Dislocation multiplication sources in copper revealed by X-ray topography

The nature of grown-in dislocations and dislocation multiplication sources in copper have been studied by X-ray topography. A number of grown-in dislocations in plates of copper single crystals, after a long-time thermal cyclic annealing, are revealed to penetrate the large surfaces without any nodes. Those dislocations have Burgers vectors with a strong edge component. Segments of grown-in dislocations act as surface multiplication sources at shear stresses smaller than 100kPa. The stress is in good agreement with that evaluated from the observed length of a single-ended multiplication source. A further increase in stress activates new sources and also cross-slip of screw dislocations onto neighbouring slip planes. The crystal becomes covered with rows of multiplied dislocations before reaching its macroscopic yield. A series of topographs, corresponding to the incrementally increasing stress, clearly show the dislocation multiplication process in the copper crystals.