Friction and wear results from sputter-deposited chrome oxide with and without nichrome metallic binders and interlayers

Friction and wear tests were conducted on optimized sputtered Cr2O3 and Cr2O3 with metallic binder coatings. The coatings were applied on the bearing surface of journal foil air bearings and were tested against chrome-carbide-coated journal surfaces. The objective of the study was to develop a coating system which would withstand 9000 start-stops and high-speed rubs (maximum acceleration, 100 gs) in temperatures ranging from room temperature to 650 C. The Cr2O3 coating completed the test sequence and the coating consisting of Cr2O3 with metallic binders completed 3000 start-stops. The coefficient of friction of the coatings at 650 C was found to be about half that at room temperature. It was concluded, therefore, that the coatings should perform much better in a high temperature environment alone. The decrease in friction at high temperature is attributed to oxidation and interactions of the coatings and substrates at the interface temperature.