Fatigue behaviors of AISI 316L stainless steel with a gradient nanostructured surface layer

By means of surface mechanical rolling treatment (SMRT), a gradient nanostructured (GNS) surface layer was formed on AISI 316L stainless steel. The mean grain size is similar to 30 nm in the topmost surface layer and increases with depth. Tension compression fatigue measurements were performed on the SMRT sample under the stress-controlled mode. In comparison with the coarse-grained sample, the fatigue strength of the SMRT sample is significantly enhanced in both the low- and high-cycling fatigue regimes. Meanwhile, the fatigue ratio is evidently elevated with an increasing tensile strength in the SMRT sample. The initiation and growth of cracks, the cyclic deformation behaviors, as well as effects of strength and residual stresses, have been investigated to clarify the fatigue mechanism of the SMRT sample. The results emphasized the GNS surface layer enhances the fatigue property by suppressing the initiation of cracks and accommodating a remarkable cyclic plastic strain amplitude. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.