Influences Of Raw Materials On Properties Of Silica-based Ceramic Core

Ceramic cores are mainly used to form the complex inner cavity of hollow turbine blades, which is very important for improving the cooling effect of turbine blades and thrust-weight ratio of aircraft engine. Silica-based ceramic core is widely used on hollow turbine blades due to its low thermal expansion, good high temperature performance and leachability. In this study, the properties of silica-based ceramic cores are investigated deeply.In this research, silica glass powders(SGP), cristobalite powders(CP) and nano- fused silica powders(NSP) are used as raw materials to prepare a series of silica-based ceramic cores. The influences of the particle size distribution of fused silica glass powders and the content of cristobalite and nano- fused silica powders on the properties of ceramic cores are investigated. The composition, surface morphology and micro-structure of ceramic cores were studied by X-ray diffraction(XRD) and scanning electron microscopy(SEM), The flexural strength was measured by three point bending method.First only SGP was used as raw material. The results showed that the properties of ceramics cores were bad when applying bimodal distribution of SGP. By adapting multimodal distribution of SGPs, whose ratio of powder 1(D(50) is 48 ?m), powder 2(D(50) is 32 ?m) and powder 3(D(50) is 9 ?m) is 1:1:1, the properties of cores increased, namely, the shrinkage of cores is 0.23%, leachability is 0.32 g/min, apparent porosity is 29.3%, flexural strength is(27.0±1.1) MPa or(29.0±1.2) MPa at home temperature or 1540 °C respectively, and the creep deformation is 0.40 mm.When adding CP into raw materials, the properties increased. Especially w hen the content of cristob alite optimize to 6 wt.%, the properties reached the climax: the shrinkage is 0.42%; apparent porosity is 29.4%; flexural strength at 1540 °C is(28.7±0.9) MPa; leachability is 0.32 g/min; flexural strength at home temperature is(25.2±0.7) MPa; creep deformation is 0.10 mm; the volume of cristobalite in the ceramic cores is 26%. When the particle size of the pre-addition CP decreases, the shrinkage, bulk density and leachability decrease first and then increase; the flexural strength of ceramic cores hardly change. When the D(50) of CP reduce to 3 ?m, the flexural strength decreases sharply. When the D(50) of cristobalite is 5 ?m, the shrinkage of ceramic cores is 0.35%; apparent porosity is 31.2%; leachability is 0.31 g/min; flexural strength at home temperature is(23.5±0.4) MPa; flexural strength at 1540 °C is(26.0±1.1) MPa; creep deformation is 0.12 mm and the cristobalite in the ceramic cores is 35%.When adding NSP into raw materials, the result showed that the pre-addition of nano- fused silica into silica-based ceramic core accelerated the crystallization of fused silica, and improved the cristobalite content of sintered ceramic core. When the content of nano-fused silica is 0.6 wt.%, the shrinkage of ceramic cores is 0.63%; apparent porosity is 27.9%; leachability is 0.27 g/min; flexural strength at home temperature is(30.0±1.3) MPa; flexural strength at 1540 °C is(29.0±1.1) MPa and creep deformation is 0.20 mm.