Influence of nano-Y2O3 addition on microstructure, mechanical properties, and oxidation resistance of laser-directed energy deposited Inconel 625

In this study, homogeneous dispersion of 1 wt% nano-sized Y₂O₃ particles in Inconel 625 powder was achieved via high-energy acoustic resonance mixing. Subsequently, a dense oxide-dispersion-strengthened (ODS) IN625 superalloy with a relative density of 99.86% was fabricated via laser directed energy deposition. Results showed that Y₂O₃ particles reacted with Al in the matrix to form Y-Al-O complex oxides with sizes ranging from 100 to 200 nm. The nano-Y₂O₃ particles exhibited an active flux effect, enlarging the melt pools and reducing the thermal gradient, which promoted coarser primary grains. Concurrently, Y₂O₃ acted as heterogeneous nucleation sites, suppressing epitaxial columnar growth and promoting a more homogeneous grain structure. This grain homogenization enhanced both room temperature and 700 °C elongation. However, strength reduction occurred due to weakened Hall-Petch strengthening from the coarser primary grains and reduced solid solution strengthening from Nb/Mo segregation, which outweighed the limited dispersion strengthening. During cyclic oxidation at 1000 °C, Y-Al-O oxides provided additional nucleation sites for Cr₂O₃, facilitating the early formation of a continuous and dense protective scale. Y segregation at Cr₂O₃ grain boundaries inhibited outward cation diffusion, shifting the oxidation mechanism to inward oxygen diffusion, thereby reducing the oxide scale growth rate and minimizing growth stresses. Compared to Y₂O₃-free IN625, the ODS-IN625 alloy exhibited a 40.9% reduction in mass gain after 100 h of oxidation, with a dense and continuous oxide scale and no significant internal oxidation.