Wear behaviour of steel-on-Si3N4 and Si3N4-on-Si3N4 systems with vapor phase lubrication of oleic acid and TCP

The wear property of Si3N4 under vapor phase lubrication of oleic acid and tricresyl phosphate (TCP) in both steel-on-Si3N4 and Si3N4-on-Si3N4 systems were investigated. The used oleic acid and TCP were fed into the evaporator simultaneously with two syringe pumps, and the vaporized lubricants were delivered by the carrier gas of nitrogen to the ball pot of a modified four-ball wear tester. Tests were made using M50 tool steel ball or Si3N4 ball against Si3N4 discs at a load of 98 N and temperature of 370 degrees C. Oleic acid, TCP and the combination of oleic acid with TCP as the vapor lubricants were evaluated for test time from 30 min to 3 h. Results indicate that the oleic acid provides effective lubrication for steel-on-Si3N4 system, and for the combination of oleic acid with TCP, the wear can be even reduced. The wear of Si3N4 disc in steel-on-Si3N4 system is always lower as compared to that of in Si3N4-on-Si3N4 system. X-ray photoelectron spectroscopy (XPS) analyses of the rubbed surfaces suggest the formation of a film containing carbonaceous deposits, iron phosphate, N-containing compounds and silicon oxides due to the oxidation of Si3N4. (C) 1998 Elsevier Science S.A.