J. W. Li, J. F. Mei, Y. S. Ni, H. B. Lu and W. G. Jiang,
Journal of Applied Physics, 108, 054309 (2010).
Multiscale simulations using the two-dimensional quasicontinuum method are performed to understand the nature of strengthening and weakening effect of Cu/Ag interface on nanoindentation at zero temperature. The investigation shows that the upper Cu film strengthens distinctly the lower Ag substrate. The nucleation and emission for first dislocation in Cu film is postponed obviously due to the effect of interface. Combined with the dislocation theory, a dislocation model of the interaction between the nucleated dislocation and the misfit dislocation is introduced to systematically evaluate the strengthening and weakening effects of interface on the Cu/Ag bilayer film system. It is found that the strengthening effect of interface on nanoindentation is governed by the resistance to the nucleated dislocation transmission, such as image force, lattice friction, and the repulsive force of the misfit dislocation. The bigger resistance will lead to the stronger strengthening effect. The weakening effect is mainly produced by the stress concentration and local misfit strain in the core region of the misfit dislocations due to the nucleation and propagation of misfit dislocations along the interface. The multiscale simulation results are in good agreement with the experimental results and dislocation theory model.