Fabrication And Properties Of High Temperature Oxidation Resistance Coating For Graphite And C/C Composites

C/C composite material is a new type of composite material with many excellent properties, which is ideal for aerospace and other industrial fields. However, when the temperature is over 370℃ and in the presence of oxygen, the carbon is oxidized, resulting in the destruction of the C/C composite material. Therefore, the high temperature oxidation resistance of C/C composite material is a major issue in current research.In this experiment, the coating is prepared by using the plasma spraying equipment with graphite matrix as the theoretical basis which is the experimental foundation of C/C composite coating system with high temperature oxidation resistance and heat resistance. The practical application of C/C composite coating is explored in the end.Si and Si-4%Al coatings are prepared by atmospheric plasma spraying on graphite substrate. The solid phase reaction between graphite and coating is prepared by heat treatment, and the SiC transition layer is generated to ease the mismatch of thermal expansion coefficient. The samples of different holding time at 1380℃ are observed by the scanning electron microscopy and XRD detection, and the transition layer growth curve, hardness and fracture toughness were plotted. The results show that the thickness of the SiC transition layer grows with the increasing of holding time, and the maximμm thickness reaches 100μm. The hardness of Si and Si-4%Al coatings decrease rapidly with the increase of holding time at first, and then decreases slowly, and finally tends to be stable.Because the Si-4%Al coating is destroyed worse than Si coating after heat treatment in the experimental process and the fracture toughness of the Si-4%Al coating is worse than that of the Si coating, Si coating is prepared by plasma spraying as inner coating on C/C composite substrate. On the basis of the Si coating, the (SiO2+5%Al2O3) coating is used as the sealing layer, and the outermost layer is coated with YSZ coating as the heat insulating layer. Do oxygen acetylene flame ablation experiment on the C/C-Si-(SiO2+5%Al2O3)-YSZ composite coating system with three times atmospheric plasma spraying. The experimental results show that the composite coating system has high oxidation resistance and ablation resistance. The total mass loss rate was 0.38% and the average mass ablation rate was about 0.22mg/s at 1200℃ for 8 times, which shows that the protective effect of the composite coating system is good, which could realize the high temperature oxidation resistance of C/C composites.