Chapter 21 - Characteristics of Martensitic Transformations

Abstract

This chapter defines the characteristic features of martensitic transformations, that is treated as an experimental criterion most useful for defining a martensitic transformation is the observation of a shape change in a transforming region. Some transformations involving diffusion may nevertheless have a coherent interface and a lattice correspondence that persists as the new phase grows. However, a shape change does imply a lattice correspondence and in most cases this means a martensitic transformation. If atomic interchange does not play a significant role in the mechanism of transformation, it indicates that the martensite must have the same chemical composition as the parent phase. The absence of atomic interchange is confirmed by the growth of martensite at very low temperatures and by the fact that ordered phases remain ordered after transformation. In the absence of diffusion, the atomic movements must be ordered and coordinated, and the neighbours of most atoms remain unchanged.