EVALUATION OF THE EFFICIENCY OF TIB2 AND TIC AS PROTECTIVE COATINGS FOR SIC MONOFILAMENT IN TITANIUM-BASED COMPOSITES

The vigorous interfacial reactions in SiC/Ti-6Al-4V composites at elev ated temperatures lead to the deterioration of the mechanical properti es of the composites. TiB2 and TiC were selected as potential protecti ve coatings for SiC fibres in titanium-based composites. These coating s were deposited on to fibres by the chemical vapour deposition techni que. Comparisons and evaluations have been made of the effectiveness o f these ceramics as protective coatings for SiC fibres by incorporatin g the coated fibres into a Ti-6Al-4V matrix using the diffusion bondin g method. Emphasis has been placed on the chemical compatibility of th e candidate coating with SiC and Ti-6Al-4V by examining the interfaces of the fibre/coating/matrix using microscopic methods and chemical an alysis. A stoichiometric TiB2 coating was found to be stable with SiC and has proved an effective barrier to prevent the SiC fibre from reac ting with the Ti-6Al-4V. The TiC coating showed no apparent reaction w ith a titanium-alloy matrix under the conditions studied, but was foun d to react with the SiC fibre substrate.