Effect of Zr on microstructure and oxidation behavior of α and α + α₂ Ti-Al-Nb alloys

To develop high-temperature Ti alloys, microstructure and oxidation behavior were investigated in Ti-(10,15)Al-2Nb-(1,2)Zr (at%) alloys. For reference, ternary Ti-15Al-2Zr alloy was also investigated. A single α phase exists in Ti-10Al-2Nb-(1, 2)Zr alloys; on the other hand, an α and α₂ two-phase was observed in Ti-15Al-2Nb-(1, 2)Zr alloys. Fine α₂ precipitates of about 10 nm were observed in the Ti-15Al alloys. The oxidation behavior of Ti-Al-Nb-Zr and Ti-Al-Zr ternary alloys was investigated to understand the effect of Zr on oxidation behavior at 1023 K. It was found that Zr improves the oxidation resistance of the α phase more effectively than Nb. TiO₂ was formed in all tested alloys. The addition of Zr drastically decreased the growth rate of TiO₂. It was also found that the addition of Nb improved adhesion of the oxide layer.