Properties and electronic structures of titanium aluminides–alumina composites from in-situ SHS process

Titanium aluminides–alumina composite was synthesized by in-situ self-propagating high-temperature synthesis (SHS) method, followed by hot-pressing process. To understand the fundamental differences between the composite and A12O3 ceramic, a comparative study was carried out using first-principles plane-wave pseudopotential method based on density functional theory (DFT). XRD analysis of final products confirmed the formation of TiAl, A12O3 and a small amount of Ti3Al phases in the composites and the reaction mechanisms of the process were proposed. SEM observation revealed that a two-phase (γ + α2) TiAl–Ti3Al lamellar structure was formed, and the composites exhibited a homogeneous microstructure. Moreover, density of states (DOS), band structure, charge density difference and Mulliken population analysis showed that metallic, covalent and ionic bonding were produced at the interfaces of the composite. O–Al interface bonds showed more covalent character with respect to pure Al2O3. Therefore, interface combination of the composite was improved, making the composite tougher (a toughness as high as 7.9 MPa m1/2) than monophase Al2O3 ceramic.