Phase equilibria and phase transformation of Co-Ni-Ga ferromagnetic shape memory alloy system

Phase equilibria and martensitic and magnetic phase transformations of theβ phase in the Co-Ni-Ga system have been investigated. It has been shown that the β phase is in equilibrium with the α-phase over a wide range compositions at 600-1100°C. The β phase exhibits both a paramagnetic-ferromagnetic transition and a thermoelastic martensitic transition from B2 to L1₀ structure. The Curie temperature T _C increases with decreases in both Ni and Ga content, and the martensitic transition starting temperature M_s decreases with decreasing Ni content and with increasing Ga content. The composition region of the β phase exhibiting the thermoelatstic martensitic transformation from ferromagnetic austenite is located near the a + β two-phase region. T _C and _s of α + β two-phase alloys increase with increasing annealing temperature.