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• 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]

Hydrogen impurities in liquid lithium have a drastic disadvantageous impact on the used structural materials. Such a problem might occur also in the planned materials testing facility IFMIF-DONES, where hydrogen isotopes are produced by a reaction of a deuteron-beam with a target of liquid lithium. Therefore, the operation of such a Li-system requires the measurement of hydrogen (seen as impurity in the Li-melt) and the control of hydrogen removal. It is one of the excellences of the tool Electrochemistry to measure dissolved species over wide ranges of concentrations in real-time conditions. This presentation will present the physical background of determining non-metallic impurities in molten metals by measuring electrochemical potentials, outlining the development of such an H-sensor system and the transformation by Nernst correlation into concentration values. Additionally, liquid lithium is a very reactive melt, thus material compatibility is an essential topic for the developments of a durable sensor. Based on these issues a sensor design for measuring hydrogen in liquid lithium was realized under consideration of all physical, chemical and metallurgical aspects, including the successful manufacturing of the sensor as a first prototype and a further first production series. The outlook will also deal with the possibility of measurements of different hydrogen isotopes. [ABSTRACT FROM AUTHOR]

Different breeding blanket designs for DEMO consider Eurofer steel as a main structural material. Nevertheless, RAFM steels suffer from severe corrosion attack if exposed to flowing Pb-15.7Li at high temperatures, as it is considered in the blanket designs HCLL, WCLL and DCLL. Two electroplating processes, i.e. ECA and ECX, were developed in the past to produce protective Al-based coatings on RAFM steels which proved already corrosion protection behavior in flowing Pb-15.7Li under fusion relevant conditions. Both electrochemical processes need reliable pretreatment processes of the RAFM substrates prior to the Al-deposition, to prevent coating defects such as insufficient covering and weak adhesion. These coating failures increase the risk of defects in the corrosion barriers after the heat treatment and therefore may promote early coating breakdowns in flowing Pb-15.7Li. This study examined some influences on defect formation by electrochemical measurements and SEM/BSE examinations. Besides storage time between mechanical preparation of the samples and electrodeposition, the impact of an anodic pretreatment of Eurofer samples prior to the Al-plating by ECX process was investigated. It is shown that the covering of Eurofer samples by aluminum depend on both parameters and optimized pretreatment parameters could be derived from these findings to increase the reliability of the whole barrier fabrication process. [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]

Plasma facing components for fusion applications must have to exhibit long-term stability under extreme physical conditions, and therefore any material imperfections caused by mechanical and/or thermal stresses in the shaping processes cannot be tolerated due to a high risk of possible technical failures under fusion conditions. To avoid such defects, the method of Electrochemical Machining (ECM) enables a complete defect-free processing of removal of tungsten material during the desired shaping, also for high penetration depths. Furthermore, supported by lithographic mask pretreatment, three-dimensional distinct geometric structures can be positive-imaged via the directional galvanic dissolution applying M-ECM process into the tungsten bulk material. New required applications for tungsten components, e.g. as adhesion promotors in W-surfaces to enable sure grip and bonding of thick plasma-spraying layers for blanket components, will define the way of further miniaturization of well-established millimeter dimensioned M-ECM shaping processes to dimensions of 100 μm and furthermore down to 50 μm. Besides current M-ECM limits the article describes inevitable needs of further developments for mask resists, mask materials and the resulting ECM parameters, to reach the needed accuracy in tungsten microstructure. The achieved progress and observed correlations of processing parameters will be manifested by produced demonstrators made by the new “μM”-ECM process. [ABSTRACT FROM AUTHOR]

Low-activation-ferritic–martensitic (RAFM) steels are candidates for structural materials in different blanket designs foreseen for DEMO and partly for TBM's tested in ITER. In all designs the liquid breeder Pb–15.7Li is in direct contact with the structural material, and thus two major topics – corrosion and T-permeation – influence the reliable, safe and economical application of such combination of breeder and structural material. As bare RAFM steels exhibit high corrosion rates of up to 400 μm/h in flowing Pb–15.7Li, Al-based coatings made by different coating processes were developed during the last 15 years and showed promising results in protecting RAFM steels from corrosion and T-permeation reduction. Especially barriers made by HDA, and electroplating (ECA, ECX), proved their ability to protect Eurofer against corrosion in flowing Pb–15.7Li. However, available T-permeation data for coated RAFM steels are rare and partly ambiguous for these coatings. This paper summarizes the state-of-the-art of aluminum-based barrier development and points out gaps and needs in future scale characterization and T-permeation barrier development. Additionally, necessary qualification steps on the path toward a reliable fabrication route are presented that is required to produce aluminum-based corrosion and T-permeation barriers on RAFM steels for blanket applications in future fusion reactors like DEMO. [ABSTRACT FROM AUTHOR]

