Subsurface defect evolution and crystal-structure transformation of single-crystal copper in nanoscale combined machining

ABSTRACT

In the paper, molecular dynamics simulation is applied to study the evolution and distribution of subsurface defects during nanoscale machining process of single-crystal copper. The chip-removal mechanism and the machined-surface-generative mechanism are examined through analysis of the dislocation evolution and atomic migration of the workpieces. The findings show that under different stresses and temperatures, the difference of the binding energy leads to a zoned phenomenon in the chip. Owing to elastic deformation, some of the dislocations could be recovered and form surface steps; moreover, the work hardening of the workpiece can be achieved on account of generation of twin boundaries, Lomer-Cottrell dislocations, and stacking fault tetrahedra (SFT) by plastic deformation. A process of evolution of an immobile dislocation group containing stair-rod dislocations into SFT is discovered, which is different from the traditional Silcox-Hirsch mechanism. Furthermore, a growth oscillation phenomenon, which corresponding stacking fault planes growth and retraction during the formation of the stable SFT, is discussed.