Electronic structures and properties of TiAl/Ti₂AlNb heterogeneous interfaces: A comprehensive first-principles study

The electronic structures and properties of ten TiAl/Ti₂AlNb heterogeneous interfaces with three Ti₂AlNb phases (B2, D0₁₉, O) and different terminations/boundaries were comprehensively studied via first-principles calculations. Their interfacial bonding features, strength and relative stability are quantitatively and qualitatively revealed by the equilibrium energy, Fermi energy, interfacial energy (γ_int), electron localization function and bonding charge density (Δρ), respectively. Accordingly, it was revealed by the partial and total electron density of states that the decreasing tendency of the bond strength in the order of Ti-Nb > Ti-Al > Nb-Al at the interfaces was attributed to the electrons hybridization of Ti-d states, Nb-d states and Al-p states. Since the γ_int decreased in the order of TiAl/B2 > TiAl/O > TiAl/D0₁₉, the TiAl/D0₁₉ interfaces with the lowest energy was regarded as the most stable phase boundaries and was further validated by the electron back-scattered diffraction analysis. It is found that the D0₁₉ phase is dominated at the interface boundaries while the B2 serves as a transition phase distributed on its both sides. On the contrary, the metastable O phase can form in the bulk Ti₂AlNb but not at the interface due to their largest distortion when precipitating at the phase boundary. This work provides an insight into the atomic and electronic basis for the bonding and strengthening mechanisms of TiAl/Ti₂AlNb heterogeneous interfaces.