Cyclic deformation and fatigue cracking behaviour of polycrystalline Cu, Cu–10 wt% Zn and Cu–32 wt% Zn

Abstract

The cyclic deformation behaviour of polycrystalline Cu, Cu–10 wt% Zn and Cu–32 wt% Zn was systematically investigated in the plastic strain amplitude range of 1 × 10⁻⁴–4 × 10⁻³. The differences in the cyclic stress–strain (CSS) responses and fatigue cracking behaviour between Cu, Cu–10 wt% Zn and Cu–32 wt% Zn were compared. It was found that the occurrence of a cyclic saturation for Cu–10 wt% Zn and Cu–32 wt% Zn strongly depends on the applied strain amplitude, whereas polycrystalline Cu always displays cyclic saturation. Surface deformation morphologies were analyzed by scanning electron microscopy (SEM). One of the major features observed is that the slip bands become increasingly homogenous with Zn addition. The fatigue cracks were found to frequently nucleate along the annealing twin boundaries (TBs) in Cu–10 wt% Zn and Cu–32 wt% Zn, but not in polycrystalline Cu. Based on these experimental results, the cyclic deformation response and fatigue cracking behaviour are discussed, and a developed TB cracking mechanism is proposed to explain the difference in fatigue cracking mechanisms in Cu, Cu–10 wt% Zn and Cu–32 wt% Zn.

Keywords:

• polycrystalline copper
• Cu-Zn alloys
• cyclic deformation
• slip bands
• grain boundary
• twin boundary
• fatigue cracking

Acknowledgements

The authors thank W. Gao, H. H. Su, J. L. Wen, and G. Yao for sample preparation, mechanical tests and SEM observations. This work was financially supported by the “Hundred of Talents Project” by the Chinese Academy of Sciences and the National Natural Science Funding of China (NSFC) under grant Nos. 50571104 and 50625103.