Subgrain formation during deformation: Physical origin and consequences
- PDF / 208,118 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 89 Downloads / 242 Views
. INTRODUCTION
MANY models of plasticity work with average dislocation densities that are the same everywhere in the crystal. While it is certainly a legitimate first step to build a model on this simplifying assumption, such models exclude the formation of deformation-induced dislocation structures and misorientations within a crystal that are important features of plastic deformation. The formation of misorientations leads to a structure of crystallites within the deforming grains that are bounded by dislocation networks in the form of subgrain boundaries or, as deformation proceeds to large strains and the misorientations increase, even by large angle boundaries. In fact, the buildup of misorientations during deformation has even led to the method of producing so-called nanocrystalline materials by severe plastic deformation. In the following, we will use the term subgrain structure to address the misoriented structure. This term is established in the field of creep where stresses are relatively low due to high temperature and the subgrain boundaries come close to ideal small angle boundaries. However, we do not mean that the subgrain boundaries resulting from the dislocation evolution during plastic deformation are ideal. Due to the fact that the crystal approaches a state of dynamic equilibrium, there is always some disturbance of the ideal state. Prolonged annealing after deformation brings the subgrain boundaries into a much more ideal state. The disturbance of the ideal structure increases with decreasing temperature. In cold working, the disturbance is so large that one does not usually use the term subgrain boundary but speaks of cell boundaries, distinguishing ´ C˘EK, Research Assistant, is with the Lehrstuhl fu¨r Mechanik, R. SEDLA TU-Mu¨nchen, 85747 Garching, Germany. W. BLUM, Professor, is with the Institut fu¨r Werkstoffwissenschaften, Universita¨t Erlanger-Nu¨rnberg, 91058 Erlangen, Germany. J. KRATOCHVI´L, Professor, is with the Faculty of Civil Engineering, Department of Physics, Czech Technical University Prague, 166 29 Prague, Czech Republic. S. FOREST, Research Assistant is with the Centre des Mate´riaux, CNRS, Ecole des Mines de Paris, 91003 Evry, France. This article is based on a presentation made in the workshop entitled “Mechanisms of Elevated Temperature Plasticity and Fracture,” which was held June 27–29, 2001, in San Diego, CA, concurrent with the 2001 Joint Applied Mechanics and Materials Summer Conference. The workshop was sponsored by Basic Energy Sciences of the United States Department of Energy. METALLURGICAL AND MATERIALS TRANSACTIONS A
between various kinds, such as geometrically necessary and incidental boundaries. However, all kinds of boundaries are similar in that they constitute dislocation networks, which evolve during deformation from “thick” walls with high dipole content to “thin” essentially two-dimensional (2-D) walls, and in that they are associated with misorientations. From this point of view, there is no real need for a difference in nomenclature, except if one wa
Data Loading...
