed in a bore hole such that the cones are adjacent the earth formation to be drilled. As the drill bit is rotated, the roller cones roll and slide across the surface of the formation, which causes the cutting teeth to crush and scrape away the underlying formation.

It is known in the art to apply wear-resistant materials, such as “hardfacing” materials, to the formation-engaging surfaces of rotary drill bits to minimize wear of those surfaces of the drill bits caused by abrasion. For example, abrasion occurs at the formation-engaging surfaces of an earth-boring tool when those surfaces are engaged with and sliding relative to the surfaces of a subterranean formation in the presence of the solid particulate material (e.g., formation cuttings and detritus) carried by conventional drilling fluid. For example, hardfacing may be applied to cutting teeth on the cones of roller cone bits, as well as to the gage surfaces of the cones. Hardfacing also may be applied to the exterior surfaces of the curved lower end or “shirttail” of each bit leg, and other exterior surfaces of the drill bit that are likely to engage a formation surface during drilling.

During drilling, drilling fluid is pumped down the wellbore through the drill string to the drill bit. The drilling fluid passes through an internal longitudinal bore within the drill bit and through other fluid conduits or passageways within the drill bit to nozzles that direct the drilling fluid out from the drill bit at relatively high velocity. The nozzles may be directed toward the cones and cutting elements thereon to clean debris and detritus from the cones and prevent “balling” of the drill bit. The nozzles also may be directed past the cones and toward the bottom of the wellbore to flush debris and detritus off from the bottom of the wellbore and up the annulus between the drill string and the casing (or exposed surfaces of the formation) within the wellbore, which may improve the mechanical efficiency of the drill bit and the rate of penetration (ROP) of the drill bit into the formation.

It is known in the art to use flow tubes to direct drilling fluid to a nozzle and out from the drill bit, particularly when it is desired to direct drilling fluid past the cones and toward the bottom of the wellbore. Such flow tubes may be separately formed from the bit body, and may be attached to the bit body (e.g., bit head section or bit leg) by, for example, welding the flow tubes to the bit body. A fluid course or passageway is formed through the bit body to provide fluid communication between the interior longitudinal bore of the drill bit and the fluid passageway within the flow tube.

As drilling fluid is caused to flow through the flow tube, the drilling fluid erodes away the interior surfaces of the flow tube. Such erosion may be relatively more severe at locations within the flow tube at which the direction of fluid flow changes, since the drilling fluid impinges on the interior surfaces of the flow tube at relatively higher angles at such locations. This erosion can eventually result in the formation of holes that extend completely through the walls of the flow tube, thereby allowing drilling fluid to exit the flow tube before passing through the nozzle, which eventually leads to failure of the designed hydraulic system of the drill bit. When the hydraulic system of the drill bit fails, the rate of penetration decreases and the drill bit becomes more susceptible to “balling.” Ultimately, the drill bit may fail and need to be replaced.

In view of the above, there is a need in the art for fluid passageways and flow tubes for earth-boring tools and components thereof that are relatively more resistant to erosion, for methods of forming such earth-boring tools and components, and for methods of increasing the erosion resistance of fluid passageways and flow tubes of earth-boring tools and components.

BRIEF SUMMARY OF THE INVENTION

In some embodiments, the present invention includes flow tubes and other structures carrying fluid passageways for earth-boring tools that include hardfacing materials for protecting the flow tubes from erosion caused by the flow of fluid through fluid passageways extending through the flow tubes. In some embodiments, the hardfacing material covers at least a portion of an inner surface of a body within a fluid passageway. In other embodiments, the hardfacing material may be applied to an outer surface of the body, and may be disposed at least partially within a recess formed in the outer surface of the body.

In additional embodiments, the present invention includes earth-boring tools that include a hardfacing material for protecting a body thereof from erosion caused by the flow of fluid through a fluid passageway extending through the body. In some embodiments, at least a portion of the erosion-resistant material covers an inner surface of a body within a fluid passageway. In additional embodiments, at least a portion of the erosion-resistant material covers an outer surface of a body, and optionally may be at least partially disposed within a groove formed in the outer surface of the body.

