Phase selection in Ti-Zr-Hf-Al high-entropy alloys was investigated by in-situ high-energy X-ray diffraction, single-crystal X-ray diffraction, and density-functional theory based electronic-structure methods that address disorder and vacancies, predicting formation enthalpy and chemical short-range order (SRO). Samples with varying Al content were synthesized, characterized, and computationally assessed to ascertain the composition-dependent phase selection, as increased Al content often acts as a stabilizer of a body-centered-cubic structure. Equiatomic TiZrHfAl was especially interesting due to its observed bcc superstructure – a variant of γ-brass with 4 vacancies per cell (not 2 as in γ-brass). We highlight how vacancy ordering mediates selection of this variant of γ-brass, which is driven by vacancy-atom SRO that dramatically suppress all atomic SRO. As vacancies are inherent in processing refractory systems, we expect that similar discoveries await in other high entropy alloys or in revisiting older experimental data.
Available at: http://works.bepress.com/duane_johnson/160/
This is a manuscript of an article published as Singh, Prashant, Shalabh Gupta, Srinivasa Thimmaiah, Bryce Thoeny, Pratik K. Ray, A. V. Smirnov, Duane D. Johnson, and Matthew J. Kramer. "Vacancy-mediated complex phase selection in high entropy alloys." 194 Acta Materialia (2020): 540-546. DOI: 10.1016/j.actamat.2020.04.063. Posted with permission.