Wire Arc additive manufacturing of Inconel 625: Process-structure-property-performance relationships and future pathways

Wire Arc Additive Manufacturing (WAAM) has emerged as a cost-effective and high-deposition-rate technology for fabricating large-scale metallic components. Inconel 625 is particularly suitable for WAAM because of its high-temperature strength, corrosion resistance, oxidation resistance, and metallurgical stability. However, the coupled effects of process parameters, thermal history, microstructural evolution, defects, residual stress, and mechanical anisotropy remain insufficiently integrated in the existing literature. This review systematically analyses research published between 2019 and 2025 using a unified Process–Structure–Property–Performance (PSPP) framework. The effects of heat input, deposition strategy, interpass temperature, cooling conditions, and thermal cycling on grain morphology, elemental segregation, phase evolution, residual stress, defect formation, and mechanical performance are critically evaluated. Particular attention is given to porosity, lack-of-fusion defects, Laves-phase formation, build-height-dependent heterogeneity, and associated mitigation strategies involving thermal management, interlayer treatments, hybrid processing, and real-time monitoring. Recent developments in laser-assisted deposition, interlayer rolling, ultrasonic and magnetic-field assistance, in situ machining, machine learning, and adaptive process control are also discussed. A comparative assessment indicates that WAAM is particularly advantageous over PBF for large-scale near-net-shape fabrication because of its higher deposition productivity and wire-based feedstock, whereas PBF generally provides superior dimensional accuracy, surface finish, and finer microstructural control. Compared with DED, WAAM offers greater productivity for large structures, while DED provides greater flexibility for localized deposition and repair. The review further identifies limitations associated with thermal accumulation, residual stress, dimensional accuracy, standardization, sustainability assessment, and long-term structural reliability. Future research priorities include predictive multi-scale modelling, adaptive closed-loop control, alloy-specific feedstock development, standardized qualification, sustainability-oriented process optimization, and long-term performance evaluation. Overall, the review provides an integrated basis for advancing reliable, sustainable, and industrially scalable WAAM of Inconel 625 components.