Abstract
Ultrafine-grained copper of commercial purity produced by ECAP technique was tested in fatigue in the range of lives from 5×10³ to 2×10¹⁰ cycles. The fatigue strength of ultrafine-grained copper is by a factor of 2 higher than that of conventional-grained copper. The density of surface slip bands decreases with the decreasing stress amplitude and is extremely low in the very-high-cycle region. Fatigue microcracks were found to initiate in cyclic slip bands, which run across many grains in regions of near-by oriented grains. The very first fatigue damage in high-cycle and very-high-cycle regions consists in formation of cavities and elongated voids representing crack nuclei. No grain coarsening was observed either in bulk or in areas underneath the surface slip markings.

Key words
ultrafine-grained microstructure, fatigue, slip bands, microcrack initiation, grain coarsening

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