Effect of Urchin-Like Mullite Whiskers on the High-Temperature Performance of Porous SiO₂-Based Ceramic Molds

Urchin-like mullite whiskers synthesized by the vapor–liquid–solid growth method were used to improve the high-temperature performance of porous gelcast SiO2-based ceramic molds. Aluminum was used to facilitate the synthesis of polycrystal urchin-like mullite whiskers which acted as bridges between particles. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the microstructures and phase compositions of the sintered ceramic samples, respectively. Urchin-like mullite whiskers with diameters of 0.2~1.0 µm and lengths of 1.0~8.0 µm were successfully synthesized in SiO2-based ceramic. When 15 vol% Al was added, the high-temperature strength at 1200 °C was improved from 8.5 to 27.5 MPa, and the creep deformation was decreased to 0.56 mm. Meanwhile, a sintering shrinkage below 0.3% was obtained, and the de-coring rate was accelerated by 67% compared to that of the pure SiO2-based ceramic. This method showed excellent high-temperature strength and high precision, having remarkable potential in the fabrication of hollow turbine blades