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A review of selected national and international thermal spraying guides and specifications for the preservation of steel and reinforced concrete using thermal spray coating of aluminum, zinc and their alloys is presented. The work program and current status of the US national organizations contributing to and developing test methods and process standards are summarized along with those of ISOATC 107/SC 5. The Secretariat of the ISO/TC 107/SC 5, Thermal Spraying was transferred from AFNOR, France, to ANSI, US, in June 1995. ANSI, in turn, designated AWS to be its delegate in thermal spray matters. The work program of the newly formed SSPC/NACE/AWS Tri-Society Committee on thermal spray coatings for the corrosion protection of steel is summarized.

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.

In the field of thermal spraying a lot of things have been and still are happening concerning education and training of personnel. The education and training of thermal sprayers according EWF-Guideline is required frequently in combination of the international standard DIN EN ISO 14918 “Approval Testing of Thermal Sprayers” - especially in the German-language countries. Meanwhile about 13 ETS courses were held at the German Welding Institute. Also interested in the education and training of thermal sprayers are countries like Poland and China. In France thermal spray personnel was educated and trained in a company internal course. Sweden and Norway run ETS courses in cooperation. The EWF education and training course of the ETSS European Thermal Spraying Specialist will be offered by the German Welding Institute in Munich - SLV München - for the nineth time in October 2005. Since about 1993 European Committees of EWF (European Federation of Welding, Joining and Cutting) and CEN (European Committee or Standardization) worked out education and training guidelines and qualification standards of thermal spray supervising personnel and sprayers and established them step by step. The meanwhile created and internationally accepted EWF-education and training guidelines of supervising personnel and thermal spray workers involve also the new ISO standards of the Thermal Spraying Co-ordinator and the Approval Testing of Thermal Sprayers. The ISO personnel qualification and quality management standards result together with the EWF education and training guidelines in a sound QM-system, which meets the increased demands of trade and industry of high quality sprayed coating. Experiences in applying these guidelines and standards are introduced.

The internal plasma spraying for the deposition of thermal barrier coating already was introduced about 20 years ago. During the last 8 years a new generation of internal plasma torch was developed and introduced in the industry. The new generation is characterized by an improved resistance against the thermal radiation and a significantly improvement of the time life of the guns. The performances of the plasma torches regarding powder feed rate and deposition efficiency also were increased to allow the using in mass production in the automotive industry. The improvement of the time life of cathode and anode was realized by using CFD program to optimize the water cooling of the plasma torch. By the production line for cylinder bore the time life of cathode and anode was increased from 50 to more than 100 hours by the modification of the cooling geometry. Several application of internal spraying for mass production in the automotive, aerospace and the electrical industry will be discussed in details. Especially the internal spraying of the cylinder bore will be shown as typical application of high volume. The advantages of the plasma spraying in comparison with alternative technology will be demonstrated. The further development and future potential applications will be discussed at the end as outlook.

Northwest Mettech Corporation has recently developed a new high power torch for spraying internal surfaces, the Axial III ID. The Axial III ID has been successfully operating at 135 kW while spraying inside a drum with an inner diameter of 34 cm. The three-electrode axial injection configuration of the new torch is based on the current Axial III torch. Various coatings were sprayed inside a drum while monitoring the torch temperature. The results of these experiments are presented in this paper.

Laser-assisted atmospheric plasma spraying (LAAPS) is a new one-step coating process performed in air whereby the laser beam interacts with the plasma torch at the substrate or coating surface during deposition to generate a coating that is metallurgically bonded to the substrate. This hybrid process was developed in order to combine the specific advantages of APS and laser cladding. In this paper, the development of a hybrid gun for coating internal surfaces of tubes and cylinder bores by LAAPS is presented. The process was optimized for spraying AlSi30 coatings on internal surfaces of aluminum alloy cylinder bores. Single-pass coatings with thicknesses of 300-400 µm and metallurgical bonding to the substrates can be realized by applying an optimized parameter set. The dependence of coating microstructure on spray parameters was investigated by metallographic preparation and optical microscopy. Surface pretreatment must be performed to eliminate the strongly adhering oxide layer on the aluminum alloy substrate and to attain metallurgical bonding of coating to substrate.

