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 degrees C were evaluated. The XRD results showed that only the beta 1' phase could be detected in the Cu-based SMAs, which was attributed to the extremely short solidification time for the precipitation of alpha and gamma(2) phases during SLM process. The grains were well refined and the average grain size was approximate 43 mu m, 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 gamma(2) phase. Remarkably, the tensile test results at 200 degrees 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 degrees 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. (C) 2019 Elsevier B.V. All rights reserved.