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 L 12 -ordered Ni 3 Al 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 -Nb 3 Al 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 -Nb 3 Al to Nb 2 O 5 causes obvious surface bulges and cracks. The matrix and Laves phase form oxide layers containing a discontinuous Al 2 O 3 . The oxidation mechanism was elucidated through the formation oxidation diagrams based on Gibbs formation energy and total valence of Al 2 O 3 . The low Al content in matrix and the high Nb content in Laves phase were identified to cause the discontinuity of surface Al 2 O 3 layer. Additionally, Nb could impede oxygen diffusion within Al 2 O 3 by reducing oxygen vacancy concentration. The findings will provide optimization guidance for the composition design and oxidation protection of novel δ -Nb 3 Al-strengthened Ni-based superalloys.