Multi-scale deformation behavior investigation of 18Cr-8Ni austenitic steel subjected to low-cycle fatigue loading

Fully reversed total-axial-strain-controlled low-cycle fatigue (LCF) tests have been conducted in air at room temperature on polycrystalline 18Cr-8Ni austenitic stainless steel samples. The cyclic deformation behavior was determined by analysis of the hysteresis loop associated with cyclic straining. Three types of hardness measurements, namely nano-indentation, micro-indentation and conventional Vickers hardness tests, with the indent size ranging from several tens of nm to several tens of μm, were performed on the cyclically deformed specimens to investigate the characteristics of the deformation resistance at various scales. A linear increasing dependence of the local deformation resistance on the applied strain amplitude was observed at both macro- and meso-scales. This local resistance corresponds with the dependence of the bulk deformation resistance on the imposed strain amplitude; however, no significant change in the deformation resistance at nano-scale was found among various strain amplitudes. Both the slip band and the dislocation structure in specimens cyclically deformed at various strain amplitudes were correlated with the multi-scale deformation resistance.