High temperature annealing of ion irradiated tungsten

Abstract

Transmission electron microscopy of high temperature annealing of pure tungsten irradiated by self-ions was conducted to elucidate microstructural and defect evolution in temperature ranges relevant to fusion reactor applications (500-1200°C). Bulk isochronal and isothermal annealing of ion irradiated pure tungsten (2 MeV W + ions, 500°C, 10 14 W + /cm 2 ) with temperatures of 800, 950, 1100 and 1400°C, from 0.5 to 8 h, was followed by ex situ characterisation of defect size, number density, Burgers vector and nature. Loops with diameters larger than 2-3 nm were considered for detailed analysis, among which all loops had b ¼ 1 2 h1 1 1i and were predominantly of interstitial nature. In situ annealing experiments from 300 up to 1200°C were also carried out, including dynamic temperature ramp-ups. These confirmed an acceleration of loop loss above 900°C. At different temperatures within this range, dislocations exhibited behaviour such as initial isolated loop hopping followed by large-scale rearrangements into loop chains, coalescence and finally line-loop interactions and widespread absorption by free-surfaces at increasing temperatures. An activation energy for the annealing of dislocation length was derived, finding E a ¼ 1:34 AE 0:2 eV for the 700-1100°C range.

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.…”

Effect of He-appm/DPA ratio on the damage microstructure of tungsten

“…Postirradiation analysis revealed the presence of small (< 5 nm) dislocation loops shown in Figure 5, it can be seen that the loops were of b = ±1/2<111> type. Monovacancy migration in W has an activation energy of 1.7 eV and becomes important at temperatures above 0.15 of the melting temperature (T m ) [20]. At the irradiation temperature of 750°C, larger bubble formation compared to the 500°C irradiation is evidence for a higher mobility of vacancies.…”

Thermal Evolution of the Proton Irradiated Structure in Tungsten–5 wt% Tantalum

“…/cm 2 . The loop hopping is significant at temperatures in the range of 300-700°C, with increasing hopping frequency with temperature, and leads to loop loss to the sample surface [32]. Besides that, detrapping of SIAs from dislocations occurs in tungsten in the annealing stage II at -170 to 430°C [28].…”