Microstructure evolution and properties of silica-based ceramic cores reinforced by mullite fibers

Composite ceramic cores reinforced by different contents of mullite fibers were prepared via injection molding. With increasing mullite fibers, the porosity showed near-exponential increase due to the accumulation of fibers, and the leaching rate showed the similar tendency attributed to the increasing porosity for the permeation of alkali solution. At room temperature or 1550 °C, the flexural strength increased as the fibers contents were below 3 wt%, due to the micro-cracking and fiber extraction; however, the flexural strength degraded as the mullite fibers contents was 4 wt%, due to the high porosity. Compared to the others, the ceramic cores with 3 wt% mullite fibers showed excellent properties, including apparent porosity of 35.2%, linear shrinkage of 0.81%, flexural strength being 25.5 MPa at room temperature and 22.3 MPa at 1550 °C, creep deformation of 0.12 mm and leaching rate of 0.34 g/min, well meeting the demands of hollow blades casting. This paper may provide new guidance for high-property ceramic cores.