In still other embodiments, the present invention includes methods of forming earth-boring tools. The methods include covering at least a portion of a surface of a body of an earth-boring with a hardfacing material. The surface may be located in a region susceptible to erosion caused by the flow of fluid through a fluid passageway extending through the body.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “abrasion” refers to a three body wear mechanism that includes two surfaces of solid materials sliding past one another with solid particulate material therebetween.

As used herein, the term “erosion” refers to a two body wear mechanism that occurs when solid particulate material, a fluid, or a fluid carrying solid particulate material impinges on a solid surface.

As used herein, the term “fluid” comprises substances consisting solely of liquids as well as substances comprising solid particulate material suspended within a liquid, and includes conventional drilling fluid (or drilling mud), which may comprise solid particulate material such as additives, as well as formation cuttings and detritus suspended within a liquid.

As used herein, the term “hardfacing” means any material or mass of material that is applied to a surface of a separately formed body and that is relatively more resistant to wear (abrasive wear and/or erosive wear) relative to the material of the separately formed body at the surface.

The illustrations presented herein are, in some instances, not actual views of any particular earth-boring tool, flow tube, or fluid passageway, but are merely idealized representations which are employed to describe the present invention. Additionally, elements common between figures may retain the same numerical designation.

FIG. 1is a perspective side view illustrating an embodiment of an earth-boring tool of the present invention. The earth-boring tool ofFIG. 1is a rolling cutter type rotary drill bit10, such bits also being known in the art as “roller cone” bits as noted above, due to the generally conical shape of the rolling cutters employed in many such bits. The embodiment of the drill bit10shown inFIG. 1includes three head sections12that are welded together to form a bit body14of the drill bit10. Only two of the head sections12are visible inFIG. 1. The bit body14may comprise a pin22or other means for securing the drill bit10to a drill string or bottom hole assembly (not shown). In some embodiments, the pin22may be configured to conform to industry standards for threaded pin connections, such as those promulgated by the American Petroleum Institute (API).

A bit leg16extends downwardly from each of the head sections12of the drill bit10. Each bit leg16may be integrally formed with the corresponding head section12from which it depends. As shown inFIG. 1, at least one of hardfacing material20and inserts21may be used to protect the outer surfaces of the bit legs16from wear. By way of example and not limitation, hardfacing material20may be applied to the rotationally leading surfaces of the bit legs16and to the lower surfaces or “shirttails” at the lower end18of the bit legs16, and inserts21may be provided in or on the radially outward most surfaces of the bit legs16, as shown inFIG. 1. The hardfacing material20and the inserts21may comprise materials that are relatively more wear-resistant relative to the material of the bit legs16at the surfaces thereof. In additional embodiments, the outer surfaces of the bit legs16may comprise only inserts21and no hardfacing20, or only hardfacing20and no inserts21. In yet further embodiments, the outer surfaces of the bit legs16may comprise neither hardfacing20nor inserts21.

A rolling cutter in the form of a roller cone30may be rotatably mounted on a bearing shaft (not shown) that extends downward and radially inward from the lower end18of each bit leg16(relative to a longitudinal centerline (not shown) of the drill bit10and when the drill bit10is oriented relative to the observer as shown inFIG. 1). The roller cones30are rotatably mounted on the bearing shafts such that, as the drill bit10is rotated at the bottom of a wellbore within an earth formation, the roller cones30roll and slide across the underlying formation.

Each roller cone30includes a plurality of rows of cutting elements32for crushing and scraping the formation as the roller cones30roll and slide across the formation at the bottom of the wellbore. In the embodiment shown inFIG. 1, the cutting elements32comprise inserts that are pressed into complementary recesses formed in the body of the roller cones30. The inserts may comprise a relatively hard and abrasive material such as, for example, cemented tungsten carbide. In additional embodiments, the cutting elements32may comprise cutting teeth that are machined on or in the surface of the roller cones30. Such cutting teeth may be coated with hardfacing material (not shown), similar to the hardfacing material20, which may comprise, for example, a composite material including hard particles (e.g., tungsten carbide) dispersed within a metal or metal alloy matrix material (e.g., an iron-based, cobalt-based, or nickel-based alloy).

