LUBRICATION OF HIGH ROLLING SPEED CERAMIC CONTACT WITH 2-PERCENT SLIPAT 815-DEGREES-C (1500-DEGREES-F)

A selection of liquid lubricants was vaporized and deposited on a hot, 705 degrees C (1300 degrees F), ceramic surface. Friction was then ev aluated in low speed, 7 MPa (1000 psi), sliding contact. The ceramic m aterials included aluminum oxide, silicon aluminum oxynitride (SiAlON) , silicon nitride, and silicon carbide. Each specimen was mated with a n equally hot specimen of the same material. Deposits reduced friction significantly compared to the unlubricated contact. Two superior lubr icants were then evaluated in continuous lubrication of silicon nitrid e using a high speed ball-on-disk contact. Rolling speed was 2.5 m/sec at a Hertzian stress of 2 GPa (300 ksi). Operating temperatures were varied between 621 degrees C (1150 degrees F) and 815 degrees C (1500 degrees F). With the slip level maintained at 2%, the traction coeffic ient recorded at 815 degrees C was 0.05, comparable to current metalli c bearings in aerospace applications. Wear volume was reduced by an or der of magnitude compared to the unlubricated case. Temporarily stoppi ng the lubricant flow resulted in a steady rise of the traction coeffi cient, while resuming the lubricant flow reduced the traction to the o riginal level.