Phenomenological theory of martensitic and reconstructive phase transitions

Abstract

The review deals predominantly with a description of martensitic phase transitions on the basis of Landau theory, using the strain of a crystal as the order parameter and the expansion of energy in powers of the strain and its gradients. The important role of compatibility equations for strain tensor components in minimizing the free energy is shown. Various models which allow for localized solutions of the nonlinear minimization equations are considered. Soliton and kink-type solutions are interpreted as the solutions representing inclusions of the martensite phase in austenite and domain boundaries between adjacent martensite domains or interfaces between martensite and austenite. For the simplest models, the shape of martensite inclusions—or that of localized objects within the pretransition region—as well as their orientation in the crystal and the orientation of domain boundaries, are determined. The role of specific atomic displacements which accompany spontaneous lattice deformations in the course or martensitic transitions, is studied.

Further in the review, the crystallography of reconstructive phase transitions of bee-fcc, bcc-hep, fcc-hep types is expounded, and types of the strain and atomic displacements corresponding to these transitions are determined. For such transitions, a brief account is given of the approach based on consideration of martensite inclusions in an austenite matrix using linear elasticity theory and it is shown how it can be used in describing martensitic transition morphology. In the conclusion, the yet unsolved problems of phenomenological theory are formulated.

Key Words:

• Martensitic transitions
• reconstructive transitions
• phenomenological theory.