Preparation And Properties Of SIC High Temperature Ceramics Coating

SiC high Temperature Ceramics coatings were prepared on the surface of graphite block by Argon-arc Cladding. The influence of different composition designs on preparation of coating was studied under some technological parameters. Analyzed interface behavior and mechanisms of coating. Microstructure, phase and hardness of coating were analyzed by use of SEM, EDS, XRD and HV-test. Ablation resistance and oxidation resistance of coating were tested by use of Plasma Flame and Box Resistor-Stove, respectively. The results showed that the craft applied to fabricate SiC high Temperature Ceramics coating by Argon-arc Cladding was feasible, in which SiC coatings were prepared by the mix of Si and C powerders. Compared with the coating,which was prepared by the mix of SiC and Si powerders. Complete chemical reaction of pre-coating occurred in the composition design of n(SiC):n(Si)=1:0.5 which formed the dense uniform organization of SiC under welding current 135A and the same other processing parameters. Perfect bond quality between coating and substrate was proved by using SEM in each design sysytem. XRD showed that each coating contained newly formedβ-SiC.The formation of SiC coating growth mechanism ofβ-SiC is proposed. SiC in the coating raw materials sublimate to the level of gaseous C-Si atoms as the source, under high temperature of Argon-arc. Si powder in the coating raw materials show liquid in the role of the Argon-arc, wet and spread in the graphite matrix, reactive formate the most easily nucleatedβ-SiC with C atoms in the graphite matrix. The newly formed SiC played a role in seed crystal. The gas of sublimated C-Si atoms also enter into the graphite matrix, under the Argon-arc to achieve epitaxial growth in theβ-SiC.The introduction of coating improved ablation resistance and oxidation resistance of pure carbon materials. Mass loss rate of Graphite materials with protective coating under the composition design of n(SiC):n(Si)=1:0.5 was 10.5mg/s, about 1/2 that of graphite substrate. The rate of mass change per unit area of the coating is just 0.7×10-3mg/(mm2h), in air for 10h at 1400℃, under the composition design of n(SiC):n(Si)=1:0.8, is much less than The rate of mass change per unit area of graphite, -3.75mg/(mm2h) in air for 12h at 800℃. During ablation or oxidation process, SiC changed into SiO₂ which formed a self-healing protective layer. Thus the introduction of SiC could strongly improve ablation resistance and oxidation resistance of the graphite matrix.The passive oxidation mechanism of the SiC coating is proposed. The coating layer formed SiO₂ oxide film which was thin, dense, combined strongly to matrix at high temperatures. The diffusion coefficient of oxygen in the coating the very small. Therefore, SiC coating is very slow oxidated.