Thrust-washer evaluation of self-lubricating PS304 composite coatings in high temperature sliding contact

PS304 self-lubricating composite coatings were successfully deposited on steel substrates at various plasma spray facilities using mixtures blended from commercially obtained constituent particles. Coatings were evaluated in thrust-washer tests against Inconel X-750 at low contact pressures to 40kPa, sliding speed of 5.4m/s, and either ambient temperature or 500 degreesC chosen to simulate conditions in air foil bearings during startup and shutdown contact. Wear factors for all PS304 coatings tested, regardless of contact pressure and temperature, ranged from 1-3*10(-4) mm(3)/Nm while coefficients of friction of approximately mu = 0.5 were measured in all cases. While wear and friction behavior of PS304 in air foil bearings appear to have been simulated, surface roughening was observed in these thrust-washer tests which used continuous sliding contact, as opposed to the evolution of smoother surfaces observed in high-temperature foil bearings experiencing cyclic startup/shutdown. Wear-induced surface smoothening of PS304 was additionally simulated in thrust-washer tests with sliding contact instead imposed intermittently.