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In this work, silica-based ceramic cores with alumina as a mineralizer were prepared via an injection molding method, and the effects of alumina on the microstructural evolution and properties at 1450 • C (simulating the process of equiaxed castings) and 1550 • C (simulating the process of columnar/single crystal castings) were investigated. It was found that alumina promoted the cristobalite crystallization of fused silica refractory during sintering but inhibited the devitrification rate in the subsequent heating. The flexural strength of silica-based ceramic cores at an ambient temperature and 1450 • C improved with an increasing alumina content, whereas the opposite trend appeared at 1550 • C. The creep resistances of silica-based cores were improved significantly and then slightly deteriorated with an increasing alumina content from 5% to 20%, depending on the competition effects of alumina hindering the viscous flow of liquid silica (favorable), but suppressing the devitrification rate (unfavorable). The results of this work show that silica-based cores need to follow different compositional design principles for equiaxed and columnar/single-crystal turbine blade castings.

Single crystal gas turbine blades and vanes, which have complex hollow structures, are one of the most important parts in gas turbine engines. The single crystal microstructure can efficiently enhance the heat bearing capacity of turbine blades so as to improve engine performance [1] . The most efficient technology for manufacturing single crystal turbine blades is the investment casting process based on Bridgman's directional solidification theory. This technology uses complex ceramic cores fabricated by injection molding to form the internal cooling passages in the hollow gas turbine blade [2,3] . A silica-based ceramic core is typically used in the manufacture of single crystal hollow turbine blades due to its superior low thermal expansion coefficient (0.55×10 -6 K -1 between 25 °C and 1,000 °C), excellent chemical stability with molten metals, and