Stability of ordered L1₂ phase in Ni₃Fe-Ni ₃X (X:Si and Al) pseudobinary alloys

The phase equilibria between γ (A1) and γ′ (L1 ₂) in Ni₃Fe-Ni₃Si and Ni₃Fe-Ni ₃Al 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 Ni ₃Fe side in the pseudobinary sections.