Reinforcement of silica-based ceramic cores based on amorphous and polycrystalline mullite fibers

In the investment casting of turbine blades, ceramic cores are key components to form complex hollow structures. Superior mechanical property and leaching rate are demanded for ceramic cores. Herein, ceramic cores were fabricated using fused silica powders as the matrix, and amorphous and polycrystalline mullite fibers as the reinforcement phases, respectively. The microstructure and property evolution of ceramic cores rely on the crystallization degree of mullite fibers are explored. Both of the mullite fibers lead to improved crystallization of cristobalite, reduced sintering shrinkage, increased apparent porosity, and benefited bending strength, creep resistance, and leaching rate of the cores. Compared to the polycrystalline mullite fibers, the amorphous fibers are metastable with large quantities of structural defects, promoting the diffusion mass transfer and forming strong interface between fibers and matrix. Therefore, the amorphous fibers have larger promotion on the bending strength and resistance to creep deformation of ceramic cores. Moreover, the structural defects of amorphous fibers ensures the high chemical activity in alkaline solutions and exhibits excellent leaching rate. The ceramic core with 4.5 wt% of amorphous mullite fibers exhibits excellent comprehensive performance with bending strengths of 28.9 MPa and 23.8 MPa at room temperature and 1550 °C, creep deformation of 0.3 mm, and leaching rate of 1.4 g/min, well meeting the casting requirements of hollow blades.