High-temperature brazing of tungsten with steel by Cu-based ribbon brazing alloys for DEMO

Self-passivating, so-called smart alloys are under development for a future fusion power plant. These alloys containing tungsten, chromium and yttrium must possess an acceptable plasma performance during a regular plasma operation of a power plant and demonstrate the suppression of non-desirable oxidation of tungsten in case of an accident. The up-scaling of the bulk smart alloys to the reactor-relevant sizes has begun and the first samples with a diameter of 50 mm and thickness of 5 mm became available. The samples feature high relative density of above 99% and good homogeneity. With production of bulk samples, the research program on joining the smart alloy to the structural material was initiated. In a present study, the novel titanium–zirconium–beryllium braze was applied successfully to join the smart alloy to the Rusfer-reduced-activation steel. The braze has survived at least a hundred of cyclic thermal excursions in the range of 300–600 °C without mechanical destruction.

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“…Ferritic grains are 10 times smaller than those observed in Ref. [54] under similar conditions and in Ref. [55] after brazing at 960 °C.…”

Section: Discussioncontrasting

confidence: 45%

Self-passivating smart tungsten alloys for DEMO: a progress in joining and upscale for a first wall mockup

et al. 2021

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“…First of all, this involves reduced activation, which narrows the amount of permitted chemical elements. A specific Periodic table of the elements [33], which is shown in Figure 4, was designed based on the data given in [34]. Chemical elements that are green-colored have a residual activity of less than 10 mSv/h at 100 years from the end of operation; yellow elements have residual activity close to 10 mSv/h; and red elements have more.…”

Section: Additional Requirementsmentioning

confidence: 99%

“…In this sense, the brazing temperature is limited, on the one hand, by tungsten's recrystallization temperature (1300 °C) [35] and, on the other hand, by the softening temperature of steel. Because the main prospective steel for DEMO applications is reduced activation ferritic martensitic steel, usually its softening temperature lies close the elements with residual activity of the elements 100 years from the end of operation: green-less than 10 mSv/h; yellow-near 10 mSv/h; red-more than 10 mSv/h [33].…”

Section: Additional Requirementsmentioning

confidence: 99%

“…Our scientific group investigated Cu-based brazing alloys that rapidly solidified into foil. Cu-28/50Ti, Cu-12/20Sn, and Cu-12/25Ge, wt.% [12,26,33,38], and a vanadium interlayer were used to overcome the mismatch in CTE between tungsten and the Rusfer steel. In all cases, Cu-50Ti brazing alloy was used to join W with V, because Cu, Sn, and Ge do not dissolve in W, while Ti has a good solubility in W. Hence, to join V to Rusfer, other brazing alloys were investigated.…”

Section: The Latest Progress Made In Tungsten/steel Brazingmentioning

confidence: 99%

“…As it was shown in [45], ductile materials like Cu and Ni reduce residual stresses more efficiently than materials with a medium CTE (V, Ta). Pure copper as a brazing alloy was first presented in [33], though copper alloys had been widely investigated before. When the 0.1-mm-thick copper was used as a brazing alloy, in brazing conditions of 1100 • C for 20 min, the shear strength was 206 MPa and 102 MPa after thermocycling between 720 • C, with water quenching.…”

Section: The Latest Progress Made In Tungsten/steel Brazingmentioning

confidence: 99%

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Overview of the Mechanical Properties of Tungsten/Steel Brazed Joints for the DEMO Fusion Reactor

Bachurina

Vorkel

Сучков

et al. 2021

Metals

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A Demonstration (DEMO) thermonuclear reactor is the next step after the International Thermonuclear Experimental Reactor (ITER). Designs for a DEMO divertor and the First Wall require the joining of tungsten to steel; this is a difficult task, however, because of the metals’ physical properties and necessary operating conditions. Brazing is a prospective technology that could be used to solve this problem. This work examines a state-of-the-art solution to the problem of joining tungsten to steel by brazing, in order to summarize best practices, identify shortcomings, and clarify mechanical property requirements. Here, we outline the ways in which brazing technology can be developed to join tungsten to steel for use in a DEMO application.

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Wettability and microstructural evolution of copper filler in W and EUROFER brazed joints

Izaguirre,

de Prado,

Sánchez

et al. 2024

Int J Adv Manuf Technol

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In terms of wettability, active systems are characterized by a reduction in interfacial energy as the time at specific conditions is increased. This article aims to investigate the evolution of wettability and microstructure, which undergoes a critical transformation at temperatures and dwell times near brazing conditions due to their significant impact on resultant mechanical properties. The objective is to enhance wettability and prevent the formation of different phases that can occur rapidly within the brazing window conditions. Up to 1105 °C, complete fusion of the filler does not occur. However, once it happens, the expansion of the copper filler in EUROFER increases up to 400%, and the contact angle reduces from 100° to 10°, indicating an active wetting behavior. On the other hand, when copper is used with tungsten, an inert behavior is observed, maintaining the contact angle around 70°. Brazed joints carried out under the most promising wetting conditions demonstrated that at 1110 °C-1 min, various phenomena began to occur. This includes solid-state diffusion of copper in the EUROFER, following the austenitic grain boundaries, and partial dissolution of Fe in the copper braze. Increasing the brazing time from 2 to 5 min achieved high interfacial adhesion properties and controlled the diffusion layer and Fe-rich band formed at the W-braze interface, resulting in the best mechanical results (295 MPa).

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High-temperature brazing of tungsten with steel by Cu-based ribbon brazing alloys for DEMO

Cited by 33 publications

References 19 publications

Self-passivating smart tungsten alloys for DEMO: a progress in joining and upscale for a first wall mockup

Self-passivating smart tungsten alloys for DEMO: a progress in joining and upscale for a first wall mockup

Overview of the Mechanical Properties of Tungsten/Steel Brazed Joints for the DEMO Fusion Reactor

Wettability and microstructural evolution of copper filler in W and EUROFER brazed joints

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