Stress-induced phase transformations and enhanced plasticity in copper-aluminium and copper-aluminium-zinc martensites

Abstract

The effect of deformation on the structure of the-type martensite has been studied in copper-aluminium and copper-aluminium-zinc alloys by X-ray analysis and mechanical testing. This study has yielded information on the stability of the crystal structure of-type martensite, i.e. the tendency of the stress-induced transformation to the fcc structure, as zinc is added in increasing amount to copper-aluminium. The detailed study of the X-ray powder diffraction patterns of the as-quenched martensites showed that as zinc is added in increasing amounts, the structure of the-type martensite becomes distorted and shows an increasing degree of orthorhombic distortion (i.e. deviation from the trigonal symmetry). When these martensites are plastically deformed, the structure is transformed more and more easily into an fcc lattice, i.e. the volume fraction of the fcc phase increases with zinc content. Tensile tests showed that the martensite showed higher and higher elongation values, when plastically deformed, which is due to the progressive increase in fcc phase.status: publishe