An investigation was carried out into the effect of the interface roughness between the metallic bond coat and the ceramic topcoat on internal stresses in a thermal sprayed ceramic thermal barrier coating (TBC). To evaluate the effect of the interface roughness on the residual stress in the top coat, the specimens with two kinds of bondcoat roughness (rough type and smooth type) were prepared. The in-plane stresses of the specimens were measured with laboratory X-rays. The in-plane stresses for the both of the rough and smooth specimens were about 60MPa and independent of the roughness of the bond coat. Using high energy X-ray, the stress of the rough specimen was compressive and the stress of smooth specimen was tensile. This tendency is different from the result measured by laboratory X-ray. This difference in the stress value is coursed by the out-of-plane stress. Theses stresses in the topcoat were estimated by the hybrid method, that is to estimate out-of-plane stress using laboratory X-rays and high-energy synchrotron X-rays. As a result, the larger the roughness of the bond coat became the larger out-of-plane-stress become.

This paper presents an assessment of the properties of three thermal sprayed coatings for a thermal barrier applied to the piston head of an internal combustion engine. Coating (1) has a topcoat of Al 2 O 3 and a bond coat of Ni-Cr. Coating (2) has a topcoat of YSZ and a bond coat of CoNiCrAlY. Coating (3) is 316 stainless steel. The investigators conducted thermal cycle tests and tensile pin tests, and evaluated the thermal barrier effect of the coatings. The results showed that coating (3) had no cracks or delamination after the thermal cycle test, while coatings (1) and (2) had partial cracks and delamination. Coating (2) had the highest adhesion strength, and its thermal barrier property was better than that of coatings (1) and (3). In terms of cost and overall evaluation, coating (3) was considered the most reasonable and appropriate thermal sprayed coating for the piston head application.

For solid fuel cell application, thin electrolyte is needed for novel materials that allow reducing their operating temperature. The influence of what called ‘the thermal management of the coating and the substrate’ is discussed. In particular, influence of substrate temperature and the nature of the substrate. It was found that adequate control of the coating and substrate temperature, together with an equivalent substrate/coating thermal expansion coefficients (CTE) are the key-factor to successfully obtain an SDC nanosized thin and dense coating free of cracks.

Different thermal spray processes are being used to provide coatings for cylinder bores in automotive engines. The internal plasma spraying technology described in this paper applies protective layers to cylinder surfaces in engine blocks made of AlSi cast alloys. This method enables a significant reduction in the coefficient of friction, a reduction in oil consumption, and an increase in wear resistance compared to cast iron, the standard material for cylinder liners. Paper includes a German-language abstract.

Aluminum oxide ceramic coatings are widely used to extend the life of machine components. These protective layers are usually applied via atmospheric plasma spraying. In this study, alumina coatings are produced using a low-power plasma spraying method and assessed based on hardness, porosity, and microstructure. Test results show that alumina coatings applied using low-power plasma spraying with internal injection are harder than those produced using traditional APS techniques. The effect of process parameters, including current, voltage, powder feed rate, and plasma energy, is also investigated. Paper includes a German-language abstract.

In this paper, a low-power plasma spraying system is used to deposit layers of tungsten carbide on carbon steel substrates. Numerous coating samples were produced and examined in order to determine how plasma gas composition, voltage, current, and other parameters affect the hardness and porosity of WC coatings and how injected particles interact with nozzle surfaces. Test results indicate that there is a tendency for less particle adherence to the nozzle at higher voltages, lower currents, and certain plasma gas compositions. Paper includes a German-language abstract.

