This paper discusses the ongoing development of a standard for manufacturing and testing thermal spray coatings used in the repair of aircraft engines. Excellent progress has been made in eliminating non-value added tests and in defining a system for preparing metallographic specimens and conducting microstructural evaluations. Paper includes a German-language abstract.

Norway is a rich country endowed with many natural resources including hydropower, oil and gas, wind power, fish, etc. Norway has nowadays a high technological and research based industry. The discovery of the first oil field in 1969 has been the driving force for the Norwegian economy, accounting for nearly 50% of exports and 30% of state revenue. Since then several technology-based industries have been created and developed not only around the oil and gas business, but also in other fields such as the Aluminium production. Thermal Spray has played an important role in the Norwegian industry, where it has been used for more than 40 years in many different applications (corrosion and wear protection in the offshore industry, aeronautical industry, etc). The Norwegian thermal spray producers and users have a long tradition in collaborating and also working with R&D institutes such as SINTEF and Universities (specially the The Norwegian University of Science and Technology, NTNU) in order to develop new and better coatings. Based on this collaboration the Norwegian Thermal Spray Group was established in 1995 and since then it has grown constantly. The members of the group are: Bandak AS, Castolin Services, CerPoTech, GBSGroup, HCStarck, Mantena, Mets AS, Norwegian armed force logistic division (LHK), Powder Tec AS, Scana, SprayService AS, SubseaDesign, Teknologisk Institute, Trio AF, Volvo Aero Norge, SINTEF and the Norwegian University of Science and Technology. The group includes materials suppliers, coating producers, end users, education and certifying, research institutes and Universities. The aim of the group is to develop thermal spray activities in Norway and find new solutions for existing and new challenges in surface protection.

Joint research work between the University of Limoges and the State University of New York, Stony Brook, has been carried out on the impact and solidification of plasma sprayed zirconia particles. A measurement device, consisting of a phase doppler particle analyser and a pyrometer, was used to correlate the characteristic parameters of splats to those of the substrate and to the size, velocity and temperature of the impacting particles.

This is the second paper of a two part series based on an interdisciplinary research investigation between the University of Limoges, France, and the State University of New York, Stony Brook, USA, aimed at fundamental understanding of the plasma-particle interaction, deposit formation dynamics and microstructure development. In this paper, the microstructure development during plasma spraying of zirconia is investigated from the point of view of deposition parameters and splat formation (part I). Splats and deposits have been produced at Limoges and Stony Brook under controlled conditions of particle parameters and substrate temperatures. The zirconia splat microstructures thus obtained are examined for their shape factors, grain size, crystallographic texture and defects. Further the deposits were analyzed for phases, porosity and mechanical properties in an effort to develop a process-microstructure property relationship. The results suggest a strong role played by the deposition temperature on the microstructure and properties of the deposit.

Within the framework of a scientific collaboration between the University of Limoges, France and the State University of New York, Stony Brook, USA, a joint work has been conducted on microstructure development and properties of plasma-sprayed molybdenum coatings. This first part of the work is devoted to the study of the effect of substrate nature and temperature on splat cooling, solidification and crystalline structure. They were investigated by means of a heat transfer model in the splat and the substrate, and the observation of splats by a scanning electron microscope and an atomic force microscope. The model takes into account melt undercooling, nucleation and crystal growth, as also a possible melting and re-solidification of the substrate. It has the capability to predict the grain size distribution under assumptions that the quality of contact between the splat and the underlying layer is uniform, nucleation takes place only on the substrate surface, crystal grains grow perpendicular to the substrate surface and no grain coalescence occurs during crystal growth.

This is part II of the two part paper based on international collaboration between the University of Limoges, France and the State University of New York, Stony Brook, USA, aimed at fundamental understanding the relationship between processing condition and microstructure development and properties of thermally sprayed materials. In this study, the effects of deposition temperature on the microstructure and properties development of molybdenum coating was investigated. It is found that with the increase of steel substrate temperature, the molybdenum splat morphology changes from fragmented to more contiguous disk-like shape. The splats on molybdenum substrate show predominantly disk shape. With the increase in deposition temperature, the coating exhibits better lamellar structure with less interlayer pores and debris. The fracture characteristics changes gradually from interlamellar to trans-lamellar and, thermal conductivity is enhanced. Higher deposition temperature improves dramatically the adhesion and bonding of the splats, therefore the physical and mechanical properties of coatings.

