Size dependence of creep behavior in nanoscale Cu/Co multilayer thin films

Research highlights: → Cu/Co superlattice structure forms with decreasing periodicity. → It exhibits size dependence of the creep behavior and power-law creep parameters. → A dislocation model for steady-state deformation of semi-coherent films is presented. → Nanoscale effects are related to dislocation generation and annihilation at interfaces. - Abstract: Cu/Co multilayers with periodicity of 4-40 nm were prepared by electron beam evaporation deposition. Microstructure and room temperature creep behavior were investigated by X-ray diffraction, transmission electron microscopy and nanoindentation test. The results show that superlattice structure forms with decreasing periodicity and coherent interfaces come into being at low periodicity of 4 nm. Size dependence of the creep behavior is observed and power-law creep parameters including stress exponent and size sensitivity index are calculated by dimension analysis. A dislocation model for predicting the steady-state deformation of multilayers with semi-coherent interfaces is presented. Nanoscale effects are explained by dislocation generation and annihilation mechanisms involving single dislocations slip in confined layers and dislocations climb at the interfaces, respectively. Model predictions agree well with experimental observation.