Deformation evolution of Cu/Ta nanoscale multilayer during nanoindentation by a molecular dynamics study

Molecular dynamics simulation of nanoindentation is performed to study the plastic deformation evolution of Cu/Ta and Ta/Cu nanoscale multilayers with effects of layer thickness and interface orientation relationship. The results reveal that the plastic deformation mechanism is determined by both the intrinsic property of monolayer and the interface characteristic, and the mechanical property has an important dependence on Ta deformation. The interface could strongly interact with and adsorb lattice dislocations, acting as the primary emission source of dislocations due to high stress concentration. The Cu/Ta interface exhibits a strong blocking effect obstructing dislocation traversing interface, while the Ta/Cu interface could transmit deformation stress to activate Cu layer deformation. The effect of interface orientation indicates that the propagation of crystal defects depends on slip system of monolayer, and the dislocation evolution in Ta layer shows a two-step mechanism: the V-shaped structure formation, and its cusp and root segments triggering the subsequently extended dislocations. Contrarily, the high-energy OT orientation interface causes random defect structures. The indentation hardness reveals two critical thicknesses (70 and 160 Å for Ta/Cu multilayer, 40 and 160 Å for Cu/Ta multilayer), which strongly depend on the size of indenter and indentation depth at nanoscale. This work provides an important understanding of the resistance of nanostructured materials to mechanical deformation for designing wear-resistant coatings and structural nanocomposites.