Morphology and Crystallography of Thermoelastic Cu–Al–Ni Martensite Analyzed by the Phenomenological Theory

Abstract

The thermoelastic martensite transformation from the β₁ phase to the γ′ phase in Cu–Al–Ni alloy has been analyzed by the phenomenological theory, special attention being given to the understanding of the unique morphology. It is shown that there are a pretty good agreement between the theory and experiment with respect to the habit plane and the orientation relationship and a less good agreement with respect to the relative twin width, for δ=1. The unique “spear-like” morphology of the martensite was found to be consistent with the theory when it is applied in the two variants independently with a different lattice correspondence, and the morphology is fully explained from crystallographic aspects. Finally, the reason why the martensites take the spear-like form in the present alloy is explained as a result of the self-accommodation effect so as to minimize the strain energy set up by the formation of martensites, by using the result of the phenomenological calculations.