DETERMINATION OF THE PARENT GRAIN-ORIENTATION AND HABIT PLANE NORMALSFOR BETA(1)' MARTENSITE IN A CU-AL-NI-MN SHAPE-MEMORY ALLOY

Martensite plates in beta(1)' shape memory alloys commonly form self-a ccommodating groups of four plate variants with habit plane normals cl ustered about a {110} pole of the parent phase. In the present work, t he crystallography of martensitic transformation in a Cu-Al-Ni-Mn shap e memory alloy has been investigated with particular emphasis on accur ate habit plane determination. The characteristically high martensite start (M-s) temperature of beta(1)' alloys makes it impossible to anal yse samples containing isolated plates within a beta(1) grain at ambie nt temperature. However, the parent beta(1) grain orientation has been determined in this work by means of a new method of junction plane tr ace analysis, which is based on the knowledge that the junction planes are precisely {110}(beta 1) planes. The mutual consistency of the exp erimental results indicates that this technique of junction plane trac es analysis is a viable method for determining the parent beta(1) grai n orientation. Habit plane normals were determined by two surface trac e measurements and referred to the parent crystal basis by using the b eta(1) grain orientation matrix. The habit plane normal was determined to be close to {155}(beta 1) with the scatter in a series of mean val ue determinations being less than +/-1.2 degrees.