126 may comprise a partially ellipsoidal, a partially cylindrical surface (e.g., a convex cylindrical surface), and/or partially spherical shape.

As depicted by the dashed lines in FIG. 3, the bearing surfaces 126 and/or the angular orientation of the first support structure 106 that positions the bearing elements 104 may collectively define a convex, partially spherical shape. Where the individual bearing surfaces 126 each exhibit partial spherical convex surface, at least a portion of each of the individual bearing surfaces 126 may define (e.g., fall within) the overall or collective convex, partially spherical shape of the first bearing assembly 102 (e.g., defined by the plurality of the spherical bearing surfaces 126, a majority of the bearing surfaces 126, and/or a substantial entirety of the bearing surfaces 126, without limitation).

FIG. 4 is a cross-sectional view of a portion of the bearing assembly 102 shown in FIG. 3. As shown in FIG. 4, bearing element 104 may comprise a superhard table 128 affixed to or formed upon a substrate 130. Superhard table 128 may be affixed to substrate 130 at interface 132.

Bearing element 104 may also include a chamfer 134 between a side surface and bearing surface 126. Chamfer 134 may comprise an angular, sloped, and/or rounded edge formed at the intersection of superhard side surface and bearing surface 126. Any suitable surface shape may be formed at the intersection of superhard side surface and bearing surface 126, such as those disclosed in U.S. Pat. No. 8,708,564, the disclosure of which is incorporated herein in its entirety by this reference. Any other suitable surface shape may also be formed between superhard side surface and bearing surface 126, including, without limitation, an arcuate surface (e.g., a radius, an ovoid shape, or any other rounded shape), a sharp edge, multiple chamfers/radii, a honed edge, and/or combinations of the foregoing.

Bearing element 104 may comprise any suitable size, shape, and/or geometry, without limitation. As depicted, bearing surface 126 may comprise a convex, partial-ellipsoidal or substantially partial-ellipsoidal surface shape. A cross-sectional view of bearing element 104 taken along a plane parallel to the central element axis may have a convex, partial-circular or substantially partial-circular profile for bearing surface 126 as shown in FIG. 4. In some embodiments, bearing surface 126 may comprise a partial-spherical shape or a substantially partial-spherical surface shape. In such embodiments, each cross-sectional view of bearing element 104 taken along a plane intersecting a central element axis of the bearing element 104 may have substantially the same or similar profile.

In some embodiments, the individual bearing surfaces 126 of the bearing elements 104 may each exhibit a convex shape that, taken together, collectively define a substantially partial-spherical or frusto-spherical shape.

Substrate 130 may comprise any suitable material on which superhard table 128 may be formed. In at least one embodiment, substrate 130 may comprise a cemented carbide material, such as a cobalt-cemented tungsten carbide material and/or any other suitable material. In some embodiments, substrate 130 may include a suitable metal-solvent catalyst material, such as, for example, cobalt, nickel, iron, and/or alloys thereof. Substrate 130 may also include any suitable material including, without limitation, cemented carbides such as titanium carbide, tungsten carbide, niobium carbide, tantalum carbide, vanadium carbide, chromium carbide, and/or combinations of any of the preceding carbides cemented with iron, nickel, cobalt, and/or alloys thereof. Superhard table 128 may be formed of any suitable superabrasive and/or superhard material or combination of materials, including, for example PCD. Any of the superhard tables disclosed herein may also comprise polycrystalline diamond materials, such as those disclosed in U.S. Pat. No. 7,866,418, the disclosure of which is incorporated herein, in its entirety, by this reference. According to additional embodiments, superhard table 128 may comprise cubic boron nitride, silicon carbide, polycrystalline diamond, and/or mixtures or composites including one or more of the foregoing materials, without limitation.

Superhard table 128 of bearing element 104 may be formed using any suitable technique. According to some embodiments, superhard table 128 may comprise a PCD table fabricated by subjecting a plurality of diamond particles to a high pressure, high temperature (HPHT) sintering process in the presence of a metal-solvent catalyst (e.g., cobalt, nickel, iron, or alloys thereof) to facilitate intergrowth between the diamond particles and form a PCD body comprised of bonded diamond grains that exhibit diamond-to-diamond bonding therebetween. For example, the metal-solvent catalyst may be mixed with the diamond particles, infiltrated from a metal-solvent catalyst foil or powder adjacent to the diamond particles, infiltrated from a metal-solvent catalyst present in a cemented carbide substrate, or combinations of the foregoing. The bonded diamond grains (e.g., sp3-bonded diamond grains), so-formed by HPHT sintering the diamond particles, define interstitial regions with the metal-solvent catalyst disposed within the interstitial regions of the as-sintered PCD body. The diamond particles may exhibit a selected diamond particle size distribution or mixture.

