Densification behavior in short carbon fiber reinforced silica-based ceramic cores via atmosphere sintering

In order to obtain high performance ceramic cores for investment casting of superalloy single crystal blade. In this paper, the short carbon fibers (C_sf) were uniformly dispersed in silica-based ceramic slurry though synergistic effect of ultrasonic vibration and mechanical stirring, and the green cores were prepared by injection molding method and sintered in air and N₂ atmosphere, respectively. The microstructure evolution and phase transformation during heating process were thoroughly observed and analyzed, and further revealed the densification behavior of C_sf reinforced silica-based ceramic cores under two sintering atmospheres. The results indicate that the C_sf can increase the mass transfer distance between ceramic particles, and provide carbon source to grow in-situ SiC crystals and affect the crystallization of cristobalite in matrix. Therefore, the diffusion and migration of solid phases and viscous flow of liquid phase in ceramic cores are inhibited by the stereo interlocked network of C_sf and the high melt point crystalline phases at high temperature. Moreover, the open porosity of silica-based ceramic cores sintered in both air and N₂ atmosphere is increased with the increase of C_sf content, while the shrinkage is gradually decreased. When the fiber content is 1.5vol%, as for samples sintered in air atmosphere, the highest open porosities in air and N₂ sintering atmospheres are about 42.95% and 39.50%, while the least shrinkages are about 0.64% and 0.48%, respectively. It can prove that the C_sf and high melting point crystals have significantly influence on the sintering densification behavior of silica-based ceramic cores.