First-principles investigation on electronic structures and energetic characteristics of γ/γ tilt grain boundaries in γ-TiAl intermetallic

The energetic and electronic characteristics of γ/γ tilt grain boundaries (GBs) in γ-TiAl intermetallic were comprehensively analyzed using first-principles methods. The interfacial bonding energy, strength, and features of GBs were quantitatively and qualitatively described by the formation energy, excess free volume (EFV), electron localization function (ELF), bonding charge density (Δρ), and density of states (DOS). The formation energies and EFV of Σ3, Σ11, and Σ5 GBs are relatively low in sequence among different GBs. The electronic structure analyses manifested that the smaller the local lattice strain, the stronger the Ti-d-Al-p bonding, the weaker Al-p-Al-p bonding nearby the GB interface, and the lower the GB formation energy. Further, the interface structure of Σ11 GBs in Widmanstätten structure and that of Σ5 GBs in feathery structure were firstly characterized by TEM. Based on the analyses, the interfacial energetic mechanism of metastable transformations, and possible alloying effects were discussed. This work provides an insight into not only the atomic and electronic basis of GBs but also the understanding of the mechanism of metastable transformations and interface engineering in γ-TiAl alloy.