Structural and martensitic transformation of MnNiSn shape memory alloys

Ferromagnetic shape memory alloys are characterized by both the structural austenite to martensite transformation and also by the magnetic transition from ferromagnetic to paramagnetic. The set of properties makes them candidates for use in several applications such as sensors, actuators, or magnetic refrigeration systems. Among the Heusler-type alloys that exhibit this behavior, the most studied system is the Ni–Mn–Ga. However, to overcome the high cost of Gallium and the generally low martensitic transformation temperature, the search for Ga-free alloys has been recently attempted, particularly, by introducing Sn. The martensitic transformation and the solidification structures of Mn50Ni50−xSnx (x = 7, 8.7 and 10.5) ribbons prepared by melt-spinning were investigated by means of scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry. While the As-spun alloys Mn50Ni43Sn7 and Mn50Ni41.3Sn8.7 displayed a single-phase (14-M monoclinic martensite) structure at room temperature, the As-spun and Mn50Ni39.5Sn10.5 displayed a single-phase cubic Heusler L21. The martensitic transformation temperatures were noted to decrease with the increase of Sn concentration.