Fatigue damage of ultrafine-grain copper in very-high cycle fatigue region

Ultrafine-grained copper produced by ECAP technique was tested in ultrasonic fatigue in the region of lives from 10(8) to 2 x 10(10) cycles. The fatigue strength of ultrafine-grained copper is by a factor of 2 higher than that of conventional-grain copper. The occurrence of surface fatigue slip markings is rare. No grain coarsening was observed either in bulk or in areas underneath the surface slip markings. Localized collective grain-boundary slip of near-by oriented grains is considered to be the main damage mechanism leading to fatigue microcrack initiation either directly in the roots of surface intrusions or underneath the surface slip markings. (C) 2011 Elsevier B.V. All rights reserved.