A study of the effect of initial grain size and strain rate on dislocation structures in copper

The effect of initial grain size and strain rate on the formation and subsequent shrinkage of dislocation cell structure was studied in commercial copper. As with earlier studies, transmission electron microscopy was performed on sections of the gauge length of broken specimens tested in tension and the dislocation cell size was plotted as a function of reduction in area. It was found that at low strains, material with the coarser grain size had larger cells than that with the finer grains for a given reduction in area. As the strain increased, this difference decreased until a critical cell size was reached. Further deformation resulted in the formation of subgrain boundaries. The cross-over between dislocation cell mechanism to a subgrain mechanism is explained in terms of a generalized Hall-Petch equation. The effect of strain rate is also examined using the same approach.