Strengthening mechanisms and deformation behavior of Au/Ag bilayer using nanoindentation

Abstract

Thin-film coatings of metals, particularly Gold (Au) and Silver (Ag), have proven to be highly promising for improving the performance and efficiency of micro/nano-electromechanical systems (MEMS/NEMS). This interest needs to explore their mechanical properties. Here, nanoindentation is used to investigate the details of deformation mechanisms and mechanical properties of Au coating film on Ag substrate using molecular dynamics (MD) simulations. The effects of coating Au thickness and indentation velocity on the indented Au/Ag bilayers are investigated by analyzing the load-displacement, hardness, structure and dislocation movement. Most interestingly, the results reveal that the Au/Ag bilayer exhibits significant strengthening when the thickness of the coating Au film is decreased. It is found that the values of force and hardness increase as the coating Au film thickness decreases. Based on extraction dislocations analysis (DXA), a large number of dislocations propagate through the interface when the Au film thickness is below 12 Å. In addition, the variation of indentation velocity shows a significant effect on the mechanical properties of Au/Ag bilayers. The Common Neighbor Analysis (CNA) demonstrates that more defects are generated during nanoindentation process. Accordingly, the force and hardness are found to increase with increasing indentation velocity.