Process optimization, microstructures and mechanical properties of a Cu-based shape memory alloy fabricated by selective laser melting

The Cu-13.5Al-4Ni-0.5Ti copper-based shape memory alloys (SMAs) were fabricated by selective laser melting (SLM). The parameters were optimized to obtain almost fully dense copper-based SMAs samples. The phases and microstructures were characterized and the tensile properties at room temperature and 200 °C were evaluated. The XRD results showed that only the β₁′ phase could be detected in the Cu-based SMAs, which was attributed to the extremely short solidification time for the precipitation of α and γ₂ phases during SLM process. The grains were well refined and the average grain size was approximate 43 μm, which was much smaller than that of the cast copper-based SMAs. The X-phase (Cu₂TiAl) is observed, which is granular and size 20–50 nm. The Cu-13.5Al-4Ni-0.5Ti copper-based SMAs fabricated by SLM exhibited excellent mechanical properties at room temperature, which was higher than that of the cast copper-based SMAs. This is attributed to two aspects: (1) grain refinement, (2) suppress of brittle γ₂ phase. Remarkably, the tensile test results at 200 °C showed both higher strength and elongation, which is attributed to the bcc structure of the parent phase and the stress-induced martensitic transformation at 200 °C. Meanwhile, the difference of microstructures and properties between SLM-fabricated Cu-based SMAs and casting Cu-based SMAs were analyzed and discussed in detail.