Bearing assemblies that include a plurality of polycrystalline diamond (“PCD”) bearing elements, bearing apparatuses including such bearing assemblies, and methods of operating and fabricating such bearing assemblies and apparatuses are disclosed. In an embodiment, the plurality of PCD bearing elements of one or more of the bearing assemblies disclosed herein include at least one first PCD bearing element. At least a portion of the first PCD bearing element exhibits a coercivity of about 125 Oersteds or more and a specific magnetic saturation of about 14 Gauss cm.sup.3/gram or less. The first PCD bearing element includes a bearing surface with at least one groove formed therein. In an embodiment, the plurality of PCD bearing elements also include at least one second PCD bearing element. The second PCD bearing element exhibits a coercivity that is less than and a specific magnetic saturation that is greater than the first PCD bearing element.

Bearing assemblies that include a plurality of polycrystalline diamond (“PCD”) bearing elements, bearing apparatuses including such bearing assemblies, and methods of operating and fabricating such bearing assemblies and apparatuses are disclosed. In an embodiment, the plurality of PCD bearing elements of one or more of the bearing assemblies disclosed herein include at least one first PCD bearing element. At least a portion of the first PCD bearing element exhibits a coercivity of about 125 Oersteds or more and a specific magnetic saturation of about 14 Gauss cm.sup.3/gram or less. The first PCD bearing element includes a bearing surface with at least one groove formed therein. In an embodiment, the plurality of PCD bearing elements also include at least one second PCD bearing element. The second PCD bearing element exhibits a coercivity that is less than and a specific magnetic saturation that is greater than the first PCD bearing element.

A bearing system configured for use on a downhole tool including a rolling cutter member having a plurality of cutting structures thereon comprises a first plurality of bearings disposed between a head washer and an at least substantially planar shaft washer, and a second plurality of bearings disposed between the at least substantially planar shaft washer and a rolling cutter washer. A downhole tool, such as an earth-boring rotary rolling cutter drill bit includes such a bearing system between a rolling cutter and a head of a bit body. Methods of forming such a downhole tool include the assembly of such a bearing system between a rolling cutter and a head of a bit body.

A bearing system configured for use on a downhole tool including a rolling cutter member having a plurality of cutting structures thereon comprises a first plurality of bearings disposed between a head washer and an at least substantially planar shaft washer, and a second plurality of bearings disposed between the at least substantially planar shaft washer and a rolling cutter washer. A downhole tool, such as an earth-boring rotary rolling cutter drill bit includes such a bearing system between a rolling cutter and a head of a bit body. Methods of forming such a downhole tool include the assembly of such a bearing system between a rolling cutter and a head of a bit body.

Bearing systems configured for use on a downhole tool may include a tensioner bolt having a complementary nut, the tensioner bolt and nut sized and shaped to secure the rolling cutter member to a head. A radial bearing may include an annular sleeve sized and shaped to surround the head. A shaft washer may be sized and shaped to surround the head between an enlarged head of the tensioner bolt and the annular sleeve. A bearing element may be configured for positioning proximate the head, the bearing element comprising an upper surface configured for sliding, frictional contact with a lower surface of the shaft washer.

Bearing systems configured for use on a downhole tool may include a tensioner bolt having a complementary nut, the tensioner bolt and nut sized and shaped to secure the rolling cutter member to a head. A radial bearing may include an annular sleeve sized and shaped to surround the head. A shaft washer may be sized and shaped to surround the head between an enlarged head of the tensioner bolt and the annular sleeve. A bearing element may be configured for positioning proximate the head, the bearing element comprising an upper surface configured for sliding, frictional contact with a lower surface of the shaft washer.

A shrouded screw apparatus includes an outer tube, a telescoping inner tube, an auger bit, and an anti-rotation pin. The outer tube has a first sidewall defining a first interior chamber. The first sidewall has an opening defined therethrough. The inner tube is positioned in the first interior chamber. The inner tube has a second sidewall defining a second interior chamber. The second sidewall has a longitudinal groove defined therein. The inner tube is configured to extend from and retract within the first interior chamber of the outer tube. The auger bit is positioned in the second interior chamber and is rotatably coupled to the inner tube. The anti-rotation pin is coupled to the first sidewall of the outer tube and extends inwardly into the first interior chamber. The pin engages the longitudinal groove of the inner tube.

A shrouded screw apparatus includes an outer tube, a telescoping inner tube, an auger bit, and an anti-rotation pin. The outer tube has a first sidewall defining a first interior chamber. The first sidewall has an opening defined therethrough. The inner tube is positioned in the first interior chamber. The inner tube has a second sidewall defining a second interior chamber. The second sidewall has a longitudinal groove defined therein. The inner tube is configured to extend from and retract within the first interior chamber of the outer tube. The auger bit is positioned in the second interior chamber and is rotatably coupled to the inner tube. The anti-rotation pin is coupled to the first sidewall of the outer tube and extends inwardly into the first interior chamber. The pin engages the longitudinal groove of the inner tube.

Methods of forming a volume of hard material on a component of a downhole tool include depositing a film of amorphous carbon on a substrate, irradiating the film of amorphous carbon to form a liquid carbon in an undercooled state, and quenching the liquid carbon to form a layer of quenched carbon on the substrate. A downhole tool comprises a component and a volume of hard material comprising quenched carbon disposed on a surface of the component. Additional downhole tools comprise a component and a polycrystalline compact comprising quenched carbon grains disposed on a surface of the component.

Methods of forming a volume of hard material on a component of a downhole tool include depositing a film of amorphous carbon on a substrate, irradiating the film of amorphous carbon to form a liquid carbon in an undercooled state, and quenching the liquid carbon to form a layer of quenched carbon on the substrate. A downhole tool comprises a component and a volume of hard material comprising quenched carbon disposed on a surface of the component. Additional downhole tools comprise a component and a polycrystalline compact comprising quenched carbon grains disposed on a surface of the component.