Preparation And Performance Study Of C/C-SiC-ZrC Composites By Reactive Infiltratio

With the rapid development of aerospace vehicles,the working environment of thermal protection materials for aircraft is increasingly harsh.In order to meet the working stability requirements of thermal protection materials at higher temperatures,ultra-high temperature ceramics（UHTCs）are often used to modify the matrix or prepare high-temperature resistant coatings to improve the performance of C/C composites in high-temperature and aerobic environments,and obtain thermal protection materials with better usability in high-temperature environments.SiC-ZrC multiphase ceramic modified C/C composite（C/C-SiC-ZrC）has become an important candidate material for thermal protection of aircraft in extreme environments due to its lightweight,high-strength,oxidation resistance and wide temperature range synergistic ablation resistance.At present,the preparation methods of C/C-SiC-ZrC composites mainly include chemical vapor infiltration（CVI）,precursor impregnation pyrolysis（PIP）and reactive infiltration（RMI）.In contrast,RMI technology has great application potential because it overcomes the disadvantages of CVI and PIP processes,such as long cycle and high cost.However,the process damage mechanism of preparing C/C-SiC-ZrC composites by RMI method is not clear,and the mechanical properties,ablation properties and industrial infiltration process of the composites are still not mastered,which limits the application of RMI as an efficient process in the preparation of aircraft heat-resistant components.In this study,the C/C-SiC-ZrC composite was prepared by using the RMI method with Zr Si₂as the infiltrating agent.The infiltrating and diffusing mechanism of Zr Si₂melt in the C/C porous body was analyzed,the infiltrating damage mechanism was clarified by combining with the microscopic analysis,the key influencing factors of the infiltrating material properties were combed,and the influence of the infiltrating temperature（1700℃,1750℃and 1800℃）on the mechanical and ablation properties of the C/C-SiC-ZrC composite was studied,The properties of composites with different interfaces were analyzed.Through research,the main research results obtained in this paper are as follows:（1）The proportion of ceramic matrix in the C/C-SiC-ZrC composites prepared by reactive infiltration is up to 30%～40%.The ceramic matrix presents a regular distribution of SiC（inner）-ZrC（outer）on the micro level,and the composite ceramic matrix is uniformly distributed in the composite along the skeleton vein of the preform on the macro level.At the initial stage of Zr Si₂infiltration,the in-situ reaction between Si-C takes a greater advantage,and a SiC layer is formed on the carbon substrate.As the reaction proceeds,the dominant number of Si atoms is consumed.At this time,the highly active Zr atoms begin to take advantage in diffusion and reaction,and a large number of ZrC substrates are formed on the surface of the SiC ceramic layer.The melting point of the fluxing agent Zr Si₂selected by the RMI method is high,and the required preparation temperature is also high.However,the high activity of Zr and Si at high temperature above 1700℃causes partial erosion damage to the fiber.On this basis,this study formulated the performance optimization principle of temperature and interface dual control.（2）With the increase of infiltration temperature（1700℃,1750℃,1800℃）,the mechanical properties of C/C-SiC-ZrC composites show a downward trend.The mechanical properties of C/C-SiC-ZrC composites prepared at 1700℃are the best,with the tensile strength and bending strength of 114.7 MPa and 259.3 MPa respectively,which are 64.56%and 60.56%higher than those prepared at 1800℃（tensile strength of 69.7 MPa and bending strength of161.5 MPa）.（3）In the oxygen-enriched（oxyacetylene）environment,the C/C-SiC-ZrC composites prepared at different infiltration temperatures showed near-zero ablation.The linear ablation rate and mass ablation rate of C/C-SiC-ZrC composites did not change with the increase of infiltration temperature.The linear ablation rate of C/C-SiC-ZrC composites prepared at1700℃was-0.0006 mm/s and the mass ablation rate was 0.00035 g/s.Under the oxygen-enriched scouring（liquid oxygen kerosene）environment,the mass ablation rates of the C/C-SiC-ZrC composites prepared at three infiltration temperatures are 0.0063 g/s（1700℃）,0.0897 g/s（1750℃）and 0.0092 g/s（1800℃）,respectively.After ablation,the ball head structure of the C/C-SiC-ZrC sample remains intact,which is because the combination of SiC-ZrC interlaced structure and chemical interface makes the composite have better erosion resistance,Its ablation performance is better than that of C/C-SiC-ZrC composites prepared by traditional PIP process.（4）Comparing the properties of Py C interface and SiC interface C-SiC-ZrC composites prepared at the same infiltration temperature,the tensile strength and flexural strength（97.4MPa and 212.1 MPa）of SiC interface samples prepared at 1700℃are lower than those of Py C interface composites,but the oxygen acetylene line ablation rate and mass ablation rate（0.003 mm/s and 0.0011 g/s）are not significantly different from those of Py C interface composites.The possible reasons for the poor mechanical performance of SiC interface samples are as follows:the strong interface bonding between SiC interface and carbon fiber is not conducive to crack deflection and buffering under external force;At 1700℃and above,the interface energy of SiC increases with the increase of temperature,and the SiC at the interface will partially penetrate into the C fiber,which will lead to a certain degree of carbon fiber damage;The transformation and growth of SiC to SiC will also take place in the high temperature environment around 1800℃,which may eventually lead to the destruction of SiC interface and the decline of material mechanical properties.