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• Electrochemical processes successfully developed for applications in fusion technology. • Electroplating of thin functional layers as fillers for joining of divertor parts. • Corrosion barriers by electrochemical ECX process resistant to long-term exposure in flowing Pb-Li. • Defect-free structuring of hard-to-machine W-parts by ECM, for first wall applications. • Promising potential of electrochemical processes for future applications in fusion technology. Electrochemical techniques such as electroplating and electrochemical machining (ECM) are well established processes in a variety of industrial applications, such as corrosion protection coatings on steel and high electro-conductive coatings in electrical industry. The main advantages of these processes are: Good controllability of coating thicknesses, cost-effectiveness and good scalability from scientific settings to industrial scale. For applications in fusion technology, material development needs to meet unique and specific requirements, e.g. high heat-flux properties and corrosion resistance to liquid metals. Therefore, uncommon materials like tungsten, CuCrZr, RAFM-steels have to be processed for which commercially available electrochemical processes show various limitations at the moment. To overcome these limitations, selected methods were introduced in research of divertor and blanket component manufacturing leading to promising electrochemical-based processes contributing their inherent advantages to a variety of fusion applications, such as the ECX process to fabricate Al-based corrosion barriers on RAFM steels resistant to flowing Pb-15.7Li. Others are the electrodeposition of metal fillers on tungsten and CuCrZr substrates for joining applications and the machining of tungsten surfaces by ECM in first wall applications. This paper provides an overview about these processes and describes the achieved benefits of using electrochemical processing techniques for applications in fusion technology. [ABSTRACT FROM AUTHOR]

Joining of the armor material tungsten to other alloys and especially to copper components which will act as heat sinks in divertor application is rather challenging due to the missing miscibility of tungsten and copper. This metallurgical behavior avoids the direct processing of W – Cu joints with sufficient mechanical stability. Introducing adapted interlayers can overcome these limitations if they exhibit extended miscibility with both partners to be joined. Electrochemical plating was chosen as deposition technology for such reactive interlayers and demonstrators were processed with a 10 μm thick reactive Pd interlayer and joined by diffusion bonding. Their metallurgical behavior was characterized in dependence on processing temperature, reaction time and applied pressing load. The fabricated joints were mechanically qualified by shear testing. Cracking of the joints never appeared at the boundary of interlayer to W. The demonstrators revealed reasonable and applicable shear strength of around 100 MPa. The observed shear strength values and formed microstructures in the joining zone will be displayed and discussed in dependence on the applied processing parameters. The developed bonding process by applying electrochemically plated interlayers has proven to be a reliable tool with industrial application potential. [ABSTRACT FROM AUTHOR]

Fusion technology requires in the fields of first wall and divertor development reliable and adjusted joining processes of plasma facing tungsten to heat sinks or blanket structures. The components to be bonded will be fabricated from tungsten, steel or other alloys like copper. The parts have to be joined under functional and structural aspects considering the metallurgical interactions of alloys to be assembled and the filler materials. Application of conventional brazing showed lacks ranging from bad wetting of tungsten up to embrittlement of fillers and brazing zones. Thus, the deposition of reactive interlayers and filler components, e.g. Ni, Pd or Cu was initiated to overcome these metallurgical restrictions and to fabricate joints with aligned mechanical behavior. This paper presents results concerning the joining of tungsten, Eurofer and stainless steel for blanket and divertor application by applying electroplating technology. Metallurgical and mechanical characterization by shear testing were performed to analyze the joints quality and application limits in dependence on testing temperature between room temperature and 873 K and after thermal aging of up to 2000 h. The tested interlayers Ni and Pd enhanced wetting and enabled the processing of reliable joints with a shear strength of more than 200 MPa at RT. [ABSTRACT FROM AUTHOR]

Highlights: [•] Active interlayers of Ni and Pd were electroplated on W to assist joining. [•] Demonstrator types of W-steel and W–W joints were successfully fabricated. [•] Diffusion processes increase operation temperature above brazing temperature. [•] Ni electro-plating is less sensitive to variation of deposition parameters than Pd. [•] Shear tests showed values in resistance comparable to those of commercial fillers. [Copyright &y& Elsevier]

