First-principles investigation on solution hardening of interstitial impurity elements (O,N) in gamma -TiAl

The authors have calculated the electronic structures of O-doped and N-doped gamma -TiAl using the first principles discrete variational method (DVM) with the aim to understand the solution hardening effects of oxygen and nitrogen in gamma - TiAl. Their combination analysis of the electronic density, the density of states (DOS) and the local environment total bond orders (LTBO) has shown that X atom (X is O or N) can strongly bind with its six surrounding atoms via electronic hybridizations of Ti-3d/X-2p and Al-3p/X-2p. As a result, there forms a hard cohesive region around the impurity atom. A pinning model based on the calculations is proposed to explain the hardening effects. The consistent results are obtained between the present calculation and the formal test experiments.