Interaction mechanism of dislocations with Bi/hBN nanoparticles in free-cutting steels: molecular dynamics simulations

To further understand the mechanical properties of free-cutting steels, we employed molecular dynamics (MD) simulations to investigate the interaction mechanisms between dislocation slip along close-packed planes and nano-inclusion particles (Bi/h-BN) within single-crystal iron (Fe). By colliding dislocations at varying slip velocities with nanometer-scale particles of different sizes and compositions, we concluded that particle diameter plays a decisive role not only in determining the dislocation cutting mode but also in influencing the dislocation's shear stress response. These indicate that: Larger particles significantly enhance the strengthening effect on the matrix. Additionally, higher dislocation slip velocities result in stronger particle interaction feedback and greater particle damage, contributing to increased matrix deformation. h-BN particles, owing to their much higher hardness compared to Bi, exhibited superior resistance to deformation, requiring higher dislocation shear stress to pass these obstacles.