Investigating the Dissolution and Evolution Behavior of Oxides in FGH96 Superalloys

The dissolution and evolution behavior of oxides in FGH96 superalloys was systematically investigated through the diffusion couples and heat treatment experiments. Results reveal that two distinct interfaces structures were identified at diffusion couple interface of the Ni-based superalloys during heat treatment, namely the contact interface and the oxide particle interface, both exhibiting notable oxygen (O) enrichment. During the heat treatment, the contact interface exhibited a gradual healing process, while the oxide particles were partly dissolute, caused by the decrease of the equilibrium O partial pressure and the diffusion of elements. This results in a reduction of O content at diffusion couple interface to a concentration equivalent to that of matrix. In the diffusion process, a gradient distribution of O concentration was observed from the diffusion couple interface to the matrix, and an apparent O segregation within γ matrix was revealed, indicating a heightened affinity between O and γ matrix. First-principles calculations demonstrated a lower formation energy for O solid solution into Ni (− 5.12 eV) than that into Ni₃Al (− 5.00 eV). Additionally, the expansion of the cell parameter was influenced by a higher concentration of O. Consequently, the γ matrix provided a conducive diffusion pathway for O migration from the diffusion couple interface to the matrix. Eventually, O atoms solidly dissolved within γ matrix, leading to the lattice expansion.