Inhomogeneous nucleation and growth of cavities in irradiated materials

Abstract

The origin of the effect of inhomogeneous swelling observed near grain boundaries in irradiated materials is examined taking into account both nucleation and diffusional growth of cavities, and the interaction of cavities with mobile interstitial clusters produced in collision cascades. The model shows the formation of a characteristic profile of inhomogeneous swelling that exhibits features similar to those observed experimentally. The rate of swelling is found to be strongly dependent on the size of cavities, with cavities growing near the boundary being able to reach substantially larger sizes than those growing in the interior area of the grain. The distance z* between the peak of swelling and the grain boundary scales with the density of cavities N 0 as z*ϳN 0 Ϫ␤ , where ␤ is close to 1/3.

Void lattice formation as a nonequilibrium phase transition

“…In the calculations we also took into account that the cross section of dislocation lines d sin / s Ќ for a closepacked direction ͑here is the angle between the dislocation line and the close-packed direction͒ averaged over all possible line orientations gives d /4s Ќ for the isotropic line distribution. 46 Thus, we arrive at Eqs. ͑32͒-͑34͒ Unlike the static or dynamic crowdions, crowdion clusters produced outside of the void supply cylinder also contribute to the number of crowdion clusters in the cylinder and, consequently, can be absorbed by the corresponding void.…”

“…The latter can be the mean lifetime of the crowdions between their creation and conversion to dumbbells, 5,18 or the average duration between consecutive changes of the Burgers vector of the interstitial clusters. 24 For an ensemble of random voids, the mean distance 1 between two voids along the close-pack directions is equal to 2/R 2 N. 46 For a void swelling S =4R 3 N / 3 of less than 1%, 1 = ͑2/ 1/3 ͒͑4/3S͒ 2/3 N −1/3 is much larger than the average 3D separation N −1/3 between the voids. In the following we assume that the mean free path of the one-dimensional random walkers is comparable with the average distance N −1/3 between voids, and, consequently, much smaller than 1 .…”

A Numerical Study on Composition Pattern Formation in Immiscible Alloys under Irradiation Condition

“…where the weight function w R (x) ≡ exp(−|x| 2 /(2R 2 )) denotes the distribution of atomic relocation distance with the average exchange distance R. In the model, for the sake of simplicity, the concentration of irradiation-induced point defects was assumed to have reached a steady value, and also the contribution of interstitials as well as defect sinks and clusters 7) was neglected. Moreover, non-ballistic mixing effects, any coupling between the degree of order and the concentration field 8) are not considered.…”

Analysis of defect structural evolution in fcc metals irradiated with neutrons under well defined boundary conditions

“…The importance of one-dimensional motion of interstitial clusters on microstructural evolution in metals has been pointed out by many researchers [4][5][6][7][8][9]. GB can be effectively used in order to detect the existence of one-dimensional motion of interstitial clusters.…”