Precipitation strengthening in nanocomposite Cr/Cu–Cr multilayer films

Abstract

Precipitation strengthening in nanostructured metallic multilayer (NMM) films of Cr/Cu–Cr was studied using nanoindentation and electron microscopy. Magnetron-sputtered NMM films having layer thicknesses of 10, 20 and 30 nm were prepared at room temperature (RT) and 100 °C. Some of the RT-deposited films were annealed at 100 °C for 30 min. Cr was introduced in the Cu–Cr layers by using a Cu–Cr target (95 at.% – 5 at.%) target. A significant increase in nanoindentation hardness was observed in the Cr/Cu–Cr. A reduction of hardness dependence on layer thickness was also observed in the Cr/Cu–Cr, such that sample having a layer thickness of 30 nm provides the equivalent strength of a 10/10 nm Cr/Cu. Uniformly distributed Cr particles in the Cu–Cr layers are key strengthening features in these new Cr/Cu–Cr NMM films. A single dislocation-based model was used to correlate the observed mechanical behaviours and microstructure. The model predicts similar trend observed from the experimental results, suggesting that the higher strength in Cr/Cu–Cr is likely the result of dislocation movement impediment due to Cr precipitates in the Cu–Cr layers.