THE COMPATIBILITY OF TIB2 PROTECTIVE COATINGS WITH SIC FIBER AND TI-6AL-4V

TiB2 coatings have been studied as prospective protective layers to inhibit the interfacial reaction between SiC fibres and Ti-alloy matrices. This protective coating has been deposited onto SIC monofilament fibres using a chemical vapour deposition (CVD) technique. The fibre-matrix compatibility of these TiB2-coated SiC fibres in Ti-6Al-4V composites was evaluated by incorporating the coated fibres into Ti-6Al-4V using a diffusion bonding technique. The interfaces of this composite were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis, to evaluate the interfacial microstructures, chemical stability and the efficiency Of TiB2 as a protective coating for SiC fibres in Ti-alloy matrices, and to study the effects of deposition temperature on the interface of the coated fibre. Results show that stoichiometric TiB2 coatings are stable chemically to both SiC fibres and Ti-6Al-4V and hinder the deleterious fibre-matrix reactions effectively. Boron-rich TiB2 coatings should be avoided, as they lead to the formation of a needle-like TiB phase at the fibre-matrix interface. These findings provide promising evidence for the value of further exploration of the use of stoichiometric TiB2 as a protective coating for SiC fibre in Ti-based composites.