Viewpoints on Microscopic and Mesoscopic Transformation Processes in Martensite

Abstract
The purpose of this presentation is to provide some perspective gained from recent studies in condensed matter physics on the microscopic processes by which martensitic transformations take place to supplement the highly developed crystallographic and thermodynamic descriptions. Atomic scale dynamics can be related to mesoscale pattern formation, in idealized systems, and the energies of twin boundaries and ferroelastic patterns can be computed from such data, at least in principle. An overview of the formalism used utilizing nonlinear and strain-gradient elasticity is given. Yet in reality probably all transformations of laboratory or manufactured materials are controlled by defects. An approach to the defect situation based on the framework developed for the idealized martensite is given. Finally a few remarks are made relating this general viewpoint to shape memory materials.