Observations of unusual stacking fault configurations using complimentary strong and weak beam images

Abstract

In this paper, the authors present both strong and weak beam images of stacking faults in FCC cobalt which indicate the presence of an unusual stacking fault configuration. Experimental images have been obtained at 100 kV from a specimen in a orientation with (1-1-1) stacking fault planes. Fig. 1 shows the (-1-11) strong beam dark field image. It can be seen that the contrast in faults A, B and D are very similar, while the fault at C is different. Using conventional techniques for identifying the nature of stacking faults in FCC materials A, B and D have been identified as single or intrinsic faults with a displacement vector R=l/3[-111]. On the other hand, the fault at C can be identified as a double or extrinsic fault. At this point, the interpretation of the faults in the image in Fig. 1 appears to be completely straightforward and in keeping with results obtained from a conventional analysis. The next image of interest is shown in Fig. 2 which shows the same four faults as in Fig. 1 obtained under weak beam diffraction conditions.