The role of Ta in the microstructure evolution and high-temperature oxidation behavior of Inconel 625 superalloy fabricated by directed energy deposition

Abstract

Directed energy deposition (DED) holds great promise for fabricating Inconel 625 (IN625) superalloy components. However, issues such as grain coarsening and element segregation during DED processes pose significant challenges to the high-temperature oxidation resistance of IN625, especially at temperatures above 1000 °C. In the present study, Ta was incorporated into the IN625 alloy to fabricate the components with outstanding high-temperature oxidation resistance at 1100 °C via plasma arc DED. The influence of different Ta contents (0.2 wt%, 0.5 wt%, and 1.0 wt%) on the microstructure and high-temperature oxidation behavior at 1100 °C of DEDed IN625 were investigated. Results showed that with the increase of Ta content, the grains of IN625 were refined, and the precipitation of Laves phase reduced. Furthermore, it was observed that adding Ta remarkably decreased the oxidation rate of DEDed IN625 during the high-temperature oxidation testing at 1100 °C for 150 h. Compared to the IN625 sample, the mass gains of sample after the addition of 1 wt% Ta are reduced by 90.77 %. The refinement of grains and reduction in Laves phase allowed more Cr to transport to the oxidized surface to form a dense and protective Cr₂O₃ film during the initial stage of high-temperature oxidation. Subsequently, Ta atoms migrated to the Cr₂O₃ oxide layer/matrix interface, and combined with oxygen to form TaNbO₅, which not only hindered the oxygen intrusion but also inhibited the outward diffusion of Nb, thereby preventing the formation of CrNbO₄ with poor adhesion to the matrix. Consequently, the oxidation rate was significantly reduced.