Molecular dynamics simulation of nanoindentation on Al-Cu50Zr50 multilayers

Abstract

We performed molecular dynamics (MD) simulation of nanoindentation on Al (metal)-Cu50Zr50 (metallic glass (MG)) multilayers aimed to investigate the effect of loading rate, MG thickness, and temperature on the load-displacement behavior and underlying deformation mechanisms. Simulation box size of (200×200×200) Å is used. At first Al–Cu50Zr50-Al crystalline model is constructed with the bottom layer (Al) of 70 Å (FCC crystal structure and lattice parameter = 4.01 Å), the middle layer Cu50Zr50 of 60 Å (FCC Cu, a = 3.61) and the top layer (Al) of 70 Å in height along y–direction under periodic boundary conditions and comprises of 538538 atoms. Cu50Zr50 region is created by randomly replacing copper atoms by zirconium atoms. Cu50Zr50 MG is obtained by rapid cooling from 2000 K to room temperature at a cooling rate of 8.6 × 1011 Ks-1 timestep=0.002 ps). EAM (Embedded Atom Method) potential is used. The layered interface models are then equilibrated at 300 K for 500 ps using NVT to relieve internal stresses. Nanoindentation is carried out using a spherical diamond indenter on the MG region at different loading rates in the range of 0.5-5 Å/ps and different temperatures (10-300) K under NPT ensemble and S P S boundary conditions along x, y and z directions. At temperature of 50 K and loading rate of 0.8 Å/ps, we observed a peak load of 88 nN. Further, we found that with increase in loading rate, the peak load increases. Stiffness is calculated form the unloading curves and is found to increase with increase in MG thickness. As anticipated, the increase in temperature decreases the strength of the multilayers. The atomic displacement vector plots reveal MG as obstacles to the movement of dislocations nucleated at the interface. The results provide significant insight into the elastic behavior, deformation mechanisms at the nanoscale.