Elevated temperature dependence of hardness in tri-metallic nano-scale metallic multilayer systems

A tri-layer nano-scale metallic multilayer (Cu/Ni/Nb) system with a mixture of incoherent and coherent interfaces was investigated to determine the effect of elevated temperature conditions on the strength at temperature and after annealing. Elevated temperature nanoindentation showed a reduction in the temperature sensitivity of hardness as individual layer thickness decreases (i.e. thinner layers retain strength better at elevated temperatures). This is explained using the confined layer slip model which suggests the drop in stress is due to both changes in the shear modulus of the film as well as dislocation/interface interactions. Molecular dynamic simulations of Cu/Nb bi-layers are presented in support of the concept that dislocation interactions at incoherent interfaces are less temperature sensitive than dislocation-dislocation interactions within the layers, supporting the experimental results.