WEAR CHARACTERISTICS OF PLASMA-NITRIDED CRMO STEEL UNDER MIXED AND BOUNDARY LUBRICATED CONDITIONS

An investigation of the sliding wear mechanisms of a plasma-nitrided C rMo steel is undertaken using a running-in procedure that eliminates s evere wear under mixed and boundary lubricated conditions. In the runn ing-in procedure, using a pin-on-disc wear machine, smooth contact sur faces are obtained rather than the rough contact surfaces generally fo und in laboratory experiments. This enables the wear mechanisms to be investigated more clearly, particularly mild wear processes. The work shows no measurable nor visible wear under full fluid film lubricated conditions, the existence of polishing under mixed lubricated conditio ns and micro-pits under boundary lubricated conditions. The results pr esented in this paper indicate that a mild abrasive wear mechanism pre dominates under mixed lubricated conditions and a micro-fatigue wear m echanism under boundary lubricated conditions. Examination of the micr ostructure reveals the formation of white layer regimes on the contact surfaces after tests under boundary lubricated conditions, which sugg ests severe work-hardening of the contact surfaces.