| With the development of the aerospace industry,some components(such as optical measurement portion of the stent and the support structure on the satellite,etc.)need the C/SiC composite properties of higher strength and modulus,and higher strength C/SiC composite material could be satisfactory for the requirement of large area thermal protection structure of a hypersonic aerocraft.At present,C/SiC composite material used Toray T300 fiber as reinforcement,performance optimized for T300 was still unable to meet the needs.Therefore,high strength and high modulus carbon fibers as reinforcement,utilizing precursor infiltration pyrolysis(PIP)process,it studied microstructure of the carbon fiber of high temperature treatment,the interfacial modification,and the structure and properties of C/SiC composite.Toughening mechanisms for different fibers reinforced C/SiC composites are discussed.The proposal to prepare C/SiC composites by precursor infiltration and pyrolysis(PIP)process using high strength(HS)and high modulus(HM)carbon fibers as reinforcement is presented to improve the properties of the existing C/SiC composites.T300 and T700(wet spinning),T700 and T800(dry spinning)as well as M40 and M55(wet spinning plus pull graphitizing)were used as the reinforcement for preparing mini C/SiC composites by PIP method.The influence of high-heat treatment for carbon fibers,chemical vapor deposition pyrolytic carbon(CVD PyC)interface coatings and pre-oxidize for carbon fibers on the microstructures and properties of the mini C/SiC composites was investigated and discussed.The influence of surface characteristics and mechanical properties of different carbon fibers on the microstructures and mechanical properties of mini C/SiC composites were investigated.The surfaces of T700 and T1000(wet spinning)are smooth,whereas T300,T800,M40 and M55(dry spinning)show rough surface with obvious ridge-like prominence and grooves.The tensile and flexural strength of T300/SiC composites are only 40 MPa and 50 MPa respectively,whereas that of T800/SiC composites are 150 MPa and 287 MPa respectively.The tensile and flexural strength of T700/SiC composites are 190 MPa and 391 MPa respectively,whereas that of T1000/SiC composites are 342 MPa and 434 MPa respectively.The tensile and flexural strength of M40/SiC composites are 422 MPa and 570 MPa respectively,whereas that of M55/SiC composites are 647 MPa and 791 MPa respectively.For the same spinning method,the strengths of HS mini C/SiC composites are proportional to the strengths of carbon fibers,whereas the strengths of HM mini C/SiC composites are inversely proportional to the strengths of carbon fibers.The strengths of HM mini C/SiC composites are higher than that of HS mini C/SiC composites obviously.Moreover,the tensile modulus and flexural modulus of T300/SiC composites are 112 GPa and 70.8 GPa respectively,lower than that of T800/SiC,is 145 GPa,70.8 GPa,respectively.The tensile modulus and flexural modulus of T700/SiC composites are 117 GPa and 73 GPa respectively,lower than that of T800/SiC,is 158 GPa,87.2 GPa,respectively.The tensile modulus and flexural modulus of M40/SiC are 117 GPa and 73 GPa respectively,whereas that of M55/SiC are 252 GPa,109 GPa,respectively.It can be concluded that the modulus of mini C/SiC composites are proportional to the modulus of carbon fibers.The influence of high-heat treatment at 1400 °C,1600 °C and 1800 °C on the microstructures and graphitization degree of different carbon fibers as well as the microstructures and properties of mini C/SiC composites were investigated.There is no significant change of the surface for different carbon fibers.The graphitization degree and modulus of HS carbon fibers are improved with temperature increasing,whereas those of HM carbon fibers are constant.As the temperature increasing,the flexural strength of T300/SiC is decreasing,751 MPa is the maximum at 1400 °C;the tensile strength is increases first and then decreasing when is above 1600 °C,the maximum is 822 MPa;while the tensile and flexural modulus are increasing,reach 181 GPa and 87.1GPa at 1800 °C respectively.The flexural strength of T800/SiC is increasing first and then decreasing,962 MPa is the maximum at 1600 °C,whereas the tensile strength is constant at 837 MPa;the tensile and flexural modulus are increasing,reach 205 GPa and 131 GPa at 1800 °C respectively.The flexural strength of T700/SiC is decreasing gradually,613 MPa is the maximum at 1400 °C;the tensile strength is increasing first and then decreasing when is above 1600 °C,the maximum is 821 MPa;the tensile strength is