Incontinuous grain growth in cobalt nanocrystalline powders prepared by high-energy mechanical milling.

Cobalt nanocrystalline powders with the average grain size of about 17 nm were prepared by high-energy mechanical milling. Grain growth in highly pure and particle-containing nanocrystalline Co powders were investigated respectively by a series of annealing experiments at different temperatures. The characteristics of incontinuous grain growth were found in both the pure and the particle-containing nanocrystalline powders. It is proposed by the authors that the sharp increase in nanograin size in the transition between the low and high temperature regions is a result of enhanced grain growth promoted by the stored energy as a supplied driving force, based on which rapid grain growth occurs through a particular dominant mechanism of nanograin rotations in the pure nanocrystalline powders, and that through off-pinning of grain boundaries in the particle-containing nanocrystalline powders.