Stability of ordered L12 phase in Ni3Fe–Ni3X (X:Si and Al) pseudobinary alloys

The phase equilibria between γ (A1) and γ′ (L12) in Ni3Fe–Ni3Si and Ni3Fe–Ni3Al pseudobinary sections were investigated to evaluate the interaction between the chemical and magnetic orderings on phase stability. Order–disorder and Curie temperatures in these sections were determined by means of metallographic observation, electron probe microanalysis, differential scanning calorimetry, electrical resistivity and vibrating sample magnetometry. It was clarified that the γ to γ′ ordering reaction exhibits first-order characteristics with the γ+γ′ two-phase field and that the Curie temperature of the γ′ ordered phase shows higher deviation from that of the γ disordered phase. Thermodynamic stability of the γ′ phase was discussed in terms of atomic and magnetic orderings, and the γ/γ′ transition temperature in paramagnetic state for Ni3Fe phase was estimated by extrapolation to the Ni3Fe side in the pseudobinary sections.