Twinning dislocations in aluminum.

Abstract

Precession patterns taken with carefully monobromated radiation show that stacking faults are present in aluminum crystals grown by the strain anneal method. The evidence for the stacking faults are the streaks through some diffraction peaks, the variation in structure factors, Fhkl, as determined from the relative intensities, and the doubling of some peaks. Arguments are advanced, on geometrical grounds, that if stacking faults exist in the crystal they will combine to produce regions in twin orientation. However, the absence of systematic "extra- twin diffraction peaks suggests that the twinned regions are very small. It is suggested that a low stacking fault energy and the occurrence of stacking faults on all stacking planes, together with the creation of substructures with other than twin orientations, explains the absence of large visible twins.