Abstract: Ultra-fine sizes and high thermal stability are often mutually exclusive for nanocrystalline (NC) materials because the high grain boundary (GB) energy of nanograins provides a large driving force for grain coarsening. Alloying is a classical strategy for stabilizing the microstructure of NC materials. However, the stabilization effects of alloying on NC materials typically rely on the segregation of solute atoms at GBs, which imposes restrictions on the selection of possible alloy systems. In this study, it is revealed experimentally and corroborated theoretically that the interface energies can be continuously regulated by simply manipulating the alloy composition in simple solid-solution alloy systems, enabling the control of the ultra-fine sizes and thermal stability of the alloys without GB segregation. In a model system of NC Au(Cu)-SiO₂ films, the dissolved Cu in Au can be used as a very accurate tool to tailor the interface energies of NC Au(Cu)-SiO₂ film, leading to ultra-fine (below 2 nm) Au(Cu) nanoparticles with exceptional thermal stability. Such Cu-induced grain refinement and thermal stabilization effects are supported by interface thermodynamic calculations. This study thus provides an alloying stabilization strategy without GB segregation, which broadens the scope for developing thermally stable NC alloy systems.

Key words: Nanocrystalline materials, Interface energy, Grain growth, Thermal stability