On the nature of the martensitic transformation

A novel conceptual approach to martensitic transformation is presented. The current concepts are discussed briefly, and a more general qualitative approach to this type of phase change is proposed. It is suggested that the transformation originates in lattice vibration modes, and that once initiated it proceeds adiabatically with no discernible division into nucleation and growth. The transformation does not occur through a dislocation mechanism, and the high dislocation densities observed as associated with martensite formation consist of immobile dislocations. These form to accommodate the transformation strains which are highly localized, but are also self-accommodating and on completion of the transformation are macroscopically nondirectional. All of the anomalies in the mechanical properties reported in the past are ascribed to the effects of an applied stress on the transformation. It is suggested that investigations of such effects on transformation, particularly in single crystal material, should be most fruitful in providing new fundamental insight into the mechanism of the transformation.