Isothermal oxidation mechanism of Nb–Ti–V–Al–Zr alloy at 700–1200 °C: Diffusion and interface reaction

• Isothermal oxidation kinetics is demonstrated to be a parabolic-linear law.
• Diffusion activation energy and interface reaction activation energy are determined.
• Oxidation is controlled by interface reaction and diffusion of Ti4+ and O2−.

Isothermal oxidation kinetics of Nb–Ti–V–Al–Zr alloy at 700–1200 °C followed a mixed parabolic-linear law. The oxidation region consisted of an outer oxidation layer (OOL) and an internal oxidation zone (IOZ). OOL was composed of TiO2 and Nb2O5 at 700–800 °C, TiO2 and Nb2O5 as well as TiNb2O7 at 1100 °C, and TiNb2O7 and TiO2 at 1200 °C. IOZ could be divided into two zones according to morphology and distribution characteristics of Ti-rich internal oxides at 1100–1200 °C. The oxidation of Nb–Ti–V–Al–Zr alloy is proposed to be controlled by chemical reaction in the oxide/alloy interface and diffusion of Ti4+ and O2−.