Role of Zr in Cu-rich single-phase and nanocomposite Cu-Zr: Molecular dynamics and experimental study

• Cu-rich Cu-Zr solid solutions obtained in both experiments and growth simulations. • Enhanced hardness of sputtered Cu from 2.5 to 3 GPa to 4–5 GPa by up to ≈3 at.% Zr. • Correlation of hardness enhancement with Zr content in solid solutions. • Transition to nanocomposites, but no further hardness enhancement, at 4–5 at.% Zr. • Early example of atom-by-atom growth simulations of a nanocomposite. The non-equilibrium atom-by-atom growth of Cu-rich Cu-Zr thin films has been investigated by a combination of magnetron sputter deposition and molecular dynamics simulations. We focus on the role of Zr in the transition from large solid solution crystals through a nanocomposite (around ≈5 at.% Zr) to a metallic glass. We find, contrary to the assumption based on equilibrium phase diagram, that in this non-equilibrium case most of the grain refinement and most of the hardness enhancement (from 2.5 to 3 to 4–5 GPa) takes place in the compositional range (up to ≈3 at.% Zr) where many or even most Zr atoms (depending on the sputtering regime) are in the supersaturated solid solution rather than at the grain boundaries. The results are important for the design and understanding of technologically important nanostructured metallic films. In parallel, from the methodology point of view, the results include an early example of modelling the atom-by-atom nanocomposite growth.