Molecular dynamics simulations of rate-dependent grain growth during the surface indentation of nanocrystalline nickel

Molecular dynamics simulations are leveraged in this study to explore rate-dependent grain growth and deformation in nanocrystalline nickel due to surface indentation at room temperature. A 50 nm thin film with approximately 700 grains is indented with a 15 nm spherical indenter at rates of 0.2 m/s, 1.0 m/s, and 5.0 m/s. We simulate the indentation, hold, and removal of the indenter, as well as compute grain growth and distribution profiles during microstructure deformation. Novel algorithms are also developed in this work to accurately distinguish individual grains and provide quantitative data for the evolution of the microstructure. Results of the simulations show that lattice deformation mechanisms, such as dislocation slip and twinning, that accompany grain growth are also functions of indentation rate and equilibration time. This work shows that grain growth in this nanocrystalline nickel structure is indeed rate-dependent, and is most prominent for grains near the indentation surface during both the hold and removal of the indenter.