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

Abstract

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(OT)-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(OT)-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.