ESCA characterization of boron and silicon carbide mixed layers deposited on HR and HM carbon fibres by RCVD: properties of the as-coated fibres

Abstract

Coatings of mixed boron and silicon carbides were produced on the surface of various carbon fibres by a reactive chemical vapour deposition process using a mixture of BCl 3, SiCl 4 and H 2. For application as reinforcing components in advanced composites, the surface of the some coated fibres was characterized by electron spectroscopy for chemical analysis since the properties of a composite material can depend on possible reactions between the two components of the material. Experimental parameters, such as treatment time, temperature and initial composition of the gaseous phase, have been studied in order to fabricate a mixed layer which did not contain boron or silicon elements, boron silicides or oxidized compounds. In addition to SiC and B 4C, the presence of BN was also found in the coating of T300 fibres based on poly(acrylonitrile); this BN formation is explained by a reaction between nitrogen which is an impurity in the raw fibre and the gas input in the reactor. Thermodynamic calculations and experiments confirmed this hypothesis. Analytical investigations were supplemented by strength measurements, which showed that the coating has only a small effect on the tensile strength of the fibres. Scanning electron microscopic examination of a coated fibre/A1 composite (fabricated by a squeeze-casting method) evidenced no trace of reaction between the fibre and matrix.