Retainer-Dependent Wear of Silicon Nitride Bearings at High Temperatures

Several retainer materials for high-temperature silicon nitride bearings to be used in air were examined with a high-temperature rolling three-ball tester. The “soft” or “self-lubricating” retainer materials (metal-bonded MoS₂-WS₂ alloys, a carbon-carbon composite and graphite) tended to yield longer bearing life, lower silicon nitride wear rate and lower traction coefficients than the hard retainers (Fe-based sintered alloys, chromia and silicon nitride). The main problem in the use of the self-lubricating retainer materials was their rapid wear by tribo-oxidation at high temperatures.