Moist-Air Results of MoS2

The M0S2 powder was rubbed onto 440C HT steel disks with three surface finishes: lapped and polished to a surface roughness of 0.09iO. 02 micrometer (CLA), sanded to a surface roughness of 0.30iO. 05 micrometer (CLA) and sandblasted to a surface roughness of 1.24.2 micrometers (CLA). Figure 3 gives photomicrographs and surface profiles of the three substrate surfaces before applying the MoSz films. Figure 4 shows photomicrographs and surface profiles after applying the MoSz films to these surfaces. The effect of substrate surface finish on friction coefficient and wear life in a moist air test atmosphere (10 000-ppm HzO) is shown in Figure 5. The gaps in the traces represented the intervals when the tests were stopped so that wear measurements could be made and the sliding surfaces could be observed with an optical microscope. The sandblasted surface gave a lower friction coefficient for a longer time than the sanded or polished surface. The failure criterion for solid-lubricant films is usually arbitrary. Failure is often assumed to be when the friction coefficient reaches some predetermined value or rapidly increases. In these experiments, failure was deemed to occur when the friction coefficient reached 0.30. This occurred for the polished surface after kilocycles of sliding, the sanded surface after 52 kilocycles, and the sandblasted surface after 60 kilocycles. Sliding was continued past this point to determine how friction and rider wear were affected. The friction coefficient increased beyond 0.30 and then dropped below 0.30.

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