Patent Publication Number: US-11655850-B2

Title: Continuous diamond surface bearings for sliding engagement with metal surfaces

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application No. 63/111,145, filed on Nov. 9, 2020, and entitled “Continuous Diamond Surface Bearings for Sliding Engagement with Metal Surfaces,” the entirety of which is incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to bearings that include continuous diamond bearing surfaces, to apparatus and systems including the same, and to methods of making and using the same. 
     BACKGROUND 
     Bearings are employed in myriad applications including, but not limited to, aircraft, aerospace, transportation, defense, agriculture, mining, construction, and energy (e.g., oil and gas drilling and production tools). Bearings can have many different configurations, such as radial bearings, axial bearings (e.g., thrust bearings), combination radial and axial bearings, linear bearings, and power transmission surface bearings. 
     When diamond elements are used in moving parts, typically both the engagement surface and the opposing engagement surface of the bearing assembly is composed of polycrystalline diamond. This is, at least in part, because thermally stable polycrystalline diamond (TSP), either supported or unsupported by tungsten carbide, and polycrystalline diamond compact (PDC) have been considered as contraindicated for use in the machining of diamond reactive materials. At certain surface speeds in moving parts, load and attendant temperature generated, such as at a cutting tip, often exceeds the graphitization temperature of diamond (i.e., about 700° C.), which can, in the presence of a diamond reactive material, lead to rapid wear and failure of components. Without being bound by theory, the specific failure mechanism is believed to result from the chemical interaction of the carbon bearing diamond with the carbon attracting material that is being machined. An exemplary reference concerning the contraindication of diamond for diamond reactive material machining is U.S. Pat. No. 3,745,623. The contraindication of diamond for machining diamond reactive material has long caused the avoidance of the use of diamond in all contacting applications with such materials. 
     When using diamond as a bearing surface, contact between an edge of the diamond and the opposing bearing surface can lead to undesirable interaction between the diamond and the opposing bearing surface, including gouging of the opposing bearing surface and wear of the diamond bearing surface and/or edges of the diamond bearing surface. 
     BRIEF SUMMARY 
     Some embodiments of the present disclosure include a bearing assembly. The bearing assembly includes a bearing and a part. The bearing has a bearing body and a first bearing surface. The part has a body and a second bearing surface. One of the first and second bearing surfaces is a polycrystalline diamond bearing surface, and the other of the first and second bearing surfaces is a metal bearing surface including a metal. The polycrystalline diamond bearing surface has a surface finish of 20 μin Ra or less. The metal contains at least 2 weight percent of a diamond solvent-catalyst based on a total weight of the metal. The bearing is coupled with the part such that the metal bearing surface is engaged with the polycrystalline diamond bearing surface along a diamond contact area of the polycrystalline diamond bearing surface. The polycrystalline diamond bearing surface is a continuous surface along the diamond contact area. 
     Some embodiments of the present disclosure include a bearing assembly. The bearing assembly includes a bearing and a part. The bearing has a bearing body and a first bearing surface. The part has a body and a second bearing surface. One of the first and second bearing surfaces is a polycrystalline diamond bearing surface, and the other of the first and second bearing surfaces is a metal bearing surface including a metal. The polycrystalline diamond bearing surface has a surface finish of 20 μin Ra or less. The metal contains at least 2 weight percent of iron, cobalt, nickel, titanium, copper, ruthenium, rhodium, palladium, chromium, manganese, or tantalum based on a total weight of the metal. The bearing is coupled with the part such that the metal bearing surface is engaged with the polycrystalline diamond bearing surface along a diamond contact area of the polycrystalline diamond bearing surface. The polycrystalline diamond bearing surface is a continuous surface along the diamond contact area. 
     Some embodiments of the present disclosure include a method of making a bearing assembly. The method includes providing a bearing and a shaft. The bearing has a bearing body and a first bearing surface. The shaft has a shaft body and a second bearing surface. One of the first and second bearing surfaces is a polycrystalline diamond bearing surface, and the other of the first and second bearing surfaces is a metal bearing surface including a metal. The metal contains at least 2 weight percent of a diamond solvent-catalyst based on a total weight of the metal. The method includes lapping the diamond bearing surface, polishing the polycrystalline diamond bearing surface, or combinations thereof such that the polycrystalline diamond bearing surface has a surface finish of 20 μin Ra or less. The method includes coupling the shaft with the bearing such that the metal bearing surface is engaged with the polycrystalline diamond bearing surface along a diamond contact area of the polycrystalline diamond bearing surface. The polycrystalline diamond bearing surface is a continuous surface along the diamond contact area. The polycrystalline diamond bearing surface is bound by boundary edges of the polycrystalline diamond bearing surface, and the metal bearing surface is engaged with the polycrystalline diamond bearing surface entirely within the boundary edges. 
     Some embodiments of the present disclosure include a method of making a bearing. The method includes providing a bearing body, and applying a polycrystalline diamond layer onto a surface of the bearing body. The polycrystalline diamond layer has a polycrystalline diamond bearing surface. The polycrystalline diamond bearing surface is a continuous surface along a diamond contact area of the bearing. The method includes lapping the polycrystalline diamond bearing surface, polishing the polycrystalline diamond bearing surface, or combinations thereof such that the polycrystalline diamond bearing surface has a surface finish of 20 μin Ra or less. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the systems, apparatus, and/or methods of the present disclosure may be understood in more detail, a more particular description briefly summarized above may be had by reference to the embodiments thereof which are illustrated in the appended drawings that form a part of this specification. It is to be noted, however, that the drawings illustrate only various exemplary embodiments and are therefore not to be considered limiting of the disclosed concepts as it may include other effective embodiments as well. 
         FIG.  1 A  is a perspective view of a radial journal bearing having a continuous polycrystalline diamond bearing surface. 
         FIG.  1 B  is a perspective view of a radial journal bearing having multiple, segmented 0bearing surfaces that extend circumferentially along an interior surface of the radial journal bearing, with each individual, segmented bearing surface being a continuous polycrystalline diamond bearing surface. 
         FIG.  2 A  is a perspective view of a bearing assembly including a radial journal bearing, the same as or similar to that shown in  FIG.  1 A , engaged with a shaft. 
         FIG.  2 B  is a cross-sectional view of the bearing assembly of  FIG.  2 A . 
         FIG.  2 C  is detail view of the bearing assembly of  FIG.  2 B . 
         FIG.  3 A  is a perspective view of a bearing assembly including a radial journal bearing, the same as or similar to that shown in  FIG.  1 B , engaged with a shaft, and with the radial journal bearing in cross-section. 
         FIG.  3 B  is a view of the bearing assembly of  FIG.  3 A  with both the radial journal bearing and shaft in cross-section. 
         FIG.  3 C  depicts the radial journal bearing of  FIG.  3 A  in isolation from the shaft. 
         FIG.  3 D  depicts the shaft of  FIG.  3 A  in isolation from the radial journal bearing. 
         FIG.  4 A  is a perspective view of a conical bearing. 
         FIG.  4 B  is a cross-sectional view of the conical bearing of  FIG.  4 A . 
         FIG.  4 C  is a perspective view of a bearing assembly including the conical bearing of  FIG.  4 A  engaged with a shaft. 
         FIG.  4 D  is a cross-sectional view of the bearing assembly of  FIG.  4 C . 
         FIG.  5 A  is a perspective view of a spherical bearing. 
         FIG.  5 B  is a cross-sectional view of the spherical bearing of  FIG.  5 A . 
         FIG.  5 C  is a perspective view of a bearing assembly including the spherical bearing of  FIG.  5 A  engaged with a shaft. 
         FIG.  5 D  is a cross-sectional view of the bearing assembly of  FIG.  5 C . 
         FIG.  6 A  depicts a bearing assembly including a spherical bearing, ball, or swivel joint engaged with a shaft. 
