Shear banding mechanisms in Cu/Ru nano-structured multilayers: effect of phase transformation

The shear banding mechanisms of sputter-deposited nanoscale Cu/Ru multilayer with single-layer thickness of 0.8 nm and 1.5 nm, respectively, were investigated by nanoindentation. Shear bands can be observed in Cu/Ru multilayer only when the layer thickness is 1.5 nm. Deformed microstructure analysis showed that the plastic deformation behavior within the shear band of Cu1.5/Ru1.5 multilayer is primarily controlled by the dislocation dominated non-crystallographic rotation through the Cu/Ru interface without changing the crystallographic orientation. By synthetical analyzing of the indentation-induced deformed microstructures, a deformation mode transition from shear banding to opening crack is suggested as decreasing the layer thickness from 1.5 to 0.8 nm, mainly relating to the phase structure of Ru layer. Moreover, the excellent toughness of Cu/Ru multilayers also could be obtained by regulating the influences of phase structure on the shear band formation.