The effect of single-step low strain and annealing of nickel on grain boundary character

Combinations of a low tensile strain and annealing temperature have been successfully processed to double the fraction of special boundaries, Σsp, in commercially pure (C.P.) nickel. Processing sequence of one step of 6% strain followed by a 900 °C anneal for 10 min, has resulted a special boundary fraction (3 ≤ Σ ≤ 29) of 74.7%, compared to the as-received material of 36.5%. A large proportion of this increased in special boundaries were found to be made up of annealing twins Σ3 and its twin variants Σ3n. Deformation applied to the sample alone without heat treatment, caused the fraction of special boundaries, to decrease, the Σsp value falling, for example to 25.6% at 12% strain. Energy minimization processes such as grain boundary migration and grain growth were suggested as means of enhancing the formation of annealing twins.