With continued reference toFIG. 1, the drill bit10includes three flow tubes36(only two of which are visible inFIG. 1). In the embodiments shown inFIG. 1, the flow tubes36are discrete structures that are separately formed from the head sections12(and integral bit legs16) of the drill bit10. The flow tubes36are attached to the bit body14by, for example, welding the flow tubes36to the bit body14after welding the head sections12together to form the bit body14. In other embodiments, the flow tubes36may be welded to one or more head sections12prior to welding the head sections12together to form the bit body14. In yet further embodiments, the flow tubes36may not be separately formed from the head sections12, but rather may be an integral part of a head section12.

The drill bit10includes an internal longitudinal bore (not shown), which may also be termed a plenum, that extends at least partially through the pin22. The internal longitudinal bore diverges into a plurality of fluid passageways that lead to the exterior of the drill bit10. At least one of these fluid passageways leads to, and extends through, each of the flow tubes36.

As previously discussed, during drilling, drilling fluid is pumped from the surface through the drill string (not shown) and the drill bit10to the bottom of the wellbore. The drilling fluid passes through the internal longitudinal bore and the fluid passageways (not shown) within the drill bit10and out from the flow tubes36toward the cones and/or the exposed surfaces of the subterranean formation within the wellbore. Nozzles (not shown) may be inserted within each of the flow tubes36. The nozzles may have internal geometries designed and configured to at least partially define the velocity and the direction of the drilling fluid as the drilling fluid passes through the nozzles and exits the flow tubes36.

Embodiments of drill bits and other earth-boring tools, such as the drill bit10shown inFIG. 1, include flow tubes36and/or fluid passageways that are relatively more resistant to erosion caused by the drilling fluid flowing through the flow tubes36, as discussed in further detail below.

FIGS. 2A-2Fillustrate an example embodiment of a flow tube36of the present invention.FIG. 2Ais an isometric view of the flow tube36,FIG. 2Bis a side view of the flow tube36, andFIG. 2Cis a front view of the flow tube36.

Referring toFIG. 2A, the flow tube36includes a tube body38, which may comprise a metal or metal alloy such as, for example, steel. As shown inFIG. 2D, which is a longitudinal cross-sectional view of the flow tube36taken along section line2D-2D shown inFIG. 2C, a fluid passageway40extends through the tube body38of the flow tube36from an inlet42to an outlet44. Drilling fluid flows through the fluid passageway40from the inlet42to the outlet44during drilling. Annular recesses48or other geometric features (e.g., threads) may be machined or otherwise provided in the inner walls39of the tube body38within the fluid passageway40proximate the outlet44to receive and secure a nozzle and any associated seals (e.g., o-rings) and retention rings therein.

Referring again toFIG. 2A, hardfacing material20may be applied to one or both of the rotationally leading outer edge50and the rotationally trailing outer edge52of the tube body38. Furthermore, hardfacing material20may be applied to exterior surfaces of the tube body38of the flow tube36over regions that are proximate to, or adjacent regions of the inner walls39of the tube body38that are susceptible to erosion caused by the flow of drilling fluid through the flow tube36.

For purposes of this application, regions “susceptible to erosion” caused by the flow of drilling fluid through the flow tube or fluid passageway are those regions of a flow tube, drill bit, or other earth-boring tool that will eventually be eroded away by drilling fluid when conventional drilling fluid is caused to flow through the flow tube or fluid passageway at conventional drilling flow rates and fluid pressures for a period of time of less than about five times the average lifetime, in terms of operating hours, for the respective design or model of the drill bit or other earth-boring tool carrying the flow tube or fluid passageway. In other words, if conventional drilling fluid is caused to flow through the flow tube or fluid passageway at conventional flow rates and fluid pressures for a period of time that is about five times the average lifetime of the respective design or model of the drill bit or other earth-boring tool carrying the flow tube or fluid passageway, and a region of the flow tube, drill bit, or other earth-boring tool has eroded away, that region may be considered to be a region “susceptible to erosion” caused by the flow of drilling fluid through the flow tube or fluid passageway for purposes of this application.

