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 beta + gamma two-phase structure. The beta(B2) phase of the Co-33Ni-27Al and Co-34Ni-28Al alloys exhibits both paramagnetic/ferromagnetic transition and a thermoelastic martensitic transformation from beta to beta' (L1(0)). The microstructure of both alloys shows the primary beta phase surrounded by the gamma (A1) phase which brings about the drastic effect in die improvement of the hot workability. By annealing in the two-phase region after solution treatment, the gamma phase precipitates along grain boundaries in the beta phase, besides in the beta 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.