Reversibility and thermal dependence of the martensitic transformation in a melt-spun Ni55Fe17Ga26Co2 Heusler alloy

An almost single phase 14 M modulated martensite is obtained in melt spun ribbon of Ni55Fe17Ga26Co2 Heusler alloy. The effect of thermal treatments on the stability of the reverse martensitic transformation from 14 M modulated martensite to austenite phase in this system has been investigated by both non-isothermal and isothermal treatments. Heating above martensitic transformation promotes a continuous reduction of the martensitic transformation temperature, which stabilizes the austenite phase at room temperature and induces the precipitation of the gamma phase. However, thermal treatments at temperatures between the austenite start and finish temperatures induce the decoupling of the austenite formation in a subsequent heating. The two successive reverse martensitic transformations could be ascribed to the untransformed martensite in the previous interrupted heating and to the new martensite formed during cooling.