Structural defect accumulation in tungsten and tungsten-5wt.% tantalum under incremental proton damage

Abstract

We have performed proton irradiation of W and W-5wt.%Ta materials at 350°C with a step-wise damage level increase up to 0.7 dpa and using two beam energies, namely 40keV and 3MeV, in order to probe the accumulation of radiation-induced lattice damage in these materials. Interstitial-type a/2 <111> dislocation loops form under irradiation, and their size increases in W-5Ta up to a loop width of 21(4) nm at 0.3 dpa, where loop saturation takes place. In contrast, the loop length in W increases progressively up to 183(50) nm at 0.7 dpa, whereas the loop width remains relatively constant at 29(7) nm and ≥0.3 dpa, giving rise to dislocation strings. The dislocation loops and networks observed in both materials at later stages act as effective hydrogen trapping sites, so as to generate hydrogen bubbles and surface blisters. Ta doping delays the evolution of radiation-induced dislocation structures in W, and consequently the appearance of hydrogen blisters.

On the use of ion beams to emulate the neutron irradiation behaviour of tungsten

“…Thus, the observation of b = <100> loops by Yi et al [44,45] in self-ion irradiated W and the lack of those loops in He, H and D ion irradiations at the same temperature [48,49,56,57] This is in contrast to the work performed using only He ion irradiation where no b = <100> type loops were observed. Under these aforementioned irradiation conditions using He [49,57], H [52] and D [56] ions only, there will be dilute cascades formed with many isolated FPs [5].…”

“…Figure 5 show a summary of the TEM damage microstructures from both ex-situ and in-situ W + ion irradiated samples and post irradiation in-situ annealed samples as a function of temperature and dose from Refs. [20,[44][45][46] and Figure 6 and Figure 7 compare the dislocation sizes and volumetric densities reported in W under neutron [32,36,41,47] and ion irradiations [20,46,48,49]. The pioneering work of Yi et al [20,44,45] examined the effects of self-ion irradiation on the damage microstructure of W using 150 keV or 2 MeV W + during in-situ and ex-situ experiments respectively, to a dose of 3 DPA at temperatures up to 800°C.…”

“…Thus, a mechanism whereby the vacancies accumulate and coalesce into extended defect clusters and dislocation loops via thermal migration can be envisaged. The response of W and W-5Ta alloys under both 3 MeV and 40 keV H ion irradiation using ex-situ and in-situ irradiations respectively, at 350°C to a dose of 0.7 DPA has been studied by Ipatova et al [48]. Dislocation loop density (~8×10 21 loops/m 3 ) and size (~6 nm) in the in-situ experiments [48] agreed well with work neutron irradiations by He et al [47] at low doses 0.1 DPA (see Figure 6 and Figure 7).…”

“…The response of W and W-5Ta alloys under both 3 MeV and 40 keV H ion irradiation using ex-situ and in-situ irradiations respectively, at 350°C to a dose of 0.7 DPA has been studied by Ipatova et al [48]. Dislocation loop density (~8×10 21 loops/m 3 ) and size (~6 nm) in the in-situ experiments [48] agreed well with work neutron irradiations by He et al [47] at low doses 0.1 DPA (see Figure 6 and Figure 7). However, loop density decreased significantly to around 2×10 21 loops/m 3 at 0.7 DPA under 40 keV H irradiation.…”

Microstructure evolution and densification during spark plasma sintering of nanocrystalline W-5wt.%Ta alloy

“…Alloying W with tantalum (Ta) brings the possible enhancement in the ductility, decreases the water oxidation, helps in mitigating surface cracking caused by the highfluence threshold for nanostructure formation on the surface of W [5,17]. In addition, Ta lowers the cluster formation under irradiation condition and hence the chances of embrittlement in W and W alloys [18].…”