Franck Lamouroux

Oxidation effects on the mechanical properties of 2D woven C/SiC composites

Abstract 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°C and 1400°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 at low temperatures ( 1100/dgC), ageing treatments led to a limited decrease of the tensile properties owing to a combined notch/overloading effect taking place only at 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°C under argon prior to the oxidizing treatments) resulted in a better oxidation resistance.

Silicon carbide infiltration of porous CC composites for improving oxidation resistance

Abstract This paper deals with the attempts made at LCTS to replace part of the carbon matrix of CC composites by silicon carbide in order to improve the oxidation resistance. Oxidation kinetics of CCSiC are presented, as well as the incidence of oxidation on the degradation of the microstructure and the tensile strength of the composites. Modelling of the oxidation kinetics allows prediction of mass losses as a function of temperature, thickness of seal-coating, level of mechanical loading, and reactivity of the components toward oxygen. On the basis of this model, it is possible to determine a mechanism controlling the oxidation kinetics, the degradation mode of the composite, and then the evolution of the tensile properties in oxidizing environments. Finally, further improvement in the oxidation resistance of the CCSiC composites is discussed, based on a change in the thickness and nature of the SiC seal-coating.