Preparation And Properties Study Of C_f/SiC-Cu Composites

According to the working requirements of solid rocket nozzle throat, a proposal toimprove anti-ablative property of composites by introduction of copper into C_f/SiC anddecrease surface temperature through copper transpiration was presented. In thisdissertation, the feasibility of C_f/SiC-Cu composites prepared by process of slurry brushwith copper or slurry infiltration with copper were investigated at first, and theablation tests of high and low condition were compared to find out the appropriatecondition for anti-ablative test. Then the preparation process, mechanical and ablativeproperties and microstructure of the composites were investigated in detail.The results show that the process of slurry brush with copper was suitable forintroducing copper into C_f/SiC composites, and the composites had high copper contents,with a density of as high as 2.03g/cm³. The strength retention was up to 68.90% because ofthe copper transpiration in composites. Two kinds of oxyacetylene torch tests wereattempted, with high condition of high temperature over 3000°C and high speed of gasstream, and the other low condition of lower temperature at 2200°C and low speed of gasstream. High condition of torch test is closer to that of nozzle throat, so the strengthretention of composites after torch test was only 46.4%, and the recession rate and masslost rate were 0.0246mm/s and 0.0360 g/s. In the following experiments torch test of highcondition was adopted.The densities of 2D C_f/SiC-Cu composites via slurry brush with copper increased withincrease of copper contents which were 1.67vol%, 6.58vol%, 12.38vol% and 17.79vol%.The flexural strength of the composites were 315.5MPa, 272.2MPa, 290.3Mpa and206.7MPa, and the fracture toughness were 14.3 MPa·m^1/2, 12.6 MPa·m^1/2, 13.0MPa·m^1/2and 14.3MPa·m^1/2, respectively. The distribution of copper in composites wasunhomogeneous with increase of copper content. The flexural strength of composites afterablative test decreased dramatically, and the composites with copper content of 12.38vol%had the highest strength retention, with strength of 290.3MPa and 141.1MPa before andafter ablation test. With the copper content increase, the recession rates decreased whilemass loss rates increased to a certain level. The microstructures were greatly influenced bytorch test, and the composites showed brittle failure mode. When the composites had ahigher copper content, the flexural strength might be better remained via coppertranspiration. After ablative test, the copper content in composites decreased significantly,with appearance of new phases Cu5Si and Cu3Si, from reaction of Si and Cu.