Effect of Aging on the Structure and Transformation Behavior of Cu–12Al–3.5Ni–0.7Ti–0.05RE High Temperature Shape Memory Alloy

In this study, the effect of isothermal aging on the thermoelastic martensitic transformation and microstructure of the as-quenched Cu–12Al–3.5Ni–0.7Ti–0.05RE (RE = Ce, La) high temperature shape memory alloy was studied. The results showed that the alloy microstructure and martensitic transformation are strongly influenced by the aging temperature rather than aging time. During aging at 350 °C the alloy was prone to both the precipitation of the γ₂ phase and the bainitic transformation, resulting in a loss of martensitic transformation and damping capacity. The prolonged aging at 350 °C caused a decomposition of parent phase into the equilibrium γ₂ phase alongside the α phase which produced a significant hardness increment. On the other hand, aging at 250 °C affected the microstructure only slightly producing insignificant shift in the transformation temperatures. It was found that, the secondary phases including Ti-rich X-phase and the RE-rich phase were not influenced by the aging process. The results prescribe a high temperature order of the stability of martensitic transformation for this new alloy which is important for its high temperature shape memory applications.