Molecular dynamics simulation of twist grain boundary effect on the plasticity of BCC Fe

Abstract

Developing sustainable and safe next-generation nuclear systems requires the structural materials to have excellent mechanical properties. Ferritic/martensitic steel (FMS), a material used to fabricate the core parts and pressure boundary components of advanced reactors and blankets for fusion reactors, consists of lath martensite with a low-carbon BCC structure. The reinforcement mechanism of lath martensite occurs simultaneously in several layers and includes interactions between dislocation-dislocation and dislocation-grain boundaries. Understanding these integrative mechanisms requires information pertaining to the effects of interactions with dislocations at hierarchically low grain boundaries on the mechanical properties of the materials. In this study, the effects of the twist grain boundary constituting the substructure of lath martensite on the plasticity of α-Fe were analyzed by means of nanoindentation in conjunction with a molecular dynamics simulation. An atomic strain analysis of the simulation results confirmed that the twist grain boundary functions as a barrier to the behavior of dislocations in the material. On the other hand, the simulation results analyzed based on the load-displacement curve showed that the twist grain boundary had a marginal effect on the mechanical properties of the material regardless of the twist angle, the number of boundary planes, or the distance between the boundary planes.