Energy of internal interfaces as a characteristic of the structural evolution of ultrafine-grained copper and nickel after annealing

Abstract

Scanning tunnel microscopy is used to directly estimate the relative energy of internal interfaces in ultrafine-grained copper after equal-channel angular pressing, followed by rolling. Estimates of the boundary energy for as-prepared samples and samples annealed at different temperatures indicate that ultrafinegrained copper has nonequilibrium boundaries with energy higher than that in coarse-grained copper. The cumulative distribution functions of the relative boundary energy in the grain–subgrain structure allow the qualitative estimation of the redistribution of excess energy between the boundaries of various types during structure evolution upon annealing. Differences between the behaviors of the cumulative distribution functions of relative boundary energy in ultrafine-grained copper and nickel produced by the same technology are revealed. These differences are related to the characteristics of the structure formation of two metals during severe plastic deformation and its subsequent evolution during annealing, which depend on the stacking fault energy and the melting point of copper and nickel.