The influence of impurities on the annealing of nickel after cold work

Abstract

Measurements of stored energy and of changes in electrical resistivity and density accompanying annealing have been made on nickel of 99.85 per cent purity deformed in torsion and compression. There are notable differences from the behaviour found previously for nickel 99.6 per cent purity. The results suggest that, in the purer nickel, little or no recovery involving dislocations occurs between room temperature and the recrystallization temperature, in contrast to previous results for 99.6 per cent pure nickel. There appear to be two stages of annealing prior to recrystallization in the 99.85 per cent material although they are not clearly resolved. These are centred at 120°C and 260°C and are tentatively ascribed to the annealing of interstitials and vacancies respectively. On this basis the observed changes in resistivity and density can be explained. Stored energy measurements on still purer nickel specimens, 99.96 per cent, deformed in compression indicate that in this material these first two stages are clearly resolved, provided the deformation is low enough to ensure that recrystallization does not interfere with their observation.