Abstract In 1913, in the dawning years of the 20th century, Doctor Schoop published a process for "depositing metal under an air flow" in the Scientific American, opening new horizons to surface treatment techniques. Therefore, surface treatments were taken into account right from the design stage by engineers, and their performances became input for devising objects right from the time they were conceived. There is a constant acceleration in the means employed, ever greater system automatisation and a continuous broadening in the applications

Abstract Solid oxide fuel cells (SOFC) are expected to gain a high importance as direct converters for transforming chemical into electrical energy. They have the potential of working with considerably higher efficiency and much less environmental problems compared to systems used so far. SOFCs of present technology operate at temperatures in the range of 950 °C. Besides an increase in performance and stability, a main precondition for a technical breakthrough of SOFCs is a drastic reduction of their production costs. Approaches are the use of less-expensive materials, new SOFC designs with thinner components and the improvement of presently applied production routes, or their replacement by other techniques such as thermal spray methods. DC- and RF-VPS show very attractive properties particularly if the cell will be manufactured in one consecutive combined process. The state of SOFC spray design will be described together with results of the process adaptation and the SOFC components development.

Abstract 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.

Abstract The Laser Megajoule (LMJ) is designed to produce, in laboratory, fusion energy with a significant gain. Such an energy could be achieved by imploding a small capsule filled with a DT mixture. Fusion experiments produce a large emission of neutrons, x-rays, laser scattered light and debris which impose a first wall protection for the laser target chamber made of a low Z and refractory material. As boron carbide appeared to be a good candidate, among others, it was decided to evaluate the potentiality of plasma sprayed B4C coatings for this application. This paper deals with the optimization of plasma spraying conditions to build up coatings that satisfy specifications required for the first wall. Coating general properties are presented as well as outgassing performances. Specific x-ray and laser tests were performed to evaluate coating behavior close to real LMJ working conditions.

Abstract The unusual effects of plasma sprayed coating on the fire-side of evaporator tubes located in an oil-fired steam generating boiler are discussed. The main heat transfer surfaces are constructed by heat exchanger tubes, evaporator tubes and superheaters. Maintenance to prevent of the boiler failure or the preserve heat exchanger effectiveness is a very important factor in the operation of boiler facilities. In a boiler which employs heavy gravity oil as a fuel, plasma sprayed Ni-Cr alloy has often been applied to boiler tubes for the relief of hot corrosion by combustion gas. However, the circulation of boiler water causes an internal deposit to form on the inner wall of evaporator tubes. The internal deposit generates excess heat load against the tubes. As the overheating of the tubes often causes the evaporator tubes to fail, they are chemically cleaned periodically. In this paper, the influence of Ni-Cr plasma sprayed coating for the heat flux, which dominates the formation of the internal deposit, is investigated. Ni-Cr plasma sprayed coating is substitutionally hot corrosion resistant and is a composite coating into which the fuel ash containing a vanadium or sulfur compound are interstitially penetrated and solidified. It is derived that the existence of the coating on the fire-side of the evaporator tubes normalizes the heat load in their inner walls. Moreover, the suppression of internal deposit formation decreases the frequency of chemical cleaning for tubes. The dual effects of plasma sprayed coating for hot corrosion resistance in the fire side and the suppression of internal deposit on the water side of the tubes are reported.

Abstract 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.

Abstract In the Automotive Industry the need for lower manufacturing costs, the use of less strategic material, and easier, faster, and more flexible routes for manufacturing are being looked for continuously. The environmental concerns relating to the use of galvanic coatings is growing. This has led to the examination of the plasma-powder spray process for the application of coatings for surface modification. In the area of engine cylinder bore coatings a major advance is taking place in the use of a rotating plasma spray device. This paper covers the use of a plasma-powder spray process for the coating of aluminum-silicon cylinder block bores using a rotating plasma gun capable of producing coatings of reliable microstructure and integrity. Properties and microstructures of the applied coatings will be presented. Test results will be shown that the necessary bond strength of the coating can be achieved without the use of a bond coat. Surface preparation prior to coating and surface finishing methods after coating will also be discussed. Experience in Europe, Japan and the Unites States will be discussed which show that the plasma-powder spray process offers a performance proven and cost effective solution for the coating of cylinder bores, thus demonstrating the future application potential for this technology.

