Effects of bismuth particle inclusions on surface and internal wear of single crystal iron: A molecular dynamics simulation

The influence of bismuth (Bi) nanoparticles on single-crystal iron (Fe) under rigid ball rollingsliding friction conditions is investigated using molecular dynamics simulations.Various aspects such as frictional force, dislocation length, dislocation configuration, and frictional surface are examined, along with the characteristics of bismuth particles at different depths of inclusion during wear provide partial theories for the application of free-cutting steels containing Bi. The results indicate that the morphology of wear chips accumulation and the lattice structure of wear chips depend significantly on the different forms of Bi inclusions and rotation periods of rigid ball. The extracted atomic displacement vectors theoretically explain the reasons for different accumulation morphologies and reveal atomic trajectories for subsurface damage due to inward movements. Furthermore, comparing the friction force curves between specimens with inclusions and pure Fe demonstrates that the softer Bi particles soften the workpiece, leading to corresponding wear and damage even at lower friction forces compared to the pure Fe model. Additionally, the study finds that dislocations play a dominant role in wear damage, with Bi particles hindering dislocation slip, as evidenced by the significant inhibition of Von Mises stresses by bismuth. Bi also prevents dislocation nucleation within itself, avoiding deeper wear damage to the iron matrix after slip, ultimately resulting in less severe subsurface frictional damage in the inclusion model compared to pure iron. Deeper inclusions significantly induce the generation of high-energy dislocations during wear, attributed to Bi aiding in strain energy storage, thereby higher strain energy for dislocations in Fe media.