Modification Of SiC Coating On C/SiC Composites

Oxidation resistance of C/SiC composites with a multi-SiC coating (SiC-C/SiC) should be improved to meet the demand of high performance aero engines up to 1650℃ for a long time. Coating cracks and defects are main reasons for the limited oxidation resistance of SiC-C/SiC. In this thesis, surface modification of SiC coating was carried out with Physical Vapor Deposition (PVD) and Ion Implantation & Deposition, using Al, B and Si. Effects of the modified coatings on the oxidation resistance of SiC-C/SiC were studied with SEM, XRD and AES and so on. The main contents and results are as follows:(1) Coating cracks were sealed or narrowed by vacuum evaporating an Al film of 3um. Wight losses of SiC-C/SiC in simulated air at 500℃, 600℃ and 700℃ were all remarkably reduced, but the values were still large.(2) Coating cracks and defects were partly sealed by magnetron sputtering a Si film of 3um, and weight loss of SiC-C/SiC in simulated air at 1300℃ was reduced.(3) SiC became amorphous as a result of Metal Vapor Vacuum Arc (MEVVA) source Al implantation. Electron Cyclotron Resonance (ECR) source B (1017 ions/cm2) implantation or Si (1016 ions/cm2) implantation had the same results. Cracks still existed and defects changed little. Oxidation resistance of SiC-C/SiC in simulated air had been improved at 1300℃ but not at 700℃ with Al implantation, and improved at 1200℃ as well as 1300℃with B implantation. No remarkable change was found at 1300℃ with Si implantation.(4) Anneal of SiC-C/SiC with Si implantation in vacuum at 1600℃ for 30min had resulted in production of new cracks, which led to larger weight loss of the composite.(5) Glassy oxide film of samples processed by MEVVA Al/PIID Si covered the surface of SiC coating thickly and uniformly, and left few holes as a result of a good ability of sealing, which made weight loss of SiC-C/SiC smaller in air at1300℃...