Relationship between Masing behavior and dislocation structure of AISI 1025 under different stress ratios in cyclic deformation

In a previous study, the hypothesis that dislocation arrangements do not change while Masing behavior occurs in materials was proposed. However, by validating the hypothesis via TEM observation, the authors incidentally found that dislocation structures are not always the same during Masing behavior. Therefore, the aim of this work was to understand the relationship between Masing behavior and dislocation structures using AISI 1025 under stress-controlled fatigue testing. In addition, to understand the more systematical relationship between Masing behavior and dislocation structures, three stress ratios, R=-1, -0.3 and 0, were applied, and each cyclic stress-strain curve (CSSC) was obtained for the first time. To investigate the Masing behavior, a new analytical method was proposed due to the difficulty of evaluating hysteresis loops with mean stress using previous methods. Based on the results, the dislocation structures are observed for the first time to determine whether the dislocation structures are same when Masing behavior occurs. As a result, the dislocation structures that exhibited Masing behavior were categorized into two types: (i) fully homogeneous dislocation structures and (ii) dislocation structures with a dual microstructure composed of cell and loop-patch structures, each of which exhibits a different volume fraction. The relationship between the CSSCs under stress ratios of R=-0.3 and 0 and the dislocation structures was examined. There are B and C regions in the CSSCs under stress ratios of R=-0.3 and 0. It was found that each dislocation structures shows loop-patch and cell structures. At the end of region C, a collapsed cell structure was observed.