Effects of hydrostatic pressure and magnetic field on martensitic transformations

Abstract

Abstract Martensitic transformations are extensively influenced by external fields, such as temperature and uniaxial stress, modifying transformation temperatures, crystallography and amount and morphology of the product martensites. Therefore, in order to clarify the effect of external fields on martensitic transformations it is very important to understand the essential problems of the transformation, such as thermodynamics, kinetics and the origin of the transformation, whose information is naturally useful for those technological application fields in which the transformation is used. Hydrostatic pressure and magnetic fields are also important external fields because there exist some significant differences in atomic volume and magnetic moment between the parent and martensitic states. In the present paper, therefore, we summarize the effects of hydrostatic pressure and magnetic field on martensitic transformations in some ferrous and non-ferrous alloys by referring to past and recent works made by our group and many other researchers. Especially, we discuss the following six topics: (i) the effect of hydrostatic pressure on the martensitic transformation start temperature and the validity of a new equation proposed by our group to evaluate the relation between Ms and hydrostatic pressure; (ii) the morphology of martensite induced by a hydrostatic pressure; (iii) the effect of a magnetic field on the martensitic transformation start temperature, Ms, and the validity of another equation proposed by our group to evaluate the relation between Ms and the critical magnetic field, Hc, for inducing the martensitic transformation; (iv) the effect of a magnetic field on the magnetoelastic martensitic transformation in an ausaged Fe–Ni–Co–Ti shape memory alloy, which occurs only while a magnetic field is applied and disappears when the magnetic field is removed; (v) the effect of a magnetic field on the morphology and arrangement of martensite plates in Fe–Ni alloy single crystals; (vi) the effects of hydrostatic pressure and magnetic field on the martensitic transformation process.