Influence of interstitial defects on the structural and mechanical properties of lamellar TiAl alloys
P. L. Veluvali.
Master Thesis, Ruhr-Universität Bochum (2016)
Titanium aluminides are among the favourite candidates for structural intermetallics for high temperature applications. TiAl alloys composed of γ-TiAl (LI_0 structure) and α2 -Ti3Al (DO_19 Structure) phases have replaced single phase alloys due to improved deformability than the latter. The lamellar structure present, offers good mechanical behaviour at high temperatures, relatively high fracture toughness and creep resistance. In our project we aim to study the influence of vacancies and antisite defects at γ/γ interfaces on interface energy and tensile properties using ab-initio density functional theory calculations. Anti-site disorder (swapping of sites) is common in intermetallics where exchange of lattice positions takes place between cations and anions. In our case we introduce Ti atoms at Al site and vice-versa at the γ/γ interface. Interface energy calculations showed that true twin structure is the most preferable with the lowest energy. The Antisite defect even at interfaces of low interface energy was seen to be stable via formation energy calculations. The influence of defects at different atomic positions along the  direction on interface energy are discussed in detail. Structural behaviour of γ/γ interfaces due to interstitial defects have also been studied. Tensile properties revealed that true twin with an antisite defect shows higher work of separation and normal strength.