Load path change on superelastic NiTi alloys: In situ synchrotron XRD and SEM DIC

The transformation behavior of commercial superelastic NiTi material was studied during uniaxial tension and load path changes by employing a novel miniaturized biaxial stage and cruciform shaped specimens. EBSD and X-rays are used to characterize the initial and final microstructure, in situ digital image correlation at the macro and micro length-scales and in situ X-ray diffraction are used to follow the transformation characteristics. The results reveal an initial microstructure where large austenitic grains are subdivided in bands containing nanoscaled sub-grains. The link between the microstructure and strain accommodation during transformation is detailed and discussed in terms of Schmid behavior and strain path. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.