Effects of strain amplitude, cycle number and orientation on low cycle fatigue microstructures in austenitic stainless steel studied by electron channelling contrast imaging

Abstract

Substructure analysis on cyclically deformed metals is typically performed by time-consuming transmission electron microscopy probing, thus limiting such studies often to a single parameter. Here, we present a novel approach which consists in combining electron backscatter diffraction (EBSD), digital image correlation and electron channelling contrast imaging (ECCI), enabling us to systematically probe a large matrix of different parameters with the aim of correlating and comparing their interdependence. The main focus here is to identify the influence of cycle number, initial grain orientation and local strain amplitude on the evolving dislocation patterns. Therefore, experiments up to 100 cycles were performed on a polycrystalline austenitic stainless steel with local strain amplitudes between 0.35% and 0.95%. EBSD and ECCI maps reveal the individual influence of each parameter while the others remained constant. We find that the dislocation structures strongly depend on grain orientation. Dislocation structures in grains with double-slip (〈112〉 // LD, 〈122〉 // LD and 〈012〉 // LD) and multiple-slip (〈111〉 // LD, M 〈011〉 // LD and 〈001〉 // LD) orientations with respect to the loading direction (LD) are characterized under the variation of strain amplitude and cycle number.