The evolution of intrinsic-extrinsic faulting in fcc crystals

Frank and Nicholas have proposed that when a trailing Shockley partial leads the leading one, the anomalous faulting can be avoided by the dissociation of partials to form an extrinsic fault. This concept has been utilized in developing the evolutionary details of node- and fault-pairs. It has been shown that the anomalies noted by Loretto and Gallagher and Washburn regarding the formation of node- and fault-pairs, respectively, can satisfactorily be resolved. In addition, experimental evidence in support of the mechanistic details has been developed by examining the fault-pairs in deformed Co-6.25 at. pct Fe and Cu-8.5 at. pct Ge alloys in detail by transmission electron microscopy. The fault-pairs appear to form in the absence of pile-ups, contrary to the suggestions of Gallagher and Washburn and Mahajan and Chin. The observed partial dislocation arrangements are totally consistent with the proposed mechanism. The break-up of a fault-pair has also been investigated. The resulting configuration can be rationalized in terms of these hypotheses as well.