Influences of grain size and grain boundary segregation on mechanical behavior of nanocrystalline Ni

Nanocrystalline Ni with mean grain sizes ranging from ∼15 to 95 nm was fabricated by electroplating and post-annealing. The influence of annealing on deformation behavior was systematically investigated by inspecting strain rate sensitivity (m) and activation volume (V) using nanoindentation. In addition to the strong dependence of the m and V values on nanograin sizes, annealing induced grain boundary change, probably caused by GB relaxation and segregation, leads to the transition from a stress-activated dislocation emission mechanism in the as-fabricated sample to a thermal activation on dislocation emission.