Investigation of the Tribological and Tribochemical Interactions of Different Ferrous Layers Applied to Nitride Surfaces

Nitriding is a widely used industrial process aiming to improve the tribological properties and performance of components. Previous studies have shown the effectiveness of the treatment with friction and wear performance, but very few have focused on the influence of different ferrous layers formed by variant nitriding treatments on tribological and tribochemical behavior. The influence of an oxide (Fe3O4) and sulfide (FeS) layer on friction and wear performance alongside tribochemical formation was investigated when using a fully formulated hydraulic lubricant. The tribological behavior of the variant nitride samples was analyzed using a tribometer and surface profiler. Scanning electron microscope, energy-dispersive X-ray (EDX) spectroscopy, electron probe micro analysis (EPMA), and X-ray photoelectron spectroscopy (XPS) were employed to identify the morphologies and chemical compositions of the treated surface before and after testing. No real effect on friction or wear was observed with the presence of an oxide (Fe3O4) layer, even though the formation of FeS2 was observed within the tribofilm. However, the formation of a sulfide (FeS) layer after sulfur nitriding produced the lowest friction and wear in comparison to the alternative nitride variants. This was due to the lubrication properties of the FeS layer. The study effectively demonstrated that the type of the ferrous layer could impact tribological and tribochemical properties of nitride samples.