| Silicon carbide(SiC)ceramics due to its high brittleness,low tensile strength and poor machinability,the development and application of SiC ceramics are hindered.Carbon fiber toughened silicon carbide composites(Cf/SiC)are composites of carbon fiber with toughening effect and SiC ceramic matrix,which can improve the shortcoming of ceramic brittleness through the characteristics of carbon fiber.With the development of science and technology,the requirement of part configuration is developing from simple structure to complex and super complex structure,which leads to the traditional ceramic and its composite material preparation process is difficult to meet the preparation and molding of these complex components.In recent years,3D printing technology can be used to form complex components.In this paper,selective laser sintering(SLS)technology was used to prepare Cf/SiC green body.By introducing Cfreinforcement phase,the brittleness of SiC ceramic material was reduced and its comprehensive mechanical properties were improved.Meanwhile,SLS technology is to prepare components by layer-by-layer printing,which can realize the preparation of complex structures of materials.The assignment of the subject is to optimize the printing material ratio,determine the printing parameters,and prepare the Cf/SiC composite material body.Subsequently,chemical precursor impregnation pyrolysis(PIP)process was used to improve the density of the composites,and finally obtain high-density 3D printing Cf/SiC composite material.Studying the evolution law of density and microstructure by changing the densityand density of different content and size specifications of Cf/SiC composite materials in thermal curing,degreasing,immersion cracking and other process stages with Archimedes drainage method,SEM,EDS,XRD and other material science analysis and testing methods.The compression and bending properties of Cf/SiC were evaluated by universal mechanical testing machine,and the mechanical failure mechanism of the material was analyzed.In this paper,#280SiC is mixed with carbon fibers of different sizes(20?m,50?m,75?m)and different ratios(5%,10%,15%)to obtain the printing powder,and then it is printed by SLS technology and PIP densification technology.The processing finally obtains Cf/SiC composite material.Research on the preparation process of Cf/SiC composites shows that with the increase of the immersion period,the density of Cf/SiC composites continues to increase and the porosity continues to decrease.Among the Cf/SiC composites with different carbon fiber content,the density of Cf/SiC composites prepared with 5%carbon fiber is the highest;the density of Cf/SiC composites prepared with 5%,75?m carbon fiber is 2.291g/cm3and the porosity is 14.65%,and the density of Cf/SiC composites was higher than that of the other two types of carbon fiber with different carbon fiber specifications.It is shown that multiple impregnation cracking is an important means to increase the density of Cf/SiC composites.The final carbon fiber in the Cf/SiC composite material prepared by the size of 75?m and the content of 5%,10%,and 15%carbon fiber the true content is reduced to 2.84%,4.53%,and 6.96%.The mechanical properties of Cf/SiC composites were evaluated by compression and three-point bending test methods on a universal mechanical testing machine.The results show that the comprehensive mechanical properties of Cf/SiC composites with 5%carbon fiber and 75?m carbon fiber are the best.The compressive strength and flexural strength are 146.43MPa and 129.94MPa respectively,and the fracture toughness is 4.48MPa·m1/2,which is 92.27%higher than that of SiC composites prepared by the same process.The fracture and mechanical properties of the composites were observed and analyzed.It is found that the toughening mechanism of carbon fiber,such as fiber pull-out and fiber debonding,greatly improves the defect of low fracture toughness of ceramic materials,and its failure mechanism is brittle fracture. |
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