Self-accommodating martensite plate variants in shape memory CuAlNi alloys

Abstract

In noble metal copper-based β-phase alloys, which exhibit the shape memory effect, martensitic transformation occurs by lattice invariant shears on close-packed {1 1 0} β planes of the matrix, called the basal plane of the martensite. The parent single crystal undergoes the martensitic transformation on cooling in a self-accommodating manner minimising the total shape change at the advanced stage of the transformation. These alloys are deformed by variant-to-variant transformation when stressed in the martensite state. The reversible shape memory effect is also considered in terms of the correspondence-variants and the formation of each martensite is accompanied by a definite shape deformation. The so-called self-accommodation is achieved by combining suitable correspondence-variants. In a single crystal of the parent phase, 24 martensite variants grouped around six {1 1 0} β planes can be formed at temperatures lower than M s. In the present study, configurations of the martensite variants in CuAlNi alloys have been investigated by an electron microscope technique.