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Diamond as a Bearing Material

Polycrystalline diamond is known for its high thermal conductivity, low coefficient of friction, high toughness and other preferred physical and mechanical properties. Having a bearing material with high thermal conductivity reduces localized temperature extremes that lead to bearing degradation. During starting and stopping, a high thermal conductivity will reduce the likelihood of causing localized welding of the surfaces, which in turn leads to scoring and galling of the bearing surface. In sliding bearings, low coefficients of friction are desired in order to decrease heat generation and reduce power loses. A bearing material exhibiting a large fracture toughness will decrease the likelihood of race damage during extreme operation conditions. Because of its extreme hardness, polycrystalline diamond is very resistant to wear from abrasive particles in lubricants or process fluids.

Physical and Mechanical Properties of Bearing Materials

Properties	Polycrystalline Diamond (PCD)	Tungsten Carbide	Steel (4140)	Silicon Nitride	Silicon Carbide
Coefficient of Friction	0.05-0.08**	0.2-0.25†	0.42‡	--	--
Thermal Conductivity (W/m*K)	543	70	42.6	30	85
Fracture Toughness (MPa√m)	13-15	10-25	50	4	3.5-4
Hardness (GPa, Knoop)	49.8	1.8	0.2	1.8	2.4
Compressive Strength (GPa)	6.9-7.6	2.68	--	--	2.5
Young’s Modulus (GPa)	841	669-696	205	296	434
Tensile Strength (MPa)	1,300-1,600	334	415	520	500

*ASI 4140 Steel, annealed at 815°C (1500°F) furnace cooled 11°C (20°F)/hour to 665°C (1230°F), air cooled, 25 mm (1 in.) roun(1100°F) temper)
** PCD on PCD in H2O, dynamic, dynamic
†Tungsten Carbide on Tungsten Carbide, static
‡Steel (Hard) on Steel (Hard), dynamic
YAt 100˚C
Sources: Bertagnolli, US Synthetic; Roberts et al., De Beers; Cooley, US Synthetic; Jiang Qian, US Synthetic; Glowka, SNL; Sexton, US Synthetic; Lin, UC Berkeley, MatWeb.com, Cerco