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.     

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.     

The tensile deformation of cobalt single crystals in the fcc phase

Single crystals of high purity cobalt have been deformed in the high temperature fcc phase. No easy glide was observed, and the work hardening rate in the linear hardening region was lower than that usually found in stage II of fcc metals. Dynamic recovery by cross-slip was found occurring in stage III. The ratio of the Schmid factor for the most favorably orientated slip system to the Schmid factor of the slip system on the transformation plane has been found to be of importance in the deformation behavior. As a result of metallographic observations, it is expected that dislocations on the transformation plane affect the work hardening behavior, and also that dislocations produced during deformation may activate the transformation. R. T. HOLT, formerly Graduate Student, University of British Columbia, Canada     

On the nucleation of persistent slip bands in fatigued copper single crystals

The onset of strain localization in a copper single crystal, oriented for single slip, and cycled at a constant plastic strain amplitude corresponding to the low end of the plateau in the cyclic stress-strain curve, has been explored by inteferometry and analysis of hysteresis loops. Current methods for analyzing behavior early in life are shown to be inadequate, and several new methods, involving the shape of the hysteresis loops, are introduced. Changes in local curvature have been observed throughout rapid hardening, and the nucleation of persistent slip bands is shown to coincide with a basic change in the shape of the hysteresis loops.