The shape-memory is a particular result of a displacive solid state phase transformation, martensitic transformation, with which the lattice structure changes abruptly. Copper based binary and ternary alloys exhibit shape memory effect in metastable beta-phase field. Martensitic transition occurs in homogenised B2(CsCl) or DO₃(Fe₃Al) -type ordered structures of beta-phase on cooling from high temperatures. Martensitic transformations occur by two or more lattice invariant shears on a {110}-type plane of austenite matrix which is basal plane or stacking plane for martensite, as a first step, and the transformed region consists of parallel bands or layered structures containing alternately two different variants. These variants form internally twinned martensite regions. The product phases have the unusual complex structures, long period layered structures such as 3R, 9R or 18R, depending on the stacking sequences on the close-packed planes of lattice.

Copper alloys are very sensitive to aging effect due to metastable character, and aging in martensitic condition give rise lattice changes and reorganization of atom in lattice sites. This effect leads to martensite stabilization with which atom exchanges occur among the lattice sites in material. This behaviour is a result of diffusional process which affects the character of diffraction profile together with the peak locations and intensities. Both martensitic and post-martensitic transition requires special changes in symmetry and relations between the lattice parameters. In the present contribution, x-ray diffraction and transmission electron microscopy (TEM) studies were carried out on two copper based ternary alloys.

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1. The Role of Ordering in Martensite Microstructures in Copper Based Shape Memory Alloys
2. Shape memory behaviours of noble metal copper based beta-phase alloys