Defect effects on grain boundary strength in Fe: A molecular dynamics simulation

Reduced activation ferritic/martensitic (RAFM) steels, whose primary composition is iron and chromium, are considered as primary candidate structural materials for fusion demo and test reactor due to its technological maturity. There are a large numbers of defects, including dislocation loops, helium clusters, voids and interfaces, existing in RAFM steels irradiated under fusion environment, which were created by neutron transmutation and induced cascades. Grain boundaries (GBs) play an important role on evolution of these defects. Correspondingly, defects absorbed at GBs have detrimental effects on strength of grain boundary. In this study, molecular dynamics (MD) and molecular statics (MS) methods are applied to investigate the effects of defects on GB strength in bcc iron. Symmetric tilt grain boundaries (STGBs) with different tilt axes, GB planes and misorientations are considered. The results show that GB cleavage fracture strength is closely related to its structure and defect concentration. Also, it is of interest to note that the fracture strength of GBs and elongation of the crystals decrease with increasing defect size.