Experimental Study On Silica-based Ceramic Core Used For Hollow Turbine Blade

Ceramic cores are playing more and more important roles with thedevelopment of air-cooled gas turbine blades technologies. Because ceramic coreshave direct effect on the rate of finished products of hollow gas turbine blades, theyare considered crucial for manufacturing gas turbine blades. Silica-based cores arewidely used in directional solidification and single crystal castings at pouringtemperature below1550℃due to the superior characteristics such as lowcoefficient of thermal expansion, good thermal shock resistance and favorable leachability in alkaline solution. However the content of cristobalite in coresmanufactured at home is unstable, and large-sized complex cores have weakproperties at high temperature, which results in core shift, core leakage and corebroken during blades manufacturing. In this study, starting with the particle sizegradation of ceramic core powder, the influence of mineralizer, sintering andstrengthening process on properties of cores have been investigated, and themanufacturability of cores with complex structure has also been investigated. Thefollowing results have been achieved.Particle size gradation of powder has obvious effect on the properties ofceramic cores. Fine powder can improve the sintering process and promote thecrystallization of fused silica. With the increase of fine powder in SA-1,SA-2andSA-3ceramic cores, the contents of cristobalite were14.5%,16.7ï¼…and21.3%respectively. There is an optimum particle size gradation of powder and when theparticle size gradation is about5（coarse）:3（medium）:2（fine）, cores have bestcomprehensive properties.Mineralizer affects phase composition and the crystallization of fused silica.ZrSiO₄does not improve the crystallization of fused silica obviously, while Al₂O₃and Y₂O₃restrain this transformation. Contrast with Al₂O₃mineral, coresmineralized by ZrSiO₄and Y₂O₃have better heat-resisting abilities and properties.Sintering temperature has significant effect on the properties of ceramic cores.The higher the sintering temperature, the more obvious the promoting effect on thecrystallization of fused silica. With the increase of sintering temperature from1160℃to1220℃, the content of cristobalite of cores mineralized by ZrSiO₄increased,from0（1160℃） to12.6%（1180℃）,19.5%（1200℃）and33.2%（1220℃）successively. Cores sintered at1180℃have best comprehensive properties. The properties of silica-based cores were improved greatly when strengthenedby hydrolyzed ethyl silicate and silica sol, while yttrium sol did not improve themapparently, alumina sol even worsened them. Cores strengthened by hydrolyzed ethylsilicate had the properties of flexural strength25.58MPa at room temperature,28.74MPa at1550℃, deflection0.4mm at1550℃,apparent porosity29.2%.The manufacturability of small and large size cores with complex structure hasbeen investigated. By means of trial-manufacturing complex cores, suitabletechnological parameters have been obtained. Through the inspection, the ceramiccores are qualified in size and surface integrity.