First-principles modeling of BCC to omega phase transition in ZrNbTaTiHf high-entropy alloy

Lobzenko, I.   ; Tsuru, Tomohito   

As for any materials, phase stability studies comprise an important part of the high entropy alloys (HEA) theory. It is recognized that the first generation HEAs exhibit single-phase structures, while alloys of the second generation might possess complicated multi-phase structure. Nowadays, achievements of software and hardware progress allow modeling of such complicated materials as HEAs from first-principles. In particular, the theoretical method of Exact Muffin-Tin Orbitals (EMTO) directly accounts for the random distribution of atomic spices in the structure. It is built on the basis of the density functional theory, and therefore demonstrates high accuracy, which is crucial for modeling of industrially important materials. The objective of the present work is studying of base center cubic (BCC) to omega () phase transition in the ZrNbTaTiHf alloy. The omega phase is formed if in the BCC elementary rectangular cell oriented in [1,1,1] direction, four out of six basis atoms are displaced along [1,1,1] direction. The two atomic percentage compositions of that alloy are set according to equi-atomic and equi-weight structures. It is known that at T = 0 K the phase is more stable than BCC phase for single Zr metal. However, additional atomic spices are able to make BCC phase more stable. From our results, achieved using the EMTO method, it is seen that Zr(1-x)Nb(x) alloy is more stable in BCC phase starting from x = 20% of atomic concentration of Nb. The equi-weigh ZrNbTaTiHf high-entropy alloy has nearly 20% of atomic concentration of Nb, so energies of BCC and phases are expected to have close energies, which means that in real experiments a multi-phase composition may be observed.