Non-equilibrium martensitic transformation in metamagnetic shape memory alloys

The martensitic transformation (MT) in ferromagnetic and metamagnetic shape memory alloys can be induced by changing the temperature or stress but also by applying a magnetic field. In this work, some non-equilibrium processes that take place in a Ni–Mn–In–Co metamagnetic shape memory alloy will be analyzed. The retained austenite at low temperatures under a magnetic field evolves to martensite as soon as the field is removed or reduced. The reduction in the applied field, apart from an instantaneous phase change, leads to a time dependent evolution of the transformed fraction. In addition to the field-related evolution of retained austenite, the cyclic magnetic field induced reverse MT will be analyzed as a function of temperature. The magnetic field induced martensitic transformation (MFIMT) fraction induced at constant temperatures depends on the distance to the equilibrium state: states farther from equilibrium promote larger MFIT fractions.

► We analyze the capacity to produce magnetic field induced martensitic transformation (MFIMT) in metamagnetic shape memory alloys. ► The retained austenite obtained during a magnetic filed cool process evolves to martensite as soon as the field is removed or reduced. ► The lower is the temperature the higher is the fraction of retained austenite at after a zero field cool process. ► The partial MFIMT induced at constant temperatures depends on the deviation of the system from the equilibrium state: at each temperature, the further the material is from the equilibrium state, the more complete is the MFIMT.