Referring toFIG. 2D, a first section41A of the fluid passageway40extends through the flow tube36in a first direction from the inlet42in a radially outward and downward direction (relative to a longitudinal centerline of the drill bit10when the flow tube36is secured to the drill bit10and the drill bit10is oriented relative to the observer as shown inFIG. 1). The first section41A of the fluid passageway40transitions to a second section41B of the fluid passageway40that extends in a generally downward direction to the outlet44. In the embodiment shown inFIGS. 2A-2E, the first section41A of the fluid passageway40is oriented at an obtuse angle (i.e., between 90° and 180°) relative to the second section41B of the fluid passageway40. In this configuration, as drilling fluid passes from the first section41A into the second section41B of the fluid passageway40, the drilling fluid may impinge on the radially outward regions of the inner walls39of the tube body38within the second section41B at an acute angle of less than ninety degrees (90°). As a result, the radially outward regions of the inner walls39of the tube body38within the second section41B of the fluid passageway40may be more susceptible to erosion caused by the passage of drilling fluid through the fluid passageway40relative to other regions of the inner walls39of the tube body38.

To reduce damage to the flow tube36caused by such erosion, a relatively thick layer of hardfacing20′ may be applied to the regions of the outer surfaces of the tube body38of the flow tube36that are adjacent the regions of the inner walls39of the tube body38that are susceptible to erosion as shown inFIGS. 2A-2E. The relatively thick layer of hardfacing20′ may be configured in the form of an elongated strip extending down and covering the radially outward most regions of the outer surfaces of the tube body38of the flow tube36(relative to the longitudinal centerline of the drill bit10(FIG.1)), as best shown inFIGS. 2A and 2C.

In using the hardfacing20′ to reduce damage to the flow tube36caused by erosion of the inner walls39of the tube body38, it may be desirable to configure the relatively thick layer of hardfacing20′ to have a thickness that is greater than a thickness of hardfacing20used to prevent or reduce abrasive wear to exterior surfaces of the flow tube36, such as the hardfacing20applied to the rotationally leading and trailing outer edges50,52of the flow tube36. By way of example and not limitation, the relatively thick layer of hardfacing20′ may have an average thickness of greater than about 5.0 millimeters (greater than about 0.2 inch), and the hardfacing20applied to the rotationally leading and trailing outer edges50,52of the flow tube36may have an average thickness of less than about 4.5 millimeters (less than about 0.18 inch). As one particular non-limiting example, the relatively thick layer of hardfacing20′ may have an average thickness of between about 6.9 millimeters (about 0.27 inch) and about 8.2 millimeters (about 0.32 inch), and the hardfacing20applied to the rotationally leading and trailing outer edges50,52of the flow tube36may have an average thickness of between about 0.8 millimeter (about 0.03 inch) and about 1.6 millimeters (about 0.06 inch).

In some embodiments, it may be desirable to configure the exterior surface of the relatively thick layer of hardfacing20′ and the exterior surfaces of the hardfacing20applied to the rotationally leading and trailing outer edges50,52of the flow tube36to be substantially flush with one another, as shown inFIG. 2A. To enable the exterior surface of the hardfacing20′ and the hardfacing20to be substantially flush with one another, the layer of hardfacing20′ may be at least partially disposed within a recess56provided in an outer surface of the tube body38of the flow tube, as shown inFIGS. 2A,2C,2D, and2E. Referring toFIGS. 2D and 2E, in some embodiments, the recess56may be configured as a groove that extends in a downward direction along the outer surface of the tube body38. As one non-limiting example, the recess56may extend into the outer surface of the tube body38to a depth of between about 5.0 millimeters (about 0.20 inch) and about 13.0 millimeters (about 0.50 inch). More particularly, the recess56may extend into the outer surface of the tube body38to a depth of between about 6.1 millimeters (about 0.24 inch) and about 6.6 millimeters (about 0.26 inch).

