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Why Diamond Bearings Underwater?
PCD bearings are ideally suited for operation in process fluids where abrasive particles can cause accelerated wear.
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
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