Thermal and structural analysis of Ni50Mn50−xInx shape memory alloys

Abstract

Due to the high cost and low martensitic transformation temperature of Gallium as the basis for the most extensively studied Heusler alloys, the search for Ga-free alloys has been recently undertaken, particularly by introducing In, Sn or Sb. Therefore, three-shape memory alloys were obtained by rapid solidification: Ni0.5Mn0.5-xInx (x=0.12, 0.13 and 0.14).The thermal and structural analyses were performed by differential scanning calorimetry (DSC), X-ray diffraction (XRD) and electron microscopy scanning (SEM), which were applied to determine the martensite transformation. The structural transformations were found to be of austenitic-martensitic character, with the transformation temperatures decreasing with the increase of In content. The austenite state was proven to have a cubic L21 structure and the martensite was found to possess a monoclinic 10M structure. The obtained results have revealed that the control of the valence electron by atom (e/a) determines the functional properties displayed by these alloys near room-temperature and it is possible to develop alloys that can be candidates in a variety of applications such as sensors and actuators. Likewise, the entropy and enthalpy change linked to transformation are lower for Ni50Mn36In14 alloy.