LATTICE SOFTENING AND THE ORIGIN OF SME.

Abstract

″Lattice softening″ or ″Soft shear mode″ has recently been found in connection with the displacive or martensitic phase transition in thermoelastic alloys and compounds. In the beta //1 (ordered bcc) alloys such as CuAuZn//2 and AuCd, lattice softening appears as a premonitory phenomenon in thermoelastic martensitic transformation and it has an intimate relation to the essential character (shear mechanism and nucleation) of the thermoelastic martensite. Lattice softening is fundamental for understanding the mechanism of ″pseudoelasticity″ (superelastic and ferroelastic behavior), which has been observed to be closely related to SME. The author suggests that the origin of SME might be contained in superelastic behavior, which is a unique stress-strain feature observed upon deformation of both the beta //1 and martensite phases.