Fretting fatigue behavior of shot-peened Ti–6Al–4V under seawater environment

The fretting fatigue behavior of the shot-peened titanium alloy, Ti–6Al–4V, was investigated under a seawater environment using a servo-hydraulic fatigue test machine equipped with a rigid fretting fixture. Fretting fatigue tests were performed over a wide range of stress levels to characterize the effects of seawater at high and low cycle fatigue regimes. The results of this study showed that (1) seawater reduces the fretting fatigue life of shot-peened Ti–6Al–4V in both high and low cycle fatigue regimes relative to their counterparts in ambient laboratory condition, and (2) shot-peening increases the fretting fatigue life of Ti–6Al–4V when tested under dry or seawater condition relative to its counterpart of unpeened Ti–6Al–4V. The seawater environment promotes an increase in crack propagation rate; however the crack initiation depends upon the combination of the detrimental effect from seawater environment and the beneficial effect from the residual compressive stress from shot-peening. In the present study, it appears that their cumulative effects were dominated by the residual compressive stress in both low cycle and high cycle fatigue regimes. On the other hand, the seawater environment has detrimental effect on the fretting fatigue life of unpeened Ti–6Al–4V than that in ambient laboratory condition in the low cycle fatigue regime while it improves slightly the life in the high cycle fatigue regime.