Processing and Characterization of Ni2MnSn FSMA

Abstract

Among Ferromagnetic Shape Memory alloys (FSMAs), Ni2MnSn Heusler alloys owing to occurrence of large magnetic field induced strain (> 10%) along with other interesting properties like premartensitic transition, high transformation temperature, large magnetocaloric effect and low stress of twin variant rearrangement. The prominent challenges facing the design and utilization of these specialized alloys are a limited range of operating temperatures, phase transformations that have high sensitivity to variations in composition, brittleness of the alloys, and changes in transformation temperatures. The functional behaviors of these alloys are as actuators, magneto-mechanical transducers, switching devices, etc. In the present study, the martensitic microstructures of Ni50Mn37.5Sn12.5 FSMAs are investigated by optical microscopy, X-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. Among the most important martensites that exist in these alloys are the 5M tetragonal, 7M orthorhombic (modulated structures) and NM tetragonal (non-modulated structure), etc. Differential scanning calorimeter is used for determining the transformation temperatures under zero stress. Crystal structures of the samples are determined by X-ray diffraction patterns using Cu-Ká radiations. Transmission electron microscopy study of this alloy revealed the presence of two martensite phases, i.e., modulated and non-modulated phases.

Keywords:  FSMA, Ni2MnSn, transformation temperature