increasing,whereas the flexural modulus is constant,140 GPa and 76.6 GPa is the maximum at 1800 °C respectively.The tensile and flexural strength of T1000/SiC are increasing continuously,the maximum are 741 MPa and 950 MPa respectively at 1800 °C;the tensile modulus is increasing,while the flexural modulus is constant,the maximum are 183 GPa and 106 GPa respectively at 1800 °C.The tensile and flexural strength of M40/SiC are decreasing gradually,so the maximum are 820 MPa and 889 MPa;while the tensile modulus is constant,the maximum are 159 GPa and 102 GPa respectively at 1800 °C.The flexural strength of M55/SiC is decreasing,899 MPa is the maximum at 1400 °C;the tensile strength is increasing first and then decreasing when it above 1600 °C,950 MPa is the maximum;while the modulus is constant,the tensile modulus and flexural modulus are 260 GPa and 113 GPa respectively.The influence of CVD PyC coating after 3 h,7 h and 11 h on the microstructures of different carbon fibers as well as the microstructures and properties of mini C/SiC composites were investigated.There is significant change of the surface for different carbon fibers.The surfaces of T700 and T1000(wet spinning)are smooth,not coating after 3 h,discontiguous coating after 7 h,and continuous coating after 11 h(thickness,0.1? m),whereas T300,T800,M40 and M55(dry spinning)show rough surface with obvious ridge-like prominence and grooves,not coating after 3 h,discontiguous coating after 7 h,and continuous and coarse coating after 11h(thickness,0.1~0.2? m).As the coating time increasing,the flexural and tensile strength of T300/SiC are decreasing first and then increasing,617 MPa and 539 MPa are the maximum after 3 h;while the tensile and flexural modulus are increasing first and then decreasing,reach 138 GPa and 81.7GPa after 7 h respectively.The flexural strength of T800/SiC is increasing first and then decreasing,791 MPa is the maximum after 7 h,whereas the tensile strength is decreasing gradually,591 MPa is the maximum after 3 h;the tensile modulu is increasing and flexural modulus is increasing first and then decreasing,reach 155 GPa at 11 h and 104 GPa after 7 h respectively.The flexural strength of T700/SiC is decreasing first and then increasing,675 MPa is the maximum after 3 h;the tensile strength is constant afer 3 h and 7 h and then decreasing after 11 h,the maximum is 480 MPa afte 3 h;the flexural modulus is constant afer 3 h and 7 h and then increasing after 11 h,the maximum is 80.9 GPa afte 11 h;the tensile modulus is increasing first and then decreasing,117 GPa is the maximum afte 7 h respectively.The flexural strength of T1000/SiC is increasing continuously,the maximum is 695 MPa respectively after 11 h;whereas the tensile strength is decreasing gradually,867 MPa is the maximum after 3 h;the flexural modulus is constant afer 3 h and 7 h and then increasing after 11 h,the maximum is 894.9 GPa afte 11 h;the tensile modulus is increasing first and then decreasing,141 GPa is the maximum afte 7 h respectively.The tensile and flexural strength of M40/SiC are increasing first and then decreasing,so the maximum are 780 MPa and 423 MPa after 7 h;while the tensile modulus is constant,the maximum are 140 GPa;the flexural modulus is increasing gradually,99.0 GPa is the maximum after 11 h respectively.The flexural and tensile strength of M55/SiC are constant afer 3 h and 7 h,but the flexural strength is increasing and the tensile strength is decreasing after 11 h,the flexural strength maximum is 669 MPa afte 11 h and tensile strength is 601 MPa after 7 h;while the modulus is constant,the tensile modulus and flexural modulus are 240 GPa and 105 GPa respectively.The influence of atmospheric oxidation after 0 h,0.5 h,1 h and 2 h on the microstructures of T700 carbon fibers as well as the microstructures and properties of mini C/SiC composites were investigated.There is significant change of the surface for T700 carbon fibers.The surface changes are as follows:a few change after 0.5 h,light grain or ditch on the axial after 1 h,and part region appearing grooves after 2 h.As the oxidation time increasing,the flexural strength is decreasing gradually,648 MPa is the maximum after 0 h;the tensile strength is increasing first and then decreasing,821 MPa is the maximum afte1 h;while the tensile and flexural modulus are increasing first and then decreasing,reach 150 GPa and 92.9GPa after 1 h respectively.So,atmospheric oxidation has litter effect on the tensile strength and raise the modulus,but no beneficial to the flexural strength. |
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