WEAR BEHAVIOR 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-Si3 N4 systems were investigated. The used oleic acid and TCP were fed int o the evaporator simultaneously with two syringe pumps, and the vapori zed lubricants were delivered by the carrier gas of nitrogen to the ba ll 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 an d temperature of 370 degrees C. Oleic acid, TCP and the combination of oleic acid with TCP as the vapor lubricants were evaluated for test t ime from 30 min to 3 h. Results indicate that the oleic acid provides effective lubrication for steel-on-Si3N4 system, and for the combinati on of oleic acid with TCP, the wear can be even reduced. The wear of S i3N4 disc in steel-on-Si3N4 system is always lower as compared to that of in Si3N4-on-Si3N4 system. X-ray photoelectron spectroscopy (XPS) a nalyses of the rubbed surfaces suggest the formation of a film contain ing carbonaceous deposits, iron phosphate, N-containing compounds and silicon oxides due to the oxidation of Si3N4. (C) 1998 Elsevier Scienc e S.A.