Martensitic transformations and kinetics in Ni-Mn-In-Mg shape memory alloys

The martensitic transformation (MT) and its kinetics in Ni-Mn-In-Mg shape memory alloys (SMAs) were calculated for the first time. The differences in the phase transition processes of alloys with various Mg contents were analyzed using two different models, and their microstructures were investigated using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). As the Mg content increased, the grain size decreased, and the MT temperature and activation energy increased significantly due to the grain refinement of the second phase. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation was used to simulate the MT time-temperature-transformation (TTT) curves of the alloys, which exhibited the same trends as the DSC test results. To study the dependence of the activation energy on the heating rate, DSC studies were conducted using nine different heating rates to study the kinetics of the thermally induced transformation process. It was clarified that the heating rate could adjust the phase transition temperature and significantly affect the activation energy, indicating that the heating rate can be used as a method for adjusting the phase change parameters. Moreover, for the same alloy system, using the same heating rate is a useful means of comparing activation energies. This study provides a reference for designing and calculating the kinetics of Ni-Mn-In memory alloys.