The Surface Coating On C_f And The Preperation And Properties Of C_f/SiBCN Composite

The surface coating on C_fwas coated by precursor impregnation and pyrolysis（PIP）, and then C_f/SiBCN composites were fabricated by hot-press sinteringtechnique （HP） under different temperatures. The effect of sintering temperature onmicrostructure, mechanical properties, thermal shock resistance and anti-ablativeproperties of the composites was investigated by means of XRD, SEM, TG, as wellas three point bending and single edge notched beam bending tests and so on. It willprovide useful references for the exploitation and development of SiBCN ceramicson high temperature fields.The experimental results show that by changing two factors-the concentrationof the impregnating solution and pyrolysis temperature, the carbon fiber surfaceformed a layer of dense, uniform coating, and the dispersion of fibers is good,coating effect is more desirable when the impregnated concentration of phenolicresin and the pyrolysis temperature is40g/L and700℃.The sintering temperature of this paper were respectively1800℃,1900℃and2000℃. The elastic modulus was the best when it was sintered in1900℃, with55.6GPa. The flexural strength of composites were becoming more outstanding withthe rising of sintering temperature. By contrast, it exhibited the best flexuralstrength when the sintering temperature was2000℃, with70.5MPa. The fracturetoughness were between2.24and2.38MPa·m1/2.Thermal shock performance after700,900and1100℃were investigated.Results show that the thermal shock resistance of the composites decreased with therising of sintering temperature. The residual strength of composite sintered in1800℃was56.9%after a thermal shock at1100℃. When thermal shocktemperature difference ranged from900℃to1100℃, because of the generation ofSiO2which can make up for part of holes and grooves after C_foxidation, thestrength almost unchanged. SEM result indicated that on the morphology of thesurface and fracture boundary, C_fwere oxidized, and left many holes and grooves onthe surface of the sample. Observing the internal morphology of the fracture, we sawthat the interior still existed undamaged C_f, it showed that C_fstill enhanced thestrength of the matrix, and the fibers gradually were becoming integral with theincrease of the distance from the surface.In the ablation experiment, the surface of the composites were ablated withoxyacetylene flame. The temperature of surface reached about2200℃. The resultsindicated that the density has an important effect on the ablation property of composites. With the increase of density, the rate of ablation decreased. When thesintering temperature was2000℃, the composite had the best ablation property,with the line ablation rate and mass ablation rate were0.0422mm·s^-1and0.0137g·s^-1.