FIG. 2Fis a longitudinal cross-sectional view of the flow tube36, like that ofFIG. 2D, illustrating erosion of the inner walls39of the tube body38of the flow tube36that may occur after causing drilling fluid to flow through the flow tube36for a period of time during drilling. As shown inFIG. 2F, the inner walls39of the tube body38within the fluid passageway40may erode until the relatively thick layer of hardfacing20′ is exposed within the fluid passageway40. The hardfacing20′ may wear due to erosion at a rate that is lower than the rate at which the material of the tube body38of the flow tube36wears due to erosion. Therefore, the hardfacing20′ may prevent the drilling fluid from eroding entirely through the walls of the flow tube36from the interior fluid passageway40as quickly as in previously known flow tubes, thereby allowing embodiments of flow tubes36of the present invention to properly function for longer periods of time and through the operational life of the drill bit10.

By way of example and not limitation, the hardfacing20and the hardfacing20′ each may comprise a composite material comprising a relatively hard first phase distributed within a second, continuous matrix phase. By way of example and not limitation, the first phase may 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 matrix phase may comprise cobalt, a cobalt-based alloy, iron, an iron-based alloy, nickel, 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. In some embodiments, the first phase may comprise a plurality of discrete regions or particles dispersed within the matrix phase. In other embodiments, the first phase may comprise a fabric structure that has been infiltrated with the matrix material, as discussed in further detail below.

In some embodiments, the hardfacing20and the harfacing20′ may have identical or similar compositions. In other embodiments, however, the material composition of the hardfacing20may differ from the material composition of the hardfacing20′. For example, in the embodiment described above with reference toFIGS. 2A-2F, the hardfacing20applied to the rotationally leading and trailing outer edges50,52of the flow tube36may be intended primarily to reduce wear caused by abrasion, while at least a portion of the hardfacing20′ may be intended primarily to reduce wear caused by erosion. Abrasion and erosion are two different wear mechanisms, and some material compositions have better resistance to abrasive wear, while other material compositions have better resistance to erosive wear. Therefore, the hardfacing20′ may have a material composition that exhibits increased erosion resistance relative to the hardfacing20, while the hardfacing20may have a material composition that exhibits increased abrasion resistance relative to the hardfacing20′ in some embodiments of the present invention.

Referring toFIG. 2E, in some embodiments, the relatively thick layer of hardfacing20′ optionally may comprise a multilayer structure having different layers that exhibit one or more differing physical properties. By way of example and not limitation, the relatively thick layer of hardfacing20′ may comprise a radially inward first layer20A′ having a material composition tailored to exhibit enhanced resistance to erosion, and a radially outward second layer20B′ having a material composition tailored to exhibit enhanced resistance to abrasion. In other words, the first layer20A′ may exhibit an erosion resistance that is greater than an erosion resistance exhibited by the second layer20B′, and the second layer20B′ may exhibit an abrasion resistance that is greater than an abrasion resistance that is exhibited by the first layer20A′. As one particular non-limiting example, the first layer20A′ of the hardfacing20′ may substantially fill the recess56formed in the outer surface of the tube body38of the flow tube36, and the second layer20B′ of the hardfacing20′ may have a material composition identical to that of the hardfacing20applied to the rotationally leading and trailing outer edges50,52of the flow tube36. Furthermore, the second layer20B′ of the hardfacing20′ may be integrally formed with the hardfacing20applied to the rotationally leading and trailing outer edges50,52of the flow tube36.

FIGS. 3A-3Dillustrate another example embodiment of a flow tube66of the present invention that may be used with embodiments of earth-boring tools of the present invention, such as the rotary drill bit10shown inFIG. 1. In other words, the drill bit10shown inFIG. 1may comprise flow tubes66in place of, or in addition to, the previously described flow tubes36.FIG. 3Ais an isometric view of the flow tube66andFIG. 3Bis a front view of the flow tube66.FIG. 3Cis a longitudinal cross-sectional view of the flow tube66taken along section line3C-3C ofFIG. 3B, andFIG. 3Dis a transverse cross-sectional view of the flow tube66taken along section line3D-3D ofFIG. 3B.

