Oxidation of the carbon protective coating in SCS-6 fibre reinforced titanium alloys

Titanium matrix composites (SiC-fibre reinforced titanium alloys) are candidate materials for high temperature applications, e.g. in gas turbines. For this reason oxidation of the commonly applied SiC-fibre SCS-6 is investigated at temperatures of 400, 500 and 600 degreesC in air up to a maximum time of 800 h (for the last temperature). The initial 3.5 mum thick protection layer of this fibre mainly consisting of carbon oxidises. Weight loss and thickness reduction is measured as a function of the time (at 600 degreesC). Further, the influence of the oxidation on the strength of the fibre is measured with the aid of single fibre tensile tests enabling the determination of Weibull strength distributions. The strength appears to drop considerably during the first similar to 4 h of oxidation (at 600 degreesC). A heat treatment in air at 400 degreesC for 24 h produced only a minor reduction in strength. SEM pictures finally reveal the embrittlement of the carbon layer due to oxidation at 600 degreesC. (C) 2002 Elsevier Science Ltd. All rights reserved.