Characterization of fatigue failed aged Cu-Ni-Si alloys

Abstract

The precipitation hardenable and non-toxic Cu-Ni-Si alloys are good alternatives to Cu-Be and Cu-Co-Ni-Be alloys due to their high strength and high conductivity that can be attained by not only alloying but also thermo-mechanical routes. In this study, the fractographic analysis was carried out to understand the fatigue failure of aged 2.55Ni-0.55Si-0.25Zr-0.25Cr (wt-%) alloy which is a member of Corson family. In fatigue tests, a constant amplitude loading was applied at a stress ratio (R = σmin/σmax) of -1 and different stress levels (400, 350, 200 and 175 MPa) were used. The fracture response of the alloy was discussed depending on the applied stress levels and microstructural features. It was concluded that (i) Ni,Zr-rich precipitates and Cr-rich precipitates at the grain boundaries caused crack nucleation at all stress levels and (ii) the interaction between Ni-rich silicides and dislocations at lower stress level resulted in localized shearing and fine striations.