Papers by Keyword: SiC Coating

Abstract: C/C composites have excellent properties, but it will be rapidly oxidized when temperature is above 500 °C, which limits its applications in high temperature environment. In order to improve Anti-oxidation, using CVD method, a SiC coating is prepared on the surface of C/C composites. We have studied the microstructure of the SiC coating, oxidation resistance and high temperature mechanical properties. The results show that SiC coating has excellent oxidation resistance. When coated sample is oxidized at 1500 °C after 50 hours, its oxidation weight loss rate is only 1.45%, and coated samples can still maintain high mechanical properties at 1200 °C.

Abstract: Three-dimensional carbon fiber reinforced mullite composites (3D-C_f/mullite) were fabricated by sol-gel method with diphasic mullite sol as raw materials. SiC interfacial coatings were deposited by polycarbosilane infiltration and pyrolysis before sol-gel process. The as-fabricated composites showed 285.7MPa in flexural strength, relatively close to 277.6MPa of those without coatings. After treated at 1300°C and 1500°C in Ar atmosphere for 1h, the retention rates of flexural strength were 80.0% and 69.9%, respectively, which showed a great improvement compared to the composites without coatings. This was attributed to the prevention of carbothermal reduction between carbon fiber and matrix by SiC coatings.

Abstract: The SiC coating on C/C composites was prepared by CVD and pack-cementation method in this paper, then SiC coated C/C composites was jointed with LAS glass ceramic at 1423K for 30min and the pressure of 15 MPa. The structure and morphology of the SiC coating and as-received joints were analyzed by SEM and XRD; shear strength of joint was examined through the Instron universal testing tensile machine. The results show that the thickness of SiC coating prepared by CVD is about 30μm, while the thickness of SiC layer by pack-cementation is nearly 100μm, and the layer is easier to connect with LAS glass ceramic owing to the rough surface and wedge-shaped structure on the SiC coating; the shear strength of joint between SiC coating coated C/C and LAS by pack-cementation is greater than the joint of C/C- LAS with SiC coating prepared by CVD.

Abstract: In order to further study the cracks initiation and distribution mechanism of SiC coating, then optimize the coating structure and composition on surface of C/C composites, CVD method is used to deposit SiC coating on C/C composites and pyrolytic carbon. Through the analysis on the reasons of cracks initiation via SEM, the influence of different kinds of substrates and the toughening of SiC whisker on the cracks initiation and distribution are researched. The results show that the cracks easily form in the area near the defects and sample edge, and the cracks also mainly distribute in the direction which are perpendicular to the first fiber layer. Compared with pyrolytic carbon matrix, cracks on C/C composites matrix are width and numerous, and SiC whisker toughening coating can significantly reduce the number of cracks.

Abstract: SiC coatings were fabricated by the Rapid Chemical Liquid Deposition (RCLD) on the surface of graphite, the influence of deposition temperature on the microstructure of SiC coatings was investigated, the oxidation behaviors of SiC coatings at different temperatures were analyzed. The results indicated that the optimum condition for the SiC coatings are at 1150°C, a smooth and dense coating will be obtained, the thickness of the coatings are between 80～120μm. The oxidation resistance test results indicated that after oxidation at 1000°C for 5h, the mass loss of the sample is only 21%.

Abstract: A two-dimensional mathematical model for deposition behavior of SiC coating on C/C composites in a hot-wall CVD reactor was developed. Deposition rate of SiC was calculated by finite element method and optimized by using an orthogonal L9(3)4 test. The single and coupling effects of process parameters on deposition rate of SiC, including deposition temperature, the flux of mixed gases, the volume ratio of H2 and Ar, and that of MTS and mixed gases, were calculated and discussed. The optimal deposition rate of SiC was obtained.

Abstract: The effects of deposition temperature on the growth characteristics of CVD SiC coatings were investigated. CVD SiC coatings were made by pyrolysis of methyltrichlorosilane (MTS) in hydrogen at a low pressure of 5kPa. The ratio of MTS to hydrogen was 1/12. The deposition temperatures were varied from 1373K to 1503K. Optical microscope and SEM were used to observe the surface morphology and microstructure of the coatings. XRD was used for characterization of the phase composition. Results indicated that the deposition rate and the surface roughness varied with deposition temperature. At 1373K, the deposited grains were mainly equiaxed with the crystallite size of 22 nm. However, when the deposition temperature was 1503K, the SiC grains were mainly showed faceted columnar structure with the crystallite size of 32 nm. Grain size increased with the increase of deposition temperature.

Abstract: The process of Electron Beam-Physical Vapor Deposition (EB-PVD) preparing SiC coating by Electron Beam evaporating 3C-SiC ingot on stainless steel (SS) substrate was firstly discussed as a preliminary estimation from thermodynamic viewpoint. The results show that, with the temperature increasing from 2500 to 3400 K, the purity of SiC coating increases from 0.58 to 0.734.

Abstract: Amorphous SiC coatings were deposited by RF magnetron sputtering from a sintered SiC target onto Si(100) substrate at room temperature. The influence of RF power on the surface morphology and the RMS surface roughness of the resulting SiC coatings was studied by using atomic force microscopy. Two types of surface morphologies were obtained. The corresponding forming mechanisms were also discussed.

Abstract: Production of reinforced surface ceramic material was investigated by radiation curing-oxidation method. The originality of this research is to use along with polycarbosilane (PCS) an admixture of another preceramic polymer, polyvinylsilane (PVS). PCS, PVS or their combination in cyclohexane solution were spin-coated onto Al2O3 plates or deposited onto porous substrate by dipping method. After radiation oxidation step, used to preserve the coat on the substrate, a heat treatment was applied for crosslinking of the polymer. Thickness and quality of silicon carbide (SiC) film were investigated after pyrolysis.