The increase of commodity prices for classical corrosion protection materials such as WC/Co and Cr 3 C 2 /NiCr are leading to significantly increased coating costs. This reduces the competitiveness when compared to other coating technologies such as electroplating, particularly if carbide coatings are representing an over engineered solution for the considered application. A promising economic alternative is the employment of advanced ferrous materials. Fe-base coatings have the potential for very good corrosion protection and favourable wear properties combined with a low cost level due to relatively low priced alloy materials. In this study three different Fe-base materials have been sprayed by liquid and gaseous fuel HVOF spraying and analysed with respect to microstructure, hardness and corrosion resistance. Corrosion tests have been carried out with sulphuric acid as well as artificial seawater.

A new cold spray process for a combustion-free spraying is studied experimentally and by modeling and simulation. The high particle velocity at the front of the substrate is achieved by using the shock tube technology. The particles have been injected downstream of the nozzle throat into a supersonic nozzle flow. The shock tube of 6.5 m length and 56 mm inner diameter provides the necessary reservoir conditions for the nozzle flow. The measurements of the particle velocity made by a laser Doppler anemometry (LDA) setup showed that the maximum velocity amounts to 1220 m/s for stainless steel particles of 15 µm diameter. The CFD-Code (Fluent) is first verified by a comparison with available numerical and experimental data for gas and gas-particle flow fields in a long Laval-nozzle. The good agreement implied the great potential of the new dynamic process concept for cold gas coating applications. Then the flow fields in the short Laval nozzle designed and realized by the Shock Wave Laboratory (SWL) have been investigated. The gas flow for experimentally obtained stagnation conditions has been simulated. The gas-particle flow without and with the influence of the particles on the gas flow has been calculated by the Surface Engineering Institute (IOT) and compared with experiments. The influence of the injection parameters on the particle velocities has been investigated as well.

The cold spray process is interesting for brazing technology due to its special properties: low oxidation of spray materials and rupture of oxide scales on the substrate and particles surfaces during deposition. In the present study, two brazing alloys AlSi 12 and AlSi 10 Cu 4 were deposited onto 6063 and 3003 aluminium alloys using the cold spray process. The influence of the spray parameters on the particle velocity was investigated by means of DPV 2000. The influence of spray materials and parameters on coating build up and on coating microstructure was investigated. Some of the AlSi 12 coated samples were heat-treated at 500 and 600 °C to investigate the effect of the rupture of oxide scales on the diffusion processes. Some of the AlSi 12 deposited samples were brazed under argon atmosphere using a flux or without any fluxes. The results show that the process gas temperature influenced the particle velocity and the deposition behaviour of the powders significantly. The AlSi 12 powder showed a much better deposition behaviour than the AlSi 10 Cu 4 powder. Due to the rupture of oxide scales, silicon in the brazing alloy coating could diffuse into the substrate. The brazed samples show a very good bond between the substrate and the brazing alloy.

Being the 7th most abundant element on the earth, magnesium and its alloys have become very promising in numerous industrial applications because of some of their distinguished properties, including high thermal conductivity, high strength/weight ratio, good machinability etc. However, some inferior properties especially the poor wear and corrosion resistance have obstructed a widespread use. As one of the most effective solutions, thermal spraying can deposit an adequate protective coating on the substrate, but the necessary grit-blasting operation before spraying leads to high grit-residues on the magnesium surface therefore degrading the deposit performance. The PROTAL® process, combining a laser surface preparation with the deposition stage, can avoid this kind of disadvantage. This paper presents the possibility of employing PROTAL® to prepare a resistant Ni-Cr coating on a magnesium substrate. The coating adhesion and interface microstructure were especially investigated.

The process parameters of atmospheric plasma spraying (APS) influence the coating formation and properties of partially yttria stabilized zirconia (PYSZ) thermal barrier coatings (TBCs). Simulations can be used to investigate this dependency and to design the coating process for a targeted production of TBCs. A whole process simulation was realized by modeling the linked sub-processes: plasma torch, plasma free jet, powder particles characteristics and coating formation. The coating formation can be described by model approaches with different physical assumptions and geometric scales. One approach is the simulation of single powder particles hitting the substrate surface. An alternative macroscale FEM-model-approach is applied in the coating formation simulation. A group of particles is pooled in a splash dependent on the pre-calculated particle distribution in front of the substrate. A third modeling approach is applied to calculate effective mechanical and thermodynamical properties of coatings dependent on the experimentally obtained or calculated microstructure of the PYSZ-TBC, which is based on different homogenization methods. The application of three simulation approaches in the whole process simulation of APS is discussed, advantages and disadvantages are elucidated. Results based on simulation and experiments are presented for a variation of process parameters. Missing links in the multiscale approach are detected to make suggestions for future modeling and simulation work.

Crank cases of modern car-engines are made in general of light metal alloys, mostly aluminium alloys. Due to the low hardness of these materials, the use of cylinder liners, in general made of grey cast iron is required. The use of cylinder liners also leads to several disadvantages, such as the increase of the engines weight. The aim of this work in the long term is to replace these cylinder liners with a thermally sprayed nano-structured composite coating, characterised by high hardness. Therefore in this study a coating process employing a plasma transferred wire arc unit and a cored wire are used.

HVOF spraying of carbides is a well established method to produce high performance wear and corrosion protection coatings for various industrial applications. Using ultrafine feedstock powders with particle sizes well below 25 µm can offer many advantages with respect to the resulting coating properties, such as improved coating density and homogeneity and high dimensional accuracy. In this study, fine powder grades of WC 10Co 4Cr, WC 17Co and Cr 3 C 2 25(Ni 20Cr) in a particle size range of –15 +5 µm, -10 +3 µm and –5 µm have been sprayed with suitable HVOF systems on outer surfaces as well as on internal diameters. Resulting coatings have been analysed with respect to coating structure and microhardness. The coatings featured a favourable microstructure and very good hardness values. Furthermore, the Cr 3 C 2 25(Ni 20Cr) material was applied as wear protection coating on piston rings. The coating performance was evaluated in engine tests and proved to be significantly better than a conventionally graded standard material system for this application.

Structuring coating materials in the nanoscale can significantly enhance the performance of Fe-based coatings. Nanostructured steel coatings with a very high hardness, the strength of carbon-based fibers and a corrosion resistance superior to nickel-based super alloys are currently commercially available. This work deals with the development of wear resistance nanostructured coatings using a commercial steel powder by high frequency pulse detonation. Results concerning the deposition of this powder using two different high velocity oxy-fuel spray systems are presented for comparison. The process parameters were optimized on the basis of the achieved coating features hardness, thickness, porosity and surