Sub-surface microstructure of single and polycrystalline tungsten after high flux plasma exposure studied by TEM

Dubinko, A.; Terentyev, D.; Bakaeva, A.; Hernández‐Mayoral, M.; Temmerman, G. De; Buzi, L.; Noterdaeme, Jean-Marie; Unterberg, B.

doi:10.1016/j.apsusc.2016.09.071

Cited by 20 publications

(14 citation statements)

References 27 publications

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“…Based on the plastic deformation mechanism of W, a pronounced dependence of the blistering behavior on the crystal orientation has been widely acknowledged and used to explain the step-like structures of blisters observed [3]. Moreover, a few nanometer-scale experiments also revealed the plastic deformation during the blister formation [15][16][17]. According to TEM observations of W samples polished from one side, Dubinko et al [15,16] suggested that plasma irradiation would strongly increase the dislocation density.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, a few nanometer-scale experiments also revealed the plastic deformation during the blister formation [15][16][17]. According to TEM observations of W samples polished from one side, Dubinko et al [15,16] suggested that plasma irradiation would strongly increase the dislocation density.…”

Section: Introductionmentioning

confidence: 99%

“…They claimed that high-heat flux plasma causes a strong temperature gradient and stress distribution across the surface, and that the severe plastic deformation leading to the dislocation microstructure is a co-product of thermal stress and intensive plasma particle uptake mainly at the beginning of the exposure. They also observed individual 'coffee-bean' dislocation loop, and attributed it to the loop punching mechanism operating while the bubbles and cavities grow during continuous plasma exposure [16]. Unfortunately, a direct link between the dislocation microstructure and the cavity structure is still missing due to the limitations of the TEM sample fabrication method used.…”

Section: Introductionmentioning

confidence: 99%

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Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

et al. 2020

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Due to a lack of direct experimental results, the detailed mechanisms that govern the blistering behavior of tungsten (W) exposed to ITER-relevant condition in nuclear fusion remain unclear. The growth mechanism of hydrogen (H) blisters is one example. In this work, recrystallized W was exposed to H plasma at 50 eV, , and 573 K. Transmission electron microscopy (TEM) samples were prepared using plasma-focused ion beam (FIB) followed by flash-polishing to effectively remove surface damages induced by FIB. The TEM images revealed that the general blisters observed on the exposed surface are associated with underlying cavities. A considerable amount of dislocations were found in the vicinity of the cavities. Prismatic dislocation loop arrays were observed, including small size 'coffee-bean' prismatic loops and large size prismatic loops. Near the tip of surfaces cavities, evidences for the emission of shear loops were also found. Based on the experimental findings, a multi-stage growth mechanism of H cavities was proposed.The loop-punching mechanism is operative for both very small cavities and cavities with sizes larger than several hundreds of nanometers. Whereas at intermediate sizes, cavities grow by emitting shear loops from the cavity tip.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

et al. 2020

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“…For the transversal cross-section of the wires samples with 5 mm length were prepared according to the standard metallographic procedures of cutting, grinding and polishing, as was earlier developed for other tungsten samples (see e.g. [17][18][19]). The samples were cut 15 to 25 mm away from the neck of the tested wire, and the analysis was performed in the center of the transversal cross-section.…”

Section: Sample Preparation Using Conventional Polishingmentioning

confidence: 99%

Correlation of microstructural and mechanical properties of K-doped tungsten fibers used as reinforcement of tungsten matrix for high temperature applications

Terentyev

Renterghem

Tanure

et al. 2019

International Journal of Refractory Metals and Hard Materials

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Reinforcement of tungsten by tungsten fibers (Wf) is considered an attractive option to mitigate the intrinsic brittleness of this material and to possibly extend the operational temperature window to ensure safe operation of the plasma facing component. By now, it has been demonstrated that tungsten fiber-reinforced tungsten composites (Wf/W)acquire pseudo ductility even at room temperature, and crack propagation is determined by the interaction of the fibers with the propagating crack. In view of strong temperature oscillations, expected during operation in the fusion plasma, the mechanical properties of tungsten fibers annealed at different temperatures (up to 2300°C) were assessed, and the role of potassium (K) doping on the modification of the mechanical properties of asannealed wires was studied. While K-doping was found to delay the brittleness induced by heat exposure at least up to 1600°C, still a strong reduction of the fiber strength was observed in tests performed at elevated temperatures. In this work, we investigate the reasons for this effect by performing scanning electron microscopy coupled with electron backscatter diffraction measurements. The longitudinal and transversal cross-sections of W fibers were analyzed to deduce the morphology and size distribution of the grains. Consistent with the mechanical data, we found that annealing at 2100°C resulted in the full recrystallization of the elongated grains, otherwise formed due to the extrusion fabrication process. Even at 1900°C, the longitudinal cross-section still exhibits elongated grains. The transversal shape of the grains undergoes a change from needle-like fine structure to equiaxed grain shape upon annealing above 1600°C. Few scans done for 2300°C annealed wire revealed that the microstructure contains one or several grains with a dimension of 70-150 µm. The obtained results are discussed and analyzed in the frame of mechanistic model connecting microstructure with the mechanical response.

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“…Recently, it has been demonstrated that initial microstructure (in terms of dislocation density and grain size) does play an important role with respect to uptake and release of plasma components as well as the modification of local mechanical properties of the surface (see e.g. [6][7][8][9][10][11]). Moreover, the reduction of the grain size should enhance the sink efficiency for neutron-induced irradiated defects, thereby potentially raising a positive effect with respect to accumulation of the irradiation-originated microstructure [12].…”

Section: -Introductionmentioning

confidence: 99%

Nano-hardness, EBSD analysis and mechanical behavior of ultra-fine grain tungsten for fusion applications as plasma facing material

Tanure

Bakaeva

Lapeire

et al. 2018

Surface and Coatings Technology

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Tungsten and its alloys have been extensively studied in order to be used in plasma facing components for future fusion nuclear reactors such as ITER and DEMO. In this work, an evaluation of nano-hardness, microstructure/texture and mechanical behavior using nanoindentation, electron backscatter diffraction (EBSD) and tensile test was performed. The investigated materials were ultra-fine grain lab-scale tungsten and ITER-specification commercial tungsten products, taken as reference in the as-received and annealed (at 1300°C for 1 hour) conditions. Three ultra-fine grain (UFG) tungsten grades were produced under different spark plasma sintering conditions, namely at 2000°C and 70MPa, at 1700°C and 80MPa and, finally, at 1800°C and 80MPa. EBSD analysis provides very relevant data as it is known that the crystallographic orientation affects some features of the surface damage caused by fusion-relevant plasma exposure. The present results will serve as a reference for future studies that will be carried out using plasma-exposed samples in order to correlate the observed damage with the microstructural characteristics and mechanical behavior.

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Sub-surface microstructure of single and polycrystalline tungsten after high flux plasma exposure studied by TEM

Cited by 20 publications

References 27 publications

Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

Growth mechanism of subsurface hydrogen cavities in tungsten exposed to low-energy high-flux hydrogen plasma

Correlation of microstructural and mechanical properties of K-doped tungsten fibers used as reinforcement of tungsten matrix for high temperature applications

Nano-hardness, EBSD analysis and mechanical behavior of ultra-fine grain tungsten for fusion applications as plasma facing material

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