Structure And Properties Of C_f/SiC And SiC_f/SiC Composites Fabricated By Precursor Infiltration And Pyrolysis Process With PCS/LPVCS

C_f/SiC?SiC_f/SiC composites have high temperature resistance,high strength,high modulus and oxidation resistance.Precursor infiltration and pyrolysis process has been widely used in peraparing C_f/SiC and SiC_f/SiC composites for its advantages of low equipment requirement and net forming complex structure.PCS is the most widely used and mature precursor of silicon carbide matrix,however there are still some problems exist,such as low ceramic production rate and product richs in carbon.LPVCS is a new type of liquid hyperbranched polycarbosilane with the properties of liquid under normal temperature and low price,which is a precursor of development potential.In this article,according to the characteristic of PIP process that weight increase quickly in the first several cycles and weight increase slowly in the last several cycles,LPVCS and PCS were used to prepare C_f/SiC?SiC_f/SiC composites by PCS for the first several cycles and LPVCS for the left several cycles.Structure of precursor and characteristic of composites were studied:structure,physical and chemical properties of PCS and LPVCS,preparation,room temperature mechanical properties,high temperature resistance,oxidation resistance and high temperature performance damage mechanism of C_f/SiC and SiC_f/SiC composites.Firstly,the molecular structure and inorganic process of PCS and LPVCS were analyzed.The results show that:?1?LPVCS has better wettability than PCS and higher impregnation efficiency;?2?PCS and LPVCS inorganic process is different,at room temperature to 600?PCS mainly happened dehydrogenation reaction,in the room temperature to 300?LPVCS main happened hydrogen hydride addition reaction,above 600?,PCS and LPVCS have similar structure evolution,from organic to inorganic structure,gradually form SiC microcrystalline.The composition,structure and properties of C_f/SiC composites were analyzed.The results show that:?1?LPVCS has better wettability than PCS and higher impregnation efficiency,with the increase of LPVCS,the porosity decreased,the The flexural strength and fracture toughness of C_f/SiC composites improved,the mechanical properties of C_f/SiC composites prepared by LPVCS were better than those of C_f/SiC composites prepared by PCS by 22.2%and 103.6%respectively;?2?With the increase of LPVCS,the SiCxOy phase increased,and the high temperature performance of C_f/SiC composites was influenced by oxygen content,the oxidation resistance of C_f/SiC composites were less affected by oxygen content;?3?Compared with PCS,the surface force between LPVCS pyrolysis product and T300 fibers is weaker.The composition,structure and properties of SiC_f/SiC composites were analyzed.The results show that:?1?LPVCS has better wettability than PCS and higher impregnation efficiency,with the increase of LPVCS,the porosity decreased,the flexural strength and fracture toughness of SiC_f/SiC composites improved,the mechanical properties of SiC_f/SiC composites prepared by LPVCS were better than those of SiC_f/SiC composites prepared by PCS by 50.7%and 21.9%respectively;?2?With the increase of LPVCS,the SiCxOy phase increased,and the high temperature performance of SiC_f/SiC composites was influenced by oxygen content,the oxidation resistance of SiC_f/SiC composites were less affected by oxygen content;?3?Compared with PCS,the surface force between LPVCS and KD-II fibers is weaker.The results show that:?1?C_f/SiC composites have higher mechanical properties than those of SiC_f/SiC composites,The flexural strength,flexural modulus and fracture toughness of the C_f/SiC composites are 301-368 MPa,50-66.5 GPa and 11.2-22.8MPa·m^1/2,respectively which of the SiC_f/SiC composites are 213-321 MPa,57.9-108GPa and 7.76-9.73 MPa·m^1/2 respectively;?2?The oxidation resistance of SiC_f/SiC composites is better than that of C_f/SiC composites,SiC_f/SiC composites showed good oxidation resistance below 1400?;?3?C_f/SiC composites and SiC_f/SiC composites showed good high temperature performance under 1400?.Raw material of LPVCS costs less than one third of PCS,so use LPVCS has the raw material cost advantage:below 1400?in the argon gas,C₃ precursor material costs only 77.2%of C₁;Under 1000?in air,C₅ precursor material cost only 23.5%of C₁;SiC₄ has best mechanical properties,and its precursor material cost is 25.6%of SiC₁.