Self-accommodation structure in the Ti-Ni-Cu orthorhombic martensite

Abstract

Self-accommodation process and the resulting structure of the orthorhombic martensite in a Ti-Ni-Cu shape memory alloy were investigated. Observations of the self-accommodation process of habit plane variants of the orthorhombic Ti-Ni-Cu martensite were made by transmission electron microscopy, and the three-dimensional configuration of the variants resulting from self-accommodation was analyzed. The results obtained are as follows. (1) The fundamental unit of the self-accommodation structure in three dimensions is cuboidal, consisting of six different variants. This structure appears to be triangular when observed in the 〈111〉P direction (P: Parent). (2) The six variants are twin related with each other and two types of twin relations exist among them. One is the (111)M[211]M type I twin and the other is the (011)M[011]M compound twin (M: Martensite). Then, on the basis of the observed relations among the variants the deformation process of the orthorhombic martensite was discussed.