Crystallography, martensite morphology, surface relief and shape memory effect in a simple hexagonal to β-Sn martensitic transition of Sn-(7.0-9.5) at.% In alloys have been investigated. The structure of β-Sn martensite consists of thin and lenticular plates. New surface reliefs appear on the reverse transition after the forward transition; that is, incomplete reversibility of the atomistic sequence of the transition has been found. Correspondingly, the degree of a shape memory effect is small. The orientation relationship between the simple hexagonal and β-Sn structures, (0001)s.h.//(100)β-Sn and [1̄21̄0]s.h.//β-Sn, has been determined. From these results, the mechanism for the martensitic transition has been proposed; simple atomic displacements corresponding to 1 2 〈101̄1〉 transverse phonons with polarization vectors along the 〈1̄21̄0〉 directions induce the transition. This mechanism predicts the formation of three types of transformation twins constituting substructures and can explain the incomplete crystallographic reversibility of the transition.
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