Cubic-Tetragonal Transformation and Shape Memory Behavior in Indium-Thallium and Indium-Cadmium Alloys

Abstract

The phase transformations in the In–Tl and In–Cd alloys have been studied by means of X-ray diffraction topography supplemented by X-ray and electron diffraction and metallographic techniques. Both alloys, when cooled to room temperature at a normal cooling rate, transform from the face-centred cubic to the face-centred tetragonal structure. The transformation is martensitic in the sense that no diffusion is involved. Tetragonal alloys show a banded structure due to transformation twinning parallel to (101) planes. Both alloys exhibit a shape memory effect when heated to a moderate temperature. It is shown from the structural observations that the shape recovery is associated with the reversion of twinned bands and also with the annihilation of the twinned structure. Intensive thermal diffuse scattering is observed on {101} planes in the reciprocal lattice and ascribed to transverse acoustic phonon modes with low frequencies. The mechanism of phase transformation and the microscopic nature of atomic movements of the phase transformation are discussed on the basis of lattice vibrations.