Study On The Additive Manufacturing Technology Of Silicon Carbide Ceramics Based On UV Curing

Silicon carbide（SiC）is a kind of structural ceramic material with excellent properties,but it is difficult to be machined because of high hardness,there are some limitations in the preparation of complex fine structure SiC ceramic parts by traditional molding process;Stereolithography（SL）can prepare ceramic body with high strength,high dimensional accuracy and surface quality.It has been widely studied in the preparation of complex fine structure ceramic parts such as alumina,zirconia and silicon nitride.However,the SL for preparing complex fine structure silicon carbide ceramic parts is much more difficult,such as the promble of dispersing hydrophilic silicon carbide powder in oil-based resin,the difficulty of ultraviolet light（ultraviolet light）curing and the low curing accuracy due to the absorption and scattering of UV by silicon carbide powder in slurry,and the prombles of debinding/sintering process for UV cured SiC green body.In order to slove those prombles when fabricate SiC parts by SL,this paper carried out the research on the additive manufacturing technology based on SL for SiC parts preparing,The main research contents and results are as follows:1.Preparation and properties of photosensitive resinFirstly,investigated and analyzed the rheological properties of monomers with different molecular structure and functional groups,the bifunctional monomers HDDA and trifunctional monomers TMPTA were selected;Then,the photosensitive resin with three component was prepared by adding monofunctional monomer according to a certain proportion,the rheological and light curing properties of the resin were investigated,and monofunctional monomer ACMO with excellent properties were selected;Finally,eight kinds of photosensitive resins were prepared by adding slected monomers according to the formula uniform design table UM₈*（8³）,the viscosity,strength,cured precision and light curing rate of the resins were investigated,the regression equation reflecting the relationship between composition and resin properties was established by regression analysis,the photosensitive resin with ratio of m _ACMO:m _HDDA:m _TMPTA=0.250:0.609:0.141 was sleceted,it has the viscosity of 12 m Pa.s（25℃±2℃）,the dimension deviation and strength of the cured resin is 0.69%and 53.0 MPa respectively under a certain UV curing condition（Irradiance 1.1 m W/cm²,exporese time 1 s,slice thickness 50μm）,shows that the resin has the advantages of low viscosity,high reactivity,high light curing precision and curing strength,which can be used to prepare the photosensitive resin based SiC slurry with high performance.2.Preparation of the photosensitive resin based SiC slurryFirstly,in order to solve the prombles when dispersing polar SiC powder in the non-polar photosensitive resin,the dispersion agent 4200 with excellent dispersing property is selected by using the principle of particle dispersion and surface modification,it is a kind of amino acid ester copolymer that can occure"space potential resistance effect"by the anchoring mechanical force of polymer,and realize the uniform dispersion of SiC powder in photosensitive resin finally.The effect of the dispersion dosage on the rheological properties of the slurry was studied also.The optimum addition of dispersant 4200 was 5.0 wt.%according to the mass of SiC powder;Then the influence of resin composition,size of SiC powder,particle grading,solid content and milling time on the rheological properties of slurry was investigated,the relationship between the rheological properties/stability of the slurry and the preparation process parameters was analyzed,and the preparation process parameters were optimized;Finally,the photosensitive resin based silicon carbide slurry with solid content of 52 vol.%was prepared by adding the SiC powder with D₅₀=10.0μm,the viscosity of the slurry was 6607 m Pa.s(25℃±2℃,shear rate 50 s^-1).3.The additive manufacturing process based on the DLP technology for the photosensitive resin based SiC slurryFirstly,investigated the effects of photoinitiator,photosensitive resin,particle size,solid content,light source energy and exposure time on the cured depth of SiC slurry,optimized the process parameters and achieved the rapid light curing of SiC slurry;Secondly,in order to avoid the interruption of UV curing process caused by the debonding of cured layer-metal substrate and cured layer-cured layer,analysed the causes of the debonding phenomenon combined with the light curing theory,and took an effective action by introducing 2-hydroxyethyl methacrylate phosphate（HEMAP）into the slurry,the bonding strength between the cured layer-metal substrate and the cured layer-cured layer is improved bothly,and the photosensitive of the slurry is enhanced at the same time,the continuous and uniform UV curing of the slurry is realized in the end;Finally,aiming at the poor light curing accuracy caused by the incomplete curing of the slurry in the non exposed area,combined with the light curing theory,the causes of the phenomenon are analyzed.According to the characteristics of the slurry,such as slurry composition,powder particle size and solid content,the light curing parameters such as light source energy,exposure time and slice thickness are adjusted to realize the high-quality light curing process of the slurry.Taking the slected 5#photosensitive resin and SiC powder with D₅₀=10μm as raw materials,the optimized irradiance,exposure time and slice thickness were 72m W/cm²,5 s and 50μm respectively.The curing depth of the slurry under this exposure condition was 61μm.The surface roughness of light cured silicon carbide green body on X-Y surface and X-Z surface is 0.19μm and 1.61μm respectively.The density of the light cured SiC green body is 1.91g/cm³,the average three-point bending strength is 20.7 MPa,and the Weibull modulus is 7.63.The light cured SiC green body has the advantages of good surface quality,high strength and good structural uniformity.4.The debinding and reactive sintering of light cured SiC green bodyFirstly,the TG-DSC curve of light cured SiC green body was investigated,established the debinding temperature schedule for green body according to its TG-DSC curves,then investigated the microstructure and properties of the debinded green body;Secondly,according to the microstructure and properties of the debinded green body,calculated the adding dosage of Si combined with the reaction sintering theory,obtained the SiC ceramic parts with densiful and uniform structure.Finally analyzed the microstructure and properties of the reaction boned SiC（RBSC）.For the light cured SiC green body fabricated by photosensitive resin based SiC slurry with solid content of 46 vol.%,the density,carbon content of the debinded green body is1.40 g/cm³ and 3.80 wt.%respectively;after reaction sintering with molten Si,the density,porosity and the three points bending strength of the RBSC is 2.74 g/cm³,0.2vol.%and 215.74 MPa respectively.This study has explored the additive manufacturing based on DLP technology for preparing SiC ceramic parts,fabricated the SiC parts with complex and fine structure finally.This work has some innovative on the items of the three component photosensitive resin fabricating and the continuous uniform high-precision additive manufacturing of photosensitive resin based SiC slurry,which has some valuable reference for the research on the additive manufacturing based on the DLP technology for ceramics.