Effect of Ge addition on the martensitic transformation temperatures of Ni–Fe–Ga alloys

A systematical study of substitution of Ge for Ni, Fe, and Ga in the non-stoichiometric NiFeGa alloys was performed in this work. The effect of Ge addition on the structure and martensitic transformation in NiFeGa alloys was investigated by an optical microscope, X-ray diffraction, and differential scanning calorimeters. The results show that the transformation temperatures decrease almost linearly with increasing Ge content in all the three types from higher than 100 down to −90 °C and even lower. The decreases in rate of the martensitic transformation temperatures are different for the three cases. It is large for Ni substituted by Ge, slow for Ga and intermediate for Fe. The determined relationship will be significant for designing a suitable NiFeGa alloy with a required martensitic transformation temperature for application at specific temperature.