A comprehensive review of materials and process parameters in Wire Arc Additive Manufacturing (WAAM): Current insights and future directions

Wire Arc Additive Manufacturing (WAAM) has emerged as a transformative metal additive manufacturing technology, capable of fabricating large-scale, geometrically complex metallic components at high deposition rates and relatively low cost. This article presents a systematic and critical review of recent WAAM research, covering five principal material systems, alloy steels, stainless steels, aluminum alloys, titanium alloys, and nickel-based superalloys, alongside a comparative analysis of key process variants including Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), Plasma Arc Welding (PAW), Cold Metal Transfer (CMT), and hybrid Laser Metal Deposition (LMD) systems. The review critically examines the influence of process parameters, particularly heat input, wire feed rate, travel speed, and interpass temperature, on microstructural evolution, defect formation, and mechanical anisotropy. Post-processing strategies, including interpass cooling, cold rolling, and heat treatment, are evaluated with respect to their effectiveness in mitigating anisotropy, reducing residual stress, and enhancing tensile and fatigue performance. A comparative analysis identifies persistent cross-material challenges, including columnar grain dominance, porosity, and directional mechanical properties, alongside targeted mitigation strategies. The review further identifies critical knowledge gaps in intelligent process monitoring through digital twin frameworks and machine learning, the processing of emerging alloy systems such as high-entropy alloys (HEAs) and functionally graded materials (FGMs), and the standardization of qualification protocols required for industrial certification. By synthesizing findings from over 100 recent publications, this review provides a structured research agenda to accelerate the transition of WAAM from laboratory demonstrations to full-scale industrial deployment.