Abstract
Fatigue crack initiation and propagation behavior was observed in ultrafine-grained Cu processed by ECAP. The integration of EBSD, AFM and SEM measurement revealed that grain coarsening occurs on smooth specimens accompanied by large slips in the scale of more than 10 μm in spite of the average grain size of 300 nm. The slips are introduced in the direction of the primary slip plane with the maximum Schmid factor. The grain coarsening with large scale slips was also observed at the tip of long fatigue cracks at the threshold of the stress intensity factor. Fatigue damage at grain boundaries without slips was dominant at higher stress intensity factor in the Paris's law region. The grain coarsening behavior is dependent on stress intensity factor.
