Chemically deposited tungsten fibre-reinforced tungsten – The way to a mock-up for divertor applications

Riesch, J.; Aumann, M.; Coenen, J. W.; Gietl, H.; Holzner, G.; Höschen, T.; Huber, Philipp; Li, M.; Linsmeier, Ch.; Neu, R.

doi:10.1016/j.nme.2016.03.005

Cited by 64 publications

(63 citation statements)

References 43 publications

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“…In potassium doped tungsten wire, the temperature for losing ductility is significantly increased while showing similar deformation behaviour [13]. The use of doped wire offers therefore an easy way to increase the allowed operation temperature [50].…”

Section: Consequence For Wf/wmentioning

confidence: 97%

Microstructure, mechanical behaviour and fracture of pure tungsten wire after different heat treatments

Zhao

Riesch

Höschen

et al. 2017

International Journal of Refractory Metals and Hard Materials

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Plastic deformation of tungsten wire is an effective source of toughening tungsten fibre-reinforced tungsten composites (Wf/W) and other tungsten fibre-reinforced composites. To provide a reference for optimization of those composites, unconstrained pure tungsten wire is studied after various heat treatments in terms of microstructure, mechanical behaviour and fracture mode. Recrystallization is already observed at a relatively low temperature of 1273 K due to the large driving force caused by a high dislocation density. Annealing for 30 minutes at 1900 K also leads to recrystallization, but causes a rather different microstructure. As-fabricated wire and wire recrystallized at 1273 K for 3 hours show fine grains with a high aspect ratio and a substantial plastic deformability: a clearly defined tensile strength, high plastic work, similar necking shape, and the characteristic knife-edge-necking of individual grains on the fracture surface. While the wire recrystallized at 1900 K displays large, almost equiaxed grains with low aspect ratios as well as distinct brittle properties. Therefore, it is suggested that a high aspect ratio of the grains is important for the ductile behaviour of tungsten wire and that embrittlement is caused by the loss of the preferable elongated grain structure rather than by recrystallization. In addition, a detailed evaluation of the plastic deformation behaviour during tensile test gives guidance to the design and optimization of tungsten fibre-reinforced composites.

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Section: Consequence For Wf/wmentioning

confidence: 97%

Microstructure, mechanical behaviour and fracture of pure tungsten wire after different heat treatments

Zhao

Riesch

Höschen

et al. 2017

International Journal of Refractory Metals and Hard Materials

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“…The tensile mechanical properties of pure W and K-doped wires were studied at room and elevated temperatures by groups of Riesch [18][19][20][21] and Terentyev [22][23][24][25]. The primary conclusion regarding the potassium doping that can be drawn from those studies is that it helps suppressing massive grain growth at least up to 1600°C for 30 min, remaining ductile at room temperature with ultimate tensile strength exceeding 1 GPa.…”

Section: Introductionmentioning

confidence: 99%

Micromechanical and microstructural properties of tungsten fibers in the as-produced and annealed state: Assessment of the potassium doping effect

Terentyev

Tanure

Bakaeva

et al. 2019

International Journal of Refractory Metals and Hard Materials

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Due to its high strength and low temperature ductility, tungsten fibers (W f) have been widely used as reinforcement elements in metallic, ceramic and glass matrix composites to improve the strength, toughness and creep resistance. Materials designed for future fusion reactors also utilize the option of W f reinforcement, i.a. with a copper (W f /Cu) or tungsten (W f /W) matrix. W f /W composites are being intensively studied as risk-mitigation materials to replace bulk tungsten which is susceptible to embrittlement induced by neutrons resulting from fusion reaction. Operation of W f /W in high temperatures (up to 1300°C and even higher) fusion environment implies a risk of recrystallization and grain growth, which dimishes the attractive properties of tungsten fibers. In this work, we assess this modification of micro-mechanical and microstructural properties of tungsten fibers by means of nanoindentation, scanning electron microscopy, electron back-scattering diffraction analysis and corelate it with the ultimate tensile strength and fracture modes observed in the tensile tests. Both pure W and pottasium doped wires in the as-fabricated and annealed states are investigated and the results were compared with bulk tungsten, also exposed to several annealing temperatures. The results highlight the postive impact of potassium doping which shifts the threshold temperature for the grain growth by about 600°C compared to pure tungsten wire.

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“…Tungsten fiber-reinforced composites (Wf/W) are extensively investigated as a potential material for advanced plasma facing components [11]. This composite structure is obtained by embedding commercially available drawn tungsten wires in a tungsten matrix which is produced either by powder metallurgy [12] or by a chemical deposition process [13]. The advantage of Wf/W is in its pseudo ductile behavior and thereby increased toughness as a consequence of extrinsic toughening mechanism such as crack bridging by intact fibers, fiber pull-out, crack deflection and ductile deformation of fibers [14].…”

Section: Introductionmentioning

confidence: 99%

The effect of heat treatments on pure and potassium doped drawn tungsten wires: Part I - Microstructural characterization

Nikolić

Riesch

Pippan

2018

Materials Science and Engineering: A

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Advanced tungsten fibre-reinforced composites (Wf/W), showing pseudo ductile behaviour even at room temperature, are a promising option for future fusion reactors as the intrinsic brittleness of tungsten can be mitigated effectively. The drawn tungsten wires used as reinforcements are the key component of the composites, thus their mechanical properties and thermal stability define the allowed operation / fabrication temperature of the composite material itself. In this work, a comprehensive characterization of the pure and potassium doped tungsten wires was performed, focusing on the influence of various heat treatments on different microstructural features (nature of grain boundaries, grain shape and size, texture analyses) and mechanical properties. Annealing in the temperature range from 900-1600°C enables the investigation of the microstructural stability of the two materials and arising annealing phenomenarecovery, recrystallization and grain growth. The results demonstrate that the pure tungsten recrystallizes fully in the temperature range 1300-1500°C accompanied with tremendous coarsening and a complete loss of the initial fibrous, elongated grain structure. In contrast to this, potassium doped wire shows superior high temperature properties, where performed heat treatments cause only milder microstructural changes, consequently suppressing recrystallization and grain growth to temperatures well above the investigated ones. Furthermore, hardness measurements and observed softening complement the discussion of the grain morphology evolution.

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Chemically deposited tungsten fibre-reinforced tungsten – The way to a mock-up for divertor applications

Cited by 64 publications

References 43 publications

Microstructure, mechanical behaviour and fracture of pure tungsten wire after different heat treatments

Microstructure, mechanical behaviour and fracture of pure tungsten wire after different heat treatments

Micromechanical and microstructural properties of tungsten fibers in the as-produced and annealed state: Assessment of the potassium doping effect

The effect of heat treatments on pure and potassium doped drawn tungsten wires: Part I - Microstructural characterization

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