Effect of grain size and temperature on the mechanical properties of nano-polycrystalline Fe-Bi complexes

This paper utilized molecular dynamics simulations to explore how grain size and temperature impact the mechanical characteristics of Fe-Bi nano-polycrystalline complexes. It was determined that the Hall–Petch relationship has a critical grain size of 10 nm, with a corresponding maximum flow stress of 2.58 GPa. In specimens where d exceeds 10 nm, the average rheological stress rises as d decreases, in line with the Hall–Petch relationship because of grain boundary fractures resulting from dislocation slips and deformation twinning. For specimens with d less than 10 nm, the change in rheological stress with respect to d aligns with the inverse Hall–Petch relationship, which is attributable to grain rotation and grain boundary migration. Moreover, as the temperature goes up, the proportion of atoms at the grain boundaries steadily increases, while that within the grains gradually diminishes. With the growth of atomic disorder, melting takes place at the grain boundaries. These discoveries hold favorable implications for the design of bismuth-based free-cutting steels.