TEM study of dislocation patterns in near-surface and core regions of deformed nickel polycrystals with few grains across the cross section

TEM investigations of dislocation structures in core and surface regions (50 μm below the free surface) were carried out on polycrystalline nickel samples of 500 μm thickness with 14, 2.5 and 1 grain across the thickness. The mean diameter of the dislocation cells was measured for different strain levels in core and surface regions of the three kinds of sample. These mean dislocation cell diameters were compared between the different samples using a statistical analysis of variance. The intragranular long-range internal backstress level was thereafter estimated in both regions for the three samples revealing a decrease in stress for specimens with few grains across the thickness. This decrease is partially responsible for the flow stress decrease of the nickel polycrystals with few grains across the thickness.