Deformation by moving interfaces

Abstract

Quite large strains may be produced by the migration of glissile interfaces in processes such as deformation twinning, martensitic transformation, and variant conversion in a martensitic product. In the absence of appreciable dislocation glide, the atomic displacements associated with moving boundaries constitute highly ordered and reversible modes of either plastic or nonlinear pseudo-elastic deformation. Pure interface deformation is most readily obtained in specimens in which preexisting interfaces move under relatively small applied stresses and there are then well-defined limiting strains associated with a given distribution of interfaces, but in some alloys it is also possible both to nucleate and to grow reorientated or transformed regions at stresses lower than those at which dislocation deformation begins. Reversibility of interface-produced deformation leads to such phenomena as elastic twinning, thermoelastic martensite, superelasticity, shape memory and two-way (or reversible) shape memory effects, and rubber-like (or ferro-elastic) behavior. It now seems possible to provide a unified description of these effects and to include discussions of the strains which may be obtained from various interface configurations, the competition between dislocation and interface-produced deformation, the importance of elastic accommodation, geometrical and atomic models of coherent and semicoherent interfaces and of twinning and transformation dislocations, and the mechanisms of nucleation and growth.