The triggering mechanism of the martensitic transformation

Abstract

The martensitic transformation involves, at least partly, a shear deformation of the parent lattice. Because the assumption that the martensitic transformation represents a macroscopic shear instability of the parent solid is at variance with experimental observations, the shear instabilities must be microscopic in nature. A model based on the dynamics of a dislocation stacking fault configuration (DSFC) adequately describes previous data as well as our own observations of a sharp decrease of the elastic constants of a Fe-28 wt pct Ni alloy just prior to the onset of the transformation. In terms of this model, theMs temperature represents the temperature at which the dislocation stacking fault configuration becomes thermodynamically unstable. In terms of the present harmonic approximation, the unhindered expansion of the DSFC will therefore trigger the martensitic transformation.