Study On Laser 3D Printing Silicon Carbide Ceramic Powder And Its Reaction Infiltration Process

Laser Selective Sintering(SLS)is one of the typical laser 3D printing technologies.It is an additive manufacturing process based on powder bed,which has some advantages,such as a wide range of materials,fast forming speed and can directly form complex structural parts without molds.In recent years,forming complex structural ceramics by SLS has become a research hotspot.Domestic and foreign scholars generally use SLS to form ceramic blanks,followed by degreasing and high temperature sintering to strengthen ceramic parts.In the field of shaped silicon carbide,SLS-formed ceramic bodies are usually treated by siliconizing reaction sintering to obtain higher-performance silicon carbide ceramic parts.However,there are few studies on the design and preparation of SiC starting materials for SLS,and the influence of SiC initial material parameters on its forming and sintering properties is crucial.Therefore,this paper combines SLS with reactive infiltration process(RMI)to study the effect of initial material carbon content on the carbon density of the SLS and the density and mechanical properties of the sintered body.The influence of density,size and flexural strength of SiC ceramic samples;reveals the influence of particle-scale paired specimen density and flexural strength,and lays a foundation for SLS to prepare complex structural SiC parts.The research work was carried out from the following aspects:The effect of carbon density on the microstructure of SLS/RMI silicon carbide was studied by adding carbon black and impregnated asphalt.he results show that the density of sintered body increases first and then decreases with the increase of carbon density;carbon density Excessive assembly causes the silicon nitride to block,resulting in a decrease in density and mechanical properties of the sintered body.Different addition amounts of carbon black(5,10,15,20wt.%)/PF/SiC composite powders were prepared by dissolution precipitation method and mechanical mixing method.The density and size change of SiC ceramic samples prepared by SLS/RMI were compared.The results show that the mechanical density of the SLS body has higher carbon density,better siliconizing performance,compacter sintered body and less sintering shrinkage.With the increase of carbon black content,the sintering shrinkage rate of the sample increases.The density and mechanical properties increase.When the carbon black content is 20wt.%,the carbon density is0.5542g/cm~3,the sintered body density is the highest,up to 2.871g/cm~3,and the flexural strength is up to 190.2MPa.The SLS body is subjected to asphalt immersion treatment,and the pores are filled with pyrolytic carbon to increase the carbon density.The immersion treatment improves the siliconizing property of the preform.When the carbon black content is 5 wt.%,the carbon density is 0.6612 g/cm ~3,and the sintered body The highest density reached 2.899g/cm~3,the relative density reached 90.31%,and the flexural strength was 161.91±1.89MPa.In order to further improve the mechanical properties of SiC,C_f/SiC ceramic composites were prepared by adding chopped carbon fiber powder to the powder for SLS.The densification,dimensional shrinkage and micro-macroscopic properties of C_f/SiC ceramics were tested and characterized.The influence of carbon fiber on the precision and flexural strength of C_f/SiC ceramics was discussed and revealed.The C_f/PF composite powder with good coating effect was prepared by dissolving and precipitating.The blank was formed by laser 3D printing.The influence of laser power on the size and density of C_f/PF blank was discussed.When the laser power was 6 W,the billet was used.The body size accuracy is the best;the asphalt body is reinforced by the asphalt impregnation/RMI process,and the obtained samples have a length,width and height average deviation of-2.84%,-3.78%,3.81%,density of2.485±0.059g/cm~3,and bending resistance.The strength is 104.46±10.25 MPa.30vol%carbon fiber was added to 10wt.%carbon black/PF/SiC powder,and the C_f/SiC material was prepared by laser 3D printing/RMI process.The average length-width deviation was-1.58%,-2.16%,1.58%.The density is 2.851±0.035g/cm~3,and the flexural strength is 190.69 MPa.The density and structure of the green body are important factors affecting thesintering properties of siliconizing.The particle density of the SiC ceramics prepared by particle-size matching SLS/RMI is studied by changing the bulk density of the powder and SLS body by particle grading.The influence of bending strength and microstructure.Experiments show that particle grading can increase the density of the green body,reduce the sintering shrinkage rate,and reduce the number of large pores inside the SLS blank to some extent,improve the efficiency of silicon infiltration,and reduce the content and size of free silicon in the sintered body.Furthermore,the flexural strength of the sintered body is improved.When the particle size is 85:10:5,the density of the green body is up to 1.304 g/cm~3,the mechanical properties of the sintered body are the best,and the density of the sintered body is up to 2.713g±0.0295/cm~3.The bending strength is 168.96±5.57MPa.