         FIG.  6 B  depicts a cross sectional view of the bearing assembly of  FIG.  6 A . 
         FIG.  7 A  depicts an axial bearing assembly including an axial bearing engaged with a shaft. 
         FIG.  7 B  depicts a cross sectional view of the axial bearing assembly of  FIG.  7 A . 
         FIG.  8 A  is a cross-sectional view of a combined axial and radial bearing assembly including a combined and integral axial and radial bearing engaged with a shaft. 
         FIG.  8 B  is a perspective view of the combined axial and radial bearing assembly of  FIG.  8 A , with the axial and radial bearing in cross-section. 
         FIG.  8 C  is a perspective view of the combined axial and radial bearing assembly of  FIG.  8 A . 
         FIG.  9 A  is a perspective view of a radial bearing element. 
         FIG.  9 B  is a perspective view of an axial bearing element. 
         FIG.  9 C  is a perspective view of a bearing housing. 
         FIG.  9 D  is a perspective, cross-sectional view of a combined axial and radial bearing including the radial bearing element of  FIG.  9 A  and axial bearing element of  FIG.  9 B  coupled with the housing of  FIG.  9 C . 
         FIG.  9 E  is a cross-sectional view of a combined axial and radial bearing assembly including the combined axial and radial bearing of  FIG.  9 D  engaged with a shaft. 
         FIG.  10    is a Stribeck Curve comparing a conventional sliding bearing system with an exemplary sliding bearing system in accordance with the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Certain embodiments of the present disclosure include bearings that include continuous polycrystalline diamond bearing surfaces, to apparatus and systems including the same, and to methods of making and using the same. 
     Diamond Bearing Surfaces 
     The bearing assemblies disclosed herein include a polycrystalline diamond engagement surface (also referred to as a polycrystalline diamond bearing surface) engaged with an opposing engagement surface (also referred to as an opposing bearing surface). The polycrystalline diamond may be or include thermally stable polycrystalline diamond, either supported or unsupported by a support, such as a tungsten carbide support. The polycrystalline diamond may be or include a polycrystalline diamond compact (PDC). In certain applications, the polycrystalline diamond disclosed herein has increased cobalt content transitions layers between an outer polycrystalline diamond surface and a supporting tungsten carbide slug. The polycrystalline diamond may be non-leached, leached, leached and backfilled, thermally stable, or coated with a material via chemical vapor deposition (CVD). In some embodiments, the polycrystalline diamond is formed via a CVD process. Throughout the descriptions of the embodiments in this disclosure, for the sake of brevity and simplicity, “diamond” is used to refer to “polycrystalline diamond.” That is, the “diamond bearing surfaces” disclosed herein are “polycrystalline diamond bearing surfaces” and the “diamond bearing elements” are “polycrystalline diamond bearing elements.” 
     In some embodiments, the engagement surfaces of the diamond disclosed herein are planar, convex, or concave. In some embodiments, the diamond has prepared edges, such as bevels, radii, or honed edges. One performance criterion is that the diamond is configured and positioned in such a way as to minimize or preclude edge contact with the opposing bearing surface. In some aspects, the diamond is subjected to edge radius treatment to facilitate avoidance of edge contact with the opposing bearing surface. The edge geometry of the diamond can be subjected to a surface roughness reduction process, such as lapping and/or polishing. In other embodiments, the edge geometry of the diamond is not subjected to a surface roughness reduction process. 
     In certain applications, the diamond, or at least the engagement surface thereof, is lapped or polished, optionally highly lapped or highly polished. Although highly polished diamond is used in at least some applications, the scope of this disclosure is not limited to highly polished diamond and includes diamond that is highly lapped or polished. As used herein, a surface is defined as “highly lapped” if the surface has a surface roughness of 20 μin Ra or less than about 20 μin Ra, such as a surface roughness ranging from about 18 to about Ra. As used herein, a surface is defined as “polished” if the surface has a surface roughness of between 2 to about 10 μin. As used herein, a surface is defined as “highly polished” if the surface has a surface roughness of less than 2 μin Ra. Typical “highly polished” surfaces have a surface roughness of from about 0.5 μin to less than about 2 μin. 
     In some aspects, the diamond bearing surfaces disclosed herein have a surface roughness ranging from 0.5 μin Ra to 20 μin Ra, or from 2 μin Ra to 18 μin Ra, or from 5 μin Ra to 15 μin Ra, or from 8 μin Ra to 12 μin Ra, or less than 20 μin Ra, or less than 18 μin Ra, or less than 10 μin Ra, or less than 2 μin Ra, or any range or value therebetween. Without being bound by theory, it is believed that diamond that has been polished to a surface roughness of 0.5 μin has a coefficient of friction that is less than (e.g., about half or more than half) of standard lapped diamond that has a surface roughness of 20-40 μn. U.S. Pat. Nos. 5,447,208 and 5,653,300 to Lund et al. provide disclosure relevant to polishing of diamond. As would be understood by one skilled in the art, surface finish, also referred to as surface texture or surface topography, is a characteristic of a surface as defined by lay, surface roughness, and waviness. Surface finish may be determined in accordance with ASME B46.1-2009. Surface finish or roughness may be measured with a profilometer, laser microscope, or with Atomic Force Microscopy, for example. 
     Opposing Bearing Surfaces 
     In some embodiments, the opposing bearing surface includes a diamond reactive material. As used herein, a “diamond reactive material” is a material that contains more than trace amounts of diamond solvent-catalyst (also referred to as a diamond catalyst-solvent). Some examples of known diamond solvent-catalysts are disclosed in: U.S. Pat. Nos. 6,655,845; 3,745,623; 7,198,043; 8,627,904; 5,385,715; 8,485,284; 6,814,775; 5,271,749; 5,948,541; 4,906,528; 7,737,377; 5,011,515; 3,650,714; 2,947,609; and 8,764,295. As used herein, a material that contains more than “trace amounts” of diamond solvent-catalyst is a material that contains at least 2 percent by weight (wt. %) diamond solvent-catalyst based on a total weight of the material. As would be understood by one skilled in the art, diamond solvent-catalysts are chemical elements, compounds, or materials (e.g., metals) that are capable of catalyzing the formation of diamond, such as by promoting intercrystallite diamond-to-diamond bonding between diamond grains to form a polycrystalline diamond. As would be understood by one skilled in the art, diamond solvent-catalysts are chemical elements, compounds, or materials (e.g., metals) that are capable of solubilizing polycrystalline diamond by catalyzing the reaction of the diamond into graphite, such as under load and at a temperature at or exceeding the graphitization temperature of diamond. Diamond solvent-catalysts are capable of catalyzing the graphitization of diamond (e.g., polycrystalline diamond), such as when under load and at a temperature at or exceeding the graphitization temperature of the diamond (i.e., about 700° C.). Diamond reactive materials include, but are not limited to, metals including metal alloys, and composite materials that contain more than trace amounts of diamond solvent-catalysts. Some exemplary diamond solvent-catalysts include iron, cobalt, nickel, ruthenium, rhodium, palladium, chromium, manganese, copper, titanium, and tantalum. Thus, a diamond reactive material can be a material that includes more than trace amounts of iron, cobalt, nickel, ruthenium, rhodium, palladium, chromium, manganese, copper, titanium, tantalum, or combinations thereof. One exemplary diamond reactive material is steel. 
