Lead, lead-bismuth, or lead-lithium are candidate materials for liquid metal-based cooling media in the new generation of nuclear fission reactors and fusion systems. There are many benefits of using this concept; however, a new problem arises too: preventing degradation of structural materials that are supposed to come into a direct contact. Therefore, new steel grades are being designed, and technological workarounds are searched for. One of the pathways could be a deposition of thick, long-term stability protective coatings onto the steel surfaces. In our opening study, we have employed CS and RF-ICP technologies to deposit Mo and Fe coatings onto ferritic-type 9% Cr Eurofer steel and its ODS variant, and tested them in the PbLi environment at 600 °C for up to 1000 hours. The results suggest that the Fe coatings showed a promising resistance to the corrosive medium and are worth studying deeper.

In nuclear fusion reactors, the first wall is the name given to the surface which is in direct contact with the plasma. A part of it is the divertor which is a device that removes fusion products from the plasma and impurities that have entered into it from the vessel lining. It is covered with water cooled tiles which have to withstand high temperatures and high heat fluxes. Moreover, resistance to neutron bombardment, low tritium absorption and low hydrogen permeation are additional demands. One materials concept under research is the application of a Reduced Activation Ferritic Martensitic Steel (RAFM) as a structural material with a tungsten protective coating. Since there is a considerable thermal mismatch between, a functional graded materials (FGM) concept was proposed. As the formation of undesired intermetallic Fe-W phases as well as oxidation should be avoided, cold gas spraying was chosen as manufacturing process. Two powder blends of EUROFER97 RAFM steel and a fine tungsten powder cut on the one hand and a coarser one on the other hand were tested in different ratios. The coatings were characterized with respect to their porosity and surface structure. Furthermore, the deposition efficiencies for steel and tungsten were determined each. It turned out, that the deposition process is a complex mixed situation of bonding and erosion mechanisms as the deposition windows of these very different materials obviously diverge. Thus, a lower working gas temperature and pressure was advantageous in some cases. Unexpectedly, the coarser tungsten powder in general enabled to achieve better results.

Light water reactors (LWR) use zirconium-alloy fuel claddings, the tubes that hold the uranium-dioxide fuel pellets. Zr-alloys have very good neutron transparency, but during a loss of coolant accident or beyond design basis accident (BDBA) they can undergo excessive oxidation in reaction with the surrounding steam environment. Relatively thin oxidation-resistant coatings on Zr-alloy fuel cladding tubes can potentially buy coping time in these off-normal scenarios. In this study, cold spraying, solid-state powder-based materials deposition technology has been developed for deposition of oxidation-resistant Cr coatings on Zr-alloy cladding tubes, and the ensuing microstructure and properties of the coatings have been investigated. The coatings when deposited under optimum conditions have very good hydrothermal corrosion resistance as well as oxidation resistance in air and steam environments at temperatures in excess of 1100 °C, while maintaining excellent adhesion to the substrate. These and other results of this study, including mechanical property evaluations, will be presented.

This paper describes the development of cold-sprayed chromium coatings that are used to increase the corrosion and wear resistance of zirconium-based nuclear fuel cladding tubes. Significant effort was necessary to deposit very thin layers of chromium on 4 m long, 10 mm diameter tubes by cold spraying. As explained in the paper, a final polishing step is used to reduce surface roughness and adjust coating thickness to the desired specifications.

Tungsten and its alloys are promising candidates for protecting plasma-facing components in fusion reactors such as tokamaks. However, processing is complicated by tungsten’s brittleness, CTE mismatch with copper and steel, susceptibility to grain growth and oxidation above 500 °C, and poor weldability. Given these factors, attention is shifting from conventional methods to powder and additive techniques. In this work, two technologies are employed for consolidation of W and WCr layers: cold kinetic spraying and inductively-coupled plasma spraying. Both methods overcome production challenges by depositing plasma-facing layers directly on structural parts, without the need for joining and the risk of oxidation. The properties of W and WCr coatings obtained by both methods are assessed by means of SEM, XRD, and mechanical and thermal analysis.

Zirconium (Zr) metal is of interest for chemical corrosion protection and nuclear reactor core applications. Inert chamber plasma spraying has been used to produce thin Zr coatings on stainless steel (SS) substrates. The coatings were deposited while using transferred arc (TA) cleaning/heating at 5 different current levels. In order to better understand thermal diffusion governed processes, the coating porosity, grain size and interdiffusion with the substrate were measured as a function of TA current. Low porosity (3.5% to < 0.5%), recrystallization with fine equiaxed grain size (3-8 µm diameter) and varying elemental diffusion distance (0-50 µm) from the coating substrate interface were observed. In addition, the coatings were low in oxygen content compared to the wrought SS substrates. The Zr coatings sprayed under these conditions look promising for highly demanding applications.

