Competing Kinetics and He Bubble Morphology in W

Abstract

The growth process of He bubbles in W is investigated using molecular dynamics and parallel replica dynamics for growth rates spanning 6 orders of magnitude. Fast and slow growth regimes are defined relative to typical diffusion hopping times of W interstitials around the He bubble. Slow growth rates allow the diffusion of interstitials around the bubble, favoring the biased growth of the bubble towards the surface. In contrast, at fast growth rates interstitials do not have time to diffuse around the bubble, leading to a more isotropic growth and increasing the surface damage.

The mobility of small vacancy/helium complexes in tungsten and its impact on retention in fusion-relevant conditions

“…The energy barrier for nucleation is thus expected to decrease due to the presence of other interstitials, while that of annihilation will increase, as it entails “unbinding” an interstitial. This is consistent with the tendency of Frenkel pair nucleations to occur in the vicinity of pre-existing interstitials that was previously observed in long-timescale simulations of bubble growth 22 . Analysis of the current simulations further shows that nucleation and annihilation tend to occur in a way that leaves the vacancy clusters as compact as possible, i.e., so as to maximize the number of vacancy first neighbors.…”

“…As this process repeats following the absorption of additional He atoms, the excess interstitials accumulate around the bubble. These are eventually released, often in the form of small prismatic dislocation loops, a process referred to as loop punching 22, 36–40 .…”

“…Such surface modifications can negatively affect the performance of the material. Due to the immense technological importance of the problem, the need for fundamental insight into the mechanisms that drive microstructural evolution has motivated a wide range of computational studies of He in tungsten, including the properties of interstitial He clusters 6–8 and their interactions with various types of defects 9–15 , the conversion of He interstitial clusters into nanobubbles 8, 16, 17 , and their subsequent growth through absorption of additional He atoms 18–22 .…”

New interatomic potentials for studying the behavior of noble gas atoms in tungsten

“…Hu et al [13] studied the trap mutation and dissociation of He clusters in the near-surface region of tungsten, which has significant impact on the W surface morphology and near-surface structure. More recently, Sandoval et al [14] have studied the growth process of He bubbles in W and found that the evolution of surface morphology is very sensitive to the growth rate of He bubbles. The above studies imply that He bubbles are necessary for the initiation of fuzz formation in W bulk.…”

Nanobubble Fragmentation and Bubble-Free-Channel Shear Localization in Helium-Irradiated Submicron-Sized Copper

“…Therefore, the dynamics of helium bubbles play an important role in determining the mechanical performance of metals. As a result, significant efforts have been made to understand the evolution of helium bubbles under thermal annealing, radiation, or mechanical loading [8][9][10][11][12][13][14][15][16].…”