DISLOCATION MULTIPLICATION SOURCES IN COPPER REVEALED BY X-RAY TOPOGRAPHY

The nature of grown-in dislocations and dislocation multiplication sou rces in copper have been studied by X-ray topography. A number of grow n-in dislocations in plates of copper single crystals, after a long-ti me thermal cyclic annealing, are revealed to penetrate the large surfa ces without any nodes. Those dislocations have Burgers vectors with a strong edge component. Segments of grown-in dislocations act as surfac e multiplication sources at shear stresses smaller than 100 kPa. The s tress is in good agreement with that evaluated from the observed lengt h of a single-ended multiplication source. A further increase in stres s activates new sources and also cross-slip of screw dislocations onto neighbouring slip planes. The crystal becomes covered with rows of mu ltiplied dislocations before reaching its macroscopic yield. A series of topographs, corresponding to the incrementally increasing stress, c learly show the dislocation multiplication process in the copper cryst als.