THE GAMMA-]EPSILON-MARTENSITIC TRANSFORMATION AND ITS REVERSION IN THE FEMNSICRNI SHAPE-MEMORY ALLOY

The hcp martensitic transformation and its reversion in an Fe-16.86Mn- 4.50Si-10.30Cr-5.29Ni alloy have been studied. The fine structure and morphologies of epsilon-martensite were systematically investigated us ing transmission electron microscopy. It is found that, in the overlap ped region of the stacking faults, the nucleus of epsilon-martensite m ay form by shear and grow along the {111} gamma plane, which is not th e stacking fault plane. The nucleus may grow into a small, thin plate and may act as the basal structure unit of epsilon-martensite. When th e stress increases, the thin plates continue to grow into an epsilon-m artensite ribbon along this preferred orientation and, during the subs equent recovery annealing, the reverse transformation of these basal s tructure units occurs. As a result, the epsilon-martensite plates shri nk in both length and thickness.