Unveiling the Regulatory Mechanism of Zr Content on the Microstructure, Mechanical Properties and Stability of Cu-Zr Nanocrystalline Alloy Films

A series of Cu-Zr nanocrystalline alloy films with varying Zr contents were fabricated via magnetron co-sputtering technology. The effect of Zr content on the microstructure and mechanical properties of the alloy films was investigated, and the strengthening mechanism was revealed. Furthermore, the stability of nanocrystalline alloy films was studied through annealing experiments at different temperatures. The results show that part of the added Zr atoms are dissolved in the Cu lattice to form a solid solution structure of Zr in Cu, while the other part segregates at the grain boundaries. No second-phase compounds or simple substances are formed in the alloy films. The addition of Zr significantly refines the grain size of the alloy films. The hardness of the films exhibits a gradual increase with the elevation of Zr content. The results indicate that there are three main strengthening factors for the alloy films: grain refinement strengthening effect (∆HGB, accounting for exceeding 70%), solid solution strengthening effect (∆HSS, accounting for approximately 20%) and nanocrystalline solute atom pinning strengthening effect (∆HNC,SS, accounting for less than 10%). Among them, the strengthening effect of grain refinement assumes a predominant role. Regarding stability, Zr atoms segregate at the grain boundaries of the alloy films. The segregation becomes more significant as the annealing temperature rises. This segregation of Zr atoms at the grain boundaries can exert a pinning effect on the grain boundaries and impede their migration, thus significantly improving the structural stability of the alloy films.