Fabrication of a gradient nano-micro-structured surface layer on bulk copper by means of a surface mechanical grinding treatment

By using a novel surface nanocrystallization technique, surface mechanical grinding treatment at cryogenic temperatures, we synthesized a gradient nano-micro-structure in the surface layer of bulk pure copper. The average grain sizes vary from about 22 nm in the topmost surface to sub-micrometers at about 200 μm deep, corresponding to a gradient change in hardness from 2.1 to 1.1 GPa in the coarse-grained matrix.