Atomistic Evaluation of Strengthening Factors in Iron Alloys Based on Computational Interaction Analysis of Lattice Defects

The interactions between lattice defects on a nanoscale have significant effects on the macroscopic mechanical properties of crystalline metals. Further understanding of the effects of lattice defects on fundamental plastic deformation units such as dislocation is key to develop structural materials with excellent mechanical properties. The advances in computer power and simulation methods enable us to evaluate the interaction between dislocation and other lattice defects from various approaches. We here focused on the dislocation-solute interactions and dislocation-grain boundary interactions in body-centered cubic iron. We investigated the interaction details and effects of lattice defects on the mechanical properties based on atomistic simulations. We evaluated the screw dislocation-solute interaction for various solute elements and solute positions using large-scale first-principles calculation. The interaction energy is affected by the relative position between dislocation and solute atoms, dislocation core types, and solute elements. The obtained interaction energies were utilized in dislocation modeling in larger time and space scales or in theoretical equations in order to predict the effects of solute atoms on dislocation dynamics and macroscopic yield strength. We also evaluated the dislocation-grain boundary interactions using atomistic simulations based on the empirical model of the interatomic interaction. The grain boundary is a planar fault and acts as an important role in grain boundary strengthening of structural materials. The dislocation-grain boundary interaction in iron was evaluated for different grain boundary types using nanomechanical simulations such as nanoindentation. When the indentation is conducted near the grain boundary, dislocation nucleation and propagation behaviors beneath the indenter are affected by the grain boundary. The simulations reveal the stress field beneath the indenter, activated slip directions, and dislocation components mainly interacting with the grain boundary. The dislocation behaviors are affected by the crystallographic orientation in the inner grain as well as the grain boundary. In experimental nanoindentation, the dislocation behaviors across the grain boundary depend on the grain boundary type. The atomistic simulation results provide factors affecting the dislocation behaviors near the grain boundary and a deeper understanding of experimental results.