Microstructure-controlled corrosion in directed energy deposited Ni-based superalloy: A review

Nickel-based superalloy Inconel 718 is widely used in aerospace, marine, and energy sectors owing to its exceptional high-temperature strength, creep resistance, and corrosion performance. However, conventional manufacturing routes suffer from long lead times, high costs, and geometric limitations for complex components. Directed energy deposition (DED) variants, including the emerging submerged arc DED (SA-DED) process, offer high deposition rates and near-net-shape capability. This review synthesizes recent advances in the development, microstructural evolution, post-processing, and corrosion behavior of Inconel 718 (and closely related Inconel 625) produced by arc-based and laser-based DED. Key findings highlight that as-built deposits exhibit coarse columnar grains, pronounced Nb-rich Laves phase networks, strong {001}⟨100⟩ texture, and micro-galvanic couples that degrade corrosion resistance in chloride environments. Effective mitigation strategies include inoculant addition (ZrO₂, TiB₂, Ti₂AlC, Re), oscillating-arc deposition, interlayer dwell control, in-situ hot forging, solution treatment, homogenization + solution-aging, hot isostatic pressing, and low-temperature powder-pack aluminizing. These approaches achieve grain refinement (down to 68 µm), Laves dissolution, stable γ′/γ″ core-shell coprecipitates, porosity elimination, and 46–70% improvement in oxidation resistance or up to 13.9-fold reduction in corrosion rate. Surface nano-hardness values exceeding 13 GPa and tensile strengths up to 1304 MPa have been realized, guiding future research toward high-performance, large-scale additive manufacturing of Ni-superalloys. This review provides a critical synthesis of microstructure–corrosion relationships in arc-based and laser DED of Inconel 718 and Inconel 625. Particular attention is given to the challenges and opportunities presented by the emerging high-heat-input, flux-assisted SA-DED variant. Critical knowledge gaps are identified, and a research framework is proposed to guide future development of corrosion-resistant SA-DED deposits.