Referring toFIG. 3A, the flow tube66includes a tube body68that is generally similar to the previously described tube body38of the flow tube36, and includes a fluid passageway40that extends through the tube body68of the flow tube66from an inlet42to an outlet44(FIG. 3C). Furthermore, hardfacing20may be applied to rotationally leading and trailing outer edges72,74of the flow tube66. The tube body68of the flow tube66, however, may not include a recess56(FIG. 2D), and the flow tube66may include a plurality of wear-resistant inserts70instead of a relatively thick layer of hardfacing20′, as previously described with reference to the flow tube36. The wear-resistant inserts70may be effective at reducing abrasive wear to the outer surface of the tube body68of the flow tubes66. The wear-resistant inserts70, however, may be relatively less effective (relative to the previously described layer of hardfacing20′ (FIG. 2D)) at reducing erosive wear to the tube body68caused by the flow of drilling fluid through the fluid passageway40.

Referring toFIG. 3C, a hardfacing material78may be applied to at least a portion of the inner walls80of the tube body68the flow tube66within the fluid passageway40. The hardfacing material78may be used to reduce erosive wear to the tube body68caused by the flow of drilling fluid through the fluid passageway40. In some embodiments, the hardfacing material78may be applied to and cover substantially all inner walls80of the tube body68of the flow tube66that are exposed within the fluid passageway40after securing a nozzle (not shown) therein. In other embodiments, the hardfacing material78may be applied only to regions of the inner walls80that are susceptible to erosion, such as the regions of the inner walls80at which drilling fluid will impinge on the inner walls at acute angles as drilling fluid is pumped through the flow tube66.

By way of example and not limitation, the layer of hardfacing material78applied to the inner walls80of the tube body68may have an average thickness of between about 1.25 millimeters (0.05 inch) and about 20 millimeters (0.8 inch).

By way of example and not limitation, the hardfacing material78, like the hardfacing material20′ previously described herein, may comprise a composite material comprising a relatively hard first phase distributed within a second, continuous matrix phase. By way of example and not limitation, the first phase may 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 matrix phase may comprise cobalt, a cobalt-based alloy, iron an iron-based alloy, nickel, 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. In some embodiments, the first phase may comprise a plurality of discrete regions or particles dispersed within the matrix phase.

In additional embodiments, the hardfacing material78may comprise a brazed composite cladding comprising wherein the first phase is formed from a fabric (e.g., a tungsten carbide fabric material) and the fabric is embedded within a metal or metal alloy matrix phase that has infiltrated the fabric in a brazing process. By way of example and not limitation, a cloth or fabric comprising carbide material (e.g., tungsten carbide) may be applied to selected surfaces of the inner walls80of the tube body68of the flow tube66using a low temperature adhesive. A second layer of material containing the metal or metal alloy matrix material may be applied over the carbide material. The resulting structure then may be heated to a temperature above the melting point of the matrix material, causing the matrix material to melt and the molten matrix material to be wicked into the tungsten carbide fabric, metallurgically bonding the tungsten carbide material to the inner walls80of the tube body68of the flow tube66and forming the hardfacing material78. Alternatively, a single cloth or fabric that includes both a carbide material and a metal or metal alloy matrix material may be used to apply the hardfacing material78to selected surfaces of the inner walls80of the tube body68of the flow tube66. Such materials are commercially available from, for example, Conforma Clad, Inc. of New Albany, Ind.

In other embodiments, the hardfacing material78may comprise a plurality of hard particles dispersed within a metal or metal alloy matrix material, and may have a material composition tailored to exhibit enhanced erosion resistance. Such hardfacing materials78may be applied using, for example, flame spray techniques and welding techniques such as oxy-acetylene, metal inert gas (MIG), tungsten inert gas (TIG), and plasma transferred arc welding (PTAW) techniques.

In additional embodiments of the invention flow tubes may be provided that include both a relatively thick layer of hardfacing20′ as previously disclosed in relation toFIGS. 2A-2Fand a hardfacing material78applied to at least a portion of an inner wall of a body within a fluid passageway, as previously disclosed in relation toFIGS. 3A-3D.

Although the flow tubes36previously described in relation toFIGS. 2A-2Fand the flow tube66previously described in relation toFIGS. 3A-3Dare illustrated as comprising separate bodies that are attached to a bit body (or one bit leg or bit head section of a bit body) by, for example, welding, additional embodiments of the present invention may comprise flow tubes that are integrally formed with (and are an integral portion of a bit body (or one bit leg or a bit head section of a bit body), as well as earth-boring tools having such integrally formed flow tubes or fluid passageways.

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.