Thermodynamics and design of nanocrystalline alloys using grain boundary segregation spectra

Abstract Solute segregation at grain boundaries (GBs) is a key mechanism to stabilize nanocrystalline alloys. To date, the standard approach to design and screen for nanocrystalline stability uses a simplified representation that treats the GB network as a single entity, and thus, uses a single “average” segregation energy to characterize solute GB segregation in an alloy. This simplification, however, fails to capture the highly anisotropic nature of GBs, which results in a spectrum of segregation energies that can be very broad. Here, we remove this simplification, and outline more formally correct thermodynamic criteria to screen for thermodynamic stability of polycrystalline structures, accounting for the spectral nature of GBs. We proceed to apply the developed criteria to screen over 200 alloy combinations based on embedded atom method potentials. Among its benefits, this spectral approach enables strict enforcement of the third law of thermodynamics, where an average segregation energy does not. The results of the screening are in general agreement with experimental observations.