Ferromagnetic Co-Ni-Al Shape Memory Alloys with β+γ Two-Phase Structure

The effects of the introduction of the γ (A1) phase into the β (B2) phase on the mechanical and shape memory properties in ferromagnetic Co-Ni-Al shape memory alloys with the β+γ two-phase structure were investigated by cold-rolling, tensile tests, and bending tests. The mechanical properties were found to be improved with an increase in the volume fraction of the γ phase, and Co-33 at%Ni-26 at%Al alloy with Vγ=36% exhibited excellent cold workability with a critical reduction ratio of 40%. Although the degree of shape recovery decreases with an increase in the volume fraction of the γ phase, it can be enhanced by training. Since two-phase β+γ Co-Ni-Al alloys have several advantages such as cost efficiency and workability, this alloy system is considered as being a new type of ferromagnetic shape memory alloys (FSMAs).