     The diamond reactive material disclosed herein may be a metal or metal alloy (collectively referred to herein as a “metal” or a “metallic material”) having a metal surface. As would be understood by one skilled in the art metals include materials that contain metal atoms that are typically characterized by metallic bonding between the metal atoms. That is, metals can be characterized as having metal atoms that are chemically bonded together, with at least predominantly metallic bonding between the metal atoms (e.g., in a crystalline structure of the metal atoms). The metals disclosed herein are not ceramics (e.g., carbides, oxides, nitrides, natural diamond), plastics, or composites (e.g., ceramic matrix composites or metal matrix composites, such as cermets, cemented carbide cobalt composites, PCD cobalt binder composites, CBN cobalt binder composites). In some embodiments the metal is a metal alloy. In other embodiments the metal is not a metal alloy (i.e., contains a single metal). The metal may be ferrous or a ferrous alloy. For example, the metal may be iron or an iron alloy, such as cast iron or steel, such as stainless steel, carbon steel, tool steel, or alloy steels. The metal may be non-ferrous or a non-ferrous alloy. For example, the metal may be nickel or a nickel alloy, cobalt or a cobalt alloy, copper or a copper alloy, titanium or a titanium alloy, ruthenium or a ruthenium alloy, rhodium or a rhodium alloy, palladium or a palladium alloy, chrome or a chrome alloy, manganese or a manganese alloy, or tantalum or a tantalum alloy. 
     In embodiments where the diamond reactive material is a metal, the opposing bearing surface is a metal surface. The opposing bearing surface may include a metal that contains at least 2 wt. % of a diamond solvent-catalyst based on a total weight of the metal. In some embodiments, the opposing bearing surface is or includes a metal that contains from 2 to 100 wt. %, or from 5 to 95 wt. %, or from 10 to 90 wt. %, or from 15 to 85 wt. %, or from 20 to 80 wt. %, or from 25 to 75 wt. %, or from 25 to 70 wt. %, or from 30 to 65 wt. %, or from 35 to 60 wt. %, or from 40 to 55 wt. %, or from 45 to 50 wt. % of diamond solvent-catalyst based on a total weight of the metal, or any range or value therebetween. In some embodiments, the opposing bearing surface is or includes a metal that contains at least 3 wt. %, or at least 5 wt. %, or at least 10 wt. %, or at least 15 wt. %, or at least 20 wt. %, or at least 25 wt. %, or at least 30 wt. %, or at least 35 wt. %, or at least 40 wt. %, or at least 45 wt. %, or at least 50 wt. %, or at least 55 wt. %, or at least 60 wt. %, or at least 65 wt. %, or at least 70 wt. %, or at least 75 wt. %, or at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, or at least 95 wt. %, or at least 99 wt. %, or 100 wt. % of diamond solvent-catalyst based on a total weight of the metal. 
     In some embodiments, the diamond reactive materials disclosed herein contain from 2 to 100 wt. %, or from 5 to 95 wt. %, or from 10 to 90 wt. %, or from 15 to 85 wt. %, or from 20 to 80 wt. %, or from 25 to 75 wt. %, or from 25 to 70 wt. %, or from 30 to 65 wt. %, or from 35 to 60 wt. %, or from 40 to 55 wt. %, or from 45 to 50 wt. % of metal based on a total weight of the diamond reactive material, or any value or range therebetween. In some embodiments, the diamond reactive materials disclosed herein contain at least 3 wt. %, or at least 5 wt. %, or at least 10 wt. %, or at least 15 wt. %, or at least 20 wt. %, or at least 25 wt. %, or at least 30 wt. %, or at least 35 wt. %, or at least 40 wt. %, or at least 45 wt. %, or at least 50 wt. %, or at least 55 wt. %, or at least 60 wt. %, or at least 65 wt. %, or at least 70 wt. %, or at least 75 wt. %, or at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, or at least 95 wt. %, or at least 99 wt. %, or 100 wt. % of metal based on a total weight of the diamond reactive material. 
     In some embodiments, the diamond reactive materials disclosed herein contain from 2 to 100 wt. %, or from 5 to 95 wt. %, or from 10 to 90 wt. %, or from 15 to 85 wt. %, or from 20 to 80 wt. %, or from 25 to 75 wt. %, or from 25 to 70 wt. %, or from 30 to 65 wt. %, or from 35 to 60 wt. %, or from 40 to 55 wt. %, or from 45 to 50 wt. % of diamond solvent-catalyst based on a total weight of the diamond reactive material, or any value or range therebetween. In some embodiments, the diamond reactive materials disclosed herein contain at least 3 wt. %, or at least 5 wt. %, or at least 10 wt. %, or at least 15 wt. %, or at least 20 wt. %, or at least 25 wt. %, or at least 30 wt. %, or at least 35 wt. %, or at least 40 wt. %, or at least 45 wt. %, or at least 50 wt. %, or at least 55 wt. %, or at least 60 wt. %, or at least 65 wt. %, or at least 70 wt. %, or at least 75 wt. %, or at least 80 wt. %, or at least 85 wt. %, or at least 90 wt. %, or at least 95 wt. %, or at least 99 wt. %, or 100 wt. % of diamond solvent-catalyst based on a total weight of the diamond reactive material. 
     In some embodiments, less than an entirety of the opposing bearing surface includes the diamond reactive material, with the provision that the metal contact area of the opposing bearing surface includes diamond reactive material in at least one position along the contact path between the metal contact area and the diamond contact area. For example, the opposing bearing surface may include a section of diamond reactive material adjacent a section of another material that is not a diamond reactive material. 
     In some embodiments, the diamond reactive material is a superalloy including, but not limited to, an iron-based superalloy, a cobalt-based superalloy, or a nickel-based superalloy. 
     In certain embodiments, the diamond reactive material is not and/or does not include (i.e., specifically excludes) so called “superhard materials.” As would be understood by one skilled in the art, “superhard materials” are a category of materials defined by the hardness of the material, which may be determined in accordance with the Brinell, Rockwell, Knoop and/or Vickers scales. Superhard materials are materials with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test. The diamond reactive materials disclosed herein are softer than a superhard material. For example, the diamond reactive materials disclosed herein may have a hardness value of less than 40 GPa, or less than 35 GPa, or less than 30 GPa, or less than 25 GPa, or less than 20 GPa, or less than 15 GPa, or less than 10 GPa, or less than 8 GPa, or less than 6 GPa, or less than 5 GPa, or less than 4 GPa, or less than 3 GPa, or less than 2 GPa, or less than 1 GPa when measured by the Vickers hardness test. The diamond reactive materials disclosed herein are softer than tungsten carbide (WC), which has a hardness of about 25 GPa. The diamond reactive materials disclosed herein include materials that are softer than tungsten carbide tiles, cemented tungsten carbide, and infiltrated tungsten carbide. The diamond reactive materials disclosed herein include materials that are softer than silicon carbide, silicon nitride, cubic boron nitride, and polycrystalline diamond. One skilled in the art would understand that hardness may be determined by different tests, including a Brinell scale test in accordance with ASTM E10-18; the Vickers hardness test in accordance with ASTM E92-17; the Rockwell hardness test in accordance with ASTM E18; and the Knoop hardness test in accordance with ASTM E384-17. 
     In some embodiments, the diamond reactive materials are in the form of hardfacings, coatings, or platings on another material, such that the diamond reactive material forms the opposing bearing surface. In such embodiments, the hardfacing, coating, or plating includes the diamond reactive material. In some such embodiment, the material underlying the hardfacing, coating, or plating is not a diamond reactive material. In other such embodiments, the material underlying the hardfacing, coating, or plating is a diamond reactive material (the same or different than the overlying hardfacing, coating, or plating). 
     In some embodiments, the opposing bearing surface has carbon applied thereto. In some such embodiments, the carbon is applied to the opposing bearing surface prior to engagement with the diamond bearing surface. For example, the opposing bearing surface may be saturated with carbon. Without being bound by theory, it is believed that such application of carbon reduces the ability of the diamond solvent-catalyst in the opposing bearing surface to attract carbon through graphitization of the surface of the polycrystalline diamond element. That is, the carbon that is applied to the opposing bearing surface functions as a sacrificial layer of carbon. In such embodiments, the opposing bearing surface that underlies the carbon includes the diamond reactive material. 
