Microstructural characterization of precipitates in Cu-10Â wt.%Al-0.8Â wt.%Be shape-memory alloy

Microstructural characterization of α1-plate and γ2 phase precipitated in hypoeutectoid Cu-10 wt.%Al-0.8 wt.%Be shape-memory alloy (SMA) aged at 200 °C for different periods of time (20-160 h) is researched in this study. High-resolution transmission electron microscope (HRTEM) was employed to investigate the α1-plate with 18R long period stacking order structure (LPSO) in the SMA aged for 20 h. According to the atomic shuffling revealed in HRTEM-micrograph, the atomic model of the 18R LPSO is proposed. The quantitative mapping of electron energy loss spectrometry shows that the α1-plates in the SMA aged for 160 h contain lower aluminum concentration than the parent phase matrix. The lattice image of the nanometer-sized γ2 phase precipitated homogeneously in the SMA aged for 160 h is also revealed by using HRTEM. Precipitation of the nanometer-sized γ2 phase cannot be impeded by means of the addition of beryllium and quenching, and such precipitate does not grow up in the SMA aged for periods of time less than 160 h.