Following sintering, various materials, such as a metal-solvent catalyst, remaining in interstitial regions within the as-sintered PCD body may reduce the thermal stability of superhard table 128 at elevated temperatures. In some examples, differences in thermal expansion coefficients between diamond grains in the as-sintered PCD body and a metal-solvent catalyst in interstitial regions between the diamond grains may weaken portions of superhard table 128 that are exposed to elevated temperatures, such as temperatures developed during bearing operation. The weakened portions of superhard table 128 may become excessively worn and/or damaged during bearing operation.

Removing the metal-solvent catalyst and/or other materials from the as-sintered PCD body may improve the heat resistance and/or thermal stability of superhard table 128, particularly in situations where the PCD material may be exposed to elevated temperatures. A metal-solvent catalyst and/or other materials may be removed (e.g., at least partially removed) from the as-sintered PCD body using any suitable technique, including, for example, leaching. In at least one embodiment, a metal-solvent catalyst, such as cobalt, may be removed from regions of the as-sintered PCD body, such as regions adjacent to the working surfaces of superhard table 128. Removing a metal-solvent catalyst from the as-sintered PCD body may reduce damage to the PCD material of superhard table 128 caused by expansion of the metal-solvent catalyst.

At least a portion of a metal-solvent catalyst, such as cobalt, as well as other materials, may be removed from at least a portion of the as-sintered PCD body using any suitable technique, without limitation. For example, chemical and/or gaseous leaching may be used to remove a metal-solvent catalyst from the as-sintered PCD body up to a desired depth from a surface thereof. The as-sintered PCD body may be leached by immersion in an acid, such as aqua regia, nitric acid, hydrofluoric acid, or subjected to another suitable process to remove at least a portion of the metal-solvent catalyst from the interstitial regions of the PCD body and form superhard table 128 comprising a PCD table. For example, the as-sintered PCD body may be immersed in or exposed to the acid for about 2 to about 7 days (e.g., about 3, 5, or 7 days) or for a few weeks (e.g., about 4 weeks) depending on the process employed.

Even after leaching, a residual, detectable amount of the metal-solvent catalyst may be present in the at least partially leached superhard table 128. It is noted that when the metal-solvent catalyst is infiltrated into the diamond particles from a cemented tungsten carbide substrate including tungsten carbide particles cemented with a metal-solvent catalyst (e.g., cobalt, nickel, iron, or alloys thereof), the infiltrated metal-solvent catalyst may carry tungsten and/or tungsten carbide therewith and the as-sintered PCD body may include such tungsten and/or tungsten carbide therein disposed interstitially between the bonded diamond grains. The tungsten and/or tungsten carbide may be at least partially removed by the selected leaching process or may be relatively unaffected by the selected leaching process.

In some embodiments, only selected portions of the as-sintered PCD body may be leached, leaving remaining portions of resulting superhard table 128 in an unleached state. For example, some portions of one or more surfaces of the as-sintered PCD body may be masked or otherwise protected from exposure to a leaching solution and/or gas mixture while other portions of one or more surfaces of the as-sintered PCD body may be exposed to the leaching solution and/or gas mixture. Other suitable techniques may be used for removing a metal-solvent catalyst and/or other materials from the as-sintered PCD body or may be used to accelerate a chemical leaching process. For example, exposing the as-sintered PCD body to heat, pressure, electric current, microwave radiation, and/or ultrasound may be employed to leach or to accelerate a chemical leaching process, without limitation. Following leaching, at least a portion of superhard table 128 may comprise a volume of PCD material that is substantially free of a metal-solvent catalyst.

