Influence of cooling and heating rates on the thermal properties of Ni-Ti shape memory alloy

The near-equiatomic NiTi shape memory alloy has many unusual thermo-mechanical properties which are dependent of various parameters such as heat treatment, manufactoring process, chemical composition... The determination of these unique properties is indispensable for studying the behavior of this alloy under different thermal, mechanical or thermo-mechanical stresses. In this paper, the study is focused on the effect of the cooling and heating rates on the thermal properties of the NiTi alloy during its phase transformation cycle. This experimental work is based on the differential scanning calorimetry (DSC) as a thermal analysis method. Calorimetric results show that by increasing the cooling/heating rates from 5°C/min to 20°C/min, Mf, the temperature which characterizes the end of direct martensitic transformation, decreases significantly. The absorbed and released heats during phase transformation also increase under the increase of this parameter. These results takes us to deduct the influence of this parameter on the thermal hysteresis of this material.