Impact of the Oxide Film Formed During the Seeding Process of Single-Crystal Superalloys

The impact of the oxide film in the remelted zone of a seed on the epitaxial solidification of single-crystal superalloys was investigated, with a specific focus on clarifying the hindrance mechanism of complex compositional oxide films during the epitaxial growth process. Experimental findings indicated that the oxide film was composed of multiple constituents, such as WO3 and Al2O3, and displayed no remarkable texture in its crystal orientation. The formation mechanism of coherent oxides during the alloy oxidation process and their potential as nucleation sites for solidification were analyzed. Owing to disparities in symmetry along the growth direction, the γ phase formed through oxide nucleation that deviated from its original orientation. Moreover, the existence of polycrystalline oxide films impeded the effective transfer of single-crystal seed orientation information, leading the epitaxial growth to mainly rely on the mechanism where dendrites penetrate through the damaged areas of the oxide film to reach the upper region. Significantly, aluminum oxide within the oxide film could act as new nucleation sites, potentially triggering the formation of stray grains in the central region of the casting.