Preparation And Mechanical Properties Of SiC_f/SiC Composites Based On SLS Technology

Silicon carbide ceramic is considered as one of the ideal structural materials because of its low density,high strength,high-temperature resistance,and thermal shock resistance.However,due to the defect of inherent brittleness,low toughness,and poor impact resistance,the application of SiC ceramic is seriously limited.SiC_f/SiC composite can effectively improve this problem by introducing silicon carbide fiber into the silicon carbide ceramic matrix,which has great application potential in aerospace,new energy,and other fields.However,for the parts with high precision and complex structure,the traditional preparation methods of SiC_f/SiC composite are difficult or even impossible to form.To solve the above problems,a new method to prepare SiC_f/SiC composite is proposed.The ceramic was prepared by selective laser sintering,and SiC fibers were grown in situ in the SiC matrix based on the principle of polymer pyrolysis.SEM,TEM,EDX and XRD were used to study the microstructure of materials in different process stages.The compression,bending and fracture toughness of materials after densification were measured by universal mechanical testing machine,and the mechanical failure mechanism was studied.The effects of different processing parameters on the physical properties and micromorphology of SiC_f/SiC composites were studied.The results show that with the increase of the mass fraction of Polycarbosilane in the printing powder,the output of SiC_f increases obviously,but at the same time,the porosity of the specimen increases and the density decreases.After the sample was pyrolyzed,when the content of Polycarbosilane increases from 5%to 15%,the porosity of the specimen increases from 56.75%to 59.66%.With the increase of pyrolysis temperature,the quantity and length of SiC_f increase,but the effect of growth is limited.In the samples with 3 or 4 hours of holding time,SiC grains are densely covered with fibers,and the fiber length reaches the micrometer level;compared with holding time and sintering temperature,the effect of heating rate on SiC fiber is less.The densification of SiC_f/SiC composite was improved by the PIP process.With the increase of impregnation period,the porosity of all specimens decreased and the density increased.After 8 times of PIP,the density of specimen with the5%Polycarbosilane content was the best,the porosity was 25.87%,and the density was 2.37g/cm³.The difference in density and porosity of samples prepared at different pyrolysis temperatures after 8 times of PIP is about 1%.After the completion of all processes,the mechanical strength of specimens with different Polycarbosilane content and pyrolysis temperature was tested.Among them,the mechanical properties with 5%Polycarbosilane content,pyrolysis temperature of 1300°C and holding time of 3 hours are the best.The flexural strength,compressive strength,and fracture toughness strength are178.71MPa,112.72MPa and 2.72MPa·m^1/2.Compared with SiC ceramics without SiC fiber toughening(the flexural strength,compressive strength and fracture toughness strength are 142.21MPa,92.56MPa and 2.33MPa·m^1/2),all the mechanical properties are improved.