Research On Key Technology Of 3D Printing Of SiC Ceramic Matrix Composites

Silicon carbide ceramic matrix composites have many advantages,such as low density,high specific strength,high specific modulus,high temperature resistance,wear resistance and corrosion resistance.Silicon carbide whisker reinforcing and toughening ceramic material can effectively improve the brittleness of ceramics.Therefore,they have broad application prospects in aerospace,energy,transportation and other fields.At present,the main disadvantage of common methods used to prepare SiC ceramics and composites is that the process control is difficult,the production cycle is long,the cost is high,and the exhaust gas products emitted are complex and polluting.It is also difficult to process because of its high hardness and brittleness,which limits its application.Additive manufacturing technology is a promising method to overcome shape limitations and has been used to produce silicon carbidebased samples.Direct ink writing is a material-increasing manufacturing technique in which ceramic slurries with high solid content are extruded through fine nozzles and deposited layer by layer into complex macrostructures.In this thesis,SiC ceramic matrix composites are prepared by direct ink writing and reaction melting sintering,and the preparation process of DIW/RB-CMC-SiC is explored.Firstly,the rheological properties of silicon carbide composite slurry for direct ink writing were studied.Ceramic slurry with shear thinning behavior is prepared from sodium alginate as binder,polyethylene glycol 400 as dispersant,silicon carbide powder,carbon black powder and silicon carbide whisker.The slurry prepared by 2.5wt.%sodium alginate solution has lower viscosity and higher plasticity.The slurry prepared by adding 1%dispersant relative to the powder mass has the lowest viscosity and the best dispersion effect.The slurry viscosity increases with the increase of solid content and carbon black content.Silicon carbide ceramic matrix composite slurry is prepared.The slurry shows shear thinning behavior and has stress yield point,and the fluidity and plasticity meet the requirements of DIW.Then,single factor test of extrusion molding process was carried out with the prepared SiC composite slurry,and the influencing factors of extrusion molding process of ceramic slurry were investigated.The process parameters of 3D printing molding of ceramic slurry were determined by the test.The parameters for 3D printing of silicon carbide ceramics are set as follows:nozzle diameter 0.6mm,air compressor pressure 0.5MPa,screw extrusion ratio 3.5,layer thickness 0.24mm and printing speed 30mm/s.In this way,the surface of the printed blank is smooth and smooth,the lines are smooth and the shape and size are closer to the model size.It has high precision.A three-dimensional forming test was carried out with this process parameter.The average dimension error in X and Y direction is 0.2mm and that in Z direction is 0.1mm.Finally,the reaction sintering process was explored and the densification and near-net forming of DIW-CMC-SiC were completed.The effects of carbon black content and silicon carbide whisker content on the sintering properties of samples were investigated.It was found that the bending strength first increased and then decreased with the increase of carbon black content.When the carbon content is 6.4wt.%,the maximum bending strength is 239.3MPa.With the increase of silicon carbide whisker content,the bending strength and fracture toughness of the material increase at first and then decrease,with a content of 20wt%.The bending strength and fracture toughness of silicon carbide whisker composites reached 301.6MPa and 4.02MPa·m1/2,which are 26%and 18%higher than single-phase silicon carbide respectively.