Evaluation of coatings on Ti–6Al–4V substrate under fretting fatigue

Four coating systems, TiCN, CrN+MoS2, Cu–Al and Ag+ irradiated layer, were evaluated for their potential towards improving fretting fatigue behavior of titanium alloy, Ti–6Al–4V. Coefficients of friction (COF) and fretting fatigue lives of the specimens with and without coating were compared. Coating damage was characterized through scanning electron microscopy and energy dispersive spectrometry. COF may increase or decrease during the fretting fatigue due to generation of coating debris. The decrease in COF can be attributed to lubrication by coating debris produced during fretting fatigue. Further, when a coating is subjected to fretting, it would degrade. Improvement in fretting fatigue life, if any, can only be achieved only when the coating degradation is reduced or eliminated.