Quantitative defect evolution of nanocrystalline nickel during cold rolling

The defect evolution of cold-rolled nanocrystalline nickel is quantitatively investigated. We report that the density of dislocations (or stacking faults) first increases and then decreases after an equivalent strain of ～0.30. The density of stacking faults decreases more significantly than that of dislocations when the grain size increases above 35?nm. This is attributed to the grain size dependence of dislocation activity. The roles of texture and deformation twins are also considered to help understanding of the decreasing density of dislocations (or stacking faults).