The plurality of diamond particles used to form superhard table 128 comprising the PCD material may exhibit one or more selected sizes. The one or more selected sizes may be determined, for example, by passing the diamond particles through one or more sizing sieves or by any other method. In an embodiment, the plurality of diamond particles may include a relatively larger size and at least one relatively smaller size. As used herein, the phrases “relatively larger” and “relatively smaller” refer to particle sizes determined by any suitable method, which differ by at least a factor of two (e.g., 40 μm and 20 μm). More particularly, in various embodiments, the plurality of diamond particles may include a portion exhibiting a relatively larger size (e.g., 100 μm, 90 μm, 80 μm, 70 μm, 60 μm, 50 μm, 40 μm, 30 μm, 20 μm, 15 μm, 12 μm, 10 μm, 8 μm) and another portion exhibiting at least one relatively smaller size (e.g., 30 μm, 20 μm, 15 μm, 12 μm, 10 μm, 8 μm, 4 μm, 2 μm, 1 μm, 0.5 μm, less than 0.5 μm, 0.1 μm, less than 0.1 μm). In another embodiment, the plurality of diamond particles may include a portion exhibiting a relatively larger size between about 40 μm and about 15 μm and another portion exhibiting a relatively smaller size between about 12 μm and 2 μm. Of course, the plurality of diamond particles may also include three or more different sizes (e.g., one relatively larger size and two or more relatively smaller sizes) without limitation.

FIG. 5 is a perspective view of a bearing assembly including a plurality of bearing elements attached to a support structure (e.g., second bearing assembly 108). As illustrated in FIG. 5, bearing elements 110 may be mounted within the second support structure 112. Bearing elements 110 may each extend radially inward from the second support structure 112 such that at least a portion of the bearing element 110 extends past an inner surface 118 of the second support structure 112. A portion of bearing element 110 extending from second support structure 112 may comprise a bearing surface 136.

The bearing surface 136 of one or more of the bearing elements 110 (e.g., each bearing element 110) may comprise an at least partially concave rounded shape that is at least partially complementary to the shape of the bearing surface 126 of the bearing elements 104 of the first bearing assembly 102. For example, the bearing surfaces 136 of the bearing elements 110 may comprise a concave partial conical surface (e.g., a portion of a conical concave surface, a frustoconical surface). As discussed in greater detail below, the bearing surface 136 may exhibit a ramped or tapered shape (when viewed in a cross-sectional view) with a central lower portion that extends along a substantial portion of the diameter of the bearing surface 136 and is bordered by two higher portions positioned at or near two outer radial sections of the bearing elements 110.

In some embodiments, when compared to bearing surface 126, bearing surface 136 may not comprise a partial spherical surface shape. Rather, the bearing surface 136 may exhibit a curvature (e.g., a major or maximal curvature that is greater than zero) substantially along only one reference axis (as opposed to a spherical surface that exhibits a similar curvature along more than one reference axis). In such an embodiment, another reference axis along the bearing surface 136 that is transverse (e.g., perpendicular) to the one reference axis with the curvature may exhibit minimal curvature (e.g., approaching or equal to zero curvature).

As depicted by the dashed lines in FIG. 5, the bearing surfaces 136 and/or the angular orientation of the second support structure 112 that positions the bearing elements 110 may collectively define a concave, at least partially conical shape (e.g., tapering smoothly with respect to a pointed apex or vertex). For example, the individual bearing surfaces 136 of the bearing elements 110 may each exhibit a concave partial conical shape where a majority (e.g., a substantial entirety) of the bearing surfaces 136 of the bearing elements 110 collectively, when taken together, define (e.g., lie within or upon) a frustoconical shape. As depicted, a portion (e.g., a majority, a substantial entirety) of each of the individual bearing surfaces 136 may be configured to accommodate the overall convex shape of the overall first bearing assembly 102 (e.g., when first bearing assembly 102 is assembled with second bearing assembly 108). The overall convex conical shape of the support structure 106 of first bearing assembly 102 may exhibit a gradually decreasing radius with an end portion including a pointed or rounded radially innermost wall that is discontinuous with the remainder of the conical shape (e.g., extending horizontally/radially inward). In some embodiments, the overall convex conical shape of the support structure 106 may be substantially conical in that it approximates a portion of a cone to define an overall partially conical bearing surface on which the second bearing assembly 108 may travel. Similarly, the bearing surfaces 136 may each be substantially cylindrical such that, when fixed at an oblique angle relative to the outer bearing axis 113, each of the bearing surfaces