Revisiting grain boundary segregation and precipitation in nanocrystalline metallic alloys

Nanostructured metallic alloys exhibit an inherently high volumetric density of grain boundaries, which could be stabilized either through kinetic pinning effects, thermodynamic solute enrichment of grain boundaries, or a combination of both. While there have been a multitude of recent strides identifying candidate systems for realizing stable nanocrystalline grain structures, experimental literature often relies on indirect evidence that is supplemented by computational models to ascertain fundamental stabilization mechanisms. This work investigates solute behavior in annealed Fe-W and Fe-Zr alloys through the lens of competing solute segregation and oxide precipitation. Ultimately, the absolute difference between enthalpies of segregation and oxide formation was demonstrated as a useful qualitative metric for evaluating nanocrystalline systems for potential grain boundary enrichment. The importance of high-resolution characterization is underscored, as seemingly thermodynamic stabilization can be easily convoluted with kinetically pinning features at the nanoscale.