Sub-micrometer structures generated during dry machining of copper

Deformation structures developed in the material ahead of the tool tip in commercial purity copper samples that were subjected to an orthogonal cutting process were investigated using transmission electron microscopy (TEM). The effect of the prior thermo-mechanical treatment has been considered by performing orthogonal cutting tests on hot extruded and fully annealed samples. Results showed that the microstructure of the primary deformation zone (PDZ) was characterized by the formation of elongated dislocation cell structures that were composed of heavily tangled dislocation walls. In the hot extruded samples, this structure was generated as a result of the activation of the pre-existing dislocations, but nucleation of fresh dislocations was needed in the annealed samples. Grain refinement occurred in the chip as a result of the subdivision of the elongated cells into smaller equiaxed sub-micron size (220 nm diameter) grains. Evidence for dynamic recrystallization has been found in the microstructure of the machined chips (MCs). However, calorimetric studies and the microhardness measurements have shown that the sub-micron structures of the machined chips were stable at temperatures up to 180 °C.