Tailoring shape memory and pseudoelastic transformation characteristics in NiTi alloys using twin-state wire arc additive manufacturing (WAAM)

Abstract

NiTi alloys are well known for their shape memory and pseudoelastic properties, still facing the issue in achieving precise control over the transformation characteristics by manufacturing processes. However, the Wire Arc Additive Manufacturing (WAAM) shows good combability with materials enables the fabrication of NiTi structures, but still have some limitation in controlling these transformation characteristics of the components. This study demonstrates an approach for tailoring transformation temperatures using twin-state cold WAAM with in-situ alloying of two distinct commercially available NiTi wires to create a compositional gradient. The shape memory alloy (SMA) and pseudoelastic (pseudo) wire were used as feedstocks for deposition of three distinct samples namely ‘SMA rich’, ‘SMA + Pseudo (50:50)’, and ‘Pseudo rich’. Thermal analysis of the depositions demonstrated a gradual shift in transformation temperatures with respect to the feed rate ratios of the two wire types, indicating effective modulation of phase transformation behaviour. By adjusting the SMA-to-Pseudo feed ratio (Blend ratio) from 5:7 to 9:7, the austenite finish temperature (Af) was successfully tuned from 37.83 °C (‘Pseudo rich’) to 76.08 °C (‘SMA rich’). This variation in transformation behaviour is supposed to be linked to the formation of Ti-rich and Ni-rich phases within each respective alloy. Microstructural analysis confirmed a corresponding increase in the Ti-rich dendritic phase area fraction from 47 to 80%. Microhardness testing showed that the compositional and transformation temperature variations had minimal influence on the hardness of the deposited NiTi alloy. These results indicate that the twin-state cold WAAM could be a potential method to produce compositionally tailored NiTi structures. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2026.