Time-dependent nature of the athermal martensitic transformations in FeNi alloys

Abstract

Martensitic transformations are well known to be classified into two groups, with respect to kinetics, athermal and isothermal ones. The former transformation has a definite transformation start temperature, Ms, and occurs instantaneously at Ms, while the latter one does not have a definite Ms temperature but occurs after some finite incubation time during isothermal holding. Hereafter, the authors call the transformation processes in isothermal and athermal martensitic transformations as the isothermal and athermal transformation ones, respectively. So far the two transformation processes have been considered to be intrinsically different than each other. Recently, the authors found that even in the Fe-Ni-Mn alloy exhibiting an isothermal martensitic transformation, a martensitic transformation occurs instantaneously under high magnetic fields, as in the athermal martensitic transformation. This means that the isothermal martensitic transformation changes to an athermal one under high magnetic fields, suggesting that the two transformation processes are closely related to each other and their difference is not intrinsic but may be explained by one basic rule.