The effect of hydrochloric acid pretreatments on 440C steel surface composition and the adhesion and endurance of sputter-deposited MoS2 solid lubricant films

Abstract The effects of substrate pretreatment on substrate surface chemistry and on film-substrate adhesion, and film endurance (wear life) of sputter-deposited molybdenum disulfide (MoS 2 ) on 440C bearing steel were investigated. Specifically, 20% hydrochloric acid-ethanol mixtures were used to etch the steel surface prior to deposition or X-ray photoelectron spectroscopy (XPS). Acid etching inhibited fractures at the film-substrate interface generated by brale indentation testing. XPS indicated that the acid etching removed an iron-rich oxide surface layer, exposing a chromium-rich oxide underlayer on the steel matrix. Acid etching did not significantly affect thrust washer sliding wear life.