Study of Machining-Induced Microstructure Variations of ECAE-Processed Ultrafine-Grained Copper

Various methods for production of bulk ultrafine-grained (UFG)/nanostructured materials have been developed. Recently, a top-down approach named equal channel angular extrusion (ECAE), a form of severe plastic deformation (SPD), has gained increasing attention in making bulk UFG materials. Such bulk materials are favored for their high strength, wear resistance, ductility, and high strain-rate superplasticity, which makes them suitable for light weight engineering and medical applications. Further precision machining work is normally indispensable for structural applications after bulk ultrafine grained materials are manufactured from any SPD processes. Unfortunately, the microstructure stability issues in precision machining such materials are frequently ignored. Using an ECAE copper bar as an example, this study has investigated its machining-induced workpiece microstructure variation. It has been found that there was a small increase in the size parameter median and the average arithmetic and area weighted grain sizes when comparing those of machined and unmachined bars, and the measured grain sizes oscillated slightly in the radial direction of the machined bar. Dislocation density was shown to have the most reduction at the outer radius location of the machined ECAE bar where more heat and/or higher pressure were experienced.