High Load Sliding, Deformation Microstructures, Strength and Hardening for Gradient Bulk Nanostructures

Plowing of wedge shaped micro asperities under large sliding loads, from 0.4 to 3.7 of the yield stress at 293 or 77 K, is utilized to induce extremely high hardness 1.7 to 2.8 GPa and strain levels in the subsurface regions of Cu. A steep gradient in the size scale with increasing depth of the deformation microstructures is measured with transmission electron microscopy including an unprecedented size of 5 nm and high dislocation density near the surface. Non equilibrium quantities of Fe are added during sliding and stabilize this structure by mechanical diffusion. Subsurface stress estimates use the measured structural parameters in a linear addition of the Hall-Petch formulation for the inverse spacing of geometrically necessary boundaries, , plus Taylor dislocation hardening, . A further unification of these parameters is made since the density is directly proportional to . Quantitative comparisons and energy balances between the friction and deformation energies corroborate the high hardness and strain levels that may be applied to hard components.