     In some embodiments, the opposing bearing surface is a treated surface in accordance with U.S. patent application Ser. No. 16/425,758. For example, the opposing bearing surface (also referred to as the opposing engagement surface) may be hardened, such as via cold working and work hardening processes including burnishing and shot peening; and/or heat-treating processes including through hardening, case hardening, and subzero, cryogenic, deep-freezing treatments. Also, the opposing bearing surface may be plated and/or coated, such as via electroplating, electroless plating, including chromium plating, phosphating, vapor deposition, including physical vapor deposition (PVD) and chemical vapor deposition (CVD); or anodizing. Also, the opposing bearing surface may be cladded, such as via roll bonding, laser cladding, or explosive welding. 
     In some embodiments, the opposing bearing surface has a surface roughness of from 0.5 to 2,000 μin Ra, or from 1 to 1,900 μin Ra, or from 5 to 1,500 μin Ra, or from 10 to 1,200 μin Ra, or from 50 to 1,000 μin Ra, or from 100 to 800 μin Ra, or from 200 to 600 μin Ra. In some embodiments, the opposing bearing surface has a surface roughness that is equal to, less than, or greater than the diamond bearing surface. 
     Engaged Bearing Surfaces 
     In some embodiments, the present disclosure provides for interfacing the contact between the diamond bearing surface of a bearing and the opposing bearing surface of a part. Interfacing the contact may include engaging the diamond bearing surface in sliding contact with the opposing bearing surface. As used herein, “engagement surface” or “bearing surface” refers to the surface of a material or component (e.g., the surface of polycrystalline diamond or the surface of a diamond reactive material) that is positioned and arranged within a bearing assembly such that, in operation of the bearing, the “engagement surface” or “bearing surface” is positioned and/or available to interface the contact between two components to bear load (e.g., radial and/or axial load). In some embodiments, the diamond bearing surface disclosed herein is in direct contact with an opposing bearing surface without a fluid film therebetween (i.e., boundary lubrication). In some embodiments, a fluid film is positioned and/or develops between the diamond bearing surface and the opposing bearing surface such that the surfaces are not directly in contact with one another, but are engaged through the fluid film (i.e., hydrodynamic lubrication). In some embodiments, the contact between the diamond bearing surface and opposing bearing surface is between (or a mixture of) or varies between direct contact and fluid film (i.e., mixed boundary lubrication). 
     Bearing Assemblies 
     In some embodiments, the diamond bearings disclosed herein are coupled with or otherwise incorporated into or with a bearing assembly. For example, the diamond bearings may be a portion of an axial bearing assembly, a radial bearing assembly, or a combined axial and radial bearing assembly. In some embodiments, the bearing assembly is a journal bearing, conical bearing, or spherical bearing. The diamond bearings are not limited to being incorporated into the specific exemplary bearing assemblies shown herein. 
     Some embodiments include a bearing assembly that includes one or more of the diamond bearing surfaces engaged with one or more of the opposing bearing surfaces. In some such embodiments, the diamond bearing surface is in sliding engagement with the opposing bearing surface. Depending on the desired configuration of the bearing assembly, the sliding engagement between the diamond bearing surface and the opposing bearing surface may be a flat surface interface, a curved (e.g., cylindrical) surface interface, or a combination of flat and curved surface interfaces. 
     Radial Journal Bearing 
     In some embodiments, the diamond bearing disclosed herein is a radial journal bearing having a diamond bearing surface. With reference to  FIG.  1 A , one embodiment of a radial journal bearing in accordance with the present disclosure is depicted. Radial journal bearing  100   a  has the form of a ring with an external surface  102 , an internal surface, and sides  106  therebetween. The internal surface is a diamond bearing surface  104 . Diamond bearing surface  104  has boundary edges  105  and a width  208 . While the width  208  is shown as being constant about the internal circumference of radial journal bearing  100   a , the bearings disclosed herein are not limited to having constant widths, and may have widths that vary. Between boundary edges  105 , diamond bearing surface  104  extends continuously, circumferentially about the internal circumference of radial journal bearing  100   a . That is, between boundary edges  105 , diamond bearing surface  104  is uninterrupted by any boundary edges. Radial journal bearing  100   a  has a cavity  108  defined by the diamond bearing surface  104 . One exemplary use of the radial journal bearing  100   a  is being coupled with a shaft such that the shaft extends through cavity  108 . In such embodiments, the shaft may be rotated (clockwise and/or counterclockwise) within cavity  108  along rotational line  111  about axis  109  such that an exterior surface of the shaft is slidingly engaged with the diamond bearing surface  104  and slides along the diamond bearing surface  104  while rotating relative to the diamond bearing surface  104 . In such an embodiment, the outer surface of the shaft would be the opposing bearing surface including a diamond reactive material. 
       FIG.  1 B  depicts another embodiment of a radial journal bearing in accordance with the present disclosure. Radial journal bearing  100   b  is substantially similar to radial journal bearing  100   a , with the exception that the diamond bearing surface of radial journal bearing  100   b  is segmented. That is, radial journal bearing  100   b  includes a plurality of diamond bearing surfaces  110 . Each diamond bearing surface  110  has boundary edges  105  and a width  208 . The plurality of diamond bearing surfaces  110  are arranged to extend continuously, circumferentially about the internal circumference of radial journal bearing  100   b . As shown in  FIG.  1 B , the edges of each segment of the plurality of diamond bearing surfaces  110  extend parallel to the edges of the other segments of the plurality of diamond bearing surfaces  110 . However, the diamond bearing surfaces disclosed herein are not limited be having edges that extend parallel to one another. In the embodiment shown in  FIG.  1 B , each diamond bearing surface  110  is a separate surface from the adjacent diamond bearing surface(s). One exemplary use of the radial journal bearing  100   b  is being coupled with a shaft such that the shaft extends through cavity  108 . In such embodiments, the shaft is rotatable within cavity  108  such that an exterior surface of the shaft is slidingly engaged with the diamond bearing surfaces  110  and slides along the diamond bearing surfaces  110  as the shaft rotates relative to the diamond bearing surfaces  110 . In such an embodiment, a plurality of outer surfaces on the shaft would be the opposing bearing surfaces, each engaged with one of the diamond bearing surfaces  110 . 
     Continuous Bearing Surface 
     In some embodiments, the bearings disclosed herein have continuous diamond bearing surfaces. For example, a bearing component (e.g., a radial journal bearing) having a diamond bearing surface may be coupled with an opposing bearing component (e.g., a shaft) having an opposing bearing surface such that the opposing bearing is slidingly engaged with the diamond bearing surface along a diamond contact area of the diamond bearing surface, and such that the diamond bearing surface is “continuous” along the diamond contact area. As used herein, “diamond contact area” refers to the entire portion of the surface area of the diamond bearing surface that contacts (directly or through a fluid film) the opposing bearing surface during operation (i.e., relative movement) of the bearing and the part that includes the opposing bearing surface. That is, the diamond contact area is the portion of the surface area of the diamond bearing surface that contacts the opposing bearing surface during operation of the bearing assembly. The diamond contact area is only a portion of the diamond bearing surface, and is spaced apart from each boundary edge of the diamond bearing surface, such that there is at least some surface area of the diamond bearing surface positioned between the diamond contact area and the boundary edges of the diamond bearing surface. In embodiments where the bearing is a radial bearing, the diamond contact area of the radial bearing is the surface area of the diamond bearing surface that contacts the opposing bearing surface during rotation of the opposing component. The diamond contact area has a surface area that is less than a surface area of the diamond bearing surface. That is, less than an entirety of the diamond bearing surface forms the diamond contact area. As used herein, a diamond bearing surface is a “continuous surface” along an entirety of the diamond contact area when the diamond bearing surface is uninterrupted by any diamond edges throughout the entirety of the diamond contact area. That is, during operation, while the opposing bearing surface slides along the diamond contact area, the opposing bearing surface does not slide on, along, or contact any edges of the diamond bearing surface. For example, with reference to  FIG.  1 A , diamond bearing surface  104  is “continuous” along the circumferential extension of the diamond bearing surface between boundary edges  105 . With reference to  FIG.  1 B , each diamond bearing surface  110  is “continuous” along the circumferential extension of the surfaces between boundary edges  105 . In some embodiments, such as in a radial bearing, the diamond contact area is a radial contact area. That is, the sliding movement of the opposing bearing surface along the diamond contact area on the diamond bearing surface is a radial, rotating movement along the diamond contact area. In other embodiments, the diamond contact area is an axial contact area. That is, the sliding movement of the opposing bearing surface on the diamond bearing surface is an axial movement along the diamond contact area. In some embodiments, the diamond contact area is both a radial and axial diamond contact area. 
