Plastic flow and microstructural instabilities during high-pressure torsion of Cu/ZnO composites

Abstract We conducted high-pressure torsion (HPT) of hybrid materials composed of two copper disks with a layer of ZnO ceramic nanoparticles sandwiched in-between. A detailed microstructural analysis of the processed samples revealed a surprisingly high level of plastic deformation introduced in individual ZnO particles, even though they possess a much high hardness than the surrounding Cu. Moreover, we demonstrated that by tailoring the initial geometry of the system (i.e. introducing holes in the cladding Cu disks), we can effectively change the flow mode of ZnO particle clusters from laminar to turbulent one and facilitate their deagglomeration process. Finally, the presence of ZnO particles decreased the microstructural stability of the Cu matrix. We discussed the obtained results in terms of hydrodynamic and microstructural instabilities during plastic deformation. This work expands our understandings of the cooperative severe plastic deformation of two dissimilar materials and sheds new light on the design of hybrid materials.