Study of Thermal Scanning Rates on Transformations of Ti-19Nb-9Zr (at.%) by Means of Differential Scanning Calorimetry Analysis

Differential scanning calorimetry (DSC) thermal analysis is a well-accepted technique used to measure the transformation temperatures of shape memory alloy and its thermoelastic transformation energies. In this study, both forward and reverse transformation temperatures of a nickel-free Ti-19Nb-9Zr (at.%) SMA were investigated using DSC technique with different cooling and heating scanning rates in a range of 10 to 100 °C/min. The results showed that the transformation temperature intervals vary substantially with respect to the thermal scanning rates. It is found that the martensitic start (M _s) temperature decreases with decreasing the cooling rates. The optimal scanning rate was found to be 40 °C/min for obtaining the maximum thermoelastic transformation energies stored between the forward and the reverse martensitic transformations. It is believed that the thermoelastic transformation energy increases with the increase in the volume fraction of martensite. Based on these measurements, these thermoelastic transformation energies between the forward and the reverse martensitic transformations were estimated to be ~21 and ~27 J/g, respectively. The appropriate selection of scanning rate for SMA analysis will be discussed.