Research On Microstructure Control And Densification Of 3D Printing SiC_f/SiC Composite Based On SLS Technology

Silicon Carbide ceramic materials have excellent properties such as high hardness,wear resistance and high temperature resistance,and are widely used in aerospace and material processing fields.Optimize the comprehensive mechanical properties of SiC materials and improve the strength and toughness of SiC materials.In addition,the 3D printing method can directly mold complex structural ceramic materials,avoiding the secondary processing of SiC ceramics,which can greatly reduce the preparation cost and manufacturing cycle of the materials.In this paper,PCS/SiC blanks are prepared by selective sintering technique,followed by in situ conversion of PCS into SiC fibers by high-temperature cracking to obtain SiC_f/SiC composites,and then the denseness of the material is improved by chemical precursor impregnation cracking process to finally obtain SiC_f/SiC composites with excellent properties.In this dissertation,the density and porosity of the materials were measured by Archimedes drainage method,the microstructure of the materials in different preparation stages was investigated by material science characterization methods such as SEM,EDS and XRD,and the mechanical properties of the densified materials were tested by a universal testing machine,and the mechanical failure mechanism was revealed.In this dissertation,we firstly investigated the factors affecting the pyrolysis of PCS under flowing carrier gas to generate SiC fibers,and studied the influence of catalyst type,carrier gas rate,heating temperature,holding time and other factors on the yield and morphology of SiC fibers,and found that after pre-crosslinking and curing of PCS at 300°C,holding at 1600°C in a flowing Ar gas carrier gas of 10sccm under the action of ferrocene catalyst a relatively high yield of SiC fibers generated by PCS pyrolysis was obtained at 4h.In this dissertation,we subsequently investigated the yield of SiC fibers in SiC_f/SiC composites and the porosity and density of SiC_f/SiC composites by first obtaining printed powders by mixing SiC with different particle sizes and different contents of PCS,followed by obtaining PCS/SiC blanks by SLS technique,and sintering the blanks in a tube furnace to obtain SiC_f/SiC composites.It was found that when the SiC particle size was 100μm and the PCS content was 30%,the SiC fibers in the generated SiC_f/SiC composites had a good yield,and it was also found that the specimens prepared in the 100μm SiC mixed with 10%PCS group had the highest density of 1.0679 g/cm3 and a porosity of 48.61%.Finally,the densification process of SiC_f/SiC composites after multi-cycle precursor impregnation cracking process was investigated.The highly densified SiCf/SiC composites were finally obtained by placing the sintered SiC_f/SiC composites into the impregnation solution containing PCS for pressurized impregnation,followed by sintering in a high-temperature sintering furnace and repeated impregnation until the weight gain rate was<1%.The SiC_f/SiC composites with 100μm SiC added with 40%PCS after PIP10 cycle were found to have the highest density of 2.261g/cm~3 and a porosity of 15.74%.Mechanical tests on the SiC_f/SiC composites revealed that the specimen with 100μm SiC added with 10%PCS after 10cycles of PIP had the highest bending strength of 124.87MPa and the damage form was brittle fracture,while the specimen with 100μm SiC added with 30%PCS after10 cycles of PIP had the highest fracture toughness of 2.405MPa·m^1/2The fracture morphology and mechanical properties of the specimens were observed,and it was found that the SiC fibers effectively improved the fracture toughness and comprehensive mechanical properties of the SiC ceramic materials.