Ensembles of gliding grain boundary dislocations in ultrafine grained materials produced by severe plastic deformation
- Russian Academy of Sciences, Ufa (Russian Federation). Inst. for Metals Superplasticity Problems
Severe plastic deformation which is now widely used to produce an ultrafine grained (UFG) structure in metals and alloys necessarily leads to the accumulation of interfacial dislocations which arise due to the incompatibilities of strains of neighbor misorientated areas. The most important result of the dislocation storage at grain boundaries (GBs) and associated internal stresses is the fragmentation which at extremely large strains is usually followed by the formation of a very fine highly misorientated granular structure. After deformation the UFG structure must preserve residual dislocation arrays in GBs, since recovery at room temperature is not enough to provide their annihilation. Recently, a hypothesis has been put forward that the internal stresses induced by these arrays are the origin of a number of fundamental properties of UFG materials different from those of coarse grained ones. The author suggested that, in addition, the nonequilibrium dislocation ensembles in GBs were characterized by disordered distribution of dislocations. Thus, three main sources of internal stresses can exist in UFG materials prepared by severe plastic deformation: (1) disordered sessile EGBD arrays, (2) excess density of sessile EGBDs, that is junction disclinations, and (3) arrays of tangential EGBDs. Each of these components can contribute to the experimentally observed elastic strain, excess GB energy and volume expansion in UFG materials.
- OSTI ID:
- 540901
- Journal Information:
- Scripta Materialia, Vol. 37, Issue 8; Other Information: PBD: 15 Oct 1997
- Country of Publication:
- United States
- Language:
- English
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