Surface strengthening behaviors of pure Cu with heterogeneous microstructures

The surface strengthening behaviors of cold-rolled (CR) Cu, fully recrystallized (FR) Cu and partially recrystallized (PR) Cu with heterogeneous microstructures were investigated by using the surface spinning strengthening (3S) method. It was found that the heterogeneous microstructure significantly affects surface strengthening behaviors as the fine grains have good plastic deformation ability, the ultrafine grains can bear a high stress, and the whole hardened layer can be divided into grain refinement and deformation zones. The maximum microhardness is 173 HV across all Cu because all the grains were refined to the nano-scale with an average size of 40 nm in the topmost layer of the grain refinement zone. The fine grains in the deformation zone of the PR Cu deform plastically to generate a thick hardened layer. In addition, the surface strengthening behaviors and mechanisms are discussed in detail.