Cyclic deformation induced strengthening and unusual rate sensitivity in Cu/Ru nanolayered films

In this work, we have systematically investigated the effect of cyclic deformation on the strength and rate sensitivity of Cu/Ru multilayers with different individual layer thickness ( h ) by nanoindentation tests. It was found that cyclic deformation remarkably enhances the hardness of Cu/Ru multilayers comparing with the specimens by monotonic loading. The rate sensitivity ( m ) of multilayer exhibits an anomalous size dependence after nanoscale cyclic deformation. When h > 10 nm, the m linearly increases with increasing cycle number of loading-unloading ( s ). However, the m sharply decreases with increasing s when h m . An obvious Bauschinger effect is observed during cyclic loading, where the evolution of effective stress is consistent with the m . Cyclic deformation induced dislocation accumulation and arrays at the heterogeneous interface are the intrinsic plastic mechanism for the enhanced rate sensitivity. The formation of amorphous layers at the critical h is mainly responsible for the inverse size m .