Oxidation resistant low-alloyed Ti alloys with good ductility

Oxidation resistance enhancement of pure Ti often comes at the cost of reduced ductility, which is frequently the problem through alloying with sole Al, Si, W, Mo and B. To overcome the short coming of single element alloying, this paper proposes a multi-element low-alloying strategy to take advantage of synergistic effects and resolve the conflict between oxidation resistance and ductility. It demonstrates that the addition of a small quantity of Ta (0.51 wt%) can boost both oxidation resistance and ductility in comparison to pure Ti. Furthermore, the combined addition of a small amount (0.54 wt%) of Ta, Nb and Si not only preserves good ductility of pure Ti, but also reduces mass gains to 14%–67% of pure Ti during 100 h oxidation at 650–850 °C in air. This indicates even better oxidation resistance than that obtained through the use of Ta, Nb, or Nb + Ta additions. The Ta + Nb + Si alloying creates an oxide layer that is less porous and more resistant to stratification and spalling. Consequently, a 3-μm N-rich layer can form in the Ti substrate beneath the oxide scale, in which phase transformation generates coherent Ti₂N with (0001)_Ti as the habit plane, with N atoms prefers to diffuse along \({[2\bar{1} \bar{1} 0]}_{\text{Ti}}\) ${[2\overline{1}\overline{1}0]}_{\text{Ti}}$ than along [0001]_Ti. The completely transformed Ti₂N region or partially transformed Ti + Ti₂N region can effectively impede oxygen invasion. Therefore, the multi-element low-alloying strategy is promising for enhancing both oxidation resistance and mechanical properties of metallic materials in the future.