Effect of f.c.c. antiferromagnetism on martensitic transformation in Fe–Mn–Si based alloys

By using resistance measurement and dynamic mechanical analysis, critical points of Fe–Mn–Si and Fe–Mn–Si based shape memory alloys (SMA) were determined and the effect of f.c.c. antiferromagnetism on the thermal and stress-induced martensitic transformation, i.e. f.c.c.(γ)→h.c.p.(ε), was studied. With the increase of Mn content in the alloys, critical points Ms, Mf, As and Af decrease and the Neel temperature TN increases until the thermal martensite has been suppressed completely. As the TN approaches Ms the f.c.c. antiferromagnetism will extend the temperature range of the martensitic transformation to −150°C. After the thermal martensite is completely suppressed by the antiferromagnetic state, the martensitic transformation can also be induced to a great extent by stress, as confirmed by the measurement of an internal friction peak during the reverse martensitic transformation.