Plasma spraying is under investigation as a method for in-situ repair of damaged beryllium and tungsten plasma facing surfaces for the International Thermonuclear Experimental Reactor (ITER), the next generation magnetic fusion energy device, and is also being considered as a potential fabrication method for beryllium and tungsten plasma-facing components for the first wall of ITER. Investigators at the Los Alamos National Laboratory's Beryllium Atomization and Thermal Spray Facility have concentrated on investigating the structure property relationship between the as-deposited microstructures of plasma sprayed beryllium coatings and the resulting thermal properties of the coatings. In this study, the effect of the initial substrate temperature on the resulting thermal diffusivity of the beryllium coatings and the thermal diffusivity at the coating/beryllium substrate interface (i.e. interface thermal resistance) was investigated. Results have shown that initial beryllium substrate temperatures greater than 600°C can improve the thermal diffusivity of the beryllium coatings and minimize any thermal resistance at the interface between the beryllium coating and beryllium substrate.

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.

Tungsten-copper composites and FGMs can find applications in various thermal management systems. One example is plasma facing components for nuclear fusion devices, where tungsten provides the heat-resistant plasma facing armor, copper provides the highly conductive heat sink, while the composite or FGM can reduce the stress concentration at the interface. In this study, W+Cu composites of various compositions were produced by water-stabilized plasma spraying. With the help of in-flight particle and plume diagnostics, the powder injection was optimized for each material, and the feed rates were adjusted to account for different deposition efficiencies. The composition, structure, thermal and mechanical properties of the coatings were characterized.

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.

Presently one of the most important tendencies is the use of tungsten (W) monoblock material for the first wall and other plasma facing components (PFCs) in tokamak. The use of low Z materials such as B 4 C for protection of PFCs is a conventional method to decrease heavy impurity influx into tokamak plasma. This study involves the fabrication and characterization of inductively coupled plasma (ICP) thermal sprayed B 4 C coating on tungsten monoblock. Thickness of the coating was about 120μm. Surface morphology of the coating is presented with scanning electron microscope and metallographic microscope analyses. X-ray diffraction analysis and X-ray photoelectron spectroscopy showed that the main phase and chemical composition of the coatings were preserved when compared with that of the initial B 4 C powder. Adhesion test result revealed that the adhesion/cohesion strength of the coating was above 13.1 MPa. This work is innovative not only for the ICP thermal sprayed method for the B 4 C coating fabrication but for the plasma sprayed B 4 C on tungsten substrate.

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.

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.

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.

Plasma Facing Materials (PFMs) suffer from very high heat load including quasi-stationary high heat load during normal operation and transient events with extremely high heat load during normal plasma operation and off-normal events. In this paper, W/Cu functional gradient coating was applied on CuCrZr substrate (250mm × 120mm × 30mm) with compositionally gradient W/Cu as bond coat (0.4-0.6 mm) and 1.5 mm thickness W coating as top coat via VPS for continuous deposition duration of 5 h. VPS-W/CuCrZr mokeup with built-in cooling channel was prepared for evaluating the transient vertical displacement and plasma disruption events applied by high energy electron beam. The formation of cracks and surface melting of VPS W/Cu mokeup were investigated under the two transient high heat loads (HHL). The coatings were able to absorb about 2 MJ/m2 in HHL without significant damage.

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.

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.

Advanced materials are the crucial factors determining the successful application of future nuclear fusion energy. Plasma facing materials (PFMs) are one of the most important armor materials in nuclear fusion experiment devices for direct facing with the extremely high thermal load, thermal shock and strong irradiation of high energy particles. W coated CuCrZr substrate has been considered as one of the candidates to the armor materials due to its high melting point, chemical stability and good thermal conductivity. However it was a challenge to obtain high strength thick W coatings because of the major difference of CTE between the W and CuCrZr substrate. In this paper, graded W/Cu layers were deposited as the bond layer via Low Pressure Plasma Spraying (LPPS) on the CuCrZr substrate. Subsequently, thick LPPS W coatings over 1.5 mm were prepared as the top layer. The adhesive and cohesive strengths for thick W coatings on CuCrZr substrates were evaluated according to the standard of ASTM C633. The results showed that the oxide formation on the W coating surface rapidly deteriorated the coating microstructure and properties.

Carbon fibre reinforced carbon (CFC) composites have been more and more used in different industrial areas as high temperature materials. Some application examples are CFC components in modern furnaces for heat-treatment and brazing. Because CFC components can react with metallic materials when they contact each other, diffusion barrier coatings are essentially important for such CFC components. The aim of the project IGF 14.880 N “Thermally sprayed diffusion barrier coatings for CFC components in high temperature applications” is to develop diffusion barrier coatings by thermal spraying technology. In the project, different coating systems have been developed and investigated regarding the coating build-up, coating microstructure, bonding, thermal shock resistance and diffusion barrier function. The research results reveal that some developed coating systems are suitable for applications in furnaces. In the present paper, some research results of this project are reported.

