Investigation on double TiN/Al(Nb,Ta)2 protective layers of TiAl-Ta alloy after high-temperature oxidation

Abstract

The formation process of the double continuous TiN/AlNb2 protective oxide layers of TiAl-Ta alloy after high-temperature oxidation is investigated by experiment and first-principle calculation in this study. It is found that Ta promotes the formation of a double continuous protective barrier consisting of 2.5 μm TiN/0.5–1 μm Al(Nb,Ta)2 layers during high temperature oxidation. And the lowest energy of twenty different AlNb2(1‾10)/TiN(110) terminations are identified by the first-principle calculation, which is significantly influenced by the distance of Nb-N bonding. Based on this, the location of Ta is studied which is preferred to be doped at Nb position of AlNb2 for the formation of Al(Nb,Ta)2 phase, thereby minimizing the total energy of the system. The formation of Al(Nb,Ta)2 phase can facilitate the precipitation of a continuous TiN layer to form a strong interface with low energy. Finally, the formation mechanism of Al(Nb,Ta)2(1‾10)/TiN(110) is discussed in detail. The results provide new insights into the development of oxidation-resistant TiAl alloys.