The effect of extrinsic grain boundary dislocations with unrelaxed and relaxed cores on the state of random boundaries i
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IT is commonly known that during plastic deformation of polycrystals, the lattice dislocations interact with grain boundaries creating new line defects which were called by Balluffi et al I extrinsic grain boundary dislocations (EGBDs). The increase of EGBD density during plastic deformation has been observed in numerous worksY 9 In general, the EGBD which is formed just after a lattice dislocation interacts with a random grain boundary will have an unrelaxed core.* The energy increase * For the purpose of this work, we will use the expression "unrelaxed core" for an EGBD which has been formed during plastic deformation at room temperature despite the fact that the EGBD core may actually be wider than that of a lattice dislocation.~~
caused by such an injection of dislocations into a grain boundary is simply the elactic energy stored in the strain fields of the dislocations. However, if there exists an interaction energy between the grain boundary plane and the dislocation strain field then one can expect that the EGBDs with unrelaxed cores would have some effect on the properties of such a grain boundary. The EGBDs which are formed during plastic deformation at room temperature are stable up to a certain temperature above which they are known to disappear. ill7 The physical mechanism of the spreading process is still controversial, being assumed either as "core widening '1~-13,18-2~or dissociation into secondary intrinsic grain boundary dislocations (IGBDs) with smaller Burgers vectors--for example those defined by the appropriate DSC lattice. 2~- 23 However, regardless of the fact whether core widening or dissociation into secondary GBDs is the mechanism for EGBD absorp-
R. A. VARIN, formerly with the Metallurgical Science Laboratory, The University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada, is now Assistant Professor, Institute of Materials Science and Engineering, The Warsaw Technical University, Warsaw, Poland and K. TANGRI is Professor, Department of Mechanical Engineering and Research Director, Metallurgical Sciences Laboratory, University of Manitoba, Winnipeg, Manitoba R3T 2N2. Manuscript submitted May 29, 1980.
tion, existing qualitative experimental evidence ~2,j3indicates that the incorporation of EGBDs during spreading may produce a nonequilibrium grain boundary structure. Pumphrey and Gleiter ~2,13have shown that moving grain boundaries (recrystallization fronts) which have swept up a certain density of lattice dislocations have nonequilibrium structure and a significantly lower spreading temperature (Ta) as compared to well-annealed, equilibrium boundaries. The purpose of this work is to investigate the changes in the equilibrium state of the boundary caused by the incorporation of EGBDs at room temperature and also due to their spreading at higher temperatures rather than determining the physical nature of the EGBD spreading process itself. Therefore, for the purpose of this work we will assume, following Darby et a l y that for random boundaries (the definition of the random boundary will be
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