The Effect of DSC Heating and Cooling Rate on the Evolution of Transformation Characteristics in NiTi-based Shape Memory Alloys

Calorimetric measurement is a widely applied method to determine the transformation temperatures in NiTi-based shape memory alloys and the release and uptake of heat during a phase change which provides an estimation of the quantity of transformed material. As recommended by the standard practice ASTM F2004-10, DSC experiments on NiTi alloys are performed at a moderate heating and cooling rate of 10°C/min which allows for a decent signal sensitivity and testing reproducibility. This facilitates the comparison of results achieved by different research groups and institutions. However, it is well known that the transformation peak position and morphology depends on the applied heating/cooling rate and thus, a faster or slower rate may alter the resulting key temperature parameters like onset and offset points of transformation and also the recorded heat dissipation. This research work presents a comparative study with the aim to bring out the effect of varying heating/cooling rate on the sensitivity of the most important key parameters like transformation temperature, thermal hysteresis and transformation enthalpy obtained by DSC measurements for NiTi-based shape memory alloys with binary and ternary compositions in as-cast or processed conditions. It is shown that both composition and thermo-mechanical treatment affect DSC results to a different extent and therefore significantly impact the interpretation of the shape memory effect.