WEAR BEHAVIOR OF TRIODE-SPUTTERED MOS2 COATINGS IN DRY SLIDING CONTACT WITH STEEL AND CERAMICS

The endurance of MoS2 sputter-coated steel balls was measured in conti nuous and stop-start sliding tests in a four-ball wear tester. Test va riables were counterface materials, uncoated steel and two ceramics (C o-bonded tungsten carbide and sapphire), and gaseous atmospheres, dry Ar and dry air. In continuous tests, coating endurance increased from 14 to 80 min; combinations were ranked as follows: steel in air=cerami cs in air < steel in Ar < ceramics in Ar. Coating endurance in stop-st art tests was the same as in continuous test for all combinations exce pt steel in Ar, which failed sooner in stop-start tests. MoS2 wear tra cks were analyzed at intervals from 1 min to failure by optical micros copy, energy-dispersive X-ray spectroscopy (EDX) and Auger electron sp ectroscopy (AES). Tracks run in Ar were smoother and showed ductile fl ow; tracks in air were rougher and developed ragged scratches. Blister s formed and contributed to failure in both atmospheres: in Ar they le d to a slower ductile failure whereas in air they led to more rapid br ittle failure. Abrasion by the worn steel ball accelerated coating wea r in Ar. EDX of wear tracks showed that 2/3 of the coating was removed within the first 10 min in both atmospheres; AES of the same tracks f ound higher levels of oxygen in MoS2 run in air. Mechanisms of wear, t ransfer and lubrication are discussed, and a quantitative model for bl ister formation in ductile MoS2 coatings is presented. It is recommend ed that hard ceramics replace abrasion-prone steel to enhance the wear life of MoS2-coated steel in oxygen-free environments.