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 M_s, M_f, A_s and A_f decrease and the Neel temperature T_N increases until the thermal martensite has been suppressed completely. As the T_N approaches M_s 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. © 1999 Elsevier Science S.A.