Abstract
-
Martensiteplates in β′1 shape memory alloys commonly form self-accommodating groups of four plate variants with habit plane normals clustered about a {1 1 0} pole of the parent phase. In the present work, the crystallography of martensitic transformation in a Cu-Al-Ni-Mn shape memory alloy has been investigated with particular emphasis on accurate habit plane determination. The characteristically high martensite start (Ms) temperature of β′1 alloys makes it impossible to analyse samples containing isolated plates within a β1 grain at ambient temperature. However, the parent β1 grain orientation has been determined in this work by means of a new method of junction plane trace analysis, which is based on the knowledge that the junction planes are precisely {1 1 0}β1 planes. The mutual consistency of the experimental results indicates that this technique of junction plane traces analysis is a viable method for determining the parent β1 grain orientation. Habit plane normals were determined by two surface trace measurements and referred to the parent crystal basis by using the β1 grain orientation matrix. The habit plane normal was determined to be close to {1 5 5}β1 with the scatter in a series of mean value determinations being less than ± 1.2°.