Low cycle fatigue of 316L stainless steel processed by surface mechanical attrition treatment (SMAT)

In this work, the effect of surface mechanical attrition treatment (SMAT) on the cyclic behaviour of a 316L stainless steel under low cycle fatigue (LCF) is investigated. The LCF results are presented in the form of cyclic stress amplitude evolution for both untreated and SMATed samples. In order to better understand the microstructure change due to cyclic loading, electron backscatter diffraction (EBSD) is used to characterize the microstructure of the SMATed samples before and after fatigue tests. A microstructure gradient is highlighted for samples after SMAT from the top surface layer in nanocrystalline grains to the interior region non-affected by impacts. Under LCF loading, new slip systems are activated in the work hardened region, whereas no plastic slip is activated in the nanostructured layer. The residual stresses generated by SMAT are measured using X-ray diffraction (XRD), and their relaxations under cyclic loading are studied by taking into account the microstructure change. The cyclic behaviour of the samples in different material states is interpreted based on these investigations.