STACKING DEFECTS IN THE 9R PHASE AT AN INCOHERENT TWIN BOUNDARY IN COPPER

In situ HRTEM observations of the growth of 9R stacked material at a S igma = 3 incoherent twin boundary in copper are presented. Stacking de fects. which break the normal ABC BCA CAB... sequence of the 9R stacki ng, are observed in the growing 9R layer. These faults are shown to ar ise from the presence of secondary grain boundary dislocations with Bu rgers vectors of type a/6[(2) over bar 11]. It is shown that both the sense (positive or negative) and character (90 degrees or 30 degrees) of the grain boundary dislocation determine the characteristics of the 9R fault. (C) 1998 Acta Metallurgica Inc. Published by Elsevier Scien ce Ltd. All rights reserved.