SHAPE RESTORATION EFFECT ASSOCIATED WITH ORDER-DISORDER TRANSFORMATION IN EQUIATOMIC AUCU AND AUCU-GA ALLOYS

Shape restoration effects associated with order-disorder transformatio n in equiatomic AuCu and Au0.47Cu0.47Ga0.06 alloys were examined by me ans of surface roughness measurements of sheet specimens and the chang e in the distance between tips of U-shaped specimens. The specimen sur face became irregular and a macroscopic shape change occurred after an ageing heat treatment. The shape change was attributed to the heterog eneity in the deformation which arose from the stress release by twinn ing at the free surface. After disordering of the age-hardened specime n, they regained completely to its original shape. When the specimen w as aged without any constraint, spontaneous deformation occurred and d id not result in any given shape. However, when the external stress wa s applied during ordering heat treatment, a given shape was obtained b y the formation of favorably oriented ordered domains and twin lamella e. It is suggested that once the direction of deformation was decided, growth of the existing variants continued. (C) 1998 Elsevier Science S.A.