Lubrication of High Rolling Speed Ceramic Contact with Two Percent Slip at 815°C (1500°F)

A selection of liquid lubricants was vaporized and deposited on a hot, 705°C (1300°F), ceramic surface. Friction was then evaluated in low speed, 7 MPa (1000 psi), sliding contact. The ceramic materials included aluminum oxide, silicon aluminum oxynitride (SiAlON), silicon nitride, and silicon carbide. Each specimen was mated with an equally hot specimen of the same material. Deposits reduced friction significantly compared to the unlubricated contact. Two superior lubricants were then evaluated in continuous lubrication of silicon nitride 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° C (1150°F) and 815°C (1500°F). With the slip level maintained at 2%, the traction coefficient recorded at 815°C was 0.05, comparable to current metallic bearings in aerospace applications. Wear volume was reduced by an order of magnitude compared to the unlubricated case. Temporarily stopping the lubricant flow resulted in a steady rise of the traction coefficient, while resuming the lubricant flow reduced the traction to the original level.