A Functionally Gradient NiTi Shape-Memory Alloy Fabricated by Selective Laser Melting

The near-equiatomic NiTi alloy has a shape memory function, but the simple forming structure limits its application. Selective laser melting is a promising way to manufacture functionally complex structures due to its layer-wise production advantage, which could broaden the applications of NiTi alloy in the engineering fields. This work explored a novel method of controlling the repetition of laser remelting to manufacture NiTi alloys with multiple phase-transformation temperatures via selective laser melting (SLM). The results demonstrates that the remelting strategy not only increases the ultimate tensile strength and elongation of the SLMed NiTi alloy, but also increases the Ms above room temperature. The increase in laser power increases the temperature at which martensite starts (Ms) to transformation in the range higher room temperature (25°C), thus increasing the critical stress of martensitic detwinning in the final sample. Through the optimized repetitive laser remelting strategy with different laser powers on specific areas of the sample, a functionally gradient NiTi build is successfully obtained. This study suggests SLM embedded with laser remelting is a potential method to realize 4D printing for NiTi alloys.