An atomic size criterion for stabilizing and strengthening multicomponent nanocrystalline engineering alloy

Previous studies have been focused on stabilizing a nanocrystalline (NC) metallic element by doping a solute element. This study aims to explore the stabilization of a NC engineering alloy, Fe-based Fe-Cr-Ni-X stainless steels (SSs) with 1 at% doped element X (X = Y, La, W, Mo, Nb, Ta Zr, Hf). We find that the larger the atomic radius difference between doped X and matrix Fe elements, the smaller the grain boundary (GB) energy. The smaller GB energy lowers the thermodynamic driving force for grain growth and results in a smaller grain size, which in turn makes the NC engineering alloy harder and stronger. The Y-and La-doped NC SSs are ten times stronger than coarse-grained SSs. The present work provides a simple criterion to select doped alloying element that can effectively stabilize and strengthen multicomponent engineering NC alloys.