Study On SiC Coating Modified By Zr,Ta Series Ceramics On C/C Composites

With the development of high thrust weight ratio aeroengine,the requirements for materials are further improved.Due to the characteristics of low density,high strength and high fracture toughness,C/C composite is the preferred material for Aeroengine hot end components.However,the problem of oxidation sensitivity at high temperature seriously restricts its application.In this paper,the protection of C/C composites at 1500℃is studied.Zr B₂-Si C,Zr Si₂-Si C,Zr B₂-Ta Si₂-Si C and Zr Si₂-Ta B₂-Si C composite coatings were prepared by embedding method.The oxidation resistance and thermal shock resistance of the coating samples were tested at 1500℃.The phase composition and microstructure before and after oxidation were characterized by XRD and SEM,and the preparation mechanism and oxidation resistance mechanism of the coating were studied.The main work is as follows:（1）Si C coating was prepared by one,two and three times embedding.With the increase of embedding times,the performance of Si C coating samples embedded three times is the best.With the increase of embedding times,the coating thickness and density increase,and the coating performance is also significantly improved.The weight loss rate of primary embedded Si C coating samples oxidized in air at 1500℃for 48 hours is3.77%,and the weight loss rate is 3.14%after three thermal cycles from room temperature to 1500℃;The weight loss rate of secondary embedded Si C coating samples oxidized in air at 1500℃for 120 hours is 4.43%,and the weight loss rate after 11 thermal cycles is 2.87%;The weight loss rate of three embedded Si C coating samples oxidized in 1500℃air for 286hours is 3.13%,and the weight loss rate after 17 thermal cycles is 1.47%.The results show that,（2）Different modified components have different effects on the microstructure and properties of the coating.The Zr Si₂-Si C coating prepared by embedding method is denser than Zr B₂-Si C coating,which is attributed to the lower melting point of Zr Si₂than Zr B₂ and the liquid phase at the preparation temperature,which is more conducive to promote the densification process of the coating.However,the thermal expansion coefficient of Zr Si₂ is higher than that of Zr B₂,resulting in the mismatch of thermal expansion coefficient,resulting in local cracking of the coating and poor coating performance.Zr Si₂-Si C coating samples were oxidized at 1500℃for 144 hours,and the weight loss rate was 1.32%;The weight loss rate of Zr B₂-Si C coating after oxidation for 216 hours is 0.11%;（3）Zr Si₂-Ta B₂-Si C and Zr B₂-Ta Si₂-Si C composite coating prepared by embedding method shows a good gradient distribution.In the preparation process,Ta atoms are dissolved into the lattice of Zr B₂ to form（Zr,Ta）B₂solid solution.The prepared composite coating has excellent oxidation resistance and thermal shock resistance.Zr Si₂-Ta B₂-Si C samples were oxidized in static air at 1500℃for 241 hours,and there was still 0.05%weight gain.After 17 thermal cycles from room temperature to 1500℃,the mass loss rate was only 0.43%.While Zr B₂-Ta Si₂-Si C samplesCompared with Si C-3,the weight loss rate of oxidation in 1500℃air for 286 hours is 3.13%,and the weight loss rate of 17 thermal cycles is2.87%.This is due to the formation of Zr-Ta-Si-O multiphase glass layer on the surface of the coating after oxidation.At high temperature,the high melting point Zr O₂,Ta₂O₅ and Zr Si O₄ phases in the form of solid phase are dispersed in the Si O₂ glass phase.Through pinning,the crack deflects,consumes the energy of crack propagation,improves the phase stability of Si O₂ glass,and cooperates with the dense coating to protect the matrix.