Wettability and interfacial reaction of ZrO2 and Y2O3 doped Al2O3-based ceramic shells in K417G superalloy investment casting

Abstract

Interfacial reactions between K417G Ni-based superalloy and Al₂O₃-based ceramic shells during investment casting negatively impact the surface quality of the resulting castings. To mitigate this issue, ZrO₂ and Y₂O₃ were introduced to modify the microstructure, phase composition, and chemical properties of the shell surface. The effects of dopant type and content (2–5–8 wt%) on interfacial reactions and wettability were systematically investigated using the sessile-drop method. The reaction products were characterized to understand the underlying mechanisms. The results show that increasing the ZrO₂ content reduced the surface porosity and roughness of the shell. During sintering (950 °C, 2 h), the dopants reacted with SiO₂ to form silicates (Y₂SiO₅ and ZrSiO₄), thereby enhancing the thermal stability of the shell. Under interfacial reaction conditions (1350 °C, 40 min), increasing the dopant content (2–5 wt%) significantly improved the alloy surface quality, reducing sand sticking defects, exposing more of the alloy matrix, and increasing the alloy-shell contact angle. However, at an 8 wt% dopant content, part of the dopant reacted with the Al₂O₃ layer on the alloy surface, forming Al₂O₃·ZrO₂ and Al₂O₃·Y₂O₃ composite oxides. These reactions intensified localized interactions, resulting in the formation of ‘special reaction pits’, which ultimately reduced both the alloy surface quality and the alloy-shell contact angle. These findings suggest that the compositional design of Al₂O₃-based ceramic shells promotes the formation of silicates, enhances thermal stability of the shell materials, thereby inhibiting alloy-shell interfacial reactions, and improving surface quality of the alloys.