The Influence of Point-Defect Clusters on Fatigue Hardening of Copper Single Crystals

In order to investigate quantitatively the influence of point-defect clusters on the saturation stress in metal fatigue, the yield stress for uni-directional deformation was measured as a function of temperature between 78 and 300 °K on copper single crystals which had been fatigue-hardened into saturation at room temperature. Weak beam transmission electron micrographs of these specimens revealed a cell-like dislocation array with a low point-defect cluster density in the dislocation-poor interior and a high cluster density in the dislocation-rich walls of the cells. The size distribution of the defect clusters was found to be exponential for both the cell interior and the cell walls. A quantitative analysis of the yield stress measurements together with the electron-microscopical data showed that the saturation stress of fatigued copper single crystals is controlled by internal stresses and defect clusters within the interior of the cells which impede the dislocation motion through these regions. Zur quantitativen Untersuchung des Einflusses von Punktfehlstellen-Agglomeraten auf die Sattigungsspannung bei der Ermudung von Metallen wurde die kritische Schubspannung fur einachsige Verformung von Kupfer-Einkristallen in Abhangigkeit von der Verformungstemperatur zwischen 78 und 300 °K gemessen, nachdem diese bei Raumtemperatur bis in die Sattigung ermudet worden waren. Elektronenmikroskopische „weak-beam„-Aufnahmen dieser Proben zeigten eine zellartige Versetzungsanordnung mit hohen Dichten an Punktfehler-Agglomeraten in den versetzungsreichen Zellwanden und niedrigen Agglomerat-Dichten im versetzungsarmen Zellinnern. Die Grosenverteilung der Agglomerate ist sowohl im Innern als auch in den Wanden der Zellen exponentiell. Eine quantitative Auswertung der Fliesspannungsmessungen unter Einbeziehung der elektronenmikroskopischen Daten zeigte, das die Sattigungsspannung ermudeter Kupfer-Einkristalle durch die Behinderung der Versetzungsbewegung durch innere Spannungen und Punktfehlstellen-Agglomerate im Zellinnern bestimmt wird.

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