Insight into the nanoscale strengthening mechanism of polycrystalline iron implanted by Cr ions

Abstract

The strengthening mechanisms of ion implantation remain a challenge for the application on high-performance precision mechanical manufacturing. Based on the molecular dynamics (MD) method, the paper aims to explore the nanoscale mechanisms of the polycrystalline iron implanted by Cr ions. The microstructural evolution under implantation is analyzed, and the mechanical properties of different models under nanoindentation are studied. The results show that the ion implantation reduces surface roughness while enhancing both Young’s modulus and hardness. The increase in hardness arises from Cr atoms and interstitials obstructing dislocation propagation and the inverse Hall-Petch effect, which works by transforming the deformation from being grain boundary-dominated to dislocation-dominated. The role of grain boundaries (GBs) in ion implantation and deformation are analyzed by the molecular statics method and atomic displacement field. It is found that GB sites have lower point defect formation energy than the bulk and GB atoms first participate in plastic deformation. Additionally, the interactions between dislocations and GBs are investigated. This article provides an innovative research approach for exploring the nanoscale strengthening mechanisms of ion implantation by MD method.