| In this paper, the mechanical properties of nanostructured materials, defined hereafter as having a mean grain size that falls in the 50-200 nm ranges, is reviewed and the underlying mechanisms are discussed. Particular emphasis is placed on nanostructured materials that are processed via two synthesis approaches: consolidation of nanocrystalline powders and electrodeposition. The present review demonstrates that processing history significantly influences mechanical behavior as revealed by the following observations. First, a low strain hardening behavior is usually observed during the plastic deformation of nanostructured materials processed by milling (also known as mechanical milling or attrition). The phenomenon can be attributed to the process of dislocation annihilation or dynamic recovery during plastic deformation. Second, the reported asymmetry of yield strength between tension and compression can be rationalized based on the existence of porosity or the presence of a bimodal phase distribution. Third, significant strain hardening behavior is generally observed in nanostructured materials processed by electrodeposition. The observation of strain hardening in nanostructured materials can be explained on the basis of dislocation multiplication. Fourth, the low ductility that is frequently reported for nanostructured materials is related to an absence of dislocation activity. Recent work reviewed suggests that this limitation may be surmounted by implementing the concept of multiple length scales in the microstructure. |
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