Since about the year 2000, cast aluminum automobile engine blocks have been coated in production lines using internal plasma spraying technology. Using this approach, the coefficient of friction between the cylinder wall and the piston assembly can be reduced to 30% and oil consumption is reduced of a factor two in comparison with cast iron. The extremely low wear rate of the friction elements increases engine life and reduces maintenance costs. The fuel consumption of the cars can be reduced from 2 to 4% in the case of gasoline and diesel engines. The coating costs are strongly dependent on production volume. For high volume production, the costs can be similar to those for cast iron liners. This paper reviews results from laboratory and field tests evaluating the performance and cost efficiency of plasma sprayed engine block liners.

Miniaturization and performance improvements of electronic devices in recent decades have significantly increased heat dissipation rates. To overcome this, researchers have developed heat sinks with miniature fluid channels to maintain small device footprints with increased heat transfer performance. These channels are often fabricated using either subtractive fabrication methods, such as etching or micro-milling, or additive methods such as direct metal laser sintering (DMLS). These methods are limited by their long processing times, low geometric accuracy, or high cost. To overcome these limitations, a novel additive manufacturing method is developed using twin wire-arc spray. Wire-arc spray was used to build complex aluminum structures with length scales varying from 0.5 mm to 74 mm. Surface structures were built on a metal plate by spraying aluminum through a 3D printed polymer mask. Internal flow passages were made by filling surface channels with a water-soluble polyvinyl alcohol (PVA) paste that was allowed to harden, spraying metal over it, and then dissolving the PVA. The influence of wire-arc spray process parameters, such as standoff distance and scanning speed, on coating solid PVA with aluminum, were also investigated.

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.

A kinetic metallization technique, which is one of the cold spraying systems, has been studied as a new coating system for metallic bond coats of thermal barrier coatings for components used in hot section of advanced gas turbines. In this study, in-situ residual stresses in atmospheric plasma sprayed yttria-stabilized zirconia (YSZ) top coating with two different bond coat spraying systems, deposited by a low pressure plasma spraying and a cold spraying, were evaluated and compared by thermal cycle tests. From the results of 1st thermal cycle, in the case of the plasma sprayed bond coat, a tensile residual stress was observed at the elevated temperature up to 400°C. Relaxation of the residual stress was started beyond 400°C. On the other hand, the gradual increase of tensile residual stress was observed up to 1000 °C in the case of cold sprayed bond coat. In addition, transition behaviors of residual stress between plasma sprayed and cold sprayed coatings were varied in 3-thermal cycles.

This paper describes an inner diameter HVOF spraying technique and associated tests methods. In the experiments, WC-CoCr was applied to an internal diameter of 150 mm and evaluated using a dedicated pin-on-disk wear test and standard axial fatigue tests. The results are presented and discussed along with the potential for further development of the inner diameter HVOF spraying technique.

Plasma spraying with axial powder injection inside the anode nozzle is a method considered to markedly enhance deposition efficiency and reduce plasma power compared to the most general method of injecting powder at the nozzle exit. However, powder injecting inside the nozzle will also likely cause problems from powder deposition on the nozzle wall and clogging of the particle feed channels. In this study, spherical stainless steel 316 and angular alumina powders with a mean size of 20-40 μm are used to deposit coatings via axial powder injection. The effect of powder feed rate, gas flow rate, and plasma power on deposition efficiency and particle clogging are investigated. The results show that particle clogging can be avoided by reducing powder feed rate and increasing the velocity of the plasma jet.

The aim of this work is to assess the ability of pulsed gas dynamic spraying to deposit coatings on the inside surface of cylindrical workpieces. Thick dense copper coatings are produced on flat surfaces and on the inner surface of cylindrical workpieces using a specially designed gun extension. The coatings are evaluated based on microstructure and microhardness in order to determine if the copper has the same characteristics on all surfaces. A comparison between pulsed gas and cold gas dynamic sprayed copper coatings is also presented.

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.