Effect of Nb on the high temperature oxidation behavior of TiNiAl alloys

The cyclic oxidation behaviors of Ti₅₀Ni₄₄Al₆ and Ti₅₀Ni₄₁Al₆Nb₃ alloys at 1073 K in air showed that the addition of Nb could improve the oxidation resistance of the alloys. After 100 h oxidation the outer oxide scale of Ti₅₀Ni₄₄Al₆ alloy consists of TiO₂ and a few of Al₂NiO₄, and the internal scale is TiNiO₃. The oxidation kinetics of the Ti₅₀Ni₄₄Al₆ alloy obeys a linear law. For the Ti₅₀Ni₄₁Al₆Nb₃ alloy under the same oxidation condition, the oxide scale mainly consisted of TiO₂ as well as Nb, Al riched complex oxide beneath the TiO₂ layer, and the oxidation kinetics obeys parabolic law. The improvement of the oxidation by Nb addition results from that the Nb, Al complex oxide impedes the inward diffusion of oxygen and outward diffusion of metallic elements, which decreases the oxidation rate of the Nb containing alloy.