Investigation of the annealing of deformed nickel powder by X-ray and stored energy measurements

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Abstract
The stored energy was measured by a calorimetric method. The measured value of 3.6 cal/g and the manner of its release suggests that a wide range of deformations is present, both the maximum and average deformations being considerably greater than those present in heavily deformed solid specimens of nickel. The diffraction patterns, measured with a Geiger counter spectrometer, show that during annealing there is no change in the background intensity. The integrated intensities of the high angle lines remain constant and small changes in the low angle lines are attributed to changes in extinction. Only small changes occur in the tails of the lines at temperatures of annealing up to 400°C. No evidence has been found for stacking faults or changes in lattice parameter. The diffraction profiles are analysed by a number of methods, the broadening in each case being attributed partly to strain and partly to small particle size. The results indicate two stages in the relief of strain. The first occurs mainly in the less severely deformed regions without increase in the ‘apparent particle size’ and is attributed to recovery. In the second, all the remaining strain is relieved by recrystallization with an increase in the ‘apparent particle size’. For the deformed powder the ‘apparent particle size’ is in the range 350–2300 Å and the energies derived from the analyses range from 0.02–1.5 cal/g. The discrepancy between the calculated values of energy and the value obtained experimentally is discussed in terms of the distribution of strain within the crystal.

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