Role of nitrogen in the high-temperature oxidation of titanium alloys

We characterized the oxidation of pure Ti, Ti-0.8Si, and Ti-2Nb at 800 degrees C in N2-20% O2 and in sequential isotopically labeled N2-20% O2 atmospheres to clarify how nitrogen influences the high-temperature oxidation mechanisms of titanium alloys. The alloys always exhibited a nitride layer beneath a compact oxide scale with localized nitrogen concentrations in the underlying metal. Nitrogen is found to limit the oxygen concentrations in the metal. The synergy between alloying and nitrogen helps maintain compact oxide scales, preventing the formation of the lamellar scales observed during oxidation in nitrogen-free atmosphere and the oxidation of pure Ti regardless of the atmosphere.