     The bearing having the diamond bearing surface may be coupled with the part having the opposing bearing surface such that a metal contact area of the opposing bearing surface is slidingly engaged with the diamond contact area. As used herein, “metal contact area” refers to the entire portion of the surface area of the opposing bearing surface that contacts (directly or through a fluid film) the diamond contact area during operation (i.e., during relative movement) of the bearing and the part that includes the opposing bearing surface. That is, the metal contact area is the portion of the surface area of the opposing bearing surface that contacts the diamond contact area during operation of the bearing assembly. In embodiments where the bearing is a radial bearing, the metal contact area is the surface area of the opposing bearing surface that contacts the diamond contact area during relative rotation of the bearing and part. During operation, while the metal contact area slides along the diamond contact area without sliding on, along, or contacting boundary edges of the diamond bearing surfaces, and the diamond bearing surface slides on, along, and contacts boundary edges of the opposing bearing surface. In some embodiments, such as in a radial bearing, the metal contact area is a radial contact area. That is, the sliding movement of the metal contact area along the diamond contact area is a radial, rotating movement. In other embodiments, the metal contact area is an axial contact area. That is, the sliding movement of the metal contact area on the diamond contact area is an axial movement. In some embodiments, the metal contact area is both a radial and axial diamond contact area. In some embodiments, the metal contact area is an entirety of the opposing bearing surface, such that an entirety of the opposing bearing surface is engaged with less than an entirety of the diamond bearing surface. Both the metal contact area and the diamond contact area are surfaces, such that the contact between the metal contact area and the diamond contact area is a contact between two surface areas (e.g., is a planar contact or contact between two curved surfaces). Thus, contact between the metal contact area and the diamond contact area is a planar contact between the contact areas, or is a contact between two curved surfaces that form the contact areas. As the metal contact area only contacts the diamond bearing surface entirely within the boundary edges of the diamond bearing surface, portions of the diamond bearing surface slide on, along, and contact (directly or through a fluid film) with the boundary edges of the metal bearing surface. 
     The diamond contact area defines a path (or paths) along which the metal contact area contacts the diamond engagement surface. The path on the diamond engagement surface that is defined by the diamond contact area provides for a purely surface area contact with the metal contact area, with the path tracing a surface area of the diamond engagement surface. Additionally, the metal contact area defines a path (or paths) along which the diamond contact area contacts the opposing engagement surface. The path on the opposing engagement surface that is defined by the metal contact area provides for a purely surface area contact with the diamond contact area, with the path tracing a surface area of the opposing engagement surface. 
     In some embodiments of operation of the bearing assemblies disclosed herein, the metal contact area does not maintain contact with the diamond contact area throughout the entire path defined by the diamond contact area. For example, the metal contact area may be intermittently spaced apart from the diamond contact area during the tracing of the metal contact area over the path defined by the diamond contact area (e.g., where the metal and diamond contact areas are not perfectly engaged, parallel, and/or aligned). In such embodiments, the contact path (or paths) of the diamond contact area may be engaged by the metal contact area at multiple discrete locations and/or multiple discrete times. In such embodiments, the metal contact area does not slide on, along, or contact the boundary edges of the diamond bearing surface at any of the multiple discrete locations and/or multiple discrete times. Thus, for the diamond bearing surface to be a continuous surface along the entirety of the diamond contact area, it is not necessary for the metal contact area to be continuously in contact with the diamond contact area, provided that the metal bearing surface does not engage with any boundary edges of the diamond bearing surface. 
     In other embodiments of operation of the bearing assemblies disclosed herein, the metal contact area does maintain contact with the diamond contact area throughout the entire path defined by the diamond contact area. In such embodiments, the metal contact area is in contact with the diamond contact area throughout the tracing of the entire path defined by the diamond contact area. In such embodiments, the metal contact area does not slide on, along, or contact the boundary edges of the diamond bearing surface at any location throughout the entire diamond contact area. In some embodiments, the diamond bearing surface is a single, continuous surface. 
     While exemplary bearing surfaces disclosed herein are shown and described as curved surfaces such that a section of surface area (the metal contact area) of the opposing bearing surface is in sliding contact with a section of surface area (the diamond contact area) of the diamond bearing surface, the bearing surfaces may have other forms and geometries than those shown herein, provided that metal bearing surface does not engage with any boundary edges of the diamond bearing surface. 
     While movement between the bearing and part within the exemplary bearing assemblies disclosed herein is described (at least primarily) as being rotational and/or axial movement, the bearing assemblies disclosed herein may exhibit other movements. For example, the bearing assembly may exhibit vibrational movements. Vibrational movements within such a bearing assembly may alter which portions of the surface area of the diamond bearing surface are occupied by the diamond contact area. In such embodiments, the size (e.g., width) of the diamond bearing surface and/or the opposing bearing surface may be designed to account for such vibrational movements such that, regardless of the vibrational movements, the opposing bearing surface does not engage with any boundary edges of the diamond bearing surface. That is, the diamond bearing surface and/or the opposing bearing surface may be provided with tolerance to account for such vibrational movements or other additional movements within the bearing assembly. 
     While the radial journal bearings of  FIGS.  1 A and  1 B  are shown and described as having continuous diamond bearing surfaces that can be coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have a continuous diamond bearing surface and the radial journal bearings of  FIGS.  1 A and  1 B  can have an opposing bearing surface of diamond reactive material. 
     Radial Journal Bearing and Shaft Assembly 
     Some embodiments of the present disclosure include a bearing assembly that includes a bearing having a diamond bearing surface that is in sliding engagement with an opposing bearing surface. With reference to  FIGS.  2 A- 2 C , bearing assembly  200  is depicted. Bearing assembly  200  includes shaft  202  slidingly engaged within the cavity  108  of radial journal bearing  100   a . Shaft  202  includes opposing bearing surface  204 . Opposing bearing surface  204  is slidingly engaged with diamond bearing surface  104  of radial journal bearing  100   a . Opposing bearing surface  204  has a width  206 , as defined by the distance between boundary edges  205  of opposing bearing surface  204 . Diamond bearing surface  104  has a width  208 , as defined by the distance between boundary edges  105  as shown in  FIG.  1 A . Width  208  is greater than width  206 , and opposing bearing surface  204  is engaged with diamond bearing surface  104  such that opposing bearing surface  204  is positioned between boundary edges  105  and does not contact boundary edges  105 . As such, opposing bearing surface  204  is engaged with diamond bearing surface  104  entirely within boundary edges  105  of diamond bearing surface  104 . As used herein, “boundary edges” of a surface are edges that are or define the perimeter of the surface. With opposing bearing surface  204  engaged with diamond bearing surface  104  entirely within the boundary edges  105  of diamond bearing surface  104 , opposing bearing surface  204  does not engage with the boundary edges  105  of diamond bearing surface  104 . Thus, bearing assembly  200  avoids contact between opposing bearing surface  204  and any edges of diamond bearing surface  104 . In some embodiments, the surface area of the opposing bearing surface  204  is smaller than the surface area of the diamond bearing surface  104 . In some embodiments, an entirety of the surface area of opposing bearing surface  204  is engaged with less than an entirety of the surface area of diamond bearing surface  104 . The portion of diamond bearing surface  104  that opposing bearing surface  204  is engaged with during operation of bearing assembly  200  is the contact area of diamond bearing surface  104 . Thus, throughout the use of bearing assembly  200 , opposing bearing surface  204  remains engaged with diamond bearing surface  104  along the diamond contact area of diamond bearing surface  104 , which diamond contact area falls entirely within the boundary edges  105  of diamond bearing surface  104 , such that opposing bearing surface  204  does not engage with boundary edges  105  of diamond bearing surface  104 . 
