EFFECT OF SOLID LUBRICANTS ON LOW-SPEED SLIDING BEHAVIOR OF SILICON-NITRIDE AT TEMPERATURES TO 800-DEGREES-C

Many studies have been published on the effectiveness of solid lubrica nts with metallic bearing materials. In contrast, little work has been reported on the behavior of these same solid lubricants with ceramic or metal/ceramic combinations. This sort of information is needed to u nderstand mechanisms and develop new concepts. Therefore, a study was made to select and evaluate the performance of a number of known solid lubricants using silicon nitride sliding on itself, and a Laves Phase Co-Mo-Cr-Si metallic alloy sliding on silicon nitride. The lubricants included MoS2, WS2, CeF3, some single and double oxides, and three di chalcogenides of Group Vb and VIb metals. The test geometry was a hemi spherically-tipped pin loaded against the ceramic flat. Tests were run with a load of 142 N, using a slow speed, reciprocating sliding motio n. Test temperatures covered the range from 23-degrees to 800-degrees- C. Coefficients of friction, surface damage or wear, and lubricant oxi dation were used to rank performance. The candidate lubricants were ju st as effective with the ceramic couple as they would have been with m etals. Except for CeF3 and some preformed oxides, all the lubricants o xidized or decomposed at high temperature. However, in some cases ther e oxidation products did reduce friction and wear. Tungsten disulfide shows advantages over MoS2 for intermediate temperature use.