To improve the ablation resistance of carbon/carbon(C/C)composites,a SiC/ZrC-ZrB2 double layer coating was fabricated by pack cementation and slurry-sintering method.The ablation resistance of the SiC/ZrC-ZrB2 coating was tested under plasma flame above 2300°C.The results indicate that the SiC/ZrC-ZrB2 double layer coating exhibits superior ablation resistance than the ZrC-ZrB2 single layer coating.After being ablated under the plasma flame for 20 s,the mass and linear ablation rates of the ZrC-ZrB2 coating are 0.89 mg/s and 15.3μm/s,while those for SiC/ZrC-ZrB2 coating are 0.09 mg/s and 24.15μm/s,respectively.During ablation,the SiC inner layer can generate SiO2 glass and result in the formation of ZrO2-SiO2 molten film.Compared with the ZrO2 molten film formed on the ZrC-ZrB2 coating surface,the ZrO2-SiO2 molten film with lower oxygen diffusion rate and viscosity enables the SiC/ZrC-ZrB2 coating to have better self-healing ability.Therefore,the enhanced ablation resistance of the SiC/ZrC-ZrB2 coating can be attributed to the formation of dense ZrO2-SiO2 molten film under the plasma flame.
LIU Han-zhouYANG XinFANG Cun-qianSHI An-hongCHEN LeiHUANG Qi-zhong
C/C-ZrC-SiC composites with different ZrC-SiC contents were fabricated by precursor infiltration and pyrolysis. The effect of ceramic content on the microstructure and ablation resistance was investigated. Both the C/C-SiC and C/C-ZrC-SiC composites exhibited good ablation resistance under the plasma flame above 2300℃. Withtheincreaseof ZrC content, a continuous oxide layer and a solid Zr-Si-O mesophase were formed during the ablation. And the structure of the formed oxides layer closely linked with the contents of ZrC-SiC ceramics. The solid ZrO2-ZrC and Zr-Si-O mesophase could increase the viscosity of SiO2 moderately and improve the anti-scouring ability. The continuous SiO2-ZrO2-ZrC-SiC layer would serve as a thermal and oxygen barrier for preventing the substratefrom further ablation. The C/C-ZrC-SiC composites with 27.2%ZrC and 7.56%SiC shows superior ablation resistance, and the mass and linear ablation rates are-3.51 mg/s and-1.88 μm/s, respectively.
A dense ZrC coating with the thickness of 130 μm is prepared on graphite by reactive melt infiltration.XRD and SEM analyses show that the phase composition of the coating is ZrC and it adheres well with the substrate.The influence of ZrC coating on mechanical properties of the graphite was investigated by compression tests and the results show that after the coating process,the compression strength of the coated sample is improved by 13.64% as compared with graphite sample.The improvement of the compression strength for ZrC coated sample can be associated to the increased density and the ZrC particle reinforcement due to the infiltration and reaction of the melted Zr with carbon substrate in the coating process.
