Theoretical investigation of the omega-related phases in TiAl-Nb/Mo alloys
2014 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 90, no 5, 054109- p.Article in journal (Refereed) Published
The incorporation of cubic beta/beta(0) phase improves significantly the ductility and workability of TiAl-based alloys. However, the ductility deteriorates with the precipitation of the ordered hexagonal omega(0) phase in the beta/beta(0) phase. To avoid the formation of the omega(0) phase in alloy design, fundamentals about the beta/beta(0) to omega(0) phase transition and its alloying element dependence have to be known. In the present work, we investigated the phase transition and phase stability in Ti4Al3Nb and Ti4Al3Mo alloys using a first-principles method based on density functional theory. Our calculations indicate that for the beta(0) to omega(0) transition, the "collapse-diffusion" pathway is easier than the "diffusion-collapse" one; however, both pathways are quite difficult due to the high-energy barriers. The beta(0) to omega '' transition occurs through the "diffusion-collapse" pathway without an energy barrier (except for the activation energy for the short-range diffusion needed for atomic rearrangement). Comparing the total energies of different phases, we find that the omega(0) phase of Ti4Al3Nb is more stable than beta(0) and vice versa for Ti4Al3Mo whereas the relative stability of omega '' to beta(0) for Ti4Al3Nb is stronger than that for Ti4Al3Mo, indicating that the addition of Mo inhibits the transition from the beta(0)- to the omega-related phases in Ti4Al3Nb. Our calculations demonstrate that omega '' is more stable than omega(0) for both Ti4Al3Nb and Ti4Al3Mo, in contrast to the previously proposed picture based on some experimental observations, the possible origins of which are discussed in detail.
Place, publisher, year, edition, pages
2014. Vol. 90, no 5, 054109- p.
quasi-random structures, 1st-principles calculations, potential model, stability, metals, transformations, approximation, aluminides, additions, design
IdentifiersURN: urn:nbn:se:kth:diva-153387DOI: 10.1103/PhysRevB.90.054109ISI: 000341256000002OAI: oai:DiVA.org:kth-153387DiVA: diva2:754108
FunderSwedish Research Council
QC 201410092014-10-092014-10-032014-10-09Bibliographically approved