A Localized Soft Mode Theory for Martensitic Transformations

Anharmonic terms of the elastic free energy of a solid are used to locate a surface of instability or “strain spinodal”. The strains near lattice defects bring some regions close to the strain spinodal causing a rapid change in local elastic properties and resulting in localized “soft mode” centers. These regions are proposed as the primary nucleation sites for martensitic transformations. A number of experiments are proposed to test the physical aspects of the theory and some recent evidence is cited supporting several features of the model.