Characterization of a nanocrystalline NiCo electroformed sheet metal

A novel electroformed nanocrystalline nickel cobalt alloy (n-NiCo) developed for sheet metal applications was investigated in terms of microstructure, as well as mechanical, thermal stability, and corrosion properties. The as-received material with a grain size of 18 ± 5 nm exhibited enhanced hardness compared with conventional polycrystalline NiCo mainly due to the Hall–Petch strengthening effect. Differential scanning calorimetry and annealing treatment results revealed that the n-NiCo was stable up to 200 °C for at least 1 h, and the onset of abnormal grain growth was observed when the material was annealed to 250 °C. While low-temperature annealing treatment was shown to increase the hardness of the material slightly, annealing at temperatures of 300 °C and above resulted in a reduction in hardness due to rapid normal grain growth. The n-NiCo sheet exhibited mixed Ni/Co anodic polarization behavior in environments of varying pH.