Ductile–brittle–ductile transition in an electrodeposited 13 nanometer grain sized Ni–8.6 wt.% Co alloy

A ductile–brittle–ductile transition in the fracture mode of the Ni–8.6 wt.% Co alloy with an average grain size of 13 nm was observed through increasing the strain rates from 1.04 × 10−5 to 1.04 s−1 at room temperature (RT). The Ni–Co alloy exhibited a limited plastic strain (about 1%) at the intermediate strain rates of 2.08 × 10−3 to 4.17 × 10−2 s−1, which was attributed to that in this strain rate range less dislocations or GB atoms would be activated. However, a gradual brittle–ductile transition occurred with the strain rate decreasing from 2.08 × 10−3 to 1.04 × 10−5 s−1. The lower strain rates allow the GB atoms diffuse easily, which would relax the stress concentration and hence enhance the ductility. Another brittle–ductile transition happened with increasing the strain rates from 4.17 × 10−2 to 1.04 s−1. The enhanced ductility at high strain rate can be explained by stress-assisted activation of GB atoms.