Comparison of the isothermal and cyclic oxidation behavior of Cr and Mo containing γ-TiAlNb alloys

The isothermal and cyclic oxidation behavior of gamma-Ti-46.5Al-5Nb-0.3B alloys containing 2 at.% Cr, 2 at.% Mo, 1 at.% each of Cr and Mo, is compared at 900 degrees C until 500 h. The alloys exhibit parabolic oxidation, similar isothermal oxidation rates, but contrasting cyclic oxidation characteristics. The Mo-containing alloys form more Al2O3, exhibit extensive oxide spallation and weight loss; and vice-versa is observed for the Cr-rich alloy. The residual stresses, strains and spallation mechanisms in the multi-layered oxide scale are analyzed. Higher Al2O3 formation, high compressive stress (similar to 1 GPa) and strain (> 0.2 %) induce early delamination of oxide scale and weight degradation.