Temperature dependence and anisotropy of self- and mono-vacancy diffusion in alpha-Zr

Abstract

Temperature dependence and anisotropy of self- and mono-vacancy diffusion is important for modeling irradiation-induced microstructure evolution and the concomitant macroscopic deformation in Zr and its alloys. For self-interstitials, direct MD simulation of the diffusion has yielded useful data. Vacancy and self-diffusion, however, proceeds at a much slower rate, so that a direct simulation is not always practicable, particularly in the reactor-operating temperature regime. In this paper, we follow an alternate route based on thermodynamic integration and calculate the enthalpy. entropy and attempt jump frequencies of vacancy migration and formation in alpha-Zr for various temperatures ranging from 100 K to 1100 K. Their jump-direction and temperature dependencies are examined. The diffusivities so derived compare very well with other calculated results. Comparison with experimental self-diffusion data shows good general agreement except in the temperature regime near the alpha-beta transformation. In this regime, the curvature in the Arrhenius plot of the self-diffusivity obtained is substantially smaller than the corresponding experimental results. Possible reasons are discussed.