. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 3. Stacking faults. Fig. 4. Steel reduced 25 "â by rolling. locity increases with decreasing gas pressure (because the ions suffer a smaller number of collisions with gas atoms). With increasing mean velocity the mean energy of the ions impinging the surface also increa- ses. High energetic ions strike out of the specimen a large number of atoms per ion, producing in this way small holes. Therefore, the lower the gas pres- sure, the rougher will the treated surface become. Thus the strength of the attac
. Electron microscopy; proceedings of the Stockholm Conference, September, 1956 . Fig. 3. Stacking faults. Fig. 4. Steel reduced 25 "â by rolling. locity increases with decreasing gas pressure (because the ions suffer a smaller number of collisions with gas atoms). With increasing mean velocity the mean energy of the ions impinging the surface also increa- ses. High energetic ions strike out of the specimen a large number of atoms per ion, producing in this way small holes. Therefore, the lower the gas pres- sure, the rougher will the treated surface become. Thus the strength of the attack can be regulated by varying the gas pressure. For our purposes, the ion bombardment did not present an advantage. The smoothest surface was obtained directly by electropolishing. The importance of ion bombardment for the work of Castaing on Al-4 "o Cu alloy seems to lie, at least partially, in the fact that the Al is preferentially electropolished (as pictures of Castaing show), but that the ion bom- bardment released the copper preferentially from the surface. It is known that it is relatively simple to sputter (release by ion-bombardment) heavy met- als such as copper, but that it is difficult to sputter aluminium because of the oxide layer (7). Micrographic appearance of dislocations in crystal foils.âMuch theoretical work has been done on dislocations in crystals to explain the behaviour of metals during plastic deformation (sec 4, 6). In a plastically deformed metal, the strongly distorted regions are concentrated on definite lines, the so- called "dislocation lines". The material around these lines is more or less elastically deformed. The theory shows that the dislocation lines have to be closed loops or have to end at the surface of the grains; they can be branched into extensive networks (figs. 1. 2). Until recently, experimental evidence on disloca- tions in metals was given by etching the surface, but here only the end-points of dislocation lines a
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