Study of Machining-Induced Microstructure Variations of Nanostructured/Ultrafine-Grained Copper Using XRD

Various methods for the production of bulk nanostructured (NS)/ultrafine-grained (UFG) materials have been developed, including equal channel angular extrusion (ECAE), a form of severe plastic deformation. Using an ECAE NS/UFG copper bar as an example, this study has investigated machining-induced workpiece microstructure variation using X-ray diffraction. It has been found that (1) under gentle cutting conditions, there was a 10% increase in the median grain size compared with unmachined ECAE NS/UFG copper bars. Increases in the arithmetic-, area-, and volume-weighted grain sizes were found to be 10%, 8%, and 8%, respectively, and (2) an average 27% drop in the dislocation density was observed between the machined and unmachined ECAE copper bars. The dislocation density was shown to have the most reduction $(−39%)$ at the outer radius of the machined ECAE bar where more heat and/or higher pressure were experienced.