Corrosion, oxidation and strength properties of Nicalon SiC fibre under loading

Hot corrosion and oxidation behavior of Nicalon fibres in air under loading were investigated and compared. Degradation of Nicalon fibres exposed at temperatures over 900°C in the presence of Na2SO4 was extremely severe compared with that in oxidation environment without Na2SO4. This is attributed to the rapid oxidation-dissolution of the fibres due to the formation of the liquid Na2SiO3. Room temperature strength of Nicalon fibre after oxidation decreased with increasing exposure temperature. Reduction of tensile strengths was most significant under the combined condition of exposure temperature and applied loading. This evident strength reduction is caused by the combination of applied load and the reaction between the inherent SiO2 and free carbon in the fibre. Fracture surfaces of oxidized fibres exhibited mirror-hackle regions, whereas the fracture surfaces of fibres corroded were planar.