Reduced activation ferritic-martensitic steels (RAFM), e.g. Eurofer 97, are envisaged in future fusion technology as structural material, which will be in direct contact with a flowing liquid lead–lithium melt serving as breeder material. Aluminum-based barrier layers had proven their ability to protect the structural material from corrosion attack in flowing Pb–15.7Li and to reduce tritium permeation into the coolant. Coming from scales produced by hot dipping aluminization (HDA), the development of processes based on electrochemical methods to produce defined aluminum-based scales on RAFM steels gained attention in research during the last years. Two different electrochemical processes are proposed: The first one, referred to as ECA process, is based on the electrodeposition of aluminum from volatile, metal-organic electrolytes. The other process called ECX is based on ionic liquids. All three processes exhibit specific characteristics, for example in the field of processability, control of coating thicknesses (low activation criteria) and heat treatment behavior. The aim of this article is to compare these different coating processes critically, whereby the focus is on the comparison of ECA and ECX processes. New results for ECX-process will be presented and occurring development needs for the future will be discussed. [ABSTRACT FROM AUTHOR]

IFMIF-DONES, the International Fusion Materials Irradiation Facility - DEMO Oriented NEutron Source, is the planned facility in Granada/Spain for fusion materials investigations using neutron irradiation in the scale of DEMO-oriented energies. This irradiation is generated by the interaction of deuteron beams with a liquid lithium flow-target system, containing huge amounts of this very reactive alkaline-metal. An important and critical issue during the operation of IFMIF-DONES is the enrichment of dissolved impurity components in the Li-melt and in the liquid melt concerning reactivity, corrosivity and radiation hazards. In the case of hydrogen, there is the danger of H-introduced embrittlement of the loop structure components as well as effects and hazards of the radioactive tritium. The application of liquid lithium in the scope IFMIF-DONES unconditionally hence requires a suitable impurity control. Regarding this subject, an electrochemical sensor for a continuous hydrogen monitoring is being developed in the frame of an international EUROFusion-WPENS task. This sensor was designed as single-rod-measuring-cell with niobium as the relevant membrane-material and a hydrogen conducting electrolyte. Potentials (Electro-Motive Force EMF) are being measured between the Li melt and a reference electrode by voltmeters with high impedances and can easily converted into H concentrations. Long-term tests (campaign-units of several hundred hours) in stagnant Li-melts with different sharply controlled hydrogen concentrations showed, that the sensor fulfills the requirements of chemical and mechanical stability and functionality also under harsher conditions (temperatures up to 500 °C). The obtained results and operational experiences will be discussed, e.g., concerning application windows, reproducibility and calibration needs. Additionally, recommendations will be outlined for upgraded systems and future qualification needs. [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]

Abstract: Plasma facing components for fusion applications must exhibit long-term stability under extreme conditions, and therefore material imperfections cannot be tolerated due to a high risk of technical failures. To prevent or abolish defects in refractory metals components during the manufacturing process, some methods of electro-chemical machining as S-ECM and C-ECM were developed, enabling both the processing of smooth plain defect-free surfaces of different geometry and the removal of bulk material for the shaping of three-dimensional structures, also without cracks. It is discussed, that tungsten ablation with accurate electro-chemical molding is very sensitive to the kind of electric current, and therefore current investigations focused also on the effects of frequency profiles on the sharpness of edge rounding. [Copyright &y& Elsevier]

Highlights: [•] Electrochemical Al deposition is industrially relevant for barrier formation. [•] Al coatings have to be converted into protective layers by heat treatments. [•] Morphology of Al coatings made by ECX process depends on deposition parameters. [•] Heat treatment behavior depends on the morphology of the coating produced by ECX. [•] ECX is proven to produce layer sequences on Eurofer similar to HDA and ECA process. [Copyright &y& Elsevier]

• 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]