Microstructure analysis of MoS2 deposited on diamond-like carbon films for wear improvement

A compound solid lubricating film containing a MoS₂ top layer deposited on DLC interlayer by UBM sputtering technique was investigated for its tribological applications in humid environments. TEM, Raman and XRD analysis revealed the amorphous nature of the MoS₂ film which contains only short-range order in its lattice structure. The as-deposited MoS₂ compound films showed well-bonded interfaces. The MoS₂, however, is very susceptible to humidity and oxidation, which resulted in higher friction coefficients and lower wear life. A friction coefficient of 0.05 was measured between steel balls and MoS₂ in atmosphere of 90% RH. Excessive abrasive wear was identified, as a result of the wear debris and the oxidized transfer layers between MoS₂ and its counterpart. The inclusion of a supportive DLC interlayer has effectively improved the wear behavior of MoS₂ films under various loading conditions. The overall wear mechanism of MoS₂ was complicated due to its oxidation problem which needs to be resolved for successful usage of MoS₂ in humid environments.