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.

This study investigates the potential of cold-sprayed tungsten coatings for use in nuclear fusion reactors. Three commercially available tungsten powders were selected from which six series of feedstock were prepared. The feedstocks were deposited on aluminum, steel, and stainless steel substrates using high-pressure nitrogen cold spraying. The coatings produced were characterized based on SEM, EDX, and XRD analysis and were found to be free of oxides with levels of tungsten that were previously unachieved. The results indicate that cold spraying is a viable technology for applying tungsten-base coatings to critical components in nuclear fusion equipment.

A new plasma chemical process has been found that produces tungsten thin films. Using fine powders or precursors as feedstocks, the process vaporizes the feedstocks and then deposits nanometer size grains. The deposition kinetics of structures produced with this technique vary greatly from classical plasma spraying methods. Equiaxed and columnar grains (30-150 nm) are formed instead of splat structures, although the grains may continue to grow after spraying.

The goal of this study is to find applicable spray conditions for producing tungsten (W), zirconium carbide (ZrC), and W-ZrC cermet layers. In the experiments, W and ZrC powder mixtures were fed into the plasma of a water-stabilized plasma gun and coatings approximately 1 mm thick were sprayed on graphite substrates. Pure W and pure ZrC were deposited under similar conditions. Microhardness, surface roughness, XRD, XRF, dilatometry, and spectroscopic techniques were used to characterize the coatings. The resulting coatings were found to be hard with a high elastic modulus.

Thick pure tungsten coatings were deposited on molybdenum and copper substrate by vacuum plasma spray for different purpose. The microstructures of tungsten coatings were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effect of preheating temperature of the substrate and introduction of gradient bond layer on the adhesive strength of the coating was investigated. High heat load was tested by high power electron beam bombardment only for tungsten coating on copper. All the results show that the properties of tungsten coating were strongly influenced by different processes, and the density of the coatings is close to 95% of theory density.

Vacuum plasma sprayed (VPS) tungsten (W) coatings hold great promise for plasma facing components in future fusion devices. However, the large coefficient of thermal expansion (CTE) mismatch between W and underlying structural steels poses a significant problem for manufacturing and service life because of the evolution of large thermally induced stresses leading to failure. In this paper both the concept of functionally graded material (FGM) W/steel interlayers and the use of steel substrate surfaces with regular surface sculptures of millimetre scale created by e-beam surface manipulation, termed surfi-sculpt and developed by TWI of the UK are investigated. The objective of these approaches is to enhance coating adhesion and to engineer macroscopic variations in the effective CTE through the thickness of the subsequently VPS deposited W coating. The effects of surface geometry on coating adhesion and microstructure have been investigated, and preliminary conclusions on the key surface sculpture geometrical features required for high adhesion dense W coatings have been identified.

Tungsten particles were sprayed by a novel plasma torch with hybrid water-gas stabilization (WSP®-H). Several spraying parameters were varied – arc current, argon flow rate, carrier gas flow rate and spraying distance. The temperature and velocity of the individual particles were monitored by the DPV 2000 optical sensor. Individual splats were collected on polished stainless steel substrates and analyzed by SEM to assess their melting, flattening and/or fragmentation. These features were correlated with the basic in-flight particle characteristics and conditions for production of dense coatings were sought for. Significant dependence of the splats morphology on spraying parameters was found, and important improvement of particle melting at WSP-H over conventional water stabilized plasma torch (WSP) was registered.

Plasma sprayed tungsten and tungsten-copper coatings are being developed for potential application as plasma facing materials for fusion reactors. Initial spray tests indicated difficulties in tungsten melting and in-flight oxidation. Numerical modeling was performed to help explain these issues. A complex study of the process and its products was performed, including: in-flight diagnostics, characterization of isolated splats, and structure, composition, thermal and mechanical properties of the coatings. Based on these results, the process was optimized, with respect to powder size and various spraying parameters, to improve melting of the particles, reduce oxidation and increase the deposition efficiency.

This paper examines the effect of spraying conditions and WC grain size on the wear behavior of WC-Co coatings. Two powders, one with a fine grain fraction and one with a more conventional grain fraction, were applied using liquid and gas HVOF systems. All coatings were subjected to sliding wear tests against an aluminum oxide ball. A sintered WC-Co composite was also tested for comparison. The sintered composite structure (cermet) exhibited the highest wear resistance, while the conventional powder sprayed by means of a gas-operated burner produced the best coating. Paper includes a German-language abstract.

For the coating of divertor wings, which in an adapted form may also be suitable for divertor targets, tungsten coatings were developed and optimized with respect to erosion and adhesion behaviour and tested in the Jülich JUDITH facility as well as in the St. Petersburg TSEFEY facility. For the improvement of adhesion, interlayers were developed and used for the coating of mock-ups. In order to achieve a further improvement in adhesion and thus better heat removal, structures were developed for the substrate surfaces. Substrate materials are copper according to DIN 1787 and the Elmedur X copper-chromium-zircon alloy. Differently produced tungsten coatings on mock-up substrates were loaded until failure by means of an electron beam. The area-related thermal loads introduced until failure were measured and correlated with the production parameters.

Self-fluxing nickel based materials are widely used as hard coating materials. HVOF process is promising to produce dense coating with high adhesion. In present study the effects of HVOF spray conditions, and WC-Co addition into self-fluxing nickel based material (NiCrBSi) and the introduction of HVOF WC-Co bond coat on the adhesion of HVOF NiCrBSi coatings are investigated. With regarding to NiCrBSi material, the spray conditions are optimized by orthogonal regression experimental design method with adhesive strength. The adhesive strength is estimated by tensile test. The results show that the adhesive strength of the NiCrBSi coating sprayed at the optimized conditions reaches to about 40MPa. It is found that the addition of WC-Co material through mechanical blending can improve the adhesion of HVOF NiCrBSi coating. The adhesive strength is increased with the increase in WC-Co content in the composite powder. The introduction of HVOF WC-Co bond coat between NiCrBSi coating and substrate can improve the adhesive strength. The multiply enhancing effect on the adhesive strength of HVOF nickel based coating is recognized by applying HVOF WC-Co bond coat to NiCrBSi-WC-Co composite coating.

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.

The aim of this study is to produce free-standing functionally-graded structures in which density varies continuously from 2.2 to 17.3 g/cm3 through a total thickness of 4.5 mm. In order to optimize material performance, it is necessary to account for the different combinations or ratios of materials (i.e., tungsten and aluminum) in the plasma jet when determining mixture laws. A relationship based on the deposition efficiency, powder feed rate, and density of individually sprayed materials has been established and was used to predict the density, thickness, and deposition efficiency of the combined materials. The mixture laws were found to be in good agreement with experimental results, making it possible to build up coatings with a parabolic density profile and uniform layer thickness.

High-Z materials such as tungsten are currently considered more suitable for the inner coatings of fusion devices than low-Z materials. The VPS parameters are being optimized for different tungsten powders with respect to uniform pore distribution and distribution of unmelted particles in the coating. High process reliability is aimed at in coating production. Copper is used as the substrate material. The spray efficiencies, coating porosities and unmelted particles in the coatings are being examined and the microstructures evaluated. Spraying parameters are determined for two different powder fractions leading to relative densities ≥ 90 % of the theoretical density.