Oxidation behavior of Hi-Nicalon SiC monofilament fibres in air and O2–H2O–Ar atmospheres

An equipment including aircraft engine simulated environmental system and sample loading stage was manufactured for annealing Hi-Nicalon monofilament fibres in corrosive environments. The fibres were exposed in air and 14% H2O/8% O2/78% Ar atmospheres at 1200 °C for 1–100 h, respectively. Experimental results indicate that tensile strength decreases, whereas oxide layer thickness and grain size of SiO2 increase with rising annealing time. The specimens show brittle/flat fracture, most of cracks initiate at the interface between SiC and SiO2 region of fibres. The control effect of water vapor on formation and structural evolution of the passive film was discussed.

► An equipment for annealing Hi-Nicalon monofilament fibers in corrosive environments.
► Monofilament fibers were exposed in air and wet oxygen at 1200 °C for 1–100 h.
► Tensile strength decreases, whereas oxide layer thickness increase with rising annealing time.
► Existence of transition region plays a positive role in preservation of fiber’s strength.
► The water vapor enhances the oxidation rates, tensile strength and passivation.