Phase equilibria in the Ni–Fe–Ga alloy system

The phase equilibria, A2/B2 and B2/L21 (or D03) order–disorder transitions and martensitic transformation on the Ni–Fe side of the Ni–Fe–Ga system were examined by electron probe microanalysis (EPMA) and differential scanning calorimetric (DSC) measurement. The equilibrium compositions of interrelations mainly among the α (A2), β (B2), β′ (L21 or D03), γ (A1) and γ′ (L12) phases were determined using diffusion triples which were fabricated by two-step diffusion coupling. It was confirmed that a bcc single-phase region composed of α, β and β′ at 850–1000 °C exists in a wide composition range and that the critical temperature of the B2/L21 order–disorder transformation in the Fe3Ga–Ni3Ga pseudo-binary section gradually increases with increasing Ni content. The existing composition region of the martensite phase at room temperature was also determined by the diffusion triple method.