     In some embodiments, the opposing bearing surface  204  is not a continuous bearing surface (i.e., is a discontinuous bearing surface), and may include multiple, discrete bearing surfaces. For example, the opposing bearing surfaces disclosed herein may be surfaces (e.g., metal surfaces) that have edges that are engaged with the diamond contact area of the diamond bearing surface within the boundary edges of the diamond bearing surface. 
     While the radial journal bearings of  FIGS.  2 A- 2 C  are shown and described as having continuous diamond bearing surfaces that are coupled with a shaft that has an opposing engagement surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have a continuous diamond bearing surface and the radial journal bearings can have an opposing bearing surface of diamond reactive material. 
     Radial Journal Bearing and Shaft Assembly with Segmented Bearing Surfaces 
     With reference to  FIGS.  3 A- 3 D , bearing assembly  300  and components thereof are depicted. Bearing assembly  300  includes shaft  302  slidingly engaged within the cavity  309  of radial journal bearing  301 . Radial journal bearing  301  may be the same as or similar to radial journal bearing  100   b  shown in  FIG.  1 B . Radial journal bearing  301  includes bearing housing  303  having sides  307 . A plurality of segmented diamond bearing surfaces  311  are on the internal circumference of housing  303 . Shaft  302  includes shaft body  306  and a plurality of segmented opposing bearing surfaces  304  on shaft body  306 . In  FIGS.  3 A and  3 B , shaft  302  is engaged within cavity  309  such that each opposing bearing surface  304  is slidingly engaged with one of the diamond bearing surfaces  311 . In the same manner as described with respect to  FIGS.  1 A- 2 C , each opposing bearing surface  304  has a smaller width  305  than the width  308  of the diamond bearing surface  311  to which it is engaged, such that each opposing bearing surface  304  is engaged with a diamond contact area that is entirely within the boundary edges of the diamond bearing surface  311  to which it is engaged. Bearing assembly  300  is configured for shaft  302  to rotate within bearing  301 . 
     While the radial journal bearings of  FIGS.  3 A- 3 D  are shown and described as having multiple continuous diamond bearing surfaces that are coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have continuous diamond bearing surface(s) and the radial journal bearings can have opposing bearing surface(s) of diamond reactive material. 
     Angular Contact Bearing—Conical Bearing 
     Some embodiments of the present disclosure include an angular contact bearing, such as a conical bearing. In some such embodiments, a conical bearing assembly that includes a conical bearing having a diamond bearing surface that is in sliding engagement with an opposing bearing bearing surface. With reference to  FIGS.  4 A- 4 D , one exemplary conical bearing and bearing assembly is depicted. Conical bearing  400  includes bearing housing  402  with cavity  408 . Bearing housing  402  includes a conical diamond bearing surface  404  thereon. Conical diamond bearing surface  404  is a continuous bearing surface within the boundary edges  405 , and has a width  407 . 
     As shown in  FIGS.  4 C and  4 D , conical bearing  400  is engaged with shaft  420  in a conical bearing assembly  490 . Shaft  420  extends through cavity  408  and includes bearing element  421  having opposing bearing surface  422  thereon. Opposing bearing surface  422  is positioned on shaft  420  to slidingly engage with diamond bearing surface  404  when shaft  420  is positioned within cavity  408 . Opposing bearing surface  422  has a width  423  between boundary edges  425  of opposing bearing surface. In the same or similar manner as described with respect to  FIGS.  1 A- 3 D , opposing bearing surface  422  has a smaller width, width  423 , than the width  407  of the diamond bearing surface  404 , such that opposing bearing surface  422  is engaged with the diamond contact area entirely within the boundary edges  405  of the diamond bearing surface  404  to which it is engaged. Thus, the contact area of diamond bearing surface  404  is continuous along the interface of diamond bearing surface  404  and opposing bearing surface  422 . Both diamond bearing surface  404  and opposing bearing surface  422  are conical surfaces. Bearing assembly  490  is configured for shaft  420  to rotate about axis  409  within bearing  400 . 
     While the conical bearings of  FIGS.  4 A- 4 D  are shown and described as having continuous diamond bearing surfaces that are coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have continuous diamond bearing surface and the conical bearings can have opposing bearing surface of diamond reactive material. 
     Angular Contact Bearing—Spherical Bearing 
     Some embodiments of the present disclosure include an angular contact bearing, such as a spherical bearing assembly. In some such embodiments, the spherical bearing assembly includes a spherical bearing having a diamond bearing surface that is in sliding engagement with an opposing bearing surface. While described as a spherical bearing, the bearings disclosed herein are not limited to this shape, and may have other shapes, including other spheroidal or ellipsoidal shapes or other shapes having arcuate surfaces. In some embodiments, the bearing is a bearing with an elliptical surface, a conical surface, or another surface that defines a curve. With reference to  FIGS.  5 A- 5 D , one exemplary spherical bearing and bearing assembly is depicted. Spherical bearing  500  is substantially the same as conical bearing  400  shown in  FIGS.  4 A- 4 D , with the exception that diamond bearing surface  504  is a concave spherical surface as opposed to a flat conical surface as in  FIGS.  4 A- 4 D . That is, an imaginary line  507 , extending between boundary edges  505  of diamond bearing surface  504  along the shortest path possible, with the provision that imaginary line  507  extends only along diamond bearing surface  504 , defines an arcuate line rather than a straight line. Similarly, within bearing assembly  590  (as shown in  FIGS.  5 C and  5 D ), shaft  520  is substantially the same as shaft  420  shown in  FIGS.  4 C and  4 D , with the exception that opposing bearing surface  522  is a convex spherical surface as opposed to a flat conical surface. The curvatures of diamond bearing surface  504  and opposing bearing surface  522  provide for a degree of misalignment compensation between shaft  520  and bearing  500  during operation of bearing assembly  590 . That is, shaft  520  is not required to be in axial alignment with axis of rotation  580  while shaft  520  rotates relative to spherical bearing  500 . Axis of rotation  580  is a theoretical axis passing through the center of cavity  508  and concentrically aligned with diamond bearing surface  504 . Thus, the curvatures of diamond bearing surface  504  and opposing bearing surface  522  allow shaft  520  to rotate relative to spherical bearing  500  when shaft  520  is not concentric with spherical bearing  500 , and when the actual axis of rotation of shaft  520  is at an angle relative to the theoretical axis of rotation  580 . Spherical bearing  500  includes bearing housing  502 . Shaft  520  includes bearing element  521  having opposing bearing surface  522  thereon. Opposing bearing surface  522  has a width  523 , defined between the boundary edges  525  of opposing bearing surface  522 . In the same manner as described with respect to  FIGS.  1 A- 4 D , opposing bearing surface  522  has a smaller width  523  than the width of the diamond bearing surface  504 , such that opposing bearing surface  522  is engaged entirely within the boundary edges  505  of the diamond bearing surface  504 . 
