Résumé
Titanium alloys are widely used in aerospace applications due to their high specific strength. However, titanium alloys are limited to service temperatures below 600 °C due to insufficient creep resistance and oxygen embrittlement. These properties can be improved by adding alloying elements. In this study, the effects of refractory alloying elements (Hf, Ta, and W) in binary (Ti-X) and ternary (Ti-Al-X) on the oxidation resistance during 500 h at 650 °C in air were assessed. Oxidation tests were also performed in Ar-20%O2 to dissociate the effects of oxygen and nitrogen. In air, the global oxidation kinetics decreased in air by adding Ta, Hf and W, with the largest effect observed for W. Oxygen dissolution was also reduced in ternary Ti-Al-W alloys. The oxygen uptake of this ternary alloy was lower than in Ti6242s, a reference alloy for high temperature applications. However, this effect was not explained by a direct effect of W addition on O dissolution or diffusion. This beneficial effect of W was linked to nitrogen uptake and to the enhanced formation of nitrides at the metal/oxide interface. The interfacial N-rich layer decreased the oxygen dissolution in the bulk alloy. First-principles calculations were conducted to calculate oxygen diffusivities in pure titanium and to evaluate the effect of aluminium on the oxygen solubility limit. Even if aluminium has a destabilizing effect on oxygen most stable site (octahedral site), this effect is not very strong and it cannot be measured experimentally.