Evaluation of the efficiency of TiB₂ and TiC as protective coatings for SiC monofilament in titanium-based composites

Abstract

The vigorous interfacial reactions in SiC/Ti-6Al-4V composites at elevated temperatures lead to the deterioration of the mechanical properties of the composites. TiB₂ and TiC were selected as potential protective coatings for SiC fibres in titanium-based composites. These coatings were deposited on to fibres by the chemical vapour deposition technique. Comparisons and evaluations have been made of the effectiveness of these ceramics as protective coatings for SiC fibres by incorporating the coated fibres into a Ti-6Al-4V matrix using the diffusion bonding method. Emphasis has been placed on the chemical compatibility of the candidate coating with SiC and Ti-6Al-4V by examining the interfaces of the fibre/coating/matrix using microscopic methods and chemical analysis. A stoichiometric TiB₂ coating was found to be stable with SiC and has proved an effective barrier to prevent the SiC fibre from reacting with the Ti-6Al-4V. The TiC coating showed no apparent reaction with a titanium-alloy matrix under the conditions studied, but was found to react with the SiC fibre substrate.