On the nanoindentation hardness of Cu-Zr-Al/Cu nanolaminates

Nanolaminates consisting of individual amorphous Cu-Zr-Al layers and nanocrystalline Cu layers on Si substrates were prepared by alternatively magnetron sputtering and hardness measurements were conducted upon nanoindentation with a standard Berkovich indenter. Indentation hardness showed a strong size effect in single Cu-Zr-Al film, its decline trend was slower in the nanolaminates with thinner amorphous layers. While experimental hardness was obviously below the expected rule-of-mixture value for all the nanolaminates. Finite element modelling (FEM) analysis was performed in each sample to explore stress distribution beneath indenter. A higher proportion of Cu layers has been involved into plastic region than the nominal value. Besides, interfacial barrier strength was estimated for each sample. The experimental results could be well described by the modified rule of mixture integrated with true ratio of Cu to Cu-Zr-Al in plastic region and the interface strengthen effect.