Machinability and microstructure stability during the machining of pure copper and titanium processed by equal channel angular pressing

The production of nanostructured or ultrafine grained (UFG) materials has been of great interest in the research community recently due to their high strength, wear resistance, ductility, and high strain-rate superplasticity. These properties, achieved through their small microstructures (100-300 nm) and unique defect structures (of grain boundaries and dislocations) make these materials ideal for lightweight medical implants and aerospace structural components. Methods of actually manufacturing UFG materials for these advanced engineering designs have yet to be considered.; For UFG materials to be manufactured and used in industry, further machining research is needed to form and shape these materials into their final dimensions. Because of their high internal energy, UFG materials are known to have microstructures which are susceptible to undesirable changes at low temperatures. Since machining is a heat dissipating process, the thermal stability of UFG materials must be carefully considered as not to deteriorate their unique properties. The machinability is also of interest due to its importance in possible part production. In this study, pure nanostructured copper and titanium as well as their respective coarse grained (CG) counterparts were tested for their relative machinability and microstructure stability through lathe turning. To evaluate the machinability cutting forces, tool wear, chip morphology, and surface roughness were studied using different cutting conditions. Tungsten carbide (WC) and polycrystalline diamond (PCD) cutting tools were utilized for turning the copper workpieces while only PCD was used for titanium. Microstructure stability was examined by measuring grain size and dislocation density using X-ray diffraction (XRD) techniques with some subsequent electron microscopy imaging.; Experimental results confirmed that both the UFG Cu and Ti bars could be machined as efficiently as their CG counterparts. Cutting forces generated were less for the UFG copper compared to the regular copper but were approximately equal for the two titanium bars. Similar tool wear patterns and mechanisms were observed for the nano and coarse grained Cu and Ti. Chip morphology changed little during the course of machining. Surface roughness was improved when machining the UFG copper bar, yet was slightly larger for the UFG titanium at higher speeds. XRD results showed little changes in grain size after machining while dislocation density was shown to reduce the greatest near the machined surface.