Oxidation Mechanism And Active/Passive Transition Boundary Of Typical SiC Based Thermal Materials

At present,the mainstream ultra-high temperature heat-resistant materials,such as C/C composite materials and ultra-high temperature ceramics,SiC,as the key component of its matrix or anti-oxidation coating,significantly improves the antioxidation performance of the heat-resistant materials.The Si O2 generated by SiC passive oxidation can cover the surface of the materials and fill the cracks and pores of the materials,bearing the anti-oxidation task of the heat-resistant materials in the temperature range below 1650°C.However,with the high temperature,the The expansion of supersonic aircraft flight space changes the oxidation environment.The heat-resistant materials at the key parts of aircraft end and wing leading edge are faced with high temperature,low pressure and atomic oxygen medium,which is more likely to lead to active oxidation of SiC and lose the ability to generate Si O2 protective layer.Therefore,it is the premise of its engineering application to define the active/passive oxidation transition boundary of SiC component in the heatresistant material.Many researchers have obtained the data points of active/passive oxidation temperature and oxygen partial pressure of SiC materials through experimental tests.Generally speaking,most of the experimental data are consistent with the theoretical boundary.However,due to the difference of test conditions and technologies,the experimental methods used by various researchers are different,and the test efficiency is generally not high,resulting in limited data points.In addition,at present,the protection threshold of SiC Based Materials for passive oxidation usually refers to the research of SiC materials by default.There are few reports on the research of the active and passive transition boundary of typical SiC based materials.According to the theoretical calculation method of the mainstream SiC transition boundary,the diffusion process of the gas body in the gas boundary layer on the surface of the material and the relationship between the partial pressures of the gas on the surface and even in the boundary layer determine the material As a result,the actual transformation boundary of SiC components in SiC based materials may be different from that of pure SiC materials.Based on this,this paper takes SiC and C/SiC?C_f/ZrB₂-SiC as the research object to study the active / passive transition boundary,mainly including the following aspects:?1?Numerical simulation of SiC oxidation based on ReaxFFThe molecular dynamics simulation method of ReaxFF reaction force field is used to calculate the oxidation reaction process of SiC and oxygen atom at different temperatures,observe the diffusion and reaction mechanism of oxidation,analyze the structure of oxide layer formed after reaction,and explore the oxidation rule and mechanism of atomic oxygen to SiC from the molecular level,so as to enhance the understanding of the oxidation reaction mechanism of SiC.?2?Study on the evolution of active / passive oxidation of SiC materialsThe oxidation behavior of high purity SiC in atomic oxygen environment is studied.The oxidation transition boundary of pure SiC in the range of 1200?2000°C and 20?200pa parameters is obtained by combining with the emission spectrum test.Referring to the transition boundary,the experimental sites are selected to carry out the oxidation experiments of SiC in different states of active and passive oxidation as well as the material test to explore the oxidation evolution law of different states of the material,To reveal the mechanism of active/passive oxidation.?3?Study on the oxidation transition boundary of typical SiC based thermal materialsThe oxidation behavior of C/SiC and C_f/ZrB₂-SiC typical heat-resistant materials under atomic oxygen is studied,and the boundary conditions of oxidation transition are obtained,compared with the boundary conditions of pure SiC,the reasons for the differences are analyzed.The experimental sites are selected to carry out the oxidation experiments and material tests of active and passive oxidation of different typical materials,so as to obtain the structural evolution of materials in different states,the oxidation mechanism of SiC components in typical thermal protection materials was analyzed by the micro morphology after oxidation.The research on the active/passive oxidation transition boundary of pure SiC and typical SiC based heat-resistant materials and the mechanism of SiC oxidation in SiC based materials is of great significance for the heat-resistant design and prediction analysis of SiC based materials.