The high-temperature oxidation behavior and mechanism in a powder metallurgy Ni-based superalloy featuring δ-Nb3Al addition.

Incorporating strengthening phase with a higher thermal stability than traditional L12-ordered Ni3Al phase offers a promising avenue for developing the next-generation Ni-based superalloys. In this study, a powder metallurgy superalloy featuring addition of high-melting-point δ-Nb3Al was fabricated to investigate the high-temperature oxidation behavior at 900 °C. Heterogeneous and accelerated oxidation resulting from the various phase transition products in the alloy were observed. Notably, the preferential oxidation of δ-Nb3Al to Nb2O5 causes obvious surface bulges and cracks. The matrix and Laves phase form oxide layers containing a discontinuous Al2O3. The oxidation mechanism was elucidated through the formation oxidation diagrams based on Gibbs formation energy and total valence of Al2O3. The low Al content in matrix and the high Nb content in Laves phase were identified to cause the discontinuity of surface Al2O3 layer. Additionally, Nb could impede oxygen diffusion within Al2O3 by reducing oxygen vacancy concentration. The findings will provide optimization guidance for the composition design and oxidation protection of novel δ-Nb3Al-strengthened Ni-based superalloys. [ABSTRACT FROM AUTHOR]