Nanostructured or ultra-fine grained metallic systems according to embodiments of the invention may be formed of: pure Cu, pure Fe, or pure Ti, with grain sizes of less than 140 nm, 348 nm, or 59 nm, respectively. The metallic systems demonstrate a monotonically increasing grain size dependence from a minimum value attained at the surface; and a converse relation of microhardness, decreasing from 160 kg/mm2, 265 kg/mm2, or 320 kg/mm2, respectively. The grain refinement process at cryogenic conditions relies on the suppression of room temperature dislocation-mediated deformation mechanisms which facilitate grain restructuring, relaxation, and reorientation. At the cryogenic conditions, alternative mechanism for grain refinement, such as shear localization or dynamic recrystallization may be more dominant. Processes for refining the grain size of these metallic systems may include: subjecting metal plates to a high-energy milling process using a high-energy milling device to impart high impact energies to its surface. Due to the high-efficiency of this attrition process, these metallic systems are ideal candidates for improved corrosion and wear resistance.