In situ EBSD investigations of the asymmetric stress-induced martensitic transformation in TiNi shape memory alloys under bending

An inverse pole figure with tensile-compressive asymmetric Schmid factor (SF) was developed for TiNi shape memory alloys. The stress-induced martensitic transformation behaviors in polycrystalline TiNi alloys were directly visualized and mapped by in situ electron backscatter diffraction (EBSD) technique. The results clearly show that the stress-induced martensitic transformations sustaining tensile and compressive stresses are asymmetric. The observed results are well interpreted by the Schmid factor inverse pole figure (SFIPF). It was also suggested that the internal stress distribution, the inter-grain accommodation and the constrained effect on the polycrystalline system are additional factors impacting the formation and selection of stress-induced SF habit plane martensitic variants.