Research On Design Fabrication And Properties Of Al25Si-C/C Dissipative Thermal Protective Composites

In this thesis,the preparation of light,high strength,high temperature ablation of the heat-resistant material as the goal,to dissipate heat for the design ideas,using different density C/C composite material as a matrix and Al25Si-C/C dissipation heat-resistant composite materials were prepared on the basis of Al25 Si alloy as the impregnating agent.Al25 Si alloy was chosen as the impregnant is based on the consideration of the physical properties and thermodynamic properties of the materials.Composites were analyzed by means of advanced analytical method,and the influencing factors were discussed.The anti-ablation properties of the microstructures were characterized by oxygen-acetylene ablation experiments.The mechanism of ablation of the materials was investigated by combining the thermodynamic and ablation behavior of the ablation process.Al25Si-C/C composites are more compact and the impregnation agent is uniformly distributed in the matrix.This microstructure plays an important role in improving the mechanical properties of the composites.The phase on the surface of the material is mainly C,Al,Si.The bending strength of the five dissipative heat-resistant composites increased by 32.05%-101.98% and the compressive strength increased by 32.37%-142.13% compared with the C/C matrix.The thermal shock resistance of Al25Si-C/C dissipation heat-resistant composite material is excellent,and the residual bending strength exhibits a significant decrease,then increases and then decreases with the increase of thermal shock temperature.C/C matrix Z direction of thermal expansion coefficient is greater than the XY direction,even a negative expansion phenomenon showes in the XY direction.The thermal expansion coefficient of the composites increases in both directions,and the thermal expansion coefficients of the matrix and dissipative heat-resistant composites show a tendency to decrease and then increase with increasing temperature.Oxygen-acetylene ablation test results show that the ablation rate of Al25Si-C/C dissipation heat-resistant composites is lower than that of C/C,especially when the ablation time is short,the linear ablation rate is obviously reduced,which indicates that the ablation resistance of the material is improved.The center area of ablation,the surface of the transition zone and the edge area showed different micro-morphology.During the ablation process,the oxide layer was formed on the surface of the material,and the main components were Al2O3 and SiO2.Thermodynamic analysis shows that the surface penetrant is more likely to react with oxygen under ablation conditions and formed an oxide film covering the surface.Therefore,the C/C matrix is protected.The surface of the liquid oxide layer is sticky,making the mechanical erosion of the material weakened.The thermochemical ablation of the surface of the Al25Si-C/C heat-resistant composite causes the oxygen dissipation,and the endothermic action of the infiltration agent,the thermal barrier of the oxide film,and the heat generated by the gas evolution caused thermal dissipation.The combined effect of these factors improves the ablation resistance of the material.