Study On Microstructure And Mechanical Properties Of A High-solid-loading Silicon-based Ceramic Core By Stereolithography Additive Manufacturing

The development of double wall cooled turbine blades is the key means to improve the overall performance of aeroengines.Because the internal cavity structure of double wall cooling turbine blade is complex,multiple cores need to be preset to form.If the traditional hot pressing injection preparation method is adopted,not only the tooling cost is high and the cycle is long,but also it is difficult to accurately locate between the cores.Therefore,it is urgent to develop an integrated preparation technology of ceramic core for double wall cooling turbine blade.This paper takes the light curing additive manufacturing technology of ceramic core as the research object.Based on the concept of integrated molding of double-layer wall ceramic core,focusing on the key scientific and technical problems to be solved in the additive manufacturing process,this paper carries out the research work on the composition design,process optimization,sintering strengthening,microstructure and performance regulation of light curing ceramic core slurry.The main results are as follows:(1)Through the study of ceramic core slurry,it is found that the content of ceramic powder,that is,solid content,has a significant effect on the curing behavior of slurry and the microstructure and properties of core.The high solid content slurry can effectively improve the Sintering Densification of ceramic particles,reduce the sintering shrinkage of samples,and improve the interlayer bonding strength and mechanical properties at room temperature and high temperature.Based on the photopolymerization theory of ceramic slurry,the solid content was increased from 45 vol%to 60 vol%by adjusting the composition ratio of resin ceramic powder.At this time,the sintering shrinkage of the sample is within 3.2%,the porosity is about 30%,the high-temperature flexural strength is about 24MPa,the room temperature flexural strength is about 10MPa,and the dimensional accuracy error is 2%.(2)The results show that the forming direction has a significant effect on the microstructure and comprehensive mechanical properties of ceramic core.On the premise of 60%of the length of the core and the height of the sintered core,the properties of the three samples were compared.It is found that due to the shear"surface effect",the properties of core samples in width forming direction are obviously sensitive to the regulation of sintering process;Due to the small area of the joint surface of the samples in the length direction,the shear surface is almost parallel to the stress direction.At the same time,the samples in the height forming direction have relatively few printing layers,large layer area and thermal stress concentrated on the sample surface.No matter how to adjust the process parameters,the performance data of the samples in the two forming directions have no obvious fluctuation and change,and are less sensitive to the sintering process.Therefore,the sample performance data in the width forming direction can effectively explain the influence law of composition regulation,process regulation and other factors on the ceramic core,which is suitable to be used as a sample to characterize the comprehensive properties of ceramic core with complex structure.(3)In order to further regulate the properties of samples,the effects of ZrO2 Mineralizer on the curing behavior of core slurry and the microstructure and properties of core were analyzed.The results show that the addition of ZrO2 intensifies the light scattering effect in the curing process and increases the false curing area.However,in terms of microstructure and properties,ZrO2 is easy to react with the matrix material fused silica glass to produce ZrSiO4,which inhibits the crack initiation and expansion and improves the high-temperature mechanical properties of the core.On the basis of comprehensive consideration of curing behavior and microstructure properties and on the premise of 60vol%high solid content,the content of ZrO2 mineralizer in the slurry should be controlled in the range of 8.4-9.2wt%.(4)Combined with the ceramic particle stacking theory,the particle size gradation of light curing additive for manufacturing high solid content ceramic core is regulated,the printing accuracy model based on bierland Lambert light scattering attenuation principle is improved,and the optimal particle size gradation design principle of taking large particles as the framework and filling them with medium and small particles to form close packing is put forward.This gradation will effectively improve the bonding degree between core particles,increase the particle contact area and reduce the sintering shrinkage.At the same time,it will promote the formation of ZrSiO4 phase at the particle link at high temperature and improve the high-temperature performance of the core.Therefore,for 60 vol%slurry with high solid content,the optimal ceramic powder particle size ratio is 2 vol%10μm ZrO2 powder+58vol%fused quartz glass powder,in which the fused quartz glass powder is composed of 60wt%polygonal powder+10wt%10 μm spherical powder+10wt%20μm spherical powder+10wt%30 μm spherical powder+10wt%40μm is composed of spherical powder.Through the research on the composition design,process optimization,sintering strengthening,microstructure and performance regulation of ceramic core slurry prepared by light curing,the component design principle of ceramic slurry suitable for light curing additive manufacturing technology and the research method of accurately controlling "shape" and "property" of integrated ceramic core are put forward.The double wall ceramic core is successfully prepared,and the single crystal superalloy hollow turbine blade with clear inner cavity structure is poured out.