Effect of Alumina-based fiber on the mid-temperature strength of integral ceramic mold for casting hollow turbine blade

The fabrication process of integral ceramic mold based on stereolithography and gelcasting can eliminate the assembly errors between cores and that between cores and shell in the traditional manufacturing process of ceramic molds. However, the bending strength of the mold at 500°C (mid-temperature strength) drops significantly during pre-sintering because the gel networks surrounded the ceramic particles are burnt off, which often causes the core fracture or shell cracking of the integral ceramic mold. In this paper, short alumina-based fibers were added into the gelcast ceramic slurry to improve the mid-temperature of the ceramic mold. Filling experiment and computed tomography (CT) test were performed to investigate the effect of fiber content and fiber length on the filling ability of ceramic slurry in the cavity with small complex structures. The mid-temperature strengths of the ceramic mold were tested. Microstructures of the ceramic mold sintered at 500°C were observed by scanning electron microscope (SEM). It was found that the filling ability of the ceramic slurry decreased as the fiber length and fiber content increased, however the mid-temperature strength of the ceramic mold increased with the fiber length and fiber content. When 1.5wt% short alumina-based fibers with lengths between 0.5 mm and 1 mm were added, the ceramic slurry could meet the requirement of gelcasting, and the mid-temperature strength of the ceramic mold was improved from 0.78 MPa to 1.65 MPa.