High-temperature strength of gel casting silica-based ceramic core

Considering the fracture problem of the silica-based ceramic core in the integrated casting of hollow turbine blades during directional solidification, the influence of various whiskers, including silicon carbide whiskers, silicon nitride whiskers, and mullite whiskers, on the high-temperature strength of the silica-based ceramic core was investigated. Additionally, the formation of microstructure morphology and phase structure was analyzed. Research results show that silicon carbide whiskers can reduce the microcracks caused by the shrinkage of cristobalite. During the sintering process, some of the silicon carbide whiskers oxidize and react with aluminum powder to form mullite, which can improve the high-temperature strength of the ceramic cores. When the content of silicon carbide whiskers is 3wt.%, the high-temperature bending strength of the cores reaches the maximum value of 21 MPa. Silicon nitride whiskers decompose in a high-temperature environment and react with aluminum powder in the matrix material to form mullite whiskers. When the content of silicon nitride whiskers is 5wt.%, the high-temperature bending strength of the cores reaches 20 MPa. By adding mullite whiskers, a structure of cristobalite wrapped mullite whiskers can be formed to achieve toughening. When the content of mullite whiskers is 4wt.%, the high-temperature bending strength can reach 17.2 MPa. By comparing the performance of silicon carbide whiskers, silicon nitride whiskers, and mullite whiskers, along with conducting slurry viscosity tests and casting experiments, it is determined that a ceramic slurry containing 4wt.% mullite whiskers is the most suitable for making the cores used in the integrated casting of hollow turbine blades.