Influence of solid solution hardening effects on the thermomechanical properties of Cu-Mn, Cu-Sn and Cu-Zn alloys after severe plastic deformation

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Severe plastic deformation processes such as high-pressure torsion (HPT) allow a structural refinement of metallic alloys. HPT deformation produces a material-dependent saturation grain size and grain sizes smaller than 100 nm can be achieved. The mechanical properties of nanostructured alloys after highly plastic deformation are characterized by very high strength in combination with good ductility. Furthermore, an increased strain rate sensitivity of the alloys is observed. Crucial for the deformation behavior of nanocrystalline alloys are complex interactions between dislocation and grain boundary mechanisms, which are not yet fully understood. The grain boundaries serve as sources and sinks for dislocations and are still subject to mechanical and thermal migration processes. It has been shown that UFG metals can exhibit lower strength than the coarse grained states at elevated temperatures and low strain rates. Thus, there is a transition from fine grain hardening to a thermally activated softening of the nanostructured alloys at low strain rates and elevated temperatures. The effects mentioned above are complex and shall be investigated in this application by means of an experimental design based on Cu-solid solution alloys (Cu-Mn, Cu-Sn, Cu-Zn), which are transformed into the nanocrystalline state by means of high-pressure torsion deformation (HPT). By selecting the alloying elements, the solid solution hardening and the stacking fault energy of the alloys can be adjusted independently of each other. The solid solution hardening effects, in turn, influence the cross slip of screw dislocations and twin formation, as well as the grain boundary migration and structure development during the severe plastic deformation. The microstructure development and the thermomechanical properties of these alloy systems are to be used to provide a better metal-physical understanding of the interaction processes between grain boundaries and dislocations in nanocrystalline alloys.