Evolution of stacking fault tetrahedral and work hardening effect in copper single crystals

Highlights: • By molecular dynamics (MD) simulation, this study investigates the evolution and influence of stacking fault tetrahedra (SFT) in copper single crystals. Nano-cutting and nano-indentation simulations are performed to produce SFT, and common neighbor analysis (CNA), dislocation extract algorithm (DXA) and von Mises stress analysis are adopted as research techniques. The formation of SFT in nano-cutting simulation and the collapse in nano-indentation are observed respectively, and finally the mechanism between SFT and work hardening effect is revealed. • This study provides some novel discussion as listed:. • By nano-cutting simulation, SFT is found to nucleate at the intersection of differently oriented SF planes. The preform of SFT only contains the surface of SFT as a hollow structure when the number of atoms inside SFT grows until it finally evolves as a stable and isolated defect. • By nano-indentation simulation, it is found that SFT provides resistance to the formation of other dislocations and improves the surface hardness of workpiece, causing the "work hardening" effect. SFT can be transformed into a smaller size until it finally crashes under the interaction with other dislocations. - Abstract: Stacking fault tetrahedral (SFT), generated in machining of copper single crystal as one type of subsurface defects, has significant influence on the performance of workpiece. In this study, molecular dynamics (MD) simulation is used to investigate the evolution of stacking fault tetrahedral in nano-cutting of copper single crystal. The result shows that SFT is nucleated at the intersection of differently oriented stacking fault (SF) planes and SFT evolves from the preform only containing incomplete surfaces into a solid defect. The evolution of SFT contains several stress fluctuations until the complete formation. Nano-indentation simulation is then employed on the machined workpiece from nano-cutting, through which the interaction between SFT and later-formed dislocations in subsurface is studied. In the meanwhile, force-depth curves obtained from nano-indentation on pristine and machined workpieces are compared to analyze the mechanical properties. By simulation of nano-cutting and nano-indentation, it is verified that SFT is a reason of the work hardening effect.