Methods for improving ductility of tungsten - A review

Ren, Chai; Fang, Zhigang Zak; Koopman, M.; Butler, Brady G.; Paramore, James D.; Middlemas, Scott

doi:10.1016/j.ijrmhm.2018.04.012

Cited by 255 publications

(71 citation statements)

References 167 publications

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“…Contrary to the behavior of most deformation-processed metals, where work hardening reduces ductility, TMP can decrease tungsten's brittleness [59][60][61][62][63][64][65][66]. The proposed mechanisms of ductilisation after TMP [54,66] are: 1) reducing porosity; 2) aiding the movement of dislocations across grain boundaries by introducing small-angle boundaries; 3) increasing the number of high-mobility mixed and edge dislocations; 4) increasing the tortuosity of the crack path by introducing grain boundary texture, and 5) reducing impurity concentrations along the grain boundaries by refining the grain size. Fig.…”

Section: Ductilisation By Thermomechanical Processingmentioning

confidence: 97%

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A high temperature W2B–W composite for fusion reactor shielding

Athanasakis-Kaklamanakis

Ivanov²,

Río³

et al. 2020

Journal of Nuclear Materials

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We have developed a new material for neutron shielding applications where space is restricted. W 2 B is an excellent attenuator of neutrons and gamma-rays, due to the combined gamma attenuation of W and neutron absorption of B. However, its low fracture toughness (∼3.5 MPa) and high melting point (2670 • C) prevent the fabrication of large fully-dense monolithic parts with adequate mechanical properties. Here we meet these challenges by combining W 2 B with a minor fraction (43 vol.%) of metallic W. The material was produced by reaction sintering W and BN powders. The mechanical properties under flexural and compressive loading were determined up to 1900 • C. The presence of the ductile metallic W phase enabled a peak flexural strength of ∼950 MPa at 1100 • C, which is a factor of 2-3 higher than typical monolithic transition-metal borides. Its ductile-brittle transition temperature of ∼1000 • C is typical of W-based composites, which is surprising as the W phase was the minor constituent and did not appear to form a fully continuous network. Compression tests showed hardening below ∼1500 • C and significant elongation of the phase domains, which suggest that by forging or rolling, further improvements in ductility may be possible.

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Section: Ductilisation By Thermomechanical Processingmentioning

confidence: 97%

“…Summarised results on studies on the DBTT of thermomechanically processed tungsten and particle-dispersed tungsten composites. Adapted fromTable 2in[54].Material TMP treatment T T M P ( • C) Grain size (µm) Testing method DBTT ( • C)…”

mentioning

confidence: 99%

A high temperature W2B–W composite for fusion reactor shielding

Athanasakis-Kaklamanakis

Ivanov²,

Río³

et al. 2020

Journal of Nuclear Materials

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“…In fact, it has already been reported that elements like carbon, oxygen and nitrogen tend to increase the brittleness of the welded material mainly due to their limited solubility within tungsten [9,10]. In particular, they tend to segregate at the grain boundaries promoting the formation of brittle compounds such as carbides and oxides [31,32]. Furthermore, the relatively low plasticity and the high modulus of elasticity of tungsten lead to the development of a considerable level of residual stresses, possibly causing the evolution of cracks upon cooling [10].…”

Section: Good Weld Morphologymentioning

confidence: 99%

Effect of shielding gas composition and welding speed on autogenous welds of unalloyed tungsten plates

Marinelli

Martina

Ganguly

et al. 2019

International Journal of Refractory Metals and Hard Materials

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Tungsten usually exhibits poor weldability and marked brittleness at room temperature. This cause tungsten welds to be affected by the evolution of cracks along the weld bead, which can be eliminated by using a pre-heating step to reduce thermal straining. In this study, based on the tungsten inert gas welding process, a working envelope, focussed on varying welding speed and five different shielding gas mixtures of argon and helium, has been defined with the view of producing crack-free autogenous welds. The bead appearance and the microstructure of the different welds were correlated to the welding parameters, whose main effects have been analysed. Welding defects such as humping occurred when using gas mixtures with relatively low content of helium, and when using relatively high welding speeds. Crack-free autogenous welds have been produced without preheating when using a high content of helium and relatively low welding speeds. Thus, this study has demonstrated that a helium-rich shielding gas is required for welding thick tungsten plates. Moreover, the low thermal shock induced by the process, coupled with the purity of the tungsten plates used, strongly contributed to avoid the occurrence of any crack.

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“…Recrystallization may lead to an increase in impurity concentrations at the grain boundary surfaces, because the impurities are redistributed and because the grain boundary surface density changes for a different average grain size. It was suggested that the ductility in tungsten may be determined by the presence of edge dislocations [10], but the mechanisms that control the ductility of tungsten are not properly understood, whereby the effects of grain size and cold working were not studied separately yet.…”

Section: Introductionmentioning

confidence: 99%

Controlled irradiation hardening of tungsten by cyclic recrystallization

Mannheim¹,

Dommelen²,

Geers³

2019

Modelling Simul. Mater. Sci. Eng.

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The economical lifetime of the divertor is a key concern for realizing nuclear fusion reactors that may solve the world's energy problem. A main risk is thermo-mechanical failure of the plasma-facing tungsten monoblocks, as a consequence of irradiation hardening induced by neutron displacement cascades. Lifetime extensions that could be carried out without prolonged maintenance periods are desired. In this work, the effects of potential treatments for extending the lifetime of an operational reactor are explored. The proposed treatments make use of cyclic recrystallization processes that can occur in neutron-irradiated tungsten. Evolution of the microstructure under non-isothermal conditions is investigated, employing a multi-scale model that includes a physically-based mean-field recrystallization model and a cluster dynamics model for neutron irradiation effects. The model takes into account microstructural properties such as grain size and displacement-induced defect concentrations. The evolution of a hardness indicator under neutron irradiation was studied. The results reveal that, for the given microstructure and under the assumed model behaviour, periodical extra heating can have a significant positive influence on controlling the irradiation hardening. For example, at 800°C, if extra annealing at 1200°C was applied after every 100 hrs for the duration of 1 hr, then the hardness indicator reduces from maximum 140 to below 70. * Correspondence to J.A.W. van Dommelen. Electronic mail: j.a.w.v.dommelen@tue.nl arXiv:1901.05859v1 [cond-mat.mtrl-sci]

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Methods for improving ductility of tungsten - A review

Cited by 255 publications

References 167 publications

A high temperature W2B–W composite for fusion reactor shielding

A high temperature W2B–W composite for fusion reactor shielding

Effect of shielding gas composition and welding speed on autogenous welds of unalloyed tungsten plates

Controlled irradiation hardening of tungsten by cyclic recrystallization

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