Influences of composition and annealing on the martensitic transformation in Ni-Fe-Ga alloys

A series of Ni-Fe-Ga alloys near the prototype Heusler composition (X2YZ) were prepared through arc-melting suction-casting method. The dependences of the transformation behavior on the alloy composition and annealing treatment were studied in detail by an optical microscope, X-ray diffraction, and differential scanning calorimeters methods. The experimental results show that the martensitic transformation temperatures increase almost linearly with increasing Ni content in all the NiFeGa alloys. Annealing the Ni55.5Fe18Ga26.5 alloy at 100–500 °C for 3 h and at 300 °C for 1–10 h shifts the martensitic transformation start temperature by almost 20 °C to high temperature. The variations in the martensitic transformation temperatures in these alloys are discussed in terms of structural differences resulting from alloy composition and annealing treatment.