Effect of annealing twinning on the microstructure and microtexture of pure nickel

Abstract

The evolution of microstructure, including recrystallization, microtexture and twinning of pure nickel under isochronal annealing at a series of temperatures, was investigated by electron backscatter diffraction (EBSD). The results indicated that the typical copper-type rolling texture was present in the as-deformed pure nickel plate. During static recrystallization (SRX), new SRX grains were found to preferentially consume higher Taylor factor components, such as the Copper component. For SRX grains, the Taylor factor and annealing twinning had an interactive effect on texture evolution. Certain recrystallization texture components, e.g., the Q component, showed a growing tendency upon recrystallization first and then declined during the grain growth phase consistent with the development of annealing twinning. The processes of SRX of pure nickel were dominated by discontinuous static recrystallization (DSRX) characterized by bulging/serration of pre-existing high-angle grain boundaries (HAGBs) and the formation of necklace-type structures between deformed grains. The preferred position of necklacing and the curvature of a bulging lay on the side of deformed grains with comparatively larger orientation gradient. Furthermore, growth twins enhanced the boundary misorientation angle of recrystallization front in the range of 10–20 deg., facilitating bulging and separation. Multiple twinning chains, even up to the third generation, were observed to support further expansion of the layered necklace grains. Continuous static recrystallization (CSRX) accompanied with annealing-induced higher angle boundaries, though present, was quite less significant.