Abstract High Velocity Oxy-Fuel Thermal Spray has been used by the Navy for repairing components for several years with great success. This paper will discuss some of the applications being done, the results of these applications and where the technology will be utilized on the future. The Office of Naval Research in conjunction with Naval Research Laboratory and Naval Surface Warfare Center is investigating replacements for chrome plating. One of the technologies being looked at is HVOF Thermal Spray. This paper will discuss this program, new materials being developed and new applications being done. The superior physical characteristic of HVOF has increased the utility of this technology from mechanical components to aircraft and submarine components. Acceptance of these coatings at various levels at NAVSEA will be discussed and criteria established for these acceptances will be reviewed. The role of these coatings in ship repairs as well as the implications for new construction will be discussed. Specific examples of repairs will be shown and updated reports will be provided as to their service. Locations that have services available will be detailed and future growth of this technology within the Navy will be reviewed. A quick overview of similar emerging technologies will be provided. A highlight of the presentation will be an update of the repair done with HVOF Tungsten Carbide on the Rudder Rams on the USS Saipan.

Abstract This paper describes variations in the microstructure/composition and mechanical properties in plasma sprayed CoCrAlY coatings and a modified Rene 80 substrate of gas turbine blades operated for 21000 h under liquefied natural gas fuels. Substantial oxidation/carbonization occurred in near surface coatings of concave blades but not in convex coatings. Aluminum and nickel/titanium rich nitrides formed in concave coatings and substrates adjacent to the interface, respectively. Small punch (SP) specimens were prepared in order that the specimen surface would be located in the near surface and interface regions of the concave and convex coatings. In SP tests, brittle cracks in the near surface and interface coatings of the concave blade initiated at low strains up to 950 °C. The convex coatings had higher ductility than the concave coatings and substrate and showed a rapid increase in the ductility above 800 °C. Thus it is apparent that the oxidation/carbonization and nitridation in the concave coatings produced a significant loss of the ductility. The in-service degradation mechanism of the CoCrAlY coatings is discussed in light of the operating temperature distribution and compared to that of CoNiCrAlY coatings induced by grain boundary sulfidation/oxidation.

Abstract Due to advanced technical, economic and environmental reasons, radial shaft and hydraulic rod seals demand new wear resistant counterface materials. Thermal spraying offers one alternative to common hardening and hard plating technologies. Applying corrosion resistant ceramic coatings by Thermal Spraying leads to new applications in sealing systems. The combination with PTFE-compound sealing materials can be used with aqueous, non-lubricating and corrosive fluids. The authors have carried out extensive research on how the coating material and the surface structure of the coating effect hydraulic rod and radial shaft sealing systems. The presented results show that the influence of the coating on the sealing is critical for the performance of both standard and new custom sealing systems.

Abstract Two different coatings were studied in this work : vacuum plasma-sprayed NiCoCrAlYTa and electrodeposited NiCoCrAlYTa. These coatings were deposited on AM3 single crystal alloy. The tensile and creep properties of coated single crystal test specimens were investigated. Ductile-brittle transition temperatures (DBBTs) were determined from tensile tests. Creep tests were performed on cylindrical specimens and on thin flat specimens. All the coatings were examined before and after testing. The two tested coatings induce a ductile/brittle transition. Strain rate has a great influence on the transition temperature. The comparison between the two processes of deposition illustrates the strong influence of coating microstructure. A marked decrease in creep properties was observed for thin single crystal specimens but contrary to cylindrical specimens, the coating has a quite positive influence, so that the creep life of coated thin specimens is increased.

Abstract Bond coats based on bioinert ceramic materials such as titania and zirconia were developed to increase the adhesion strength of the coating system hydroxyapatite/bond coat to Ti6A14V alloy surfaces used for hip endoprostheses and dental root implants. The bond coats improved the adhesion strength, measured by a modified ASTM D3167-76 peel test, by 50 to 100% and also the resorption resistance as determined by in vitro leaching in simulated body fluid (Hank's Balanced Salt Solution, HBSS) for up to 28 days.

