Study on PHIT Heat Input Regulation for WAAM Components Towards Synergistic Control of Forming and Performance

Wire Arc Additive Manufacturing (WAAM) holds promise for large-scale metal components but is hindered by residual stress and deformation. This study introduces Plasma In-situ Heat Treatment (PHIT) to address the challenge of synergistic "formability-property" control in 304 stainless steel WAAM. A multidisciplinary approach combining a validated 3D transient thermo-mechanical finite element model and experimental measurements was used to analyze the effects of PHIT heat input (0.384–0.768 kJ/mm). Results show that PHIT effectively regulates the thermal cycle and improves temperature field uniformity, although excessive heat input causes accumulation and peak temperature spikes. The influence on substrate deformation and residual stress is nonlinear, revealing an optimal process window. At 0.672 kJ/mm, substrate deformation minimized (1.17 mm), equivalent stresses reduced by ~ 58%, and stress distribution anisotropy significantly improved. This optimized parameter yielded the best comprehensive mechanical properties: enhanced and more uniform tensile strength (Long.: 577 MPa, Trans.: 623 MPa), elongation (Long.: 16%, Trans.: 17%), and microhardness (225 HV). Microstructural analysis confirmed an effective balance between grain refinement and second-phase precipitation, avoiding the pitfalls of overly fine or coarsened structures.