On the Burgers vector of dislocations produced by a cyclic b.c.c./9R martensitic transformation

Abstract

The Burgers vector of dislocations produced by a cyclic b.c.c./9R martensitic transformation has been studied by electron microscopy, using a Cu-39·26 Zn (at.%) alloy. The Burgers-vector analysis was made by the image matching method, because the conventional method utilizing a vanishing condition of g · b = cannot be applied, owing to a well known large elastic anisotropy of the alloy used. The results show that most of the dislocations have <100>_b.c.c. Burgers vectors and lie on {011}_b.c.c.. The formation mechanism of those dislocations is discussed in detail, and it is concluded that the origin for the generation of the dislocations is the internal stress due to a volume change accompanied by the transformation. A mechanism for the dislocation formation proposed previously by Kajiwara and Kikuchi is found to be inadequate for the present case. The above conclusion may give an important suggestion on how to improve the fatigue resistance of shape memory alloys.