Dislocation Mobility in the {1122} 〈1123〉 Slip System of Zinc Single Crystals

Abstract

Results are presented of measurements of the stress dependence of screw dislocation velocities in the { 1122) (1123) slip system (pyramidal slip) of zinc single crystals. The investigations have been carried out on zinc single crystals of 99.999% purity at room temperature. The dislocation mobility has been studied within a wide range of velocities and shear stresses below and above the critical resolved shear stress. When the shear stress t changed from 20 to 4000 p/mm2 the dislocation velocity v varied from to lo4 cm/s. A strong dependence of o on z is observed in the stress range 20 t o 100p/mm2, which can be described by an exponential and the dislocation mobility is determined by a thermally activated mechanism. A weak linear dependence of v on t is observed at shear stresses greatly exceeding the critical shear stress (300 to 4000 p/mm2). These results are explained in terms of a phonon viscosity mechanism. The measured drag constant is of the same order of magnitude as that calculated for the mechanism of phonon viscosity.Ergebnisse von Messungen der Geschwindigkeit von Schraubenversetzungen in einem { 1122) (1123) Gleitsystem (pyramidale Gleitung) an Zink-Einkristallen, die von der Scherspannung abhiingen, werden mitgehilt. Die Untersuchungen wurden an Zink-Einkristallen von 99,999yo bei Zimmertemperatur durchgefuhrt. Die Versetzungsgeschwindigkeit wurde in einem breiten Geschwindigkeits-und Scherspannungsbereich unterhalb und oberhalb der kritischen Scherspannung gemessen. Bei h d e r u n g der Scherspannung T von 20 auf 4000 p/mm2 variiert die Versetzungsgeschwindigkeit v von 10-3 bis lo4 cm/s. Eine starke v(t)-Abhiingigkeit wird im Scherspannungsbereich 20 bis 100 p/mm2 beobachtet, die durch ein Exponentialgesetz beschrieben werden kann, wobei die Versetzungsgeschwindigkeit durch einen thermischen Aktivierungsmechanismus bestimmt wird. Eine schwache lineare Abhiingigkeit von ~( t ) wird bei Scherspannungen, die die kritische Scherspannung betriichtlich uberschreiten (300 bis 4000 p/mm2), beobachtet. Diese Ergebnisse werden durch einen Viskositiitsmechanismus der Phononen erkliirt. Die gemessene Hemmungskonstante stimmt innerhalb der GroBenordnung mit der fur den Mechanismus der Phononenviskositiit berechneten fiberein. IntroductionThe process of plastic deformation is mainly determined by the dynamic properties of dislocations. Thus, the characteristics of dislocations as, for example, starting stress for the beginning of dislocation motion and the shear stress dependence of dislocation velocity are extremely important when analysing and calculating the stress-strain dependence. But the shear stress dependence of dislocation velocity has been studied only in crystals of a very restricted number of materials. In ionic crystals the dislocation motion has been extensively investigated within a wide range of velocities [1 to 31. In metal crystals [4 to 71 the l ) Results of this work were reported on the VIJ. International Congress of Crystallography, Moscow, July 1966.

The mechanics and physics of high-speed dislocations: a critical review

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