Spectrum of grain boundary segregation energies in a polycrystal

Solute segregation at grain boundaries (GBs) is emerging as an alloy design tool, uses of which include the stabilization of nanocrystalline alloys. To predict the equilibrium segregation state in a given alloy, most thermodynamic models treat the full network of GBs as a single "entity", and thus use an "effective" segregation energy to describe it. This simplification ignores the spectral nature of available GB segregation energies in a polycrystal, which we elucidate here computationally for a Mg solute in an Al polycrystal; the distribution is found to be captured accurately with a skew-normal function. A thermodynamic segregation isotherm that incorporates this spectrum is outlined and employed to study the effect of such a spectrum on predictions of the equilibrium GB segregation state. The ramifications for experimentally-extracted GB segregation energies are shown to be potentially significant, and nanocrystalline stability criteria are extended to account for this spectral nature of GB segregation. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.