Oxidation And Ablation Properties Of SiC Coating C/C Composites Prepared By Precursor Conversion Method

Carbon/carbon(C/C)composites have received considerable attention because of its prominent performance as high-temperature structural material.However,the serious oxidation and erosion of C/C composites at high-temperature aerobic environment would affect the mechanical properties and reduce the service life.In this paper,aiming to improve the oxidation and ablation resistance of C/C composites,the precursor conversion method was adopted to fabricate single-layer Si C coatings.On this basis,the combinative method of precursor conversion and CVD,the combinative method of embedding and precursor conversion were separately adopted to fabricate the double-layer Si C coatings,and the combinative method of embedding,precursor conversion and CVD was adopted to fabricate the tirple-layer Si C coatings.The phase compositions,microstructures,oxidation resistances and ablation resistances of fabricated coatings were investigated,and the mechanisms of oxidation and ablation were researched,separately.The main conclusions are listed as follows:(1)Single-layer Si C coatings were prepared on C/C composites with different densities by the precursor conversion method,and the influence of different filler ratios and preparation temperatures to the morphologies,phase compositions and oxidation resistances of single-layer Si C coatings were investigated,separately.It was found that the coating fabricated on high-density C/C composites at 1300 ℃ with PMS:Si:Si C=1:0.5:2exhibited the best oxidation resistance,which had highest compactness and intensity of Si C diffraction peak.After oxidation for 20 min,the weight loss of the coating was 9.9%.(2)Double-layer Si C coatings were fabricated by the combinative method of precursor conversion and CVD,and the combinative method of embedding and precursor conversion,separately.The influence of different preparation technics and filler ratios to the morphologies,phase compositions,oxidation resistances and ablation resistances of doublelayer Si C coatings were investigated,separately.During the oxidation process,the Si C coatings prepared by the combinative method of embedding and precursor conversion had overall advantage at both oxidation and ablation resistance,in which coatings prepared with different filler ratios revealed similarity at oxidation resistance,but obvious distinction at ablation resistance.Among these double-layer Si C coatings,the coating with PMS:Si:Si C=1:0.5:1 had the best oxidation and ablation resistance,its weight loss was 4.85% after 2 h oxidation,and mass ablation rate was 0.015 mg/s after 60 s ablation.(3)Tirple-layer Si C coatings were fabricated by the combinative method of embedding,precursor conversion and CVD,and the influence of filler ratios to the morphologies,phase compositions,oxidation resistances and ablation resistances of triple-layer Si C coatings were investigated,separately.The result revealed that coatings with different filler ratios had no obvious dintinction at oxidation resistance,in which the Si C coating prepared with PMS:Si:Si C=1:0.5:1 was the best,and its weight loss was 0.76%.After 60 s ablation,it can be found that all tirplelayer Si C coatings exhibited better ablative performance comparing with double-layer coatings under the same ablation condition.The ablation resistance of all tirple-layer Si C coatings revealed similarity,among them the coating with PMS:Si:Si C=1:0.5:1 displayed the best ablative performance,and its mass ablative rate was 0.009 mg/s.