Abstract
In the past few years there has been a striking advance in the development and refinement of various experimental methods for the study of imperfections in crystals. This has resulted in the experimental confirmation of the existence and behaviour of many of these imperfections which previously could be only the subject of theory. In a recent review, Hirsch has described in detail how this has come about in the case of the dislocation—the crystal defect most directly related to the process of plastic deformation. He has also described some of the experimental results, such as the nature of the defects found in quenched or irradiated metals and the dislocation arrangements observed in deformed metals, which can more properly be classed as new contributions to our knowledge of the subject. Though such simple and general discoveries in the study of dislocations are of supreme importance and will doubtless continue to be made, there are indications that the more detailed and quantitative investigations of dislocations by means of the new experimental techniques will become of increasing importance and will indeed be essential, if our knowledge of crystal plasticity is to progress. It therefore seems opportune at this juncture to review the quantitative results that have been recorded and the methods used to obtain them in the field of transmission electron microscopy, since this has proved the most fruitful of the new techniques for the study of dislocations in metals. This review is intended therefore as a supplement in one particular field to the article by Hirsch, and the reader who is unfamiliar with the concepts and properties of dislocations, stacking faults, and extended dislocations is referred to that article for a simple account or to the standard texts 2-5 for fuller discussions of these subjects.
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