Relationships between structure and hardness developed during the high temperature ageing of a smart Cu-based alloy

Smart shape memory alloys are used industrially due to their novel properties. Copperbased shape memory alloys are strongly influenced by ageing treatments which involve microstructural changes. The present work has been carried out on a CuZnAlCo alloy which has been aged at 400, 500 and 600 °C for time durations ranging from 5 min to 12 h. Hardness measurements have been performed and the microstructural evolution has been determined by electron microscopy. The results show that microstructural changes are strongly dependent on the ageing temperature and time. A maximum hardness of 300 Hv _0.2 has been obtained after ageing treatments. Equilibrium and phase and non-equilibrium phases ( or martensite) are present in the alloy depending on the ageing temperature and the ageing time. The maximum hardness has been associated with the presence of the and phases.