Pseudoelasticity in Au-Cu-Zn thermoelastic martensite

Abstract

Pseudoelaatioity in quasibinary Au-Cu-Zn alloys (e/a = 1·45, 1·46, 1·47 and 1·48) was studied by an analysis of stress-strain curves, and explained on the basis of lattice softening. The growth morphology of stress-induced martensite was observed, and its crystal structure and axial ratio were found to be an orthorhombic structure (2H) and a : b : c = 0·66 : 1·09 : 1, respectively. The superelasticity of the martensite phase was recognized, and this behaviour was explained as the looking interaction between the mobile twin boundaries of half-dislocations and lattice defects produced by the martensitic transformation. It was discovered that creep has an anomalous influence on the stress-strain behaviour of Au₂₆-Cu₂₇-Zn₄₇ alloys. The anomalous effect, in which the critical stress increased and the plateau length diminished after creep, can be explained on the assumption that embryos for martensites are exhausted by the diffusional process, and that the activation of embryos takes place in sequence.