Analysis of sliding wear tests of plasma processed AISI 316L steel

In this paper, the influence of different plasma treatments on wear regime transitions during sliding wear tests carried out on AISI 316L steel was investigated. Selected plasma treatments included plasma nitriding, plasma carburizing and a sequential process involving plasma carburizing followed by plasma nitriding. During sliding wear tests, sharp transitions in frictional force were detected after the initial running-in period. These transitions in frictional force, which were measured as a function of sliding distance, could be correlated to different plasma-modified layers at the surface of the AISI 316L steel. They were also associated with concentrations of nitrogen and/or carbon along sample depths and also with instrumented indentation hardness-depth profiles. Once sliding distances that corresponded to such transitions were determined, additional tests were performed and then interrupted at these distances to record EDS (energy dispersive spectroscopy) composition maps of wear tracks. Additionally, both depth and wear volume of wear tracks were determined by stylus profilometry. Significant reductions in nitrogen and/or carbon contents were detected for each wear track analyzed, indicating that plasma modified layers were almost worn out for these sliding distances at which sharp transitions in frictional force were recorded. The smallest overall wear volume was measured for the sequentially treated sample, which exhibited the best wear resistance among all tested samples. Results indicated that transitions in friction coefficient were distance-dependent during sliding wear tests; this dependence could be attributed to variations in material hardness and/or concentration of interstitial solutes (carbon, nitrogen) in the austenite phase.