Annealing twin development during recrystallization and grain growth in pure nickel

Abstract : A 99.995% pure Ni sample, compressed to 25%, was annealed in a SEM chamber and changes in the density of annealing twins were monitored in situ during recrystallization and grain growth. In addition to average microstructural measurements, the evolution of individual grains was also observed. Both the average annealing twin density in the recrystallized domain and the annealing twin density per grain increased during recrystallization. The rate of increase in twin density correlates with the velocity of the recrystallization front. During grain growth, however, the average annealing twin density decreased. The in situ EBSD observations showed both the formation of new twins and the extension of existing twins during annealing. The observations reported here suggest that the existing models for annealing twin formation are incomplete.