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

Abstract

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.