Ferromagnetic shape memory alloys with a body-centered-cubic ordered structure in a Ni–Ga–Fe system have been developed. The alloys with the composition range of Ni 27 at. % Ga (20–22 at. %)Fe exhibit a thermoelastic martensitic transformation from a B2 and/or an L21 parent to a martensite phase, with a seven-layer modulated (14M) and a five-layer modulated (10M) structure, in the ferromagnetic state. The parent phase transforms from the B2 to the L21 structure at about 970 K during cooling, and the degree of the L21 order in the parent phase is increased by annealing at 773 K, resulting in the increase of both the martensite starting and the Curie temperatures. The ductility of these alloys is improved by introducing of a small amount of a γ-phase solid solution. Consequently, we can conclude that the present alloys are promising for ferromagnetic shape memory alloys.

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The martensitic and magnetic transitions of Ni 54 Ga 27 Fe 19 alloy were investigated by differential scanning calorimetry and X-ray powder diffraction and with a vibrating sample magnetometer. The alloy is martensitically transformed from a L2 1 to a martensite phase with a 14M (7R) structure. The ferromagnetic transition is also accompanied by the martensitic transformation from a paramagnetic parent phase to a ferromagnetic martensite phase in the temperature interval between M s (= 293 K) and M f (= 274 K). The Ni-Ga-Fe system is promising as a ferromagnetic shape memory alloy.

The effects of the introduction of the (A1) phase into the (B2) phase on the mechanical and shape memory properties in ferromagnetic Co-Ni-Al shape memory alloys with the þ 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 phase, and Co-33 at%Ni-26 at%Al alloy with V ¼ 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 phase, it can be enhanced by training. Since two-phase þ 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).

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