| In order to understand the fatigue behavior of ultra fine grained copper, rotating bending fatigue tests were carried out. After the 4 and 8 pass of ECAP (equal channel angular pressing) with Bc route (after each pressing, the billet bar is rotated around its longitudinal axis through 90œ), grains with about 300 nm diameter were formed. Significant morphological difference in fatigued surfaces between high and low cyclic stress amplitudes was observed. To clarify the formation process of surface damage, morphological change in surface damage caused by cyclic stresses was monitored successively by using optical microscope and scanning electron microscope (SEM). It was found that the surface feature for the ECAPed copper varied substantially with damage accumulation during cyclic stresses. |
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