Locally Fluidized Thermal Spray Powder Feeders have been commercially available for the past 25 years and have fundamentally different operating characteristics than the classic Volumetric Powder Feeder. This paper explores the design principles and factors effecting the operation and performance of this technology. The discussion will include the challenges faced in accurately and safely metering powder into high backpressure spray torches.

Because of their characteristic spray geometry, pressure-gas-atomizers can be used to create thick coatings from molten metal. Production rates of pressure-gas-atomizers are substantially higher compared to conventional Thermal Spraying (100 – 200 kg/h based on molten tin). The shape of the spray cone can be designed by the geometry of the atomizer. The mean particle sizes and velocities (molten tin and tin-copper alloys) are controlled by the gas flow. Powder products and coatings of several millimeters on steel substrates were investigated. The average density of the layer was higher than 99%.

The high-velocity oxy-fuel (HVOF) process is commonly used to deposit WC-Co coatings. There are some problems with this process, especially the decomposition and decarburization of WC during the spraying. To eliminate these degradation, the warm-spray (WS) process originally developed by our group, which provides a possibility to control the flame temperature and the fabrication of WC-Co coatings can be made at lower temperature ranges that those of HVOF process, was applied to deposit WC-Co coatings. Microstructural characterization and phase analysis were carried out on deposited coatings by SEM and XRD. The mechanical properties such as hardness, fracture toughness, and wear properties were investigated. The results showed that WS coatings did not contain any detrimental phase such as W 2 C and W, which are usually observed in HVOF coatings. The hardness of WS coatings were lower than those of HVOF coatings, however, the relation of hardness-Co content of WS coatings showed the similar trend as that of the sintered WC-Co. The improvement of wear behavior was also observed in WS coatings.

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 high frequency pulse detonation (HFPD) process has shown to be a cost effective spray technique for the deposition of highly dense and erosion resistant YSZ ceramic coatings. In comparison to the coatings produced by conventional APS, a significant improvement of the wear performance can be achieved by the HFPD process as result of the high coating compactness. This work deals with the deposition of different ZrO 2 and Al 2 O 3 based ceramic powders by the HFPD technique, for the development of highly dense and wear resistant ceramic layers. During this development, the gun configuration and the process parameters (gas flows, explosion frequency, spray distance and cinematic conditions) have been optimised to get the best deposition performance. The resulting coatings have been characterised in terms of the microstructure, the microhardness and the sliding wear performance under dry conditions. In comparison to the plasma sprayed coatings produced with equivalent process conditions, the coatings deposited with the HFPD process are significantly harder and their sliding wear resistance is two–three-fold higher for YSZ coatings and five-six-fold higher for Al 2 O 3 coatings. Furthermore, the HFPD process is able to produce highly dense and hard functional coatings in one spray pass, suitable for wear protective applications.

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 disadvantage of plasma torches using conventional single cathode techniques is the occurrence of azimuthal and axial instabilities inside the plasma torch. This causes electrical power fluctuations which result in inhomogeneities of the plasma jet enthalpy and with that an uneven plasma particle interaction. Hence, variations in particle properties occur and consequently an uneven coating quality is produced. Using the triple-cathode technique these electrical power fluctuations were successfully reduced, resulting in a stationary plasma flow. Thus this technique appears to offer the potential to homogenize coating properties. Similar results have been shown for plasma torches with triple anode arrangements. The goal of this research group is to homogenize properties of plasma sprayed coatings using of 3-cathode and 3-anode technologies based on numerical simulations. The approach used is to subdivide the complete APS process into the areas plasma torch, free jet as well as coating formation and characteristics. By simulation of the individual areas and combination with experimental results the corresponding process parameters will be obtained for the desired coating properties.

The paper is devoted to gaseous detonation spraying and presents the state of current knowledge, as well as the following research and development needs: gaseous detonation as spraying heat source; operation cycle of detonation guns and its possible versions; operating frequency; impulse jet formation; basic detonation guns design concepts, as fuel and oxidant types, features of barrel design, predetonation distance control, valved and valveless detonation guns concepts, etc.; gas dynamic characteristics of detonation spraying.

The coating stresses induced by thermal spray using a High Velocity Gas Fuel (HVOF) and Liquid Fuel (HVLF) gun and a High Velocity Plasma (HVP) gun with the high velocity nozzle are compared using a curvature based in-situ coating stress analysis approach that measures the deflection of a beam while a coating is applied to it. This novel diagnostic tool provides new insights into the internal stresses generated in a coating system during the actual application of the coating. Coatings were sprayed with three process guns and the same material feed stock that result in similar coating structures and properties. HVOF, HVLF and HVP processes induce similar particle energy states at high velocity regimes as measured with particle diagnostic tools during spraying but due to the differences in particle history are expected to result in different coating stresses. In some cases the actual measured stress conditions using the in-situ coating stress method were dramatically different. Analysis is presented to explain the reason for these surprising results. The understanding of these differences will lead to an improved methodology for mapping coating processes from one another along with a more in depth understanding of coating stresses buildup.

Seven years after its introduction, the KINETIKS cold spray system from Cold Spray Technology GmbH is proving its reliability in various industrial applications. As pressure and temperature of the process gas are the primary parameters generating high particle velocities, the improvement respective development of the system family was focused on those. A further step of improving coating properties was the development of a powder preheating feature. Applications using this technology are now starting in a wide field from automotive up to aerospace products.

The LARGE is a new generation DC-plasma torch featuring an extended arc which is operated with a perpendicular gas flow to create a wide (up to 45 cm) plasma jet well suited for large area plasma processing. Using plasma diagnostic systems like high speed imaging, enthalpy probe, emission spectroscopy and tomography the LARGE produced plasma jet characteristics have been measured and sources of instability have been identified. With a simple model/simulation of the system LARGE III-150 and numerous experimental results, a new nozzle configuration and geometry (LARGE IV-150) has been designed, which produces a more homogenous plasma jet. These improvements enable the standard applications of the LARGE plasma torch (CVD coating process and surface activation process) to operate with higher efficiency.

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.

One important aspect concerning the coating of surfaces using thermal spray is the improvement of the injection of material particles into the gas jet and thus the deposition efficiency. Therefore a better knowledge of the temperature distribution within the jet is relevant in order to optimize spraying conditions. Particularly interesting is the existence of a well-defined threefold finger structure in the plasma jet produced by triple electrode torches, which allows an efficient injection of coating material due to the existence of zones with higher and lower viscosity. The jet structure, however, lacks rotational symmetry and can therefore not be analyzed by systems relying on the validity of the Abel inversion, thus new systems have to be developed. In this work an innovative tomography device is described that has been designed for this purpose. By circling half around the plasma jet and taking simultaneously intensity images under different view orientations, a three-dimensional intensity distribution of the jet is generated, which can be used to determine the temperature distribution.