Environmental embrittlement of SiCf/SiC composites

The effects of surface condition, moisture and temperature on the mechanical behavior of SiCf/SiC composites produced by Dupont Lanxide are described. Elastic moduli and tensile strengths have been established at temperatures between 25 and 1200°C. A degradation in properties is noted by thermal exposure alone, but the effect is altered by the presence of moisture in the test atmosphere. The influence of a surface coating on the observed behavior is described. Changes in microstructure accompanying environmental embrittlement are described. Implications for structural applications of these composites are discussed.