Effect of nano-Al₂O₃p on shape memory effect of Cu-Al-Mn alloy manufactured by additive manufacturing

Balancing increased recoverable strain with high phase transformation temperature is crucial for Cu-Al-Mn SMAs to cost-effectively overcome the service temperature limitation (<100°C) of NiTi-based SMAs. This study fabricated four types of Cu-12.5Al-3Mn SMAs modified with nano-Al₂O₃ p (0, 0.5, 1.0, and 1.5 wt%) using wire arc additive manufacturing (WAAM) with cored wires. It investigated the effects of nano-Al₂O₃ p on shape memory properties, exploring mechanisms via microstructural, phase, and hardness analysis. Results show that adding an appropriate amount of nano-Al₂O₃ p significantly enhances memory performance while maintaining high martensite transformation temperatures. The 0.5 wt% nano-Al₂O₃ p modified alloy exhibited optimal properties: a shape recovery rate of 87.77 % (13.8 % higher than the base alloy) and a recoverable strain of 7.02 % (>40 % higher than the commonly reported 5 %) under 8 % bending pre-strain. Its Ms temperature remained above 100°C (As, Af, Mf were largely unchanged), and full recovery time was halved compared to the unmodified alloy. The enhancement is attributed to nano-Al₂O₃ p strengthening the parent phase and improving thermoelastic martensite order via pinning. Their high stability under WAAM's high-energy heat source minimizes impact on alloy composition, while dispersed particles create lattice distortion and stress fields, reducing the energy barrier for martensitic transformation.