Phase equilibrium of ferromagnetic shape memory alloy Co39Ni33Al28

Co39Ni33Al28 ribbon with a β phase structure, which exhibited a martensitic transformation to L10 phase, was found to be unstable and decomposed into a β + γ phase mixture upon heating to above 973 K. The double-phase structure was found to exhibit no martensitic transformation, despite the presence of the β phase. This is ascribed to the change of the β phase composition due to the formation of the γ phase. Annealing of the decomposed sample at 1473 K, followed by rapid cooling, was effective in restoring the B2 → L10 martensitic transformation.