Modulated oscillatory hardening and dynamic recrystallization in cryomilled nanocrystalline Zn Original Research Article

Oscillatory variation of the hardness with milling time was observed in cryomilled nanocrystalline Zn. Transmission electron microscopy showed that large variations in the dislocation density and grain-size distribution occurred during cryomilling. The observations suggest that recrystallization takes place in larger grains when the dislocation density due to strain-hardening reaches a critical level. A reaction-rate model was developed which accounts for the dynamic recrystallization effect and the observed oscillations in hardness. Good agreement was obtained with the experimental data. The results provide unique insight into grain-size effects and the interplay of these with deformation mechanisms and recrystallization effects in nanocrystalline materials.