Computer simulation of solid solution strengthening in Fcc alloys: Part II. At absolute zero temperature
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I.
INTRODUCTION
T H E stress required for plastic deformation, i.e., the macroscopic yield stress, is generally identified with the minimum stress needed to induce the movement of the component of the dislocation, which is the most difficult to move. For example, it is generally assumed that the screw dislocations, which are the most difficult to move, are the rate-controlling type in bcc metals. However, it is possible there could be circumstances when the generation of dislocations requires a larger stress and, hence, the latter stress would be identified with the yield stress. Most theories of solid solution strengthening have focused on the influence of the solute-dislocation interactions on dislocation motion. However, a few studies, such as those of Suzuki m and Butt and Feltham, [2l have focused on dislocation generation. Examples of theories that have focused on dislocation motion have included the following types of solute-dislocation interactions: (1) Elastic interactions on moving dislocations due to size and modulus difference between the solute and solvent additions: Mott-Nabarro, I31 Fleischer, I4,5,61 Friedel tvl and Labusch, 18,91 and others, tl~ (2) Chemical interactions due to either (a) the phase change associated with a stacking fault and a dislocation core (Kocks[~4l), where strengthening is due to dislocation source operations, or (b) the direct solute-solvent atom bonding (Tyson [151). (3) The electrical interaction between the charges of the solute atoms and dislocation (Cottrell, Hunter, and N a b a r r o [161).
The charge around a solute atom is produced by a disturbance in the conduction electron density by solute additions. Some near-edge dislocation electrons tend to move from the region of compression to that of tension, thus creating an electrical dipole. This dipole may react
R.J. ARSENAULT, Professor and Director, and S. PATU, Visit ing Scholar from the Institute of Metals Research, Academica Sinica, Shenyang, The People's Republic of China, Research Associate, are with the Metallurgical Materials Laboratory, University of Maryland, College Park, MD 20742-211 I. D.M. ESTERLING, Professor, is with the Civil, Mechanical, and Environmental Engineering Department, George Washington University, Washington, DC 20052. Manuscript submitted January 20, 1988. METALLURGICAL TRANSACTIONS A
electrostatically with the charge on the individual solute. Some of these interactions are either small or interrelated; for example, the changes in lattice parameter and the modulus are reflections of the electronic changes (bonding characteristics) that occur. The elastic interactions are believed to be a major contributor and are a convenient measure of the electronic energy change. This electronic energy change is very difficult to obtain experimentally, whereas the modulus differences and the lattice parameter changes can be readily measured experimentally. As a result, only the elastic interactions were considered in most of the investigations. Most theories of solid solution hardening in terms of
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