On the high cycle fatigue resistance of austenitic stainless steels with surface gradient microstructures: Effect of load ratio and associated residual stress modification

The effect of gradient microstructure generated by ultrasonic surface mechanical attrition treatment (SMAT) on the fatigue performance an austenitic stainless steel has been evaluated in context localized and general plasticity comparing two load ratios: fully reversed tension-compression (TC) RTC = -1 tension-tension (TT) RTT +0.1, respectively. After identical SMAT processing conditions, limit was enhanced +17% for while it reduced -7% RTT. Under cyclic loading, self-heating specimens sub-surface martensitic transformation occurred but not residual stress measurements have also revealed that smoothed after completely reverted one. In turns, crack initiation sites propagation were modified between loading conditions. Considering stabilized use a Crossland criterion allowed to explain both effects ratio high cycle behavior steel. It turns out under studied conditions modifications state can be considered as primary factor governing varying performances observed triggering at different sites.