In situ characterization of martensite variant formation in nickel–titanium shape memory alloy under biaxial loading

Martensite morphology in a NiTi alloy under uni- and biaxial loading was studied in situ using high-resolution microscopy, electron backscatter diffraction and local strain analyses. The results obtained clearly indicate that a different martensite morphology, including a higher number of martensite variants, evolved in NiTi under biaxial stress states. However, the phase transformation was still triggered by shear stresses, eventually affecting deformation and fatigue-related phenomena.