Research On Design Fabrication And Properties Of Al25Si-xMo/(C/C)dissipative Thermal Protective Materials

Hypersonic aircraft nose cone and solid rocket engine laryngeal lining material in which the ambient temperature above 2000?,the need for anti-heat material to meet its ablation resistance on the basis of both low density and high mechanical properties.In this paper,Al25Si-xMo/(C/C)dissipation heat-resistant composites with light,high strength and long-lasting ablation were prepared by liquid-phase impregnation and pressure impregnation.The microstructures and phases of dissipative heat-resistant composites were studied by means of metallographic microscope(OM),scanning electron microscopy(SEM),Raman spectroscopy,X-ray diffraction and X-ray fluorescence spectroscopy.The three-point bending test The mechanical properties of the composites were studied.The thermal expansion properties and thermal shock resistance of the composites were investigated.The ablation performance and ablation behavior of the composites were studied by the ablation test of oxyacetylene(OA),and the effect of Mo on the properties of the composites was investigated.The carbonaceous C/C composites with density of 1.73g/cm3 were used in the composites.The graphitization of the composites varied between 23.5% and 56.8%.Porosity of 20.26%,more than 90% of the three-dimensional connectivity hole.The preparation method of C/C-MoO3 preform was obtained by using ammonium molybdate as the precursor of Mo.The preparation method of Al25Si-x Mo/(C/C)was prepared by pressure impregnation method.Composites.The compressive properties of the composites were 243MPa~259MPa,and the compressive properties were 187.2~192.3MPa,which was nearly doubled compared with the matrix.The elastic modulus of the composites was up to 37.1GPa,and the content of the composites increased with the increase of the Mo content The modulus has increased,more than 20% higher than the matrix.The thermal expansion coefficient of the X-Y surface of the prepared composite material is between(0.3~0.9)×10-6/K,and the Zdirection thermal expansion coefficient is between(3.7~5.7)×10-6/K.The thermal shock resistance of Al25Si-xMo/(C/C)composites is good,and the critical temperature difference is about 1000?.Mo element improves the thermal shock resistance of the composites.The ablation rate of Al25Si-xMo/(C/C)composites is less than one order of magnitude,and the ablation rate of composite materials with different Mo content is maintained at the order of 10-3mm / s in 80 s.And the ablation rate of the composite with Mo content of 3% was 120×10-3mm / s within 120 s.The results show that the Al/Si alloy melting process occurs first in the ablation of the Al25Si-xMo/(C/C)dissipation heat-resistant composite material,and the ablation begins to absorb heat instantaneously.And the Mo element is present in the form of particles in the Al-Si alloy to reduce the rate of dissipation of the dispersant and improve the time of the protection of the dispersant.After 10 s,the surface of the composite material will produce high temperature MoSi2,extend the protection time of the composite material and improve the ablation performance.