     While the spherical bearings of  FIGS.  5 A- 5 D  are shown and described as having continuous diamond bearing surfaces that are coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have continuous diamond bearing surface(s) and the spherical bearings can have opposing bearing surface(s) of diamond reactive material. 
     Angular Contact Bearing—Spherical Bearing with Articulation 
     Some embodiments of the present disclosure include an angular contact bearing that includes a spherical bearing that allows the opposing bearing element to which it is engaged to pivot and/or articulate relative to the spherical bearing. With reference to  FIGS.  6 A and  6 B , one exemplary spherical bearing and bearing assembly is depicted. Spherical bearing assembly  690  includes shaft  620  engaged with spherical bearing  600 . Spherical bearing  600  includes housing  602  and diamond bearing surface  604 . Diamond bearing surface  604  has boundary edges  605  and width  607 . Shaft  620  includes opposing bearing surface  622 , having boundary edges  625  and width  623 . Diamond bearing surface  604  is a curved, concave surface, and opposing bearing surface  622  is a curved, convex surface. As is evident from  FIGS.  6 A and  6 B , shaft  620  is capable of an articulating and/or pivoting movement relative to spherical bearing  600 , with the provision that the shaft  620  does not articulate sufficiently to cause the opposing bearing surface  622  to contact boundary edges  605  of the diamond bearing surface  604 . That is, shaft  620  can tilt relative to spherical bearing  600 , with opposing bearing surface  622  sliding along the diamond contact area of the diamond bearing surface  604  entirely within the boundary edges  605  thereof, while still maintaining shaft  620  engaged with spherical bearing  600 . Spherical bearing  600  also includes debris clearance hole  611 . In the same manner as described with respect to  FIGS.  1 A- 5 D , opposing bearing surface  622  has a smaller width  623  than the width  607  of the diamond bearing surface  604 . 
     In some embodiments, the bearings assemblies disclosed herein include a hybrid bearing engagement surfaces. For example, the diamond bearing surface can be a conical or cylindrical bearing surface and the opposing bearing surface can be a spherical bearing surface (or vice versa). 
     While the spherical bearings of  FIGS.  6 A and  6 B  are shown and described as having continuous diamond bearing surfaces that are coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have continuous diamond bearing surface(s) and the spherical bearings can have opposing bearing surface(s) of diamond reactive material. 
     Axial Bearing 
     Some embodiments of the present disclosure include an axial bearing assembly that includes an axial bearing having a diamond bearing surface that is engaged with an opposing bearing surface. With reference to  FIGS.  7 A and  7 B , axial bearing assembly  790  includes axial bearing  700 . Axial bearing  700  includes bearing housing  702 . Diamond bearing surface  704  is on one end of bearing housing  702 . Diamond bearing surface  704  has width  707  defined between boundary edges  705 . Axial bearing assembly  790  includes shaft  720 , including shaft body  724  and shaft end  726 . Shaft  720  has opposing bearing surface  722  on a portion of shaft end  726 . Opposing bearing surface  722  has width  723  defined between boundary edges  725 . Axial bearing  700  is slidingly engaged with shaft  720 , such that shaft body  724  is engaged within bearing cavity  708  and such that diamond bearing surface  704  is engaged with opposing bearing surface  722 . In the same manner as described with respect to  FIGS.  1 A- 6 B , opposing bearing surface  722  has a smaller width  723  than the width  707  of the diamond bearing surface  704 . 
     While the axial bearings of  FIGS.  7 A- 7 B  are shown and described as having continuous diamond bearing surfaces that are coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have continuous diamond bearing surface(s) and the axial bearings can have opposing bearing surface(s) of diamond reactive material. 
     Combined and Integral Axial and Radial Bearing 
     Some embodiments of the present disclosure include a combined axial and radial bearing assembly that includes a combined axial and radial bearing having diamond bearing surfaces that are engaged with opposing bearing surfaces. With reference to  FIGS.  8 A- 8 C , combined axial and radial bearing assembly  890  includes combined axial and radial bearing  800 . Combined axial and radial bearing  800  includes bearing housing  802 . Diamond bearing surface  804   a  is on one end of bearing housing  802 . Diamond bearing surface  804   b  is along an interior surface of cavity  808  of bearing housing  802 . As shown, diamond bearing surfaces  804   a  and  804   b  are a single, integral structure connected together at bend  899 , such that diamond bearing surface  804   a  is on one side of bend  899  and diamond bearing surface  804   b  is on another side of bend  899 . Axial bearing assembly  890  includes shaft  820 , including shaft body  824  and shaft end  826 . Shaft  820  has opposing bearing surface  822   a  on a portion of shaft end  826  and opposing bearing surface  822   b  as an outer surface of shaft body  824 . Axial bearing  800  is slidingly engaged with shaft  820 , such that shaft body  824  is engaged within bearing cavity  808 , such that diamond bearing surface  804   a  is engaged with opposing bearing surface  822   a  and diamond bearing surface  804   b  is engaged with opposing bearing surface  822   b . In the same manner as described with respect to  FIGS.  1 A- 7 B , opposing bearing surface  822   a  has a smaller width than the width of the diamond bearing surface  804   a  and opposing bearing surface  822   b  has a shorter width (or height) than the width (or height) of the diamond bearing surface  804   b . Thus, opposing bearing surface  822   a  is engaged with diamond bearing surface  804   a  entirely within the boundary edges  805  of the structure that forms diamond bearing surfaces  804   a  and  804   b , and opposing bearing surface  822   b  is engaged with diamond bearing surface  804   b  entirely within the boundary edges  805  of the structure that forms diamond bearing surfaces  804   a  and  804   b . The bearing surfaces  804   a  and  822   a  bear axial loads (e.g., thrust loads), and the bearing surfaces  804   b  and  822   b  bear radial loads. 
     While the combined axial and radial bearings of  FIGS.  8 A- 8 C  are shown and described as having continuous diamond bearing surfaces that are coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have continuous diamond bearing surface(s) and the combined axial and radial bearings can have opposing bearing surface(s) of diamond reactive material. 
     Combined and Discrete Axial and Radial Bearing 
     In some embodiments of a combined axial and radial bearing assembly, rather than being integral, as is shown in  FIGS.  8 A- 8 C , the axial load bearing diamond bearing surface is a separate and discrete structure from the radial load bearing diamond bearing surface. With reference to  FIGS.  9 A- 9 E , combined axial and radial bearing assembly  990  includes combined axial and radial bearing  900 . Combined axial and radial bearing  900  includes bearing housing  902 . Bearing housing  902  includes radial bearing receptacle  905  and axial bearing receptacle  903 . Combined axial and radial bearing  900  includes radial diamond element  907  having diamond bearing surface  904   a , and axial diamond element  909  having diamond bearing surface  904   b . To assemble combined axial and radial bearing  900 , radial diamond element  907  is engaged within radial bearing receptacle  905  and axial diamond element  909  is engaged within axial bearing receptacle  903 . Combined axial and radial bearing assembly  990  includes shaft  920 , including shaft body  924  and shaft end  926 . Shaft  920  has opposing bearing surface  922   a  on a portion of shaft end  926  and opposing bearing surface  922   b  as an outer surface of shaft body  924 . Opposing bearing surface  922   a  has a width  921  defined between boundary edges  919  thereof. Opposing bearing surface  922   b  has a width  923  defined between boundary edges  925  thereof. Diamond bearing surface  904   a  has a width  913  defined between boundary edges  911  thereof. Diamond bearing surface  904   b  has a width  917  defined between boundary edges  915  thereof. Axial bearing  900  is slidingly engaged with shaft  920 , such that shaft body  924  is engaged within bearing cavity  908 , and such that diamond bearing surface  904   a  is engaged with opposing bearing surface  922   a , and such that diamond bearing surface  904   b  is engaged with opposing bearing surface  922   b . In the same manner as described with respect to  FIGS.  1 A- 8 C , opposing bearing surface  922   a  has a smaller width  921  than the width  913  of the diamond bearing surface  904   a  and opposing bearing surface  922   b  has a shorter width  923  (or height) than the width  917  (or height) of the diamond bearing surface  904   b . The bearing surfaces  904   a  and  922   a  bear axial loads, and the bearing surfaces  904   b  and  922   b  bear radial loads. 
