Motion and Rotation of Small Glissile Dislocation Loops in Stress Fields
Atomistic computer simulations of small clusters of self-interstitials have revealed that these clusters are highly mobile along certain crystallographic directions. Their thermal mobility and Brownian motion along these directions rapidly decreases, however, as the size of the cluster increases. A review of these computer simulations has been provided by Osetsky et al. [1], and more recent studies are given by Marian et al. [2]. All these studies have shown that the activation energy for cluster diffusion reaches a saturation value, while the pre-exponential factor continues to decline with the cluster or loop size. The diffusion of loops containing more than one hundred interstitials becomes too slow to be quantified with molecular dynamics simulations. Nevertheless, since the activation energy for migration becomes nearly independent of the loop size, they remain very mobile if forces act on them, even though their Brownian motion becomes insignificant. Such forces naturally exist in real crystal due to internal stress fields originating from other defects, in particular from dislocations. Small clusters of self-interstitials, when no longer subject to rapid Brownian migration, are of course synonymous with small prismatic dislocation loops. When their Burgers vectors are aligned along one of the possible glide directions, they can move on one-dimensional trajectories in response to the force exerted by their elastic interaction with stress fields of other defects. As we shall see, this force depends among other factors on the orientation of the dislocation loop, and in turn, the orientation is affected by the stress field. In other words, the motion of a small prismatic dislocation loop on its glide prism has three degrees of freedom, namely its position along the glide prism, and the orientation of its normal vector (normal on the loop plane) in relation to its Burgers vector or glide direction. The specification of the latter requires then two angles, hence a total of three degrees of freedom for one-dimensional motion. Kroupa [3] has long ago pointed out that stress fields exert both a net force and a net torque on small dislocation loops that he derived from the Peach-Koehler force. Numerical studies of both force and torque have been carried out by Ghoniem et al.[4] for small prismatic dislocation loops interacting with a near-by dislocation, assuming however, a fixed orientation of the loop normal vector.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 862208
- Report Number(s):
- UCRL-JRNL-200164; PRLTAO; TRN: US0600608
- Journal Information:
- Physical Review Letters, Vol. 92, Issue 8; ISSN 0031-9007
- Country of Publication:
- United States
- Language:
- English
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