In-situ TEM investigation of 30 keV he+ irradiated tungsten: Effects of temperature, fluence, and sample thickness on dislocation loop evolution

In-situ transmission electron microscopy observation of the evolution of dislocation loops and gas bubbles in tungsten during H2+ and He+ dual-beam irradiation

“…TEM foils with 3 mm diameter and 50 μm thickness were prepared from the polycrystalline tungsten bulk (99.95 wt% purity). The detailed preparation process can be found in our published paper [7].…”

“…Many research works have been devoted to uncover the formation mechanism of ⟨100⟩ loops through in-situ irradiation [7,13], computational simulation [44,45] and theory analysis [34,46]. To our best knowledge, there are seven main mechanisms: (I) 1/2 ⟨111⟩ loop reaction mechanism [33]; (II) Eyre-Bullough mechanism [34], through ⟨110⟩ shear (the reaction between 1/2[110] loop and 1/2[ 110] loop to form [010] loop); (III) cascade overlapping mechanism [47]; (IV) punch-out mechanism [35]; (V) C15 transformation mechanism [48]; (VI) direct transformation of 1/2 ⟨111⟩ loop mechanism [45]; (VII) high-density helium cluster inducement mechanism [7]. Because 30 keV H 2 + and He + belong to low energy ions and mainly produce isolated Frenkel pairs and hardly induce dense collision cascade damage and high shockwave, the formation mechanism of ⟨100⟩ loops should not include cascade overlapping mechanism [47] and punch-out mechanism [35].…”

“…Recently, the formation of ⟨100⟩ loops in the tungsten irradiated by low energy helium was found by Li et al [7] and El-Atwani et al [18]. El-Atwani [18] attributed its formation to the reactions between 1/2 ⟨111⟩ loops, while Li et al [7] proposed another mechanism where the high-density helium clusters induced ⟨100⟩ loop formation. However, whether ⟨100⟩ loop is formed and its formation mechanism under H 2 + and He + dual-beam irradiation needs to be studied.…”

“…However, tungsten will be subjected to the bombardment of 14.1 MeV neutrons, deuterium and tritium escaping from plasma, and helium ash (the product of deuterium (D)-tritium (T) fusion reactions) [5,6]. Energetic particle irradiation will induce the formation of defect structures such as stacking fault tetrahedrons, voids, dislocation loops, and gas bubbles [7,8], which causes the degradation of tungsten properties, such as irradiation hardening and embrittlement. Therefore, it is important to study the irradiation behavior of tungsten, which is very useful for tungsten application and new irradiation-resistant tungsten-based alloy development.…”

“…As the formation energy of ⟨100⟩ loops is higher than that of 1/2 ⟨111⟩ loops [31] and ⟨100⟩ loops have an obvious effect on irradiation hardening [32], many works are done to explore the formation mechanism of ⟨100⟩ loops [33][34][35][36]. Recently, the formation of ⟨100⟩ loops in the tungsten irradiated by low energy helium was found by Li et al [7] and El-Atwani et al [18]. El-Atwani [18] attributed its formation to the reactions between 1/2 ⟨111⟩ loops, while Li et al [7] proposed another mechanism where the high-density helium clusters induced ⟨100⟩ loop formation.…”