     While both diamond bearing surfaces  904   a  and  904   b  are shown as continuous bearing surfaces, in some embodiments one of the diamond bearing surfaces  904   a  and  904   b  is replaced with discrete diamond bearing elements rather than a single continuous diamond bearing surface. While the combined axial and radial bearings of  FIGS.  9 A- 9 E  are shown and described as having continuous diamond bearing surfaces that are coupled with a shaft that has an opposing bearing surface of diamond reactive material, this arrangement can be reversed. For example, the shaft can have continuous diamond bearing surface(s) and the combined axial and radial bearings can have opposing bearing surface(s) of diamond reactive material. 
     Tilting Pad Bearings 
     In some embodiments, the concepts described herein are applied to tilting pad bearings. In some such embodiments, the tilting pads of the tilting pad bearings have the opposing bearing surfaces thereon, and the shaft (or other component) has the continuous diamond bearing surface thereon. In other such embodiments, the tilting pads of the tilting pad bearings have the diamond bearing surfaces thereon, and the shaft (or other component) has the opposing bearing surface thereon. The tilting pads can articulate to engage or disengage from the shaft. When the tilting pads are engaged with the shaft, the opposing bearing surfaces on the tilting pads are in contact with the diamond contact area of the diamond bearing surface on the shaft. In such embodiments, the opposing bearing surfaces contact the diamond contact area entirely within the boundary edges of the diamond bearing surface. Such tilting pad bearings may be used to bear radial and/or axial loads. Some examples of tilting bearing pads are disclosed in U.S. Patent Publication No. 2020/0325933. 
     Bearing Characteristics 
       FIG.  10    is a graph showing a Stribeck curve plotting the Hersey number on the horizontal axis and the friction coefficient on the vertical axis. In the graph of  FIG.  10   , a curve for a conventional sliding bearing system, curve  1102  is plotted, as well as a curve for a system in accordance with the present disclosure using a diamond bearing surface engaged with a diamond reactive material (steel), curve  1104 . The bearing assemblies disclosed herein provide for a low sliding contact friction that, in turn, provides for low wear on the bearing assembly. When conditions are not conducive to the formation of a fluid film between the diamond and opposing bearing surfaces, the bearing assembly disclosed herein is still capable of exhibiting a low contact friction. Conditions that are not conducive to the formation of a fluid film between the diamond and opposing bearing surfaces include, but are not limited to, start-up, shut-down, vibration in the bearing assembly, shock loads, geometric changes affecting bearing clearances, or other transient events. The bearing assemblies according to the present disclosure provide for low friction during boundary lubrication conditions. In some embodiments, the bearing assemblies according to the present disclosure may provide less friction than exists in certain hydrodynamic lubrication regimes. 
     In some embodiments, the coefficient of friction (CoF) exhibited by the engagement between the diamond bearing surfaces and the opposing bearing surfaces disclosed herein is less than 0.1, 0.09 or less, 0.08 or less, 0.07 or less, 0.06 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. In some embodiments, the CoF exhibited by the engagement between the diamond bearing surfaces and the opposing bearing surfaces disclosed herein ranges from 0.01 to 0.09, or 0.01 to 0.07, or 0.01 to 0.05, or 0.01 to 0.03, or any range or value therebetween. 
     The continuous surface of the diamond bearing surface, along the diamond contact area, provides for the avoidance of the opposing bearing surface contacting a diamond edge or diamond point, which facilitates bearing surface integrity, such as by avoiding gouging of the opposing bearing surface by the diamond. Without being bound by theory, it is believed that continuous diamond bearing surfaces impart less stress on the bearing surfaces of the bearing assembly, at least in part due to the avoidance of diamond edge contact, in comparison to an otherwise identical bearing assembly where the diamond bearing surface is formed of multiple discreet bearing elements. Without being bound by theory, it is also believed that the continuous diamond bearing surfaces disclosed herein are more conducive to the development of a fluid film between the bearing surfaces, in comparison to an otherwise identical bearing assembly where the diamond bearing surface is formed of multiple discreet bearing elements. 
     Methods of Making the Diamond Bearing Surfaces 
     In some embodiments, the diamond bearing surfaces disclosed herein are made by a high-pressure and high-temperature process (HPHT diamonds). In some embodiments, the diamond bearing surfaces disclosed herein are made by chemical vapor deposition (CVD) or physical vapor deposition (PVD). The thickness of the diamond layer that has the diamond bearing surface may be 0.200″ or less, or 0.150″ or less, or 0.100″ or less, or 0.09″ or less, or 0.08″ or less, or 0.07″ or less, or 0.06″ or less, or 0.05″ or less, or 0.04″ or less, or 0.03″ or less, or 0.02″ or less, 0.010″ or less. The thickness of the diamond layer that has the diamond bearing surface may be from 0.010″ to 0.200″, from 0.02″ to 0.150″, from 0.03″ to 0.100″, from 0.04″ to 0.09″, from 0.05″ to 0.08″, from 0.06″ to 0.07″, or any range or value therebetween. For example, when the diamond layer is made via CVD or PVD, the thickness of the diamond layer that has the diamond bearing surface may be 0.010″ or less, and when the diamond layer is made by a high-pressure and high-temperature process the thickness of the diamond layer that has the diamond bearing surface may be 0.200″ or less. In some embodiments, the diamond is leached, un-leached, or leached and backfilled. As an example, to make a diamond layer using the CVD process, seed diamond particles are attached to a substrate and then placed in a chamber under conditions sufficient to promote the crystalline growth of the seed diamond particles. 
     Applications 
     While the bearing assemblies disclosed herein are not limited to particular applications, some exemplary applications include journal bearings for an airplane propeller, bearings in a planetary gear box, marine bearings, turbo bearings, gas or steam turbine main shaft bearings, downhole pump bearings (such as an electronic submersible pump), bearings in downhole motors, driveline bearings, and roller ball bearings. 
     While described as applied to particular bearing geometries, the concepts described in the present disclosure are not limited to being applied to these specific bearing geometries. The concepts described in the present disclosure may be applied to axial bearings, radial bearings, combined axial and radial bearings, roller ball bearings, cam followers, linear bearings, power transmission surfaces (e.g., gears and drivelines), rod guides, pipe protectors, valves, and other assemblies or machines that have moving parts with surfaces that are in sliding engagement with one another. The concepts described in the present disclosure may be applied to assemblies or machines that include two load-transmitting bearing surfaces that are slidingly engaged with one another, in which one of the load-transmitting bearing surfaces is a diamond surface and the other of the load-transmitting bearing surfaces is a metal alloy surface that contains more than 2 wt. % of a diamond solvent-catalyst. In some such embodiments, the slidingly engaged contact area between the two load-transmitting bearing surfaces is contained within a continuous diamond bearing surface that is defined by the boundary edges of the diamond bearing surface. In some such embodiments, the boundary edges of the metal alloy surface contact the diamond surface. 
     In some embodiments, the bearing assemblies disclosed herein include hybrid bearing bearing surfaces that have different geometries and surface profiles. For example, the diamond bearing can have a first geometric shape with a first surface profile (e.g., a conical or cylindrical bearing surface) and the opposing component can have a second geometric shape with a second surface profile (e.g., a spherical bearing surface). For example, an axial bearing can include a diamond bearing surface that is planar and an opposing bearing surface that is non-planar (or vice versa). 
     Although the present embodiments and advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the disclosure. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.