Twin/domain pattern memory in aged Au-49.5Cd martensite

We performed in-situ optical microscopy observations on a Au-49.5Cd single crystal during heating/cooling and tensile loading/unloading runs. We found that for aged martensite domain pattern can be reproduced or memorized during heating/cooling or stress loading/unloading runs. This mesoscopic memory effect contradicts the basic notion of martensitic transformation that variants/domains are crystallographically and energetically equivalent. It points to the interaction of point defects with martensitic transformation. We show that the interesting mesoscopic memory effect can be fully explained by a general symmetry property of point defects, the symmetry-conforming short-range order property (Ren and Otsuka, Nature, 1997).