PREPARATION OF B4C-SIC COMPOSITES BY REACTIVE CHEMICAL-VAPOR-DEPOSITION FROM A GASEOUS BCL3-SICL4-H-2 PHASE

This paper focuses on the reactive chemical vapour deposition of compo site B4C-SiC coatings onto porous graphite substrates from a BCl3-SiCl 4-H-2 vapour phase. The mixed layer seems to exhibit promising propert ies such as oxidation resistance. However, its preparation as a thin f ilm from the vapour is very difficult owing to the complexity of the s ystem. The experimental parameters such as temperature, number of mole s H-2, and the amounts of BCl3 and SiCl4 in the reactive vapour phase are systematically discussed. The results are compared with a thermody namic approach. Also, this paper reports investigations on boron and b oron silicide coatings. Scanning electron microscopy, X-ray photoelect ron spectroscopy and electron microprobe analysis were used to charact erize the various coatings. The compositions, microstructures and prop erties such as oxidation behaviour of the coatings were also studied. Optimal experimental parameters of the process were reached in order t o achieve a dense, adherent and continuous mixed B4C-SiC layer on bulk graphite substrates with a view to coating further carbon fibres and protecting them from oxidation in air at temperatures less than 1000 d egrees C.