Ab initio study of chemical disorder as an effective stabilizing mechanism of bcc-based TiAl(+Mo)

Neda Abdoshahi, Petra Spörk-Erdely, Martin Friák, Svea Mayer, Mojmír Šob, David Holec

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung

4 Zitate (Scopus)

Abstract

To shed a new light on the complex microstructural evolution in the Ti-Al-Mo system, we employ ab initio calculations to study bcc-fcc structural transformations of ordered βo-TiAl(+Mo) and disordered β-TiAl(+Mo) to ordered γ-TiAl(+Mo) and hypothetically assumed disordered γdis-TiAl(+Mo) alloys, respectively. In particular, tetragonal (Bain's path) and trigonal transformations are combined with the concept of special quasirandom structures (SQS) and examined. Our calculations of the ordered phases show that the βo→γ tetragonal transformation of TiAl is barrierless, i.e., proceeds spontaneously, reflecting the genuine structural instability of the βo phase. Upon alloying of ≈7.4at.% Mo, a small barrier between βo and γ-related local energy minima is formed. Yet a higher Mo content of ≈9at.% leads to an opposite-direction barrierless transformation γ→βo, i.e., fully stabilizing the βo phase. Considering the disordered phases, the β-Ti0.5Al0.5-xMox and γdis-Ti0.5Al0.5-xMox are energetically very close. Importantly, for all here-considered compositions up to 11at.% of Mo, a small energy barrier separates β-TiAl(+Mo) and γdis-TiAl(+Mo) energy minima. Finally, a trigonal path was studied as an alternative transformation connecting disordered β and γdis-TiAl phases, but it turns out that it exhibits an energy barrier over 60meV/at. which, in comparison to the Bain's path with 9meV/at. barrier, effectively disqualifies the trigonal transformation for the TiAl system.

OriginalspracheEnglisch
Aufsatznummer103604
Seitenumfang14
FachzeitschriftPhysical review materials
Jahrgang24.020
Ausgabenummer10
DOIs
PublikationsstatusVeröffentlicht - 2 Okt. 2020

Bibliographische Notiz

Funding Information:
This research was funded by the Austrian Science Fund (FWF) Project No. P29731-N36. Additional resources were provided by the Ministry of Education, Youth, and Sports of the Czech Republic under the Project CEITEC 2020, LQ1601 (M.Š, M.F.) and the Academy of Sciences of the Czech Republic from its institutional support [Institutional Project No. RVO:68081723 (M.Š, M.F.)]. The computational results presented were achieved, in part, using the Vienna Scientific Cluster (VSC). Additional computational resources were made available by the Ministry of Education, Youth, and Sports of the Czech Republic under the Project IT4Innovations National Supercomputer Center (project e-Infrastructure CZ-LM2018140) within the program Projects of Large Research, Development and Innovations Infrastructures and partly also via the CESNET (Project No. LM2015042) and CERIT-Scientific Cloud (Project No. LM2015085). Parts of Figs. , to , and were visualized using the vesta package .

Publisher Copyright:
© 2020 American Physical Society.

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