Thermonuclear fusion is a promising source of clean energy for the future. Max-Planck-Institute für Plasmaphysik (IPP, Greifswald, Germany) is currently working on the new type of fusion reactor, the stellarator Wendelstein 7-X. The extreme operating conditions of fusion reactor devices have lead to an increasing interest in the field of high performance materials. The present work describes the development of coating systems acting as efficient absorbers for 140 GHz radiation, which is the microwave frequency to which the analyzed components of Wendelstein 7-X are subjected. Several types of oxide ceramic coatings were applied by Atmospheric Plasma Spraying. Different powders were used as feedstock material for the coating operation. The influence of the process parameters on the coating properties and microwave absorbing capability was analyzed. The coatings microstructure and mechanical properties were characterized in terms of porosity, microhardness, roughness, adhesion and residual stresses. XRD and SEM were carried out. It was found that thickness and microstructure of the coatings have a significant influence on microwave absorption behavior. For Al 2 O 3 /TiO 2 coatings, absorption values over 90% were obtained. After optimization of the coating structure, the coating process was adapted to several real reactor components that will work in Wendelstein 7-X.

Zirconium metal coatings applied by plasma spraying and electrospark deposition (ESD) have been investigated for use as diffusion barrier coatings on low enrichment uranium fuel for research nuclear reactors. The coatings have been applied to both stainless steel as a surrogate and to simulated nuclear fuel uranium-molybdenum alloy substrates. Deposition parameter development accompanied by coating characterization has been performed. The structure of the plasma sprayed coating was shown to vary with transferred arc current during deposition. The structure of ESD coatings was shown to vary with the capacitance of the deposition equipment.

An investigation was conducted to assess the potential of water-stabilized plasma (WSP) spraying for applying protective boron carbide coatings to fusion reactor components. This paper describes how test samples were produced and how coating quality was determined. The authors sprayed boron carbide powder onto steel and stainless steel substrates using different powder feeding and spraying distances, substrate preheat temperatures, and carrier gases. They also investigated methods for optimizing the plasma jet and improving coating adhesion. The boron carbide coatings were characterized based on phase composition, porosity, oxygen content, and flexural strength. Paper includes a German-language abstract.

Ultrafine MoSi 2 powders have been synthesized from commercial MoSi 2 powders by using an Ar-H 2 induction plasma. Reactor pressure and plate power were taken as the experimental parameters to optimize the phase as well as the size distribution of ultrafine MoSi 2 powders. The powders were collected from porous metal fibers. They were composed of both metastable hexagonal structure (β-MoSi 2 ) and stable tetragonal structure (α-MoSi 2 ) with small levels of Mo 5 Si 3 and free silicon.

Tungsten coatings on copper substrates were produced and subjected to thermal shock loads in an electron beam device. The aim was to minimize the erosion rates thus caused. They are basically dependent on the level and type of porosity. Moreover, material erosion can also be directly influenced by the spraying parameters in coatings with the same relative density. In this connection, the chamber pressure, powder size and spraying distance play a decisive role.

The development of nuclear fusion reactors is presently considered to be the only possible answer to the world's increasing demand for energy, while respecting the environment. Nuclear fusion devices may be broadly divided into two main groups with distinctively different characteristics: magnetic confinement fusion (MCF) and inertial confinement fusion (ICF) reactors. Although the two nuclear fusion technologies show similarities in energy levels (as high as 3 J/cm2) and type of environment (high temperature plasmas) to be contained, the materials of choice for the protective shields (first wall in the ICF and deflectors in the MCF) differ significantly. In ICF reactors, multiple laser beams are used to ignite the fuel in single pulses. This process exposes the first wall to microshrapnel, unconverted light, x-rays, and neutrons. B4C is a low Z material that offers high depth x-ray absorption to minimize surface heating, is not activated by neutrons (will not become radioactive), and offers high hardness and vapour temperature. The long term operation envisioned within MCF reactors, where a continuous nuclear fusion of the fuel is sustained within the confinement of a magnetic field, favours the use of high Z materials, such as W, to protect the plasma exposed deflectors. The reason is a lower erosion rate and a shorter ionization distance in the plasma, which favours the redeposition of the sputtered atoms, both resulting in a lower contamination of the plasma. The production of the first wall and the deflector shields using solid B4C and W materials respectively, is obviously unthinkable. However, ProTeC has developed high density coatings for both ICF and MCF nuclear fusion reactors. W coatings with less than 2% porosity have been produced for both, the Tokamac MCF reactor and its Toroid Fueler. The toroid fueler is a plasma generating device designed to accelerate particles and inject them into the centre of the operating fusion reactor in order to refuel. For the application in an ICF reactor, B4C coatings exhibiting porosity levels below 3% with a hardness above 2500 HV have been deposited directly onto Al substrate. Properties such as outgassing, resistance to erosion and shrapnel, and the influence of x-rays have been studied and showed exceptional results.