Thermal history and abnormal thermal-expansion of Fe₃Ga alloy

Fe₃Ga oriented crystals alloy Fe_72.5Ga_27.5 was prepared by optical zone melting method. Two heat treatment ways were as follows, one is 1100℃ for 4 h, the other is 1100℃ for 1 h and 500℃ for 3 d and 350℃ for 15 d. Phase composition and thermal expansion of Fe_72.5Ga_27.5 alloy were investigated after the two heat treatment processes. The results show that Fe_72.5Ga_27.5 alloy contains single D0₃ phase. Samples annealed at 1100℃ for 4 h are composed of two-phase mixture of D0₃ and L1₂. Single L1₂ phase can be obtained for long time aging (500℃ for 3 d and 350℃ for 15 d) after diffusion-annealing at 1100℃. There is a co-occurrence of magnetic transition and phase transition of L1₂ type Fe₃Ga alloy between 600℃ and 645℃. This phenomenon gives rise to abnormal thermal-expansion (near zero expansion) of Fe₃Ga alloy near the transition temperature.