THE INFLUENCE OF AGING ON MARTENSITE MORPHOLOGY IN SHAPE-MEMORY CUZNAL ALLOYS

The martensitic transformation behaviour, morphology and microstructur es in copper-based shape memory alloys are strongly influenced by the post-quench heat treatments and ageing. Martensitic transformation ini tiates at a critical temperature and grows by the formation of martens ite variants on cooling up to martensite finish temperature. These all oys are metastable at the matrix beta-phase condition, and reversibili ty of transformation and formation of martensite variants from the mat rix are related to the elementary mechanisms. ?The interfacial motion between martensite variants is also important in shape memory. Vickers hardness shows a trend to increase with holding duration at ageing te mperature of 200 degrees C for both alloys. Martensite plates have sim ilar morphology in as-quenched and post-quench heat treated specimens, and growth units of two or four plates constitute self-accommodating systems.