Nano-grained nickel produced by electroforming technique was investigated for its microstructure evolution and mechanical properties upon annealing. It was found that during low temperature annealing (T<250 oC), electroformed nano-grained nickel showed scattered and isolated abnormal grain growth, followed by a major abnormal grain growth at 320 oC. A secondary abnormal grain growth, featuring faceted grain boundaries, was observed at a higher annealing temperature (T=528 oC). A semi-in-situ observation using optical microscopy was conducted to track the movement of the faceted grain boundaries, and it was found that these boundaries were mostly immobile. The mechanical properties under various annealing conditions were studies using hardness and tensile testing. The hardness was observed to decrease with increasing annealing temperature. The material became very brittle after annealing at 320 oC or higher temperatures. Fractography investigation showed that the brittleness is caused by intergranular fracture.

Nano-grained nickel produced by electroforming technique was investigated for its microstructure evolution and mechanical properties upon annealing. It was found that during low temperature annealing (T<250 oC), electroformed nano-grained nickel showed scattered and isolated abnormal grain growth, followed by a major abnormal grain growth at 320 oC. A secondary abnormal grain growth, featuring faceted grain boundaries, was observed at a higher annealing temperature (T=528 oC). A semi-in-situ observation using optical microscopy was conducted to track the movement of the faceted grain boundaries, and it was found that these boundaries were mostly immobile. The mechanical properties under various annealing conditions were studies using hardness and tensile testing. The hardness was observed to decrease with increasing annealing temperature. The material became very brittle after annealing at 320 oC or higher temperatures. Fractography investigation showed that the brittleness is caused by intergranular fracture.