The crystallography of the β-TO-β″ AuCd martensitic transformation

The crystallography of the martensitic transformation in near-equiatomic AuCd alloys is re-examined, experimentally and theoretically, from the viewpoint that the low-temperatureβ″ phase has either trigonal or hexagonal symmetry. The elements of the Bain strain accompanying the transformation are found to be smaller than those reported for any other metallic system. As a result, only the habit plane and the twin ratio are useful quantities for characterizing the transformation. Predictions of the present study are in accord with existing measurements of these quantities. The reported lattice correspondence is believed to be unique for the martensitic transformation of a beta phase alloy.