Caractéristiques mécaniques et chimiques des fibres de carbone protégées par un revêtement de carbure formé par dépôt chimique réactif

Silicon, titanium and boron carbide layers were formed on carbon fibres by reactive chemical vapour deposition (RCVD) using mixtures of SiCl₄-H₂-Ar, TiCl₄-H₂ and BCl₃-H₂ gases. Two types of fibres were considered: fibres made using a polyacrylonitrile precursor (ex-pan) and fibres made using a tar precursor (ex-brai). The mechanical properties of the coated fibres were determined on monofilaments. The high temperatures involved in RCVD resulted in degradation of the fibres. In order to use these fibres as reinforced aluminium-matrix composites, the influence of thermal treatment in air or in the presence of metal was investigated. In both cases, the coating decreased the carbon reactivity. In air, at 450°C, the properties of the fibres increased after a few minutes of treatment, whereas at 600°C, the tensile strength decreased in Une with the microcrystallinity of the oxides obtained. In the presence of liquid aluminium, the silicon carbide protects the fibres as long as there is no chemical reaction between the two components. In particular, silicon oxide, present as an impurity in the coating, easily reacts with the metal to produce defects on the fibre surface.