Kinetics of flow and strain-hardening☆
Abstract
The kinetics of glide at constant structure and the kinetics of structure evolution are correlated on the basis of various experimental observations in pure f.c.c. mono- and polycrystals. Two regimes of behavior are identified. In the initial regime, the Cottrell-Stokes law is satisfied, hardening is athermal, and a single structure parameter is adequate. With increasing importance of dynamic recovery, be it at large strains or at high temperatures, all of these simple assumptions break down. However, the proportionality between the flow stress and the square-root of the dislocation density holds, to a good approximation, over the entire regime; mild deviations arc primarily ascribed to differences between the various experimental techniques used. A phenomenological model is proposed, which incorporates the rate of dynamic recovery into the flow kinetics. It has been successful in matching many experimental data quantitatively.
Résumé
Nous avons relié la cinétique du glissement à structure constante et de l'évolution de la structure à partir de diverses observations sur des monocristaux et des polycristaux c.f.c. purs. Nous avons distingué deux régimes. Au cours du premier régime, la loi de Cottrell et Stokes est vérifiée, le durcissement est athermique et il suffit d'un seul paramètre pour la structure. Lorsque l'importance de la restauration dynamique augmente, que ce soit aux grandes déformations ou aux températures élevées, toutes ces hypothèses simples s'effondrent. Cependant, la contrainte d'écoulement reste proportionnelle à la racine carrée de la densité de dislocations, à une bonne approximation, dans tout le régime; quelques faibles déviations sont principalement attribuées aux différences entre les diverses techniques expérimentales utilisées. Nous proposons un modèle phénoménologique, qui permet d'introduire la vitesse de la restauration dynamique dans la cinétique de l'écoulement. Il a permis de rendre compte quantitativement d'un certain nombre de résultats expérimentaux.
Zusammenfassung
Anhand verschiedener experimenteller Beobachtungen an reinen kfz. Ein- und Vielkristallen wurden die Kinetik der Gleitung bei konstanter Struktur und die Kinetik der Strukturentwicklung miteinander korreliert. Zwei Bereiche unterschiedlichen Verhaltens wurden aufgefunden. Im Anfangsbereich ist das Cottrell-Stokes-Gesetz erfüllt, die Verfestigung ist athermisch und ein einziger Strukturparameter ist ausreichend. Mit zunehmendem Einfluβ der dynamischen Erholung bei groβer Dehnung oder hoher Temperatur werden alle diese einfachen Annahmen ungültig. Der lineare Zusammenhang zwischen Flieβspannung und Wurzel aus der Versetzungsdichte dagegen bleibt in guter Näherung im gesamten Bereich bestehen. Kleinere Abweichungen werden im wesentlichen den Unterschieden zwischen den verschiedenen experimentellen Techniken zugeschrieben. Es wird ein phänomenologisches Modell vorgeschlagen, welches die Geschwindigkeit der dynamischen Erholung bei der Kinetik des Flieβens berücksichtigt. Dieses Modell kann viele experimentelle Daten quantitativ beschreiben.
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Work supported in part by the U.S. Department of Energy.
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Now at Technical University, Hamburg-Marburg, W. Germany.