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Preparation Of Al2O3 Modified Zr-Si System Ceramic Composites And Its Ablation Properties

Posted on:2021-05-07Degree:MasterType:Thesis
Country:ChinaCandidate:X LiuFull Text:PDF
GTID:2381330602489867Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
Ultra-high temperature ceramic matrix composites have excellent properties such as high temperature resistance,corrosion resistance,oxidation resistance,and ablation resistance.The Zr-Si system is the most widely studied because the Zr-Si system can form a melt on the surface of the material during the ablation process State oxide layer,which can effectively alleviate the ablation of the substrate.However,the Zr-Si system still has disadvantages during the ablation process.When the ablation temperature is higher than 1800?,the rapid evaporation and decomposition of SiO2 leads to cracks and holes in the material,which accelerates the oxidation of the substrate.In order to improve the ablation resistance of Zr-Si system carbon ceramic composites,adding a third phase is a feasible method.In this paper,Al2O3 was used as the third phase.Al2O3 modified Zr-Si carbon-ceramic composites were prepared by slurry impregnation method,hot-press sintering method and hydrothermal co-deposition method.The effects of Al2O3 modified Zr-Si carbon-ceramic composites prepared by different methods and different Al2O3 contents on the properties of the materials were investigated.The specific conclusions are as follows:(1)C/C-ZrB2-SiC-Al2O3 composites were prepared by slurry impregnation method,and the influence of different Al2O3 content on the structure and ablation performance of composites was studied.Studies have shown that:due to the difference in ceramic particle size,non-uniformity in slurry impregnation occurs,and the content of Al2O3 is different from the experimental design ratio.There is an obvious gradient structure in the slurry impregnation.The impregnation depth of the slurry is about 2 mm,including a dense layer of about 1.5 mm and a transition layer of 500 ?m.The Al2O3 content has a significant effect on the ablation of the composite.When Al/Si>0.4,acicular mullite whiskers can be precipitated on the surface of the composite.The mullite whiskers precipitated during the ablation process can greatly increase the viscosity of the molten glass layer,and slow down the merger of the gas inside the material,suppress the formation of escaped bubbles,and improve the anti-ablation performance of the material.When the Al/Si molar ratio is 0.8,the Z1S1A0.8 sample exhibits the lowest mass ablation rate and linear ablation rate,which are 1.57×10-4 g·cm-2·s-1 and 0.85 ?m·s-1,respectively.(2)C/C-ZrB2-SiC-Al2O3 composites were prepared by hot pressing.The content of the ceramic component in the composite material is basically the same as the experimental design.However,due to the low sintering temperature,the direct interface bonding between the fibers of the matrix is weak,and the prepared material is prone to delamination,which results in a comparison of the mechanical properties of the material.Poor,with the increase of Al2O3 content,the material's anti-ablation performance has improved.Among them,the Z1S1A0.8 composite material has the best anti-ablation performance,the quality ablation rate and line ablation rate are 1.65×10-4 g·cm-2·s-1 and 0.89 ?m·s-1.(3)C/C-SiC-ZrC-Al2O3 composites with different alumina contents were prepared by hydrothermal co-deposition method,and Zr,Si,Al were evenly distributed inside the material.With the increase of Al2O3 content,the mechanical properties of C/C-SiC-ZrC-Al2O3 composites are better.Among them,Z1S1A0.8 has the best mechanical properties,and the bending strength can reach 140.4 MPa.This is because Al2O3 promotes the generation of SiC nanowires,thereby improving the mechanical properties of the material.With the increase of alumina content,the C/C-SiC-ZrC-Al2O3 composite material has better anti-ablation performance,because mullite whiskers are generated by Al2O3 and SiO2 during the ablation process,thereby improving the anti-ablation performance.Z1S1A0.8 has the best anti-ablation performance.The mass ablation rate and line ablation rate are 0.65×10-4 g·cm-2·s-1 and 0.29 ?m·s-1,respectively.(4)The effects of different heat treatment temperatures on the microstructure and ablation properties of C/C-SiC-ZrC-Al2O3 composites prepared by hydrothermal co-deposition were studied.The composites prepared at 1600? have fine grains and a good combination of matrix and fibers,which makes them have excellent mechanical properties.During the ablation process,a dense oxide layer can be formed quickly,showing excellent resistance to ablation.The composite particles prepared at 1400? are fine,but few SiO2 and ZrO2 have undergone a carbothermal reduction reaction.Therefore,the material's anti-ablation performance is not as good as the composite prepared at 1600?.The composite prepared at 1800? due to heat treatment temperature Higher,the carbon fiber is damaged,so the mechanical properties and anti-ablation performance of the material are poor.
Keywords/Search Tags:Slurry dipping method, Hot pressing sintering method, Hydrothermal co-deposition method, Mechanical properties, Ablation performance
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