Self-Accommodation Structure in the Ti-Ni-Cu Orthorhombic Martensite

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 a 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.