First principles calculations are used to study the preferential occupation of ternary alloying additions into the binary Ti-Al phases, namely γ-TiAl, α2-Ti3Al, βo-TiAl, and B19-TiAl. While the early transition metals (TMs, group IVB, VB , and VIB elements) prefer to substitute for Ti atoms in the γ-, α2-, and B19-phases, they preferentially occupy Al sites in the βo-TiAl. Si is in this context an anomaly, as it prefers to sit on the Al sublattice for all four phases. B and C are shown to prefer octahedral Ti-rich interstitial positions instead of substitutional incorporation. The site preference energy is linked with the alloying-induced changes of energy of formation, hence alloying-related (de)stabilisation of the phases. We further show that the phase-stabilisation effect of early TMs on βo-phase has a different origin depending on their valency. Finally, an extensive comparison of our predictions with available theoretical and experimental data (which is, however, limited mostly to the γ-phase) shows a consistent picture.
@article{arxiv.1512.07601,
title = {Preferential site occupancy of alloying elements in TiAl-based phases},
author = {David Holec and Rajeev K. Reddy and Thomas Klein and Helmut Clemens},
journal= {arXiv preprint arXiv:1512.07601},
year = {2016}
}