The segregation of niobium (Nb) at the FeΣ3(111) grain boundary and its influence on interfacial cohesion were investigated via spin-polarized density functional theory calculations. Nb atoms exhibit strong site-selective segregation, with Site 1 being the most thermodynamically favorable one (segregation energy of –2.47 eV), owing to its largest local Voronoi volume. Electronic structure analyses reveal pronounced Nb-4d/Fe-3d orbital hybridization and localized charge accumulation between Nb and neighboring Fe atoms, enhancing covalent bonding at the boundary. First-principles tensile simulations show that single-Nb segregation increases the critical strain from 13.58% to 15.76% and the theoretical tensile strength from 16.32 GPa to 19.64 GPa. However, double-Nb segregation reduces the work of separation to 3.26–4.24 J/m2, revealing a competition between segregation strengthening and solute-induced weakening that implies an optimal Nb concentration window for grain boundary engineering.
Zhang et al. (Fri,) studied this question.