Fabrication And Performance Of Silicon Carbide Fibre Reinforced Silicon Matrix Composites

Thermal protection system?TPS?is one of the most significant structures of aerocrafts.This structure can protect aerocrafts with high velocity in the aerosphere from invalidation or even burning.On the background of thermal protection structure based on aerocrafts with high velocity,and based on the research of the sandwich integration thermal protection structure materials,to solve the high temperature?>1200??resistance to the bread of the structure,silicon carbide fibre reinforced silicon dioxide?SiC_f/SiO₂?composites were fabricated by sol-gel process and the properties of the composites were investigated.Meanwhile,the sol-gel process was matched to the process of the sandwich integration thermal protection structure materials.The composition and strength evolutions of SiC fibre after heat-treatments have been investigated.The SiC fibre has high crystalline degree.After heat-treated at 1000? in air,the single fiber tensile strength was 2.55 GPa,and the strength retention was86.14%.After heat-treated at 1500? in air,the strength retention was as high as50.51%,which showed that SiC fibre has good properties of high temperature and oxidation resistance.The solid content of the silicon dioxide sols was 23.01%.After heat-treated at 1300?,the phase of the sols changed from amorphous to crystal.The fabrication process and properties of SiC_f/SiO₂ materials as the bread of sandwich structure?hereinafter referred as the bread materials?have been studied.The results showed that the porosity decreased while the density and the flexural strength of the bread materials increased as the heat-treated temperature increased.The difference of the fabrication temperature such as 800?,900?,1000? have little influence on the flexural strength of the bread materials.And the 800? is matched to the sandwich integration thermal protection structure preparation technology.So 800? was as the fabrication temperature of the bread materials.Moreover,the fillings of the sandwich integration thermal protection structure materials were aerogel.The heat-treatment cycles were restricted because the aerogel cannot be heated with time after time or long time.The density the bread materials with once heat-treatment was 1.68 g·cm^-3.And the flexural strength was 67.51 MPa.As for the bread materials,attention was paid on problems about shout production cycle and properties.The flexural strength of the SiC_f/SiO₂ composites after a number of cycles?socking?drying?heat-treated?was investigated.The results showed that the porosity decreased while the density and the flexural strength of the SiC_f/SiO₂ composites increased as the cycles increased.When the cycles reached 5,the flexural strength of SiC_f/SiO₂ composites reached the maximum,and was 178.62 MPa.The mechanical,thermal-physical thermal-stability?oxidation resistance and thermal-shock resistance?properties and the oxyacetylene ablation performance of the bread materials were studied.The flexural strength,tensile strength,interlaminar shear strength and fracture toughness of the bread materials fabricated at 800? were 67.51MPa,135 MPa,7.9 MPa,3.9 MPa·m^1/2,respectively.The materials retained 111.24%?75.10 MPa?of its raw strength when tested at 1200?.Thus the bread materials displayed good high-temperature mechanical properties.The coefficient of thermal expansion?CTE?increased as the testing temperature?from RT to 1300??increased,and reached a maximum of 5.05×10^-6 K^-1 at 1300?.And the thermal conductivity was1.541 W·m^-1·K^-1 at RT.The bread materials that were heat-treated once retained over90%of its raw strength after 1300?/1500? oxidation under static air for 30 min.And the bread materials retained over 80%of its raw strength after 1300?/1500? thermal shock?shocking 10 min?.The oxyacetylene flame test was performed with a center temperature of 2240? for 15s.The result suggested that he molten SiO₂ was flowed to the edge due to the high velocity scouting of the heat flow,leading to the rough ablation surface.The mass ablation rate and the linear ablation rate were 0.060g·s^-1?0.077 mm·s^-1,respectively.The oxidation resistance and the oxyacetylene ablation performance of the SiC_f/SiO₂ composites were investigated.The flexural strength retention ratios were over80%after 1300?/1500? oxidation under static air for 30 min.And the composites showed the mass ablation rate and the linear ablation rate were 0.049 g·s^-1?0.067mm·s^-1,respectively.