Mechanical alloying produces grain boundary segregation in Fe–Mg powders.

Although mechanical alloying can force immiscible elements into homogeneous solid solution due to its chemically "randomizing" nature, as microstructure design of powder-processed alloys advances, other alloy configurations are also sought. Here we study ball milling of Fe–Mg alloys and obtain a heterogeneous nanostructure, with grain boundaries decorated by solute even after reaching complete supersaturation and a steady-state grain size. Such nanocrystalline powders having grain boundary segregation in the as-milled state are particularly useful for thermal stability against grain growth. The high diffusivity of Mg is thought to shift the competition between ballistic mixing and equilibration, permitting such a structure to form. Image, graphical abstract [ABSTRACT FROM AUTHOR]