ABSTRACT

Two-dimensional quasicontinuum simulations of nanoindentation processes are conducted on aluminum thin films with nickel, copper, and silver coatings of different thicknesses under various indenter widths using the embedded atom method (EAM) potentials. To study the effects of protective coating on the mechanical behavior of coated aluminum thin films, the nanoindentation process is performed to determine the hardness, the critical indentation load for first dislocation emission, the critical indentation depth and other associated physical phenomena, such as defect nucleation and evolution beneath the indenter. The obtained results reveal that surface coatings at nanoscale contacts may have a pronounced effect on the perceived hardness of the surface. Aluminum thin films with nickel and copper coatings can adopt the hardness and critical indentation load of the coating material, whereas silver coating cannot improve the aluminum hardness at nanoscale contacts. The critical indentation depth increases with the decrease of coating thickness, which indicates that a softening phenomenon happens in the coated aluminum thin film. The critical indentation depth and the critical indentation load increase with the increase of the indenter width, while the indentation hardness decreases as the indenter width increases. The results are shown to be in good agreement with limited available experimental data and the analytical Rice-Thomson and Peierls-Nabarro dislocation models.