Role of structural parameters of ultra-fine grained Cu for its fatigue and crack growth behaviour

► High cycle fatigue and near threshold crack growth of HPT Cu were investigated. ► HPT materials show increased HCF life but also increased crack growth rates. ► Higher stability of commercial purity HPT Cu leads to superior HCF behaviour. ► High purity HPT Cu coarsens during fatigue loading and very slow crack growth. ► Bimodally structured HPT Cu has higher stability but no improvement in fatigue. High cycle fatigue (HCF) life time curves and fatigue crack growth rates of bulk ultra-fine grained (UFG) copper deformed by high pressure torsion (HPT) were determined. Cu of two different purities as well as a bimodally structured HPT Cu were investigated. The results show increased HCF properties of the UFG materials compared to coarse grained (CG) Cu. Especially HPT Cu with lower purity shows enhanced fatigue resistance due to higher microstructural stability. Contrary, crack growth rates in HPT Cu are increased. In case of the high purity Cu, cyclic deformation induced coarsening of the UFG microstructure nearby the crack is found at threshold crack growth rates leading to a retardation of the fatigue crack propagation. Within these coarse grains typical fatigue surface slip marks as observed in CG Cu are found.