Comparative study on the fretting fatigue and fretting wear behaviors of titanium alloy subject to various surface modifications

The fretting fatigue (FF) and fretting wear (FW) behaviors of a Ti alloy were comparatively investigated. The effects of shot peening and nitriding on the fretting wear and fretting fatigue behaviors of the Ti alloy were examined. And the correlation between the fretting wear and fretting fatigue behaviors of the Ti alloy was explored. It was found that the FF Ti alloy surface had similar morphology to that of the FW Ti alloy surface. The fretting wear at the fretted contact region contributed to delay the FF crack initiation as the fretting amplitude was large enough and the fretted zone was characterized by complete slip. While in the mixed stick and slip regime corresponding to a small fretting amplitude, the localized fretting wear accelerated the FF crack initiation. The shot-peening induced surface residual compressive stress of the Ti alloy was beneficial to decreasing the friction coefficient and increasing the fretting fatigue resistance and fretting wear resistance. Nitriding of the Ti alloy led to the increase of the surface hardness, which was beneficial to increasing the fretting wear resistance. However, the decreased surface toughness of the Ti alloy after the nitriding was harmful to the fretting fatigue resistance. Therefore, it was imperative to get rid of the negative effect of the decreased surface toughness on the fretting fatigue resistance of the Ti alloy when using surface modification techniques to increase its surface hardness and fretting wear resistance.