Study On Rapid Prototyping And Siliconization Densification Of SiC Pellet

As a material for a new generation of space mirrors,SiC ceramics have the advantages of light weight,low thermal expansion coefficient,high modulus of elasticity,high melting point,good thermal stability,and optical properties comparable to optical glass.Therefore,it has been a research hotspot in the field of aerospace.The traditional molding process of silicon carbide ceramics can no longer meet the growing demand for complex structure silicon carbide ceramic parts in industrial production.Therefore,3D printing rapid prototyping process without relying on mold has become a research hotspot in the field of silicon carbide ceramic molding in recent years.Selective Laser Sintering?SLS?is a rapid prototyping process based on the idea of discrete stacking.Firstly,a spatial mirror model with complex structure is designed by computer software.The file is converted into STL format for layered cutting process.A series of two-dimensional cross-section information is transmitted to the CNC forming system,and then the laser beam is controlled by the forming system according to the cross-section information.The ceramic powder is selectively irradiated for layer-by-layer sintering to obtain a SiC ceramic green body.After carbonization and reaction sintering,a SiC space mirror with a complicated structure is finally obtained.Observing the microscopic morphology of the material,it was found that there were some holes on the surface,and the ceramic contained a high silicon content with a density of 2.729 g/cm³.The flexural strength of the material was 198±14 MPa,and the fracture toughness was2.97±0.13 MPa·m ^1/2.In order to further improve the density and mechanical properties of SiC ceramics,a thermal curing molding process of silicon carbide ceramics was proposed.In the heat curing rapid prototyping process,the prepared silicon carbide slurry is brushed on a glass plate and superposed in layers in an oven to obtain a silicon carbide blank,which is subjected to carbonization to degrease the phenolic resin in the body and remove the residue.The organic solvent obtains a porous carbonaceous body,and a dense silicon carbide ceramic excellent in properties is finally obtained by silicon infiltration by reaction sintering.The most critical step in the thermal curing rapid prototyping process is the preparation of SiC ceramic slurry.The thermal curing rapid prototyping process requires the preparation of a ceramic slurry having a high solid content and a small volume shrinkage before and after curing.The control variable method was used to study the content of dispersant,the particle size of silicon carbide particles,the solid phase content and the proportion of silicon carbide particles.Four different slurry ratio schemes were designed.Determine the viscosity of the slurry,the volume change before and after solidification,the density of the green body and observe the fracture morphology of the green body after the carbonization.Determine the optimum content of the dispersant in the slurry to be 20%of the mass of the powder in the slurry,and the solid content in the slurry.The mass ratio of silicon carbide powder of 65%,240 mesh and 100 nm is 1:1.The obtained silicon carbide ceramic optimal slurry was applied to the thermal curing molding/RBCS composite process to prepare silicon carbide ceramics,and the properties were tested to have a density of 3.03 g/cm³,a bending strength of 462±13 MPa,and a fracture toughness of 4.32±0.17 MPa.·m^1/2.By comparing the microstructure and mechanical properties of SiC ceramics prepared by two different rapid prototyping processes,it is concluded that the thermal curing rapid prototyping process is more suitable for the preparation of SiC ceramics with high density and excellent performance.