Impurity-induced vacancy clustering in cold-worked nickel

Abstract
Isochronal and time-linear annealing of pure nickel and dilute NiSb-alloys (0.03 and 0.1 at.%Sb) cold rolled to different thickness reductions have been studied by positron lifetime, angular correlation and Doppler-broadening measurements. The results show that free vacancy migration occurs at the stage III around 80 degrees C. A small amount of Sb impurities induces three-dimensional vacancy clustering during the stage III. These microvoids grow continuously with further heating. After an annealing at 335 degrees C they become visible in the transmission electron microscope. The average microvoid size as a function of annealing temperature is estimated. The microvoids anneal out at 450 degrees C during the recrystallisation.

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