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.

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.

Amorphous alloys have attracted extensive attention due to their unique atomic arrangement and excellent properties. However, the application in practical engineering is seriously limited due to the size, crystallization and other problems. Laser additive manufacturing technology has the characteristics of high heating, cooling rate and point by point melting deposition, which provides a new idea for the preparation of amorphous alloys. Zr 50 Ti 5 Cu 27 Ni 10 Al 8 amorphous alloy was prepared on the surface of pure zirconium substrate by selective laser melting technology. The composition and structure of the samples were characterized. The results show that the samples are mainly composed of amorphous phase, and the crystallization mainly occurs in the superimposed zone of heat affected zone. With the decrease of laser power, the area of crystallization zone and the number of crystallization particles decrease. However, if the laser power is too low, there will be non-fusion defects and cracks, which will seriously affect the forming quality and amorphous rate of amorphous alloy.

The quality and durability of coatings produced by virtually all thermal spray techniques could be improved by increasing the velocity with which coating particles impact the substrate. Additionally, better control of the chemical and thermal environment seen by the particles during flight is crucial to the quality of the coating. A high velocity thermal spray device is under development through a BMDO SBIR project which provides significantly higher impact velocity for accelerated particles than is currently available with existing thermal spray devices. This device utilizes a pulsed plasma as the accelerative medium for powders introduced into the barrel. Recent experiments using a Control-Vision diagnostic system showed that the device can accelerate stainless steel and WC-Co powders to velocities ranging from 1500 to 2200 m/s. These high velocities are accomplished without the use of combustible gases, and without the need of a vacuum chamber, while maintaining an inert atmosphere for the particles during acceleration. The high velocities corresponded well to modeling predictions, and these same models suggest that velocities as high as 3000 m/s or higher are possible.

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.

This paper describes a coating process, called internal centrifugal projection coating, in which rotating additive materials and substrate surfaces are melted by an electron beam to facilitate adhesion. It explains that the process was developed mainly to apply coatings inside engine bores and examines the microstructure of a molybdenum coating centrifugally projected onto an aluminum substrate. Paper includes a German-language abstract.

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.

Supersonically Induced Mechanical Alloy Technology (SIMAT™) also known as gas-dynamic spraying is under development for corrosion protection and material repair for aluminum airframe structures. This technology enables material powder consolidation that is not possible using other spray technologies. Similar to cold spray but based on compact spray head with nozzle powder feed, SIMAT™ is a low temperature process and does not create the high-temperature environment that affects both the substrate (especially thermally non-stable substrates) and the deposited coating. The emerging SIMAT™ technology, now in development, has the potential for coating, repairing, joining and rapid prototyping powder based materials. The SIMAT™ method adds new flexibility to powder material deposition producing thin to very thick deposits of various metals and metal-ceramic mixtures based on a cold spray particle kinetic approach inducing impact fusion. Solid particles in the size range of 10 to 100 microns are accelerated into a supersonic stream (ranging from 300 to 1200 m/s) using compressed air. These high velocity cold particles are projected on to a work piece. There is no heat discharge in the spray device itself, thus the powder material retains original characteristics. This spraying technique can generate a wide range of deposited layers with thickness ranging from tens of microns up to as much as centimeters. The process extends beyond the concept of “coatings” and includes the capability for in-situ material build-up and consolidation to three-dimensional structures and joining of the components. The deposition and consolidation can be performed from a range of hybrid powders consisting of metals, alloys, ceramics and glasses. Sample tests demonstrate examples of the process on typical aircraft components for new or restored corrosion protection and demonstrate damage repair for potential service life extension of the aircraft structure.

There is a continued need within the aerospace and space communities to increase the structural efficiency of launch vehicles in order to increase the payload and/or lower fuel usage. Many of these structures have critical stiffness demands because of deflection, buckling, or acoustic/vibration damping. Aluminum-beryllium (Al-Be) is a candidate material for many such structural components because it has a very high stiffness to weight ratio (second only to pure beryllium) and has superior formability and weldability as compared to beryllium. The strength to weight ratio of commercial Al-Be is superior to aluminum alloys (7050 and 6061-T6) that are currently used for aerospace and space applications. Plasma spray forming of Al-Be alloys is being investigated at Los Alamos National Laboratory for producing axial symmetric components for aerospace and space applications. Plasma spray forming of beryllium and beryllium alloys was investigated during the 1960's and 70's by Union Carbide Speedway Laboratories and the Atomic Weapons Establishment for producing axial symmetric launch vehicle components for defense related applications. Information is presented on the thermal and mechanical properties of plasma sprayed AlBeMet which is a commercial Al-Be alloy produced by Brush Wellman Inc.

In the materials world, there are two distinct usages of the term nanotechnology; Particulate Materials Nanotechnology (PMN) and Bulk Materials Nanotechnology (BMN). Both approaches have been used in attempts to produce nanoscale coatings with characteristic length scales from 10 to 100 nm. While particulate strategies are widespread, a different approach is presented which focuses on producing coatings through a solid / solid state transformation which results in the refinement of the microstructural scale (i.e. phase / grain size) down to the nanoscale regime. The essential features of BMN are the 2-d grain and phase boundary defects and achieving this nanoscale regime is key to enhancing bulk properties. This paper will attempt to clarify the terminology, definitions, and usages of the term nanoscale to clear up misconceptions and clearly show the salient features allowing for the production of nanoscale microstructures on an industrial scale. A clear demonstration of this achievement will be presented with a case study on the formation of amorphous / nanocomposite coatings while processing in air using off the shelf thermal spray technology using conventionally sized feedstock. Examples of nanostructured HVOF and wire-arc as-sprayed and heat treated coatings with average phase sizes of 50 nm and 80 nm respectively will be presented using detailed TEM micrographs.

For over 60 years, thermal spraying technology has advanced steadily in aerospace, power generation, and biomedical applications. Worldwide R&D efforts have produced new coating materials, new functionalities, and new processes with significant application potential in the near term. Likewise, more project teamwork, more market driven R&D, and end used education will carry thermal spraying into the next millennium.

This paper presents a simulation method in which robot trajectories can be optimised to produce an even coating thickness and how they can be used to predict transient coating temperatures on complex geometries. The coating thickness was simulated by the use of a commercial Offline programming (OLP) system. A robot trajectory was calculated, maintaining a constant spraying distance and normal orientation to the surface. The trajectory was optimised to give a uniform coating thickness while also handling non collision requirements. The plasma was represented as an ideal gas with temperature dependent thermodynamic and transport properties. The governing equations were solved by a developed finite difference elliptic code using a simplified turbulence model. The particles were modelled by a stochastic discrete particle model. The robot trajectory together with the heat transfer model were then used to calculate transient coating and substrate temperatures by the use of the finite element method (FEM). The model predictions were tentatively compared with experimental measurements and reasonable correlations were obtained.

Diagnostics of particles produced from Value-Arc 100 twin-wire-arc spraying system was found using DPV2000 monitoring tool. Effect of different operating parameters on the diagnostics of the particles, namely, temperature, velocity, and size distributions, were experimentally studied and discussed. It was found that the particle characteristics are not symmetric about the center line of the plume. It was also found that the divergence angle in the plane parallel to both wires is less than the divergence angle in the symmetry plane of the wires, which is observed in the actual oval-shape coating structure and is explained by the geometry of the system. Size distribution and volumetric size distribution of particles are also analyzed and compared with log-normal distribution function. It is shown that the size distribution consists of two different peaks believed to be associated with anodic and cathodic particles in the process.