The Granularity Of The Oxidation Of Silicon-based Ceramic Core To Prepare And Strengthen The Process

Silica-based ceramic core is 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. Because of its low thermal expansion, good high temperature performance and leachability, silica-based ceramic core is widely used both at home and abroad. Results show that particle size and strengthening process directly affect the core's performance.In this paper, silica-based ceramic core was prepared by heat-press molding method, using ethyl silicate for high-temperature strengthening, mixture of polyamide, epoxide resin and propanone for room-temperature strengthening. Technology of how to control the fine powder content in core was studied as well as the effect of particle size and strengthening process on the microstructure and properties of the core, by measuring its sintering strength, shrinkage, open porosity and high temperature deformation with SEM and XRD, aiming to determine the optimum particle size ratio and strengthening process. The main results can be summarized as follows:1. It's very effective by means of sedimentation to separate the fine particles (<10μm). The optimum separation process was as follows: solution for sedimentation was clean water whose volume and height were 180L and 50cm, adding power in water 500g every time, settling for 4～5 times.2. Results show that particle size affects the microstructure and properties of the core significantly. With the particle size increasing, the sintering strength and shrinkage decreased gradually, whereas the open porosity enhanced. However, the increase of open porosity was useful for the raising of flexural strength after room-temperature strengthening. The higher the open porosity was, the more the raising of flexural strength was, otherwise the less. When the particle size was as follows: <10μm= 19.95%, D50≈27μm, D90≈65μm, the max particle size below 112μm, the comprehensive performance of core was good.3. Additional of cristobalite to the cores can reduce the shrinkage and improve the high property at high temperature. However, a large amount of cristobalite led to the occurrence of microcrack and decrease of the strength due to the variation of volume during crystallite structural transformation.4. The optimum concentration ratio (volume fraction) of high temperature strengthing liquid was:TEOS 90%, H2O 5%, C2H5OH 3.5%, HC1 1.5%. With the increase of strengthen times, the high temperature deformation of core decreased slowly, open porosity and flexural strength also dropped significantly. Therefore, during the high temperature strengthening, the strengthen times should be controled reasonablely for the optimum properties both at room and high temperature. After high temperature strengthing, the deformation of core droped from 3.43mm to 1.89mm.5. The optimum concentration ratio (quality fraction) of room temperature strengthing liquid was:polyamide/(epoxide resin)=0.8, propanone/(polyamide + epoxide resin)=60%. The best strengthening process was:ambient temperature 30℃, soaking time 30min, air-drying time 12h, curing temperature 170℃, curing time 45min. After room temperature strengthing, the flexural strength of core increased from 34.68MPa to 83.73Mpa. Strengthing at ambient temperature had slightly effect on high temperature properties.