Abstract

A recently developed Green function approach informed by ab initio calculations models vacancy-mediated transport of 61 solutes in a hexagonal close packed magnesium. The 8- and 13-frequency diffusion models approximate vacancy jump rates near a solute, leading to the inaccurate calculation of Onsager coefficients. We identify all the symmetry-unique vacancy jumps in the Mg lattice and use the Green function approach to calculate the Onsager coefficients exactly in the limit of dilute solute concentration. Density functional theory-computed solute-vacancy interactions and vacancy jump rates inform the Green function approach and previous diffusion models. Solutes with positive size misfit diffuse faster compared to the self-diffusion of Mg due to the relaxation of solute towards vacancy while solutes with negative size misfit diffuse slower. Transition metal solutes show drag for attractive solute-vacancy binding as well as for repulsive binding, due to faster reorientation rates of the vacancy around the solute compared to dissociation rates. Solutes from the s-block, p-block and lanthanide series with attractive solute-vacancy binding and slower reorientation rates compared to the dissociation rates show drag due to vacancy motion around the solute through alternate dissociation and association jumps. The prediction of activation energy of diffusion from the 8-frequency model deviates by more than 50 meV for solutes with significant correlations effect. Our GF approach prediction of solute diffusion coefficients agree well with the available experimental measurements.

Original languageEnglish (US)
Pages (from-to)339-350
Number of pages12
JournalActa Materialia
Volume150
DOIs
StatePublished - May 15 2018

Keywords

  • Ab initio calculations
  • Diffusion
  • Green function approach
  • Magnesium alloys

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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