Y2O3-based Ceramic Cores with optimized leachability and high-temperature properties based on buried sintering process in investment casting of titanium alloys

Due to inherent high-temperature chemical stability, Y2O3 ceramic cores serve as critical components in the investment casting of titanium alloys. CaO is generally doped in Y2O3 cores to benefit leachability, but compromises their high-temperature performance. To address the contradiction between chemical leachability and high-temperature performance of Y2O3 cores, this work prepared Y2O3-4 wt.% CaO cores via buried sintering process, in which the effects of four filler powders (Y2O3, Al2O3, ZrO2, and SiO2) with varying particle sizes on microstructure, high-temperature performance, and chemical property were systematically investigated. After sintering at 1600 °C with Al2O3 filler, the low-melting-point phase C12A7 (Ca12Al14O33) was formed, resulting in a surface mechanical weak layer and poor mechanical properties at high temperature based on grain boundary sliding of calcium oxide particles between yttria grains. In comparison, with Y2O3 filler, the dense Y2O3 surface layer is developed, and partially mitigates the high-temperature softening of CaO induced by point defects, thereby enhancing the high-temperature performance. Furthermore, the contradiction between the support points and the dewaxing speed is highly alleviated by the controlled particle size of the filling powder. Y2O3 filling powder in particle size of 11.2 μm achieves the optimal comprehensive performance in Y2O3-based cores, displaying high-temperature flexural strength of 29.27 ± 1.10 MPa, deflection deformation of 2.2 ± 0.05 mm, and a leaching time of only 4.5 h in 80% citric acid at 95 ℃. Following centrifugal casting with TC4 titanium alloy at 1550 ℃, a sharp and clean metal-ceramic interface is observed, without detectable reaction layers.