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

Aiming at the serving environment characteristics of solid missile engine, thedemand for material includes stable performance at ultra high temperature, stable sizeand ablation resistance for a long time. C/C composites have the property of highmechanical strength, low density, excellent toughness, good shock resistance, except forthe poor oxidation resistance at high temperature. ZrB2ultra high temperature ceramicshave stable physical and chemical properties, good oxidation resistance and erosionresistance at high temperature, but it has poor thermal shock resistance. So thecombination of the two materials has great application potential. In view of theapplication of background of existing combination structure, studying high temperatureoxidation resistance and stress slow-release composite coatings for C/C composites isthe key technology to combine C/C composites and ultra high temperature ceramics. Inthis paper, the fabrication technology, system design and optimization of componentsfor oxidation resistant coating is studied, which lays the foundation of the combinationstructure of C/C composite and ultra high temperature ceramics. Si80/1800preparationof SiC is chosen as inner transition coating.Composite coating was fabricated in order to improve high-temperature oxidationresistance for C/C composites in this paper. The inner layer is SiC buffer layer, which isfabricated by embedding method. The outer layer is yttrium silicate oxygen barrier layer,which is fabricated by slurry method. SEM, XRD, DSC/TG, oxidation experiments andother analytical methods were used in studying the effects of different components onthe properties of high-temperature oxidation resistant coating. The results show that:In the four different coating material components during fabricating C/C compositesSiC buffer layer by embedding method:60wt.%Si-30wt.%C,70wt.%Si-20wt.%C,80wt.%Si-10wt.%C,60wt.%Si-20wt.%C-10wt.%Ferrocene, the80.wt%Si-10wt.%CSiC coating has dense structure, the least oxidation weight loss ratio and the mostexcellent resistance to oxidation. In six different sintering temperature:1500°C,1600°C,1700°C,1800°C,1900°C,2000°C, the coating fabricated at1800°C has dense structure,the least oxidation weight loss ratio and the most excellent resistance to oxidation. The80wt%Si-10wt%C SiC coating fabricated at1800°C has only0.83%oxidation weightloss ratio at1200°C thermal shock eight times. The surface morphology shows that the surface is covered with glassy SiO2, which constitutes a good barrier to restrain thediffusion of oxygen to the substrate, and avoids the oxidation of substrates.Yttrium silicates oxygen barrier layer is fabricated by slurry method. Y2O3, SiO2andsilicon high-temperature adhesive is used as raw materials. For the C/C compositesspecimen only with yttrium silicates oxygen barrier layer, its weight loss ratio at1200°Cis far higher than that of yttrium silicates/SiC composite coating for C/C composites,which shows that SiC coating can improve the interface binding force between yttriumsilicates coating and the inner. In the three different coating components: Y2O3·SiO2,Y2O3·1.7SiO2, Y2O3·2SiO2, Y2O3·1.7SiO2has the lowest weight loss ratio at1200°Cand shows the most excellent antioxidant capacity. SiO2and Y2O3react in a ratio of1:1to generate Y2SiO5. Y2O3·SiO2has the lowest weight loss ratio at1400°C and showsthe most excellent antioxidant capacity. SiO2and Y2O3react in a ratio of2:3togenerate Y4Si3O12. In the1400°C oxidation experiment, a large number of glass phaseis produced, and the weight loss ratio is less than in the1200°C oxidation experiments.