Abstract The degradation of materials, connected to ageing and wear, can be limited by suitable treatments aimed at the increase of surface properties Among the surface modification techniques thermal spraying processes allow a lot of advantages improving the performance and extending the life of materials and components. The convenience for the substitution of nodular cast iron with coated steel for the manufacture of rolls to be employed in a rod mill plant was studied by means of disk on disk wear tests on plain carbon samples coated with the fuse and spray technology, using 7 different type of nickel or cobalt based powders, comparing their wear resistance with the behaviour of nodular cast iron specimens. On the basis of the wear tests, the most promising coating materials were applied to steel rolls and their behaviour and duration on a rod rolling plant were compared with those of nodular cast iron rolls. The rolls coated with nickel based alloy admixed with WC-Co powder reached the best performance, with a duration about 40 % higher than the cast iron ones.

Abstract Plasma transferred arc (PTA) welding is widely used in the petroleum and chemical industry to deposit nickel and cobalt-based materials on key parts for the purpose of surface modification. As test results show, the process improves corrosion, wear, and high-temperature resistance, prolonging the service life of components and equipment and reducing production costs.

Abstract The paper discusses the testing methodology and identifies the analytical protocols, with proper validation, in order to evaluate the compatibility of thermal spray coatings in the food production technology, according to EU and FDA applicable standards. A brief state-of-the-art analysis of the international standards on food additives and human health is given, namely on indirect food additives (as defined in 21 CFR 170.3(e)), that can migrate into the food during the process. An outline of the test protocols, based on contact between coating and food simulating solvents in a set time/temperature conditions, are presented, and the main phases for the proposed testing methodology, as the choice of the simulating solvent, the migration cell design and the time/temperature conditions, are discussed. Finally the proposed methodology and protocols are validated through a thermal spray coating for food process application test case.

Abstract Experimental apparatus simulating a horizontal belt caster has been constructed for the study of thin strip casting of steels and light metal alloys. In this apparatus, the solidifying metal is deposited onto a moving substrate. The substrate was flame sprayed with various commercial coatings while its speed and the thicknesses of strip produced matched industrial values. The main objective of the present work was to determine the influence of various operational variables on local cooling rates and final microstructures. To this end, experiments were carried out to study the effects of various types of coating, roughness of the substrate, initial superheat, and strip thickness on heat fluxes. An interesting feature of this equipment is that the strip is subjected to different rates of cooling at the lower and upper surfaces, allowing two different rates of solidification to be studied simultaneously.

Abstract Many components in helicopter dynamics systems depend on hard, wear resistant coatings for reliable performance. Component replacement times are currently limited by performance of these coatings in many cases. Thermal spray coatings have been evaluated for these applications to replace nickel and chromium electroplate. The effect of coatings on fatigue strength is quantified by a strain limit concept to reduce test requirements during development phase. Full scale bench testing and coupon wear testing were conducted to reveal large improvement in sliding and fretting wear resistance. A fine porosity network in thermal spray coatings, high hardness and high fatigue strength are shown to be the main contributors to improved wear performance. Thermal spray coatings also exhibited enhanced corrosion resistance in salt fog and crevice corrosion conditions. These data permitted implementation on several critical helicopter components.

Abstract This paper describes some of the problems solved in the development of a mold-making process in which the molds are coated using a 2mm wire arc-spraying system. A water solution release agent has been chosen to meet industry standards and requirements. The composition of backup materials was chosen based on compression strength testing. The material selected has high ultimate compression strength and high thermal conductivity and can be readily incorporated in the mold-making process.

Abstract Polymer injection is an effective technique for increasing oil production in the later stage of petroleum exploitation. The pumps used typically incorporate ceramic plungers because they do not produce metal ions which tend to decrease polymer viscosity. This paper compares the performance of plasma sprayed and sintered alumina plungers and includes the results of stress analysis using finite elements and field testing. Under real working conditions, plasma sprayed plungers achieved an average lifetime of 12,000 hours, approximately double that of their sintered ceramic counterparts.

Abstract Air separation plants employ centrifugal compressors where air and electrical energy are the only raw materials used in the production process. In order to optimize compressor performance and efficiency, abradable coatings, originally developed for gas turbines, have been designed into turbocompressors. This paper describes the optimization and performance improvements achievable using aluminium silicon-boron nitride materials.