Formation and migration behavior of vacancy in multi-component alloys

The formation and migration behaviors of vacancies in the crystal and on the surface of Al₂CrCoFeNi with a body-centered cubic (BCC) structure and CrCoFeNi with a face-centered cubic (FCC) structure were studied to provide some support for the mechanism of sluggish diffusion in multi-component alloys; the first-principles calculations based on density functional theory were applied in this study. The most probable configurations of the mono-vacancy and divacancy and the most probable mechanisms of vacancy migration were systematically discussed. The lower formation energy indicated that the mono-vacancy of the Cr atom was the most likely to occur in the crystal and on the surface of the BCC and FCC alloys; it was easier to form a mono-vacancy on the surface than in the inner crystal. Based on the formation and binding energies of the divacancy, Cr–Co and Cr–Ni of the first neighbor showed higher stability and were the main divacancy configurations for the BCC and FCC alloys. The results of the displacement-energy curves showed that the most probable migration mechanisms in the crystals of the BCC and FCC alloys were the migrations of Cr mono-vacancies along the [111] and [110] directions, respectively. Regarding the (100) surface of these alloys, interlayer migration of the nearest neighbor required the lowest activation energy and was the primary migration mode for the vacancy. The results indicated that the migration behavior of vacancies in the crystal and on the surface of multi-component alloys was more difficult than that in other binary alloys. These results provide a useful theoretical basis for further analysis of element diffusion in multi-component alloys.