Study On Fabrication And Ablation Resistance Of Al-Si-B/Gr Dissipative Thermal Protective Composites

This paper adheres to the concept of providing high-throughput preparation of light-weight,high-strength,high-temperature ablation and high-speed particle-washing heat-resistant materials for key parts such as supersonic aircraft,solid rocket motors,and missile ends,based on the basic theory of dissipative heat protection,four kinds of Gr with density of 1.50g/cm³,1.60g/cm³,1.74g/cm³and 1.83g/cm³ were selected as the matrix materials,and the mass ratios were Al₁₀Si₈₀B₁₀,Al₂₀Si₇₀B₁₀ and Al₃₅Si₅₅B₁₀.The six component dispersants of Al₂₂Si₇₈,Al₂₁Si₇₄B₅ and Al₁₉Si₆₆B₁₅ were prepared by optimized pull-type vacuum infiltration method for 24 kinds of AlSiB/Gr composites.And a series of advanced analytical testing methods were used to analyze the microstructure,bending and compression properties,thermal conductivity,thermal expansion coefficient and thermal shock resistance of the surface and interior of AlSiB/Gr composites,and the law of the permeability depth of the dispersant with the porosity of the Gr matrix and the composition of the dissipating agent is summarized,and the infiltration mechanism of the AlSiB ternary dispersing agent is explained.Through the characterization of the oxy-acetylene ablation samples and the ablation rate of the composite and Gr matrix,the evolution of the surface ablation products at different ablation times was observed and combined in different stages of the ablation process.The ablation behavior of the sample explains the ablation resistance mechanism of the AlSiB/Gr dissipative heat-resistant composite.The phases in the prepared composite are mainly C,Al,Si,SiC,AB10 and SiB6.Dissipative volume fraction reaches up to 28.88%.Taking AlSiB/1.50Gr composite as an example,the performance of compression and bending is 308.78%and 165.27%higher than that of Gr matrix,respectively,reaching 140.17MPa and 260.87MPa respectively.The thermal conductivity of the composite material is 92.203W/?m·K?,which is slightly lower than that of the 1.50Gr 102.390W/?m·K?.When the temperature rises,the thermal conductivity of AlSiB/Gr decreases,and the Gr matrix is slowed down.The thermal expansion coefficient of the composite at 100? is about 2.8×10^-6K^-1,which is flat with the Gr matrix.The temperature rises and the value increases.The 70%residual bending strength thermal shock temperature is raised from 600? of the Gr matrix to 1420?.With the increase of the density of Gr matrix,the porosity decreases,and the thickness of the layer of the same kind of dispersant in the Gr matrix increases linearly with the increase of porosity;Al₂₀Si₇₀B₁₀ has a thickness of 4.31mm in1.50Gr and 0.41mm in 1.83Gr;with the content of Al and B in the dispersant The thickness of the disintegrating layer of the dissipating agent is increased to different degrees,and the thickness of the infiltrated layer is up to 5 mm or more when the dissipating agent is elemental Si.The oxygen-acetylene ablation test shows that the ablation rate of AlSiB/Gr composites is one order of magnitude lower than that of Gr matrix.Under the premise that the layer is not burned through during ablation,the higher the density of Gr matrix,the composite of AlSiB/Gr The better the ablation resistance of the material,the introduction of proper amount of Al and B is also beneficial to improve the ablation resistance of the composite.It is the best dissipative component of the composite with ablation resistance.Al:Si:B=2:7:1?mass ratio?.The mass ablation rate of Al20Si70B10/1.74Gr with the best ablation resistance of 60s is 0,and the line ablation rate is as low as 0.7000?m/s.The components of the ablation products are mainly Al2O3 and SiO2 ceramic membranes and the B2O3 vapor membrane further protects the oxygen dissipation;when the ablation occurs,the dissipative phase change heat absorption,the thermal insulation of the ceramic membrane and the gas escaping cause thermal clogging to form heat dissipation.The double action of oxygen dissipation and heat dissipation greatly improves the ablation resistance of AlSiB/Gr composites.