Grain growth in ultrafine grain sized copper during cyclic deformation

Abstract

The nano-sized grain microstructure of pure copper was achieved by Equal Channel Angular Pressing (ECAP) in which the average grain size of 4 and 8 passed ECAP was about 320 and 300 nm. The grain refining increased the tensile strength of ECAPed copper to 420 MPa from 210 MPa of annealed counterpart. Despite the increase in strength level, the nano-grained copper fabricated by ECAP process did not show the expected level of fatigue strength, such that the fatigue limit was similar to that of coarse grained copper at low applied stress range. In this study, the damage accumulation during fatigue was found to be accelerated in ultrafine grained copper compared to coarse grained counterpart. The damage accumulation mechanism in ultrafine grained copper was discussed based on the micrographic observation. (C) 2014 Elsevier B.V. All rights reserved.