Elastic trapping of dislocation loops in cascades in ion-irradiated tungsten foils

Abstract

Using in situ transmission electron microscopy (TEM), we have observed nanometre scale dislocation loops formed when an ultra-high-purity tungsten foil is irradiated with a very low fluence of self-ions. Analysis of the TEM images has revealed the largest loops to be predominantly of prismatic 1/2〈111〉 type and of vacancy character. The formation of such dislocation loops is surprising since isolated loops are expected to be highly mobile, and should escape from the foil. In this work we show that the observed size and number density of loops can be explained by the fact that the loops are not isolated-the loops formed in close proximity in the cascades interact with each other and with vacancy clusters, also formed in cascades, through long-range elastic fields, which prevent the escape of loops from the foil. We find that experimental observations are well reproduced by object Kinetic Monte Carlo simulations of evolution of cascades only if elastic interaction between the loops is taken into account. Our analysis highlights the profound effect of elastic interaction between defects on the microstructural evolution of irradiated materials.

Irradiation Induced Defect Clustering in Zircaloy-2

“…This also results in the growth of a limited number of clusters, and hence a lower DY and a larger loop size. The similar trends of DY vs. temperature and loop size vs. temperature were also recently found in other materials regardless of their different crystal structures, such as in bcc pure Fe [28][29][30][31] and pure W [32][33][34], and in fcc pure Ni [35] and Ni alloys [36].…”

Cascade fragmentation: deviation from power law in primary radiation damage

“…The corrected prediction is also plotted in Figure 4, with the full calculation given in the supplementary information. For simulations of microstructural evolution under irradiation, the uncorrected distribution naturally should be used, since the correction in effect accounts for the evolution, and in fact gives the same results as OKMC simulations building on the same assumptions of loop mobility and trapping [24].…”

Substrate temperature and ion kinetic energy effects on first steps of He+ implantation in tungsten: Experiments and simulations

“…The type of defects is also affected by the temperature: at high temperature He filled vacancies are mainly formed, while larger free voids are detected at low temperatures. This is in contradiction with the literature since the rise of the temperature leads in general to the formation of larger He-vacancy complexes due to the increased mobility of such defects which merge together [44,45]. This point will be discussed in the next paragraphs.…”

“…higher temperature can lead to their migration toward sinks e.g. surface or grain boundaries 22 [46,47], hence instead of merging and growing in size, most of them are lost to the substrate surface [44,45]. In other words, the thermal motion of W atoms hinders the He trapping process while enhancing the motion of the He-vacancies defects toward the surface.…”

“…To study He accumulation versus lattice temperature, snapshots and He concentration profiles are displayed in figure 13 for the same retention of 1.410 19 He.m with temperature that will induce large vacancy clusters formation [44,45,48]. However, their mobility is increased toward the surface where they are lost.…”