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

The phase equilibria between gamma (Al) and gamma' (L1(2)) 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 gamma to gamma' ordering reaction exhibits first-order characteristics with the gamma + gamma' two-phase field and that the Curie temperature of the gamma' ordered phase shows higher deviation from that of the gamma disordered phase. Thermodynamic stability of the gamma' phase was discussed in terms of atomic and magnetic orderings, and the gamma/gamma' transition temperature in paramagnetic state for Ni3Fe phase was estimated by extrapolation to the Ni3Fe side in the pseudobinary sections. (C) 2004 Elsevier Ltd. All rights reserved.