Early stage damage of ultrafine-grained tungsten materials exposed to low energy helium ion irradiation

El-Atwani, Osman; Gonderman, S.; Suslov, Sergey; Efe, Mert; Temmerman, G. De; Morgan, T.W.; Bystrov, K.; Hattar, Khalid Mikhiel; Allain, Jean Paul

doi:10.1016/j.fusengdes.2015.02.001

Cited by 37 publications

(19 citation statements)

References 34 publications

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“…In another account [25], a He ion fluence of ∼ 10 24 m -2 on tungsten is shown to lead to a He uptake of ∼ 5 × 10 20 m -2 in the near surface, and according to [26], this level of trapped He in the tungsten surface gives rise to the onset of a dense nanobubble field under examination by TEM. At lower retained He fluence the authors of [26,27] note only platelet formation and dislocation loops; the precursor stages of bubble growth. The low fluence behavior of the fuzz layer thickness data in figure 2, is thus remarkably similar to that associated with the production of a near surface He bubble field found in earlier accounts.…”

Section: Analysis and Discussionmentioning

confidence: 99%

Tungsten ‘fuzz’ growth re-examined: the dependence on ion fluence in non-erosive and erosive helium plasma

Petty¹,

Baldwin²,

Hasan³

et al. 2015

Nucl. Fusion

145

115

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The thickness x, of tungsten fuzz layers are measured for non-varying helium (He) plasma exposure conditions spanning four orders of ion fluence Φ 10 24 − 10 28 m-2 and flux Γ 10 19 − 10 23 m-2 s-1 , at 1000−1140 K under low energy He ion impact (50 − 80) eV. The data obtained are complemented by previously published data of similar growth conditions, and collectively analysed. The new analysis allows for the reconciliation of fast high flux growth with commonly observed slower growth at lower flux. It is demonstrated that the standing t 1/2 time dependence is a special case of a more general expression for determining the layer thickness, x(Φ) = (C(Φ − Φ 0)) 1 2 , that depends on Φ, an incubation fluence Φ 0 , and the growth constant C = 2.36 +1.54 −0.56 × 10-38 m 4 , which is temperature dependent. The incubation fluence, which must be exceeded before the observation on the onset of fuzz surface morphology is determined to be Φ 0 = 2.5 +1.5 −1.0 × 10 24 m −2. In fuzz growth-erosion regimes, characterized by an erosion constant fuzz , that is proportional to the sputter yield, an analytic solution for x(Φ) has been found, by solving the growth-erosion equilibria problem of prior work with the Lambert W function. Simple limit expressions follow from the solution for determining the equilibrium fluence and fuzz thickness; the predictions of such being in good agreement with previous fuzz growth-erosion equilibria results in the literature. * Values of P disch. pertain to maximum Γ. Values of Te and ne are conditions at mid-range Γ. † Calculated from ∼27 h (10 5 s) of exposure time.

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Section: Analysis and Discussionmentioning

confidence: 99%

Tungsten ‘fuzz’ growth re-examined: the dependence on ion fluence in non-erosive and erosive helium plasma

Petty¹,

Baldwin²,

Hasan³

et al. 2015

Nucl. Fusion

145

115

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“…Detrimental changes in the mechanical properties such as swelling, hardening and embrittlement 16 can ultimately result in failure 17 . In addition to the microstructural changes caused by freely migrating defects, any energetic particle introduced to the sample (helium for example) can also coalesce and combine with vacancies and voids to form bubbles, which have been shown to exacerbate the unfavorable effects on the irradiated materials 13 , 18 – 20 .…”

Section: Introductionmentioning

confidence: 99%

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

El-Atwani

Nathaniel

Leff

et al. 2017

Sci Rep

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Crystal defects generated during irradiation can result in severe changes in morphology and an overall degradation of mechanical properties in a given material. Nanomaterials have been proposed as radiation damage tolerant materials, due to the hypothesis that defect density decreases with grain size refinement due to the increase in grain boundary surface area. The lower defect density should arise from grain boundary-point defect absorption and enhancement of interstitial-vacancy annihilation. In this study, low energy helium ion irradiation on free-standing iron thin films were performed at 573 K. Interstitial loops of a 0/2 [111] Burgers vector were directly observed as a result of the displacement damage. Loop density trends with grain size demonstrated an increase in the nanocrystalline (<100 nm) regime, but scattered behavior in the transition from the nanocrystalline to the ultra-fine regime (100–500 nm). To examine the validity of such trends, loop density and area for different grains at various irradiation doses were compared and revealed efficient defect absorption in the nanocrystalline grain size regime, but loop coalescence in the ultra-fine grain size regime. A relationship between the denuded zone formation, a measure of grain boundary absorption efficiency, grain size, grain boundary type and misorientation angle is determined.

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“…However, experiments have indicated that line dislocations will collect helium preferentially [7,8], but comparisons of dislocation effects under low-energy helium across different tungsten microstructures are lacking. Grain boundaries also sequester plasma-introduced helium differently than the matrix.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental studies (e.g., Refs. [3,7,8,19,20], amongst many others) have well-explored individual aspects of surface morphology changes.…”

Section: Introductionmentioning

confidence: 99%

Effect of starting microstructure on helium plasma-materials interaction in tungsten

et al. 2017

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In a magnetic fusion energy (MFE) device, the plasma-facing materials (PFMs) will be subjected to tremendous fluxes of ions, heat, and neutrons. The response of PFMs to the fusion environment is still not well defined. Tungsten metal is the present candidate of choice for PFM applications such as the divertor in ITER. However, tungsten's microstructure will evolve in service, possibly to include recrystallization. How tungsten's response to plasma exposure evolves with changes in microstructure is presently unknown. In this work, we have exposed hot-worked and recrystallized tungsten to an 80 eV helium ion beam at a temperature of 900°C to fluences of 210 23 or 2010 23 He/m 2. This resulted in a faceted surface structure at the lower fluence or short but well-developed nanofuzz structure at the higher fluence. There was little difference in the hotrolled or recrystallized material's near-surface (50nm) bubbles at either fluence. At higher fluence and deeper depth, the bubble populations of the hot-rolled and recrystallized were different, the recrystallized being larger and deeper. This may explain previous high-fluence results showing pronounced differences in recrystallized material. The deeper penetration in recrystallized material also implies that grain boundaries are traps, rather than high-diffusivity paths.

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Early stage damage of ultrafine-grained tungsten materials exposed to low energy helium ion irradiation

Cited by 37 publications

References 34 publications

Tungsten ‘fuzz’ growth re-examined: the dependence on ion fluence in non-erosive and erosive helium plasma

Tungsten ‘fuzz’ growth re-examined: the dependence on ion fluence in non-erosive and erosive helium plasma

Direct Observation of Sink-Dependent Defect Evolution in Nanocrystalline Iron under Irradiation

Effect of starting microstructure on helium plasma-materials interaction in tungsten

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