Isothermal oxidation mechanism of a newly developed Nb-Ti-V-Cr-Al-W-Mo-Hf alloy at 800-1200 °C

Oxidation performance of a newly developed Nb-Ti-V-Cr-Al-W-Mo-Hf alloy at 800-1200 °C for 5 h in flowing air was investigated via isothermal oxidation testing, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and electron probe microanalysis. The results indicated that the kinetics followed a mixed parabolic-linear law and the oxidation activation energies were obtained. The oxidation region consisted of external oxide layer (EOL) and internal oxidation zone (IOZ). EOLs were composed of TiO2, Nb9VO25 and CrVNbO6 at 800 °C, TiO2 and TiNb2O7 at 1100 °C, and CrVNbO6 and TiNb2O7 at 1200 °C. Ti-, Hf- and Nb-rich internal oxides were observed in IOZ. The theoretical and experimental analysis suggested that the chemical reactions in oxide/alloy interface and diffusion of Ti4 + and O2 − in alloy were the mechanism to understand the oxidation process.