Effect of in situ synthesised mullite whiskers on the high-temperature strength of Al₂O₃-based ceramic moulds for casting hollow turbine blades

In situ synthesised mullite whiskers were used to improve the high-temperature strength of Al₂O₃-based ceramic moulds for casting hollow turbine blades fabricated by the geŠlcasting method using Al₂O₃, SiO₂ and AlF₃·3H₂O as the raw materials. The microstructures and phase compositions of the sintered ceramic samples were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The bending strengths of the samples were tested at 1500 °C. Mullite whiskers with diameters of 0.5–0.6 µm and lengths of 4–8 µm were synthesised in the Al₂O₃-based ceramic moulds. These whiskers acted as bridges between the pore walls of the ceramic moulds, enhancing the strength of the ceramic moulds. The bending strength of the ceramic mould at 1500 °C increased from 8.3 to 16.9 MPa when 10 vol% AlF₃·3H₂O and 12 vol% SiO₂ were added.