High-temperature oxidation behavior of Ti-22Al-27(Nb, Zr) alloys

The oxidation behavior of Ti-22Al-(27-x)Nb-xZr (x=0, 1, 6, at%) was evaluated over a temperature range of 650~800℃ in air. The phase composition and the morphology of the formed scales were investigated by X-ray diffraction and scanning electron microscopy. The results show that the alloys containing Zr exhibit better oxidation resistance than Ti-22Al-27Nb alloy. The main oxidation product is TiO₂ for all the alloys oxidized at 650℃ for 100 h. A mixture of TiO₂, Al₂O₃ and AlNbO₄ is formed for Ti-22Al-27Nb and Ti-22Al-26Nb-1Zr oxidized at 800℃ for 100 h; however, ZrO₂ is also traced in Ti-22Al-21Nb-6Zr. The improved oxidation resistance for Ti-22Al-26Nb-1Zr can be ascribed to the refinement of oxides. While in Ti-22Al-21Nb-6Zr alloy, although formation of Al₂O₃ is obvious at 800℃, ZrO₂ in the scale can provide sites for rapid oxygen transport, leading to the high mass gain.