Influence of Heat Input on Microstructural Evolution and Mechanical Behavior of WAAM-Fabricated Nitinol

Wire Arc Additive Manufacturing (WAAM) has emerged as a promising arc-based metal additive manufacturing technique for fabricating large-scale metallic components with high deposition efficiency and structural integrity. However, the inherent thermal cycling associated with arc processes significantly influences microstructural evolution and mechanical performance, particularly in thermally sensitive alloys such as Nitinol (NiTi). Heat input plays a critical role in governing solidification rate, grain morphology, phase stability, and residual stress distribution.In this study, ten experimental WAAM cases were designed by systematically varying current, voltage, and torch travel speed to produce a heat input range between 283.6 J/mm and 531.8 J/mm. The calculated heat input values were correlated with microstructural observations, X-ray diffraction analysis, hardness measurements before and after heat treatment, and tensile behavior of representative samples. Moderate heat input conditions demonstrated refined grain morphology and stable mechanical performance, while excessive heat input promoted grain coarsening and reduced tensile response.The results establish a comprehensive process–structure–property relationship for WAAMfabricated Nitinol, identifying an optimal thermal window that promotes balanced microstructural refinement and mechanical stability. The findings provide practical guidance for thermal control in arcbased additive manufacturing of shape memory alloys.