Effect of the ratio of CO2 in the shielding gas on the microstructure and mechanical properties of maraging steel fabricated by wire arc additive manufacturing

This study investigated the effect of the CO₂ ratio in shielding gas on the microstructure and mechanical properties of maraging steel fabricated by Wire Arc Additive Manufacturing. By employing mixed shielding gases with varying CO₂ proportions (100 % Ar, 95 % Ar + 5 % CO₂, and 90 % Ar + 10 % CO₂), the formation quality, thermal cycling characteristics, microstructural evolution, and mechanical performance were systematically analyzed. The results indicated that increasing the CO₂ proportion elevated the arc heat input and reduced cooling rates, leading to grain coarsening and the precipitation of Ti-Al oxides. Microstructural evolution reduced material hardness and tensile strength, but significantly enhanced ductility. Ti-Al oxides cause stress concentration while also acting as a nucleation site for promoting localized plastic deformation. The study revealed the synergistic mechanism of CO₂ through thermal decomposition-induced reactive oxygen, altered arc characteristics, and heat input modulation, providing theoretical guidance for optimizing WAAM process parameters.