MD simulation study on the microstructural evolution of single-crystal Fe with pre-existing defects by Cr ion implantation

In this study, we present the molecular dynamics simulation of metal ion implantation, investigating the strengthening mechanism from a microstructural perspective. A single crystal Fe with pre-existing defects is constructed based on actual dislocation density and the effects of Cr ion implantation are investigated. Additionally, nanoindentation simulations are conducted to analyze the mechanical properties of workpieces with and without ion implantation. Effects of implantation energy and dose on the microstructure and hardness of workpieces are analyzed. The results indicate that (i) ion implantation introduces Fe-Cr bonds with higher bond energy while reducing the original Fe-Fe bond energy, (ii) increasing implantation energy and dose corresponds to a greater number of point defects and a higher amorphous structures proportion, (iii) the microstructure transformed by ion implantation promotes dislocation nucleation during nanoindentation, (iv) ion implantation enhances workpiece hardness due to the dual effects of interstitials impeding dislocation motion and the heightened mutual obstruction attributed to a higher dislocation density. Notably, the hardness initially enhances with increasing implantation energy and dose, followed by a slight decrease. The computational approach in this paper can serve as a valuable tool for studying the microstructural evolution of metal ion implantation by molecular dynamics simulations.