Comparative investigation of oxidation behavior and hot corrosion behavior in NaCl-Na2SO4 mixture for a Ti2AlNb based alloy at 1023 K

Oxidation behavior of a Ti2AlNb based alloy (Ti-22Al-23Nb (at.%)) and hot corrosion behavior of this alloy coated with a salt mixture of NaCl-Na2SO4 at 1023 K were comparatively investigated. The results showed that the alloy possessed relatively good oxidation resistance while suffered severe hot corrosion attack. The mass gain of the hot-corroded alloy was much larger than that of the oxidized alloy. The oxide scale was mainly composed of TiO2. During the oxidation, the oxide scale could keep intact. In the corrosion product scale, TiO2 + Al2O3 layers and NaNbO3 layers existed alternately and Al2O3 was distributed in the lower parts of the TiO2 + Al2O3 layers. The formation of the TiO2 + Al2O3 layer and the NaNbO3 layer should promote each other by altering the acidity/basicity of the salt film, and thus the growth of the scale was accelerated. The escape of the gaseous chlorides, the fast growth of the scale and the coefficient of thermal expansion (CTE) mismatch between TiO2 and NaNbO3 resulted in serious cracking and spalling of the scale.