Water vapor thermal treatment of silicon carbide-nanostructured ferritic steel alloy (SiC-NFA) composite materials

Under water vapor treatment between 500 °C and 1000 °C, pure nanostructured ferritic steel alloy (NFA) and silicon carbide-nanostructured ferritic steel composites (SiC-NFAs) exhibit breakaway oxidation and produce a bi-layer oxidation surface. The morphology of the hematite outer layer exhibits flake-donut-stub transformation with varied growth orientation. SiC addition in the NFA matrix alters the inner layer by forming SiO2 within a Cr-rich magnetite inner layer. The thickness of the oxidation layer is related to the sample density, composition, and temperature. The γ-Fe precipitation in the pure NFA accelerates oxidation. The SiC-NFAs show much improved corrosion resistance by SiO2 formation in the inner oxidation layer.