Abstract: Tungsten is considered in fusion technology as functional and structural material in the area of blanket and divertor for future application in DEMO. The KIT design of a He-cooled divertor includes joints between W and W-alloys as well as of W with Eurofer-steel. The main challenges range from expansion mismatch problem for tungsten/steel joints over metallurgical reactions with brittle phase formation to crack stopping ability and excellent surface wetting. These requirements were only met partly and insufficiently in the past e.g. by direct Cu-casting of tungsten onto steel. Both, the joining needs and the observed failure scenarios of conventionally joined components initiated the development of improved joining technologies based on electro-chemical processing routes. As electrolytes aqueous and aprotic, water free, system are integrated into this development line. In the first step principle requirements are presented to guarantee a reproducible and adherent deposition of scales based on Ni and Cu acting as inter layers and filler, respectively, to generate a real metallurgical bonding as demonstrate by 1100°C joining tests. The development field aprotic systems based on ionic liquids is discussed with respect to enable development of refractory metal based fillers with focus high temperature W–W brazing. [Copyright &y& Elsevier]

• Precipitates are formed to reduce oversaturation in the cold leg of PICOLO loop. • Precipitates were collected by the magnetic trap but not completely. • The electro-magnetic pump was plugged by precipitates and highlights the risk. • Precipitates are migrating with breeder flow and can growth up to some 100 μm. • The Fe/Cr precipitates exhibit a Cr amount of 9% similar to the Eurofer composition. Several blanket concepts (e.g., HCLL, WCLL, DCLL) are based on the application of the liquid breeder Pb-15.7Li, which is in direct contact with the structural components. Compatibility testing has shown that the structural materials (e.g., Eurofer) always suffer from corrosion attack. The governing mechanism can be attributed to dissolution of the steel by the liquid breeder. A fusion device with blanket modules or also corrosion testing loops, e.g., the PICOLO loop of KIT, are non-isothermal systems. The components dissolved at higher temperature are transported with the breeder flow. At sections with cooler temperature oversaturation of the breeder will occur. Effects such as deposition, precipitate formation and transport of corrosion products will take place. Corrosion testing in PICOLO showed that such particles are formed and that they can seriously affect safe and reliable operation of Pb-15.7Li systems up to blocking of components. Thus, during maintenance work tubing sections and components were removed for analyzing the issue of corrosion product deposition. The operation conditions of the components and the loop are given in detail to assess the deposition scenarios together with the size and shape of the formed particles to support future loop design and purification measures. [ABSTRACT FROM AUTHOR]

Protective aluminum-based coatings represent a promising anti-permeation and anti-corrosion barrier for breeding blanket systems developed for European DEMO fusion reactor. Following the prior in-depth characterizations, selected coating candidates were subjected to a combined test consisting of contact with liquid Pb-16Li, its repeated in-situ solidification and re-melting, tritium permeation during gamma and neutron irradiation in the LVR-15 fission reactor. During the sample exposure in the reactor, the temperature of Pb-16Li was between 300 and 425 °C. The irradiation damage averaged over the sample volume estimated by FISPACT code was limited to 0.037 dpa. This article presents post-irradiation characterization of cylindrical Eurofer97 samples coated by electro-chemical X-metal deposition from ionic liquid (ECX) and pulsed laser deposition (PLD) techniques. The coating damage relative to a reference uncoated sample is discussed. [ABSTRACT FROM AUTHOR]

Tritium permeation from breeder material to the Water Coolant System (WCS) in Water Cooled Lithium Lead (WCLL) Breeding Blanket (BB) is one of the technological issues to be solved in the design of the European DEMO. Since the tritium extraction from the Water Coolant System is more challenging and expensive than the extraction from the eutectic alloy PbLi, it is mandatory to use of a protective coating on the blanket wall to minimize the permeation rate. Moreover, a protective coating can prevent the corrosion of EUROFER steel by the action of PbLi. alumina-based coatings are considered as reference for barriers thanks to their good chemical compatibility with the PbLi alloy and their capability to reduce permeation. Three coating technologies were selected in the frame of the EUROfusion project: electrochemical ECX (chemical deposition) process, Pulsed Laser Deposition (PLD) and Atomic Layer Deposition (ALD) coating. The coatings were developed and optimized in order to satisfy the design requirements of good mechanical compatibility with steels, strong adhesion, corrosion compatibility in PbLi at relevant BB design conditions and a Permeation Reduction Factor at least of 200 under neutron irradiation. The present paper aims to describe the status of the technologies and the main results obtained. The final objectives of the R&D activities are to demonstrate the applicability of the coating to WCLL BB and therefore the scale-up of the technologies from laboratory scale to the BB scale. [ABSTRACT FROM AUTHOR]