Enhanced high-temperature performance of CaO doped Y2O3 ceramic cores reinforced by nano-CeO2 in investment casting of titanium alloys

Due to the inherent high-temperature chemical compatibility accompanied with superior leachability, CaO doped Y2O3 ceramic cores serve as critical components in investment casting of titanium alloys. However, the poor high-temperature mechanical property is a problem to be solved, due to the promoted grain boundary diffusion and grain boundary sliding. In this study, CaO-doped Y2O3 composite cores were fabricated, and nano-CeO2 (n-CeO2) powders were employed as reinforcement phase, to address the trade-off between chemical leachability and high-temperature performance. The effects of n-CeO2 on the microstructure evolution, high-temperature mechanical performance, and chemical properties of the ceramic cores were investigated. n-CeO2 effectively suppresses the excessive oxygen vacancies generated by the substitution of Ca2+ for Y3+, maintains charge balance in point defects, and inhibits the lattice diffusion induced by low-melting-point CaO, thereby improving the high-temperature creep resistance of the cores. Compared with the sample without n-CeO2, the sample doped with 1 wt.% n-CeO2 shows a significant enhancement in high-temperature mechanical performance, with deflection reducing from 2.54±0.41 mm to 0.60±0.10 mm, strength increasing from 37.67±0.22 MPa to 44.14±3.07 MPa, while the superior leachability is maintained with complete dissolution in 6.5 h. Furthermore, the sample doped with 1 wt.% n-CeO2 exhibits superior comprehensive performance, whose open porosity is 16.1 ± 1.18%, surface roughness is 2.06 ± 0.28 μm, room-temperature flexural strength reaches 37.72 ± 2.94 MPa. After centrifugal casting of TC4 titanium alloy at 1550 °C, a distinct and clean metal-ceramic interface is observed, without detectable reaction layers. This study provides essential technical support for optimizing process parameters of Y2O3-based ceramic cores with superior leachability and high-temperature performance.