On APB Dragging and APB Energy Anisotropy in Binary Ni 3 Al
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ON APB DRAGGING AND APB ENERGY ANISOTROPY IN BINARY Ni 3 A1 DENNIS M. DIMIDUK*, J. C. WILLIAMS" AND A. W. THOMPSON*** *AFWAL Materials Laboratory, Wright-Patterson AFB, OH 45433-6533 "**Engineering Materials and Technology Laboratory, General Electric Co., One Neuman Way, Cincinnati, OH 45215-6301 *** Carnegie-Mellon University, Department of Metallurgical Engineering and Materials Science, Pittsburgh, PA 15213-3890 ABSTRACT Recent weak-beam electron microscopic studies of Ni 3 AI provided evidence indicating that glide of Kear-Wilsdorf locked dislocation segments may occur on ( 1111 planes, accompanied by APB dragging, during deformation at high temperature. A direct implication of those studies is that a mechanism other than the onset of (010) slip may be important in controlling the peak in yield strength in Ni 3 Al. The present weak-beam investigations of Ni 3 AI have centered on the possibility that such configurations result from thermally induced dislocation kink and jog activity rather than the APB dragging mechanism. previously proposed. INTRODUCTION Theoretical descriptions of mechanisms governing the anomalous temperature dependence of flow stress in Ni 3AI alloys have evolved over the last twenty-eight years [1-8]. Aspects of this theory have been supported by transmission electron microscopic (TEM) investigations of the deformation substructure in both polycrystalline and single crystal materials [2,3,9-22]. Mulford and Pope [10], provided the first microscopic evidence indicating that at any temperature the microyield behavior of Ni 3 Al is dominated by the nucleation and mobility of edge dislocations. They further suggested, as did others before them, that with increasing deformation temperature, screw dislocations, immobilized by Kear-Wilsdorf (K-W) lock formation, dominate the flow stress. Staton-Bevan and Rawlings [11] added further support to this view through TEM investigations of the deformation substructure in single crystals deformed at temperatures from 166K-775K. Recently, Veyssi~re, et al., [16,17] provided microscopic evidence of dislocations exhibiting climb or non-conservative dissociations, proposed by Flinn [1], after high temperature deformation. All of these investigations agree on the dominance of "sessile" screw dislocation configurations (known as Kear-Wilsdorf locks [2]) after deformation in the regime of increasing flow stress with temperature. Veyssi~re, et al., [221 recently reported observations of ao type superdislocations dissociated in an (0011 plane, and yet, bowed or curved in the ( 111 glide plane. They concluded that such configurations arise from portions of dislocations which have formed K-W locks, with their adjoining antiphase boundary (APB) on the (001) plane, experiencing further glide in the 1111) plane accompanied by dragging their out-of-plane APB. Veyssi~re, et al., argued further that this process occurred by local "atomic interchanges" roughly perpendicular to the dislocation line. They regarded this observation as an indication of higher than expected mob
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