Quantification of void pinning effects during grain growth of nanocrystalline iron

In-situ transmission electron microscopy (TEM) annealing experiments, coupled with an analytical model, compared void pinning effects in nanocrystalline Fe films during grain growth. Voided grain boundaries were shown to have nearly four orders of magnitude less grain boundary mobility than void-free grain boundaries. However the coverage of the grain boundaries by pores was over three times that which would be required for static particles to completely halt grain boundary migration. Grain boundary migration continued because the pores were dragged by the grain boundaries and continued to evolve and coalesce. Thus, pores can slow grain boundary migration but are not an effective means of fully stabilizing nanocrystalline grain size at high temperatures.