OXIDATION EFFECTS ON THE MECHANICAL-PROPERTIES OF 2D WOVEN C/SIC COMPOSITES

The effects of oxidizing treatments on the room-temperature tensile properties of 2D woven C/SiC composites partly protected with a SiC seal-coating have been investigated between 700-degrees-C and 1400-degrees-C, for durations corresponding to a maximum of 6% relative mass loss. Results have shown three main mechanisms of composite property degradation corresponding to three well differentiated morphological changes. Oxidation al low temperatures (<800-degrees-C) induced a drastic decrease of the composite tensile properties in relation to a notch-like partial degradation of the carbon fibers located near the matrix microcrack tips. The intermediate temperature ageing treatments (800 < T < 1100-degrees-C) resulted in a less important decrease of the tensile properties in connection with rupture arising from the sudden overloading of the inner carbon plies. At high temperatures (>1100-degrees-C), ageing treatments led to a limited decrease of the tensile properties owing to a combined notch/overloading effect taking place only al high stress levels from the superficial degradation of the composite reinforcement. Both decreasing the oxygen content of the environment (i.e. from pure oxygen to dry air) or using unstabilized materials (i.e. unaged at 1600-degrees-C under argon prior to the oxidizing treatments) resulted in a better oxidation resistance.