Development of the Co-Ni-Al ferromagnetic shape memory alloys

Ferromagnetic shape memory alloys have been developed in the Co-Ni-Al ternary system with β + γ two-phase structure. The β(B2) phase of the Co-33Ni-27Al and Co-34Ni-28Al alloys exhibits both paramagnetic/ferromagnetic transition and a thermoelastic martensitic transformation from β to β' (L1₀). The microstructure of both alloys shows the primary β phase surrounded by the γ (A1) phase which brings about the drastic effect in the improvement of the hot workability. By annealing in the two-phase region after solution treatment, the γ phase precipitates along grain boundaries in the β phase, besides in the β grain. The alloys annealed at 1273 K showed a good cold workability and a thermal activated shape memory effect. These ferromagnetic and ductile shape memory alloys are very promising for one of the new smart materials.