Plasma spray torches for spraying internal diameters have typically been limited to 40 kW in the past. A new internal plasma spray torch has been developed with an operational power limit above 90 kW. This high power torch was primarily developed to decrease the spray time required to apply coatings to large inside diameters such as land based gas turbine components. This paper explores the factors effecting the operation of this torch as well as the functional limits of its operation. The factors investigated are gas flow, gas ratios, current, voltage, water flow, and water temperature. Thermal efficiency and plasma enthalpy are presented.

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.

Molten metals are extremely corrosive against steel-made molds. In addition to alternating thermal loads and erosion by hard particles the lifetime of molds in the permanent-mold casting industry is rather short. Tungsten-based pseudoalloys are able to increase the lifetime of these molds significantly, but, by now, their use is limited to sintered inlays at the mostly stressed parts of the mold. Coating the whole mold with these materials offers an increase of the lifetime and at the same time a reduction of the amount of deployed feedstock. Within this research project it was possible to increase the lifetime of a kernel in used in casting brass by a factor of 20 by cladding it with tungsten-based pseudoalloys. The metallurgical behaviour of the tungsten-based pseudoalloys is quite complex. By modifying the coating process different shapes and amounts of tungsten precipitations in the nickel-iron-binder can be realized. The different microstructure within the coating does strongly affect the mechanical and anti-corrosion properties of the coating.

The paper will describe a collaboration of the DoD Propulsion Environmental Working Group (PEWG), Oklahoma City Air Logistics Center (OC-ALC), Pratt & Whitney and Engelhard Corporation to qualify and transition High Velocity Oxy Fuel (HVOF) thermal spray of tungsten carbide coatings to replace electrolytic chrome plating for the repair of Pratt and Whitney (PWA) engines at the OC-ALC. This depot is the primary location for engine repair for the US Air Force. The paper details the engineering effort to qualify the HVOF tungsten carbide coating on PWA TF33 engine components as an precursor to qualifying the coatings for other military PWA engines. The paper also provides details of the transition of HVOF thermal spray technology into a new state-of-the-art production facility at the OC-ALC depot. The paper highlights a notably successful industry and government partnership to rapidly transition a world-class thermal spray capability into OC-ALC. The PEWG is a special management group that works with US military propulsion managers to educate/apprises government and industry collaborations of mature advanced pollutant free technologies and then facilitate the transition to full-scale production. Pratt and Whitney is the original equipment manufacturer of the TF33 engine and supplies other gas turbine engines to the Air Force and other military services. Engelhard Corporation is a surface and science company that develops technologies to improve customers’ products and processes. A Fortune 500 company, Engelhard is a world-leading provider of technologies for environmental, process, appearance, performance application and engineering solutions. Engelhard led the technology transition effort under contract to the PEWG. [This effort, as will be described in the paper, encompasses process engineering, coating qualification, spray parameter definition, tooling concepts, accelerated mission engine test support, inspection techniques, and production bed-down at the OCALC depot.]

Typically, standard alloys do not have the wear resistance properties necessary to combat the aggressive wear and corrosive conditions prevalent throughout the oil sands mining process. For production-critical components, it is common to apply tungsten carbide-based metal matrix composite (WC-MMC) overlays to extend equipment life and prevent unplanned outages. The performance of composite overlays is very much dependent on the wear-environment. This paper will discuss how the interactions between abrasive conditions and the mechanical and structural properties of the WC-MMCs are key in determining the resultant levels of performance. Such information can lead to a better selection of materials and subsequent extended component life.

Near net shape spray forming technologies have matured into viable manufacturing techniques. Spray forming can be accomplished with many different thermal spray technologies yielding a range of materials with different properties. Monolithic materials, composite materials, and multi-layer materials have all been made. Mechanical properties comparable to cast versions of the parent material are achievable for some materials and processes. Tailored properties can also be achieved for such characteristics as high hermeticity, thermal protection, electrical isolation, wear resistance, etc. A review of materials and properties is presented.

The development of beryllium first wall components for future magnetic confinement fusion experiments such as the International Thermonuclear Experimental Reactor (ITER) is a topic of great importance as the ITER construction phase is about to begin. The beryllium components must be able to survive the harsh plasma environment for extended periods of time during operation. Furthermore, cost and detrimental health effects must be kept to a minimum during the fabrication and operation processes. The work described here details the requirements for ITER first wall components and describes experiments to produce beryllium high heat flux components by plasma spray deposition. Experimental parameters and characterization results from the components are presented. Results of initial high heat flux testing under electron beam irradiation show performance exceeding that required for ITER first wall components.