Characterization of the as-cast microstructure, precipitates stability and corrosion resistance of Alloy 718 modified with ex-situ WC nanoparticles

The extension of service life of Ni-based superalloys requires repair materials capable of operating in wear and corrosive environments, where conventional filler alloys often lack sufficient robustness. This work evaluates Alloy 718 reinforced with WC nanoparticles as candidates for such applications. Ex-situ composites containing 1.25–5.0% WC were produced by suction casting, and their microstructure, phase composition, tribological and corrosion behavior were characterized. A dendritic structure consisting of a γ-matrix was observed in all variants. In the unreinforced alloy, segregation to interdendritic regions led to precipitation (Nb,Mo)C carbides and Laves phase. Synchrotron-based analyses, coupled with electron microscopy, confirmed partial dissolution of WC during solidification, leading to complex (Nb,Mo,W)C carbides and a marked reduction in the Laves phase. Steam oxidation at 704 °C for 1000 h showed that all WC-modified variants exhibited lower mass gain compared with Alloy 718. Exposure in Ar+ 0.25% SO₂ revealed that increasing WC content suppressed Ni₃S₂ formation and reduced mass gain to 1.144 mgꞏcm⁻² at 5% WC. Hardness increased from 198HV10 to 221HV10 with 5% WC, accompanied by a modest improvement in dry-sliding wear resistance. These results demonstrate that WC-reinforced Alloy 718 offer enhanced environmental resistance and improved mechanical response, making them promising repair materials for Ni-based superalloys.