The void nucleation strengths of the Cu-Ni-Nb- based nanoscale metallic multilayers under high strain rate tensile loadings

The mechanical behavior of Cu-Ni-Nb- based nanoscale metallic multilayers (NMM) under high strain rate loadings is investigated in this work using molecular dynamics simulations. The simulations of NMMs with various individual layer thicknesses under uniaxial tensile strains at two different controlled strain rates (109/s and 1010/s) are performed. This type of loading condition generates a stress state necessary for void nucleation commonly observed under shock loading. The mechanisms for void nucleation in the NMMs are examined and identified; the void nucleation strengths (VNS) of the NMMs and their variations with respect to increasing individual layer thickness as well as available nucleation sites (affected by addition of interfacial disconnections) are obtained and explained. It is discovered that the void always nucleate from within the Cu layers, where the partial dislocations intersect with each other or with existing stacking faults. The void nucleation strength of the NMMs is closely related to the density of available sites for void nucleation. By introducing interfacial steps into the incoherent interfaces of the NMMs the abundance of dislocation sources is changed, thus more (less) sites for void nucleation are produced which decrease (increase) the void nucleation strength of the NMMs.