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

Abstract

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 0.5–0.6µm and lengths of 4–8µm 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 16.9MPa when 10vol% AlF3·3H2O and 12vol% SiO2 were added.