First-principles study of the bonding characteristics of TiAl(111)/Al₂O₃(0001) interface

First principles calculations were carried out for α-Al₂O₃(0001) surface and γ-TiAl(111)/α-Al₂O₃(0001) interface to study the adhesion properties of the interface and to clarify the mechanisms that govern the adhesion of TiAl and its oxidation product Al₂O₃. Two type interface models, the TiAl(111) with Al- and O-terminated α-Al₂O₃(0001) surfaces denoted as T(A₁)-type and T(O_T)-type interface, respectively, were considered. The Universal Binding Energy Relation (UBER) was used to determine the separation between TiAl and Al₂O₃ and the work of adhesion of the γ-TiAl(111)/α-Al₂O₃(0001) interface. Optimization was then performed for all interfaces considered here using the separation obtained with UBER. The lowest work of adhesion is -1.05 J/m² for the T(A₁)-type interface and is -4.04 J/m² for the T(O_T)-type interface. There exists competition between O-Ti and O-Al (on the TiAl side) interactions; however O-Al bond is stronger than O-Ti bond because the main body of the Al valences is involved in the hybriding with O p electrons, while only part of the Ti d valence is involved in the O-Ti bonding. Thus the O-Al interaction dominates the adhesion between TiAl(111) and Al₂O₃(0001) surfaces, and it can be inferred that an Al-rich TiAl surface will favor the adhesion between TiAl/Al₂O₃.