Thermal sprayed coatings often need to be removed for maintenance, repair or recycling and are accomplished by various conventional methods such as grinding, abrasive blasting and chemical removal processes. The coating removal for repair is typically done for expensive and/or very complex parts. Parts of turbines, equipped with functional coatings, are stripped for inspection and repair as well as old coatings are renewed. When removing a thermal sprayed coating, damage to the part or ablation of the substrate must be avoided. A new process of dry ice blasting alone as well as in combination with a laser beam in a hybrid process has been approved for the removal of thermal sprayed coatings in a project aided by the Federal Ministry of Economic Affairs and Employment via the Federation of Industrial Research Associations (AIF). The aim of the project is to obtain the properties for the comparison and benchmarking of coating removal processes. Comparative studies have been made with the water jet and the abrasive water jet process at the Institute of Materials Science of the University of Hanover.

For the last seven years, Oxford University and the Ford Motor Co. have been researching jointly the development of the large-scale spray forming of steel tooling capable for use in mass production, particularly for the pressing of sheet metal in automotive applications. These investigations have involved: comprehensive microstructure and property studies, modelling of shape evolution and heat flow, real-time feedback control of tool temperature to eliminate tool distortion, high speed imaging and particle image velocimetry of droplet deposition on 3D shapes, the testing of full-scale tools for different applications in the production environment, and detailed studies of the cost and time savings realised for different tooling applications. This paper will provide an overview of the scientific and technical progress to date, present latest results, and describe the current state-of-the-art. Many of the insights described have relevance and applicability across the family of thermal spray processes and applications.

Current HVOF systems available on the world market are relatively complicated to operate and expensive. At the Bauman State Technical University in Moscow (BMSTU) a new portable HVOF spraying and cutting system MiniJet-30 has been developed. This rugged system offers the ease of operation of conventional gas welding equipment and produces high quality HVOF coatings. In this paper, the results of numerical simulation calculations of supersonic gas/powder flows, with and without a particle mask, are presented and compared with experimental outcomes. Additionally, typical HVOF coatings were sprayed and evaluated for bond strength, porosity, microhardness, abrasive wear, and phase composition (OM, XRD). The results are compared to those of other HVOF systems. Lastly, the cutting efficiencies for stainless steel, cast iron, and non-ferrous metals are discussed.

In previous studies at McGill University, tin was successfully cold sprayed onto carbon fiber reinforced polymers (CFRPs). A “crack-filling” mechanism was described as the deposition mechanism that allowed deposition of tin onto the CFRP. Improving the coating conductivity for lightning strike protection (LSP) purposes was achieved by adding other metal powders (aluminum, copper, zinc) to tin and cold spraying on the CFRP. At the same time, it was noticed that the addition of this secondary component (SC) provided an increase in deposition efficiency (DE), tamping was initially hypothesized to explain this improvement, thus prompting a study solely on the effect of SC hardness, which is reported elsewhere in this conference. However, it is recognised that other powder characteristics may also be influencing the DE. Thus, in this study, SCs with a wider variety of particle sizes, morphologies, densities and hardness values were mixed with tin and sprayed on CFRPs. The effect of SC properties on tin deposition is discussed and an optimal combination of SC properties for cold spraying of tin is suggested.

Over the last years, the grain size reduction to the nanometric scale has experienced an increasing interest because of its enhanced properties. This study is based on WC-Co cermet materials, which have a great application in the wear resistance materials field. In the Thermal Spray Center (CPT) of the University of Barcelona, two coatings using nanostructured and bimodal WC-Co cermet powders have been obtained by means of High Velocity Oxygen-Fuel (HVOF) technique. Both were sprayed under the same spraying parameters. Structural characterization for both feedstock materials and coatings have been performed using XRD, SEM and TEM. The friction wear resistance of the coatings has been studied by Ball-on-Disk test (ASTM G99-90), and the abrasive wear resistance has been quantified by Rubber-Wheel test (ASTM G65-91). Finally, the corrosion resistance has been studied by electrochemical techniques and a salt fog spray test. The nanostructured coating shows more hardness, but the bimodal coating shows better abrasive and friction wear resistance. Both coatings shows good corrosion resistance, better than the conventional coatings of WC-Co. The bimodal powder have the added advantage of being not as expensive as the nanostructured powder, and even providing better properties.

