Study On SiC Coating Properties Of C/C Composites

C/C composites have many excellent properties such as low density,low thermal expansion coefficient,good friction performance and high temperature stability,so they are one of the most important materials in aerospace and other scientific fields.However,due to its poor oxidation resistance and low erosion resistance,the application of c/c composites in more fields is severely limited.The best way to solve these defects is to prepare a SiC protective coating on the surface of the C/C composite.The traditional coating preparation method has an embedding method,and the method has the advantages of mature process and simple operation,but has the disadvantages of uncontrollable preparation process and low preparation efficiency,and preparation of C/C composite material coating for large-sized and anisotropic workpieces.This shortcoming is particularly prominent.The chemical vapor phase reaction method which has appeared in recent years has been significantly improved for coating preparation of large-sized and anisotropic workpieces.In view of the characteristics of the above two coating preparation methods,the SiC coating was prepared on the surface of C/C composite by a new chemical vapor phase reaction(CVR)method and a traditional embedding method.The oxidation resistance,thermal shock resistance,mechanical properties and friction and wear properties of C/C composites prepared by the two coating methods were compared,and the method for preparing SiC coating on the surface of subsequent C/C composites was selected.Provide a reference basis.Studies have shown that both the embedding method and the chemical vapor phase reaction method can prepare SiC coating on the surface of C/C composite.The coating prepared by the common embedding method is rough,sparse,and has a small number of pores;the coating prepared by the chemical vapor phase reaction method is flat and uniform,and has no penetrating cracks.The embedding method produces free Si in the coating,while the chemical vapor phase reaction coating only has SiC.Both coatings have a greater improvement in oxidation resistance and thermal shock resistance than uncoated C/C composites.The SiC coating prepared by embedding method reduces the oxidative weight loss rate of C/C composites by 53.2% at 1000 °C/2h,and the chemical vapor phase reaction coating decreases by 47.1%.The thermal shock life and thermal shock failure of chemical vapor phase reaction coatings The temperature is higher than the embedding coating.The mechanical properties of the two coatings were greatly improved compared with the uncoated samples.The chemical vapor phase reaction method prepared the coating to increase the maximum bending strength of the matrix material by 15.8%.The embedding coating sample exhibited a brittle fracture tendency,and the chemical vapor phase reaction coating sample still retained the same pseudoplastic fracture tendency as the matrix material.Friction and wear performance,the friction coefficient of the coating prepared by chemical vapor phase reaction is closer to that of C/C composite,while the friction coefficient of coating prepared by embedding method is quite different from that of C/C composite,but its friction life is compared with chemical vapor.The reactive coating increased by 60.6%.In comparison,the embedding method is applicable to the preparation of coating with no strict requirements for sample size changes and high wear resistance,while the chemical gas reaction method is applicable to the preparation of coating of large-size heterogeneous workpiece with strict requirements for sample size,good thermal shock performance and high production efficiency.