Effects of bismuth nanoparticles on the nano-cutting properties of single-crystal iron materials: a molecular dynamics study

The aim of the current research was to explore the influence of bismuth (Bi) nanoparticles on the single-crystal iron (Fe) nano-cutting process using molecular dynamics (MD) simulations. The existence of Bi nanoparticles in the workpiece affected the variation of cutting force, Von_mises stress distribution and dislocation generation during nano-cutting process. Thus, based on the study of one nanoparticle presence in this paper, the influences of different cutting depths and nanoparticle distribution were also considered separately. The results demonstrated that when the tool cut through Bi nanoparticles, the cutting force and Von_mises stress in the cutting zone were both decreased owing to the smaller hardness of Bi nanoparticles than Fe substrate and the nanoparticles undergo deformation. Dislocation Analysis (DXA) analysis revealed that the presence of Bi soft nanoparticles hindered the dislocation generation, which is unlike the presence of hard nanoparticles, and the BCC Defect Analysis (BDA) analysis showed dislocations, twins and vacancy defects in the workpiece. In addition, the cutting force, workpiece temperature and Von_mises stress increased with the cutting depth, yet the cutting force still decreased when the tool cut through the upper surface of the Bi nanoparticles without contacting the Bi nanoparticles, which was caused by the deformation of Bi nanoparticles under the stress of the shear deformation zone. When two Bi nanoparticles were present in the Fe matrix, the second Bi nanoparticle impedes the movements of the generated dislocations and the cutting force would be reduced when the tool cut over two nanoparticles. This research contributes to understanding the role of Bi nanoparticles in free-cutting steels from the nano perspective.