The technical and economical potential of innovative materials is gaining growing interest for technologically orientated companies. The use of lightweight materials is an extremely important consideration, especially when designing moving components (e. g. in aerospace, automotive or machine construction). Magnesium is a promising alternative to other lightweight materials, such as aluminum and titanium, due to its relatively high specific strength and stiffness. Further advantages are high thermal conductivity and good joining and machining capabilities. However, the use of magnesium alloys is restricted by relatively poor wear behavior and corrosion resistance. In order to overcome the limitations associated with magnesium alloys, a project was founded by the Materials Science Institute (MSI), at the RWTH Aachen, and the Institute of Materials Science (IW), at the University of Hannover, to deal with the application of wear and corrosion protective coatings on Mg alloys by means of thermal spraying. A variety of coating materials were applied on Mg substrates using several thermal spray processes (like Arc Spray and HVOF). The coatings were then characterized particularly with regard to their wear and corrosion properties. To further enhance the overall corrosion resistance two additional approaches were investigated. On the one hand various duplex coating systems were designed and applied. With the objective of decreasing the open porosity coatings were either densified by shot peening or sealed by applying organic sealers on the other hand.

The quality and operation performance of layer composites manufactured by thermal spraying is influenced by two different processes, the activation process of the surface prior to coating deposition and the coating process itself. The activation of the substrate surface is mainly performed by grit blasting operations. Surface activation by grit blasting is used in order to improve the bonding between substrate and coating, which is strongly related to the size and nature of the surface topography and roughness generated by the blasting process. Besides the roughening effect, grit blasting induces compressive residual stresses into the substrate surface which can be critical especially for thin walled components, e.g. piston rings, where the component shape is an important factor for the operation behavior and functionality. Another effect is an increase of hardness in the surface region related to the induced compressive stresses. A variety of blasting parameters can influence the surface characteristics, like nozzle diameter, grit medium and size, blasting pressure, distance and time. The influence of these parameters on the surface roughness, hardness, component deformation and residual stresses was investigated by tactile surface metrology, universal hardness and Almen tests as well as experimental residual stress analysis with the incremental hole drilling and milling method. All investigations were performed on rectangular steel strips. The results are discussed concerning quality control features for grit blasting processes in serial production.

The University of Limoges developed a compact sensing module that measures particle beam properties and substrate surface temperatures during plasma spraying. In this paper, the authors explain how they built and tested a closed-loop controller for APS processes using the sensing module. One of the key elements in the online control system is an empirical model that relates process inputs, in-flight particle parameters, substrate temperatures, and coating properties. The paper discusses the development and implementation of the model and the determination of the main input parameters. Paper includes a German-language abstract.

This paper will outline the results of a study underway at Utah State University aimed at developing technology to alter the direction and profile of thermal spray flows using the Coanda effect. Coanda-assisted Spray Manipulation (CSM) makes use of an enhanced Coanda effect on axisymmetric geometries through the interaction of a high volume primary jet flowing through the center of a collar and a secondary high-momentum jet parallel to the first and adjacent to the convex collar. The control jet attaches to the convex wall and vectors according to Coanda effect principles, entraining and vectoring the primary jet, resulting in controllable r - θ directional spraying. The basic turning effect was investigated in a fundamental experimental study. The results of the fundamental study were applied to the design of an add-on CSM attached to a Metco 2P powder flame spray gun.

The thermal spray industry requires universal and economical HVOF systems for the production of high-quality coatings with high deposition efficiencies. In the last years classic HVOF guns have been adapted insufficiently to these requirements. This paper shows how modern numeric simulation and new inventions in gas safety engineering enable the development of a spray system for powder and wire feedstock that is optimized especially for the needs of the market. The new IBEDA TopGunAirJet is equipped with an air-cooled ‘de Laval’-like nozzle. The optimized expansion of the gas leads to high gas and particle velocities as well as to moderate flame and particle temperatures. Advantages of the TopGunAirJet are the achievable high coating quality, the low energy consumption (propane, ethene), the utilization of powder or wire and the efficient air cooling of the thermally loaded nozzle parts. Additionally, as a result of the axial powder injection, the free jet divergence and the nozzle wear are minimized. By varying the powder gas flow, the dwell time of the particles inside the flame can be influenced in order to avoid fusing of hard phases. As an example, WC-Co 88-12 coatings are presented and compared to coatings sprayed with a standard HVOF system of the 3rd generation. Different 316L coatings are produced and tested in comparison to standard HVCW coatings to show the workability of solid and cored wires. Finally, extensive LDA measurements are used for in-flight particle analysis, and investigations concerning the achievable deposition efficiencies are carried out.

The main argument against the use of the internal HVOF process is the high thermal stress to which the substrates are subjected during the coating process. Traditional HVOF guns operate with a flame-stream energy level of 100–200 kW. Rendering HVOF technology usable for the application of internal coatings requires the reduction of the energy level of the flame stream to 20 kW, while safeguarding high particle velocity and sufficient temperature despite the reduced energy level. This requires an integrated process consisting of the HVOF gun, powder feeder, fuel control, and fine powder; the particle sizes of the powder are -25+5 µm, -15+5 µm, and -10+3 µm. Thermico’s ID CoolFlow M HVOF internal spraying gun comes equipped with a 5 mm acceleration nozzle and radial powder feed. It is suitable for internal diameters of 80 mm and above and eliminates the typical overheating problem. The ID CoolFlow M HVOF gun is suitable for internal coatings with Thermico 776 WC-CoCr powder, which comes in grain sizes of -15+5 µm and -30+15 µm. A comparison of both processes requires a number of specimen coatings with different parameters, which have to be compared to reference coatings. These reference coatings are produced using a Thermico CJS K4.2-776/G gun in combination with WC-CoCr 86 10 4 powder with a grain size of -30+15 µm, and a CJS K5.2-776 gun, using a finer powder with a grain size of -15+5 µm. The base material consists of heat-treated steel rings with a hardness of 45 HRC, an internal diameter of 130 mm and a wall thickness of 10 mm. Subsequently, the density, porosity, and structure of the specimen is assessed, and they are checked metallographically and with a scanning electron microscope, including EDX analysis. The specimen wear is monitored using the prototype of an internal coating test stand, developed by the Institute of Materials Science at the University of Applied Sciences Gelsenkirchen. It is essentially based on the same principle as the pin-on-disc tribometer for relative movements.

This work assesses the potential of using an ultrasonic probe attached to the back of the substrate to monitor the cold spraying process. While this is only a preliminary study, focusing more on presenting the results than analyzing them, a few conclusions may be drawn. With acoustic sensing, not only can the final value of thickness be estimated, it is also possible to see the dynamics of how the buildup takes place in real time. As shown in the data plots, the buildup process for aluminum-alumina composites is fairly universal across the spray with slower buildup at the outer edges of the coating. More importantly, it is shown that nozzle speed, spray diameter, and thickness estimates fit well with measured values.

The following contribution deals with carbide composite powders. These composite powders were made by the SHS-process. The present work is a result of a co-operation between the Institute for Powder Metallurgy Minsk (PMI) and the Department of Composites and Surface Technology at the Chemnitz University of Technology (TUC). The main aspect of this research activity is the improvement of the wear protection due to the deposition of the composite coatings. Paper text in German.

ln co-operation with industrial companies, education and training institutes, and universities, an interactive multimedia learn-ing programme was developed. The project was sponsored over three years by the European Community. Structure and contents of this programme are based on the EWF-guideline “European Thermal Sprayer - Minimum requirements for education and training”. The multimedia programme contains the module of theoretical basis of the training course and covers training subjects as spraying processes, base and spray materials, bonding mechanisms, coating characteristics, measuring and testing, environmental and safety aspects. The interactive multimedia programme may be used to shorten the duration of the ETS-course, for spray company internal education and training, for settling into a new job concerning thermal spray technique, or for supporting a training course itself. The multimedia programme will be demonstrated during the poster sessions. Paper text in German.