X-ray diffraction studies of the reversible phase transformation in NiTi shape memory alloy

In the present paper the phase transformations occurring in hot worked and heat-treated Ni-rich NiTi shape memory alloy were studied using X-ray diffraction, differential scanning calorimetry and bend and free recovery measurements. Based on conducted measurements it can be seen that in the studied alloy two-step B2 ↔ R ↔ B19' phase transitions occurred. Due to the fact that during heating the phase transition B2 → R and R → B19' occurs in a very narrow temperature range and differential scanning calorimetry peaks overlap additional X-ray diffraction measurements were performed. Obtained characteristic temperatures from applied different experimental methods are in good agreement. The optimum heat-treatment was selected to obtain rods with a shape recovery temperature A_{f} below 37°C to prepare prototypes of medical implants activated by patients body heat.