Oxidation behaviour of iridium-aluminum and iridium-aluminum-silicon systems at very high temperatures (1500°C to 1800°C)

Abstract

Recent results for the oxidation behavior of iridium-aluminum and iridium-aluminum-silicon systems at temperatures between 1550 (2822) and 1800°C (3272°F) are summarized. Iridium-aluminum intermetallics with high aluminum concentrations (above 55 atomic percent) form protective alumina scales. The observed parabolic oxidation rates are controlled by grain-boundary transport of oxygen through the alumina scale. The addition of 10 atomic percent silicon decreases the aluminum concentration necessary for the formation of a protective alumina scale to 30 atomic percent. The ternary iridium-aluminum-silicon system initially exhibits parabolic growth of an alumina scale with subsequent decreasing rates, presumably due to the formation of an amorphous silica layer at the alumina/substrate interface. Thermal cycling does not cause spallation of the alumina scale formed on either the binary or ternary systems.