Temperature-dependent behavior of a polycrystalline NiTi shape memory alloy around the transformation regime

The mechanical and microstructural behavior of a polycrystalline Ni49.9Ti50.1 (at.%) shape memory alloy was investigated as a function of temperature around the transformation regime. The bulk macroscopic responses, measured using ex situ tensile deformation and impulse excitation tests, were compared to the microstructural evolution captured using in situ neutron diffraction. The onset stress for inelastic deformation and dynamic Young’s modulus were found to decrease with temperature in the martensite regime followed by an increase starting near the austenite start temperature, attributed to the reverse transformation.