Dislocation path lengths in Cu single crystals of low dislocation density after pulse loading

Path lengths of fresh dislocations in low dislocation density Cu crystals of high and moderate purity are measured by etching before and after pulse loading at 300 K in four-point bending. The histograms of path lengths indicate a distinct effect of back movement of dislocations during unloading. This is consistent with the absence of a significant dependence of the histograms on pulse height (σr = 0.058 to 0.103 N/mm2) and pulse time (tp = 6.7 to 13.7 ms) and is supported by measuring directly the percentage Wb of back moving dislocations during unloading. Wb is found to be appreciable in particular in the case of high purity Cu. The difficulties for measurements of dislocation velocities in materials of high dislocation mobility by pulse methods are discussed.