Thermally Activated Plastic Deformation of High‐Purity Copper Single Crystals

Changes in strain rate during dynamical tensile deformation of high‐purity copper single crystals are used to determine the activation volume associated with plastic deformation as a function of flow stress, temperature, and strain rate. In work‐hardening stage I the activation volume is almost constant, whereas in stage II the reciprocal activation volume increases linearly with flow stress. It is shown that the flow‐stress ratios are not constant in any of the stages I to III, in violation of the so‐called Cottrell‐Stokes law. The experimental results are discussed in terms of the work‐hardening model of Seeger and co‐workers and indicate that the strain‐rate dependent (thermally activated) but not the temperature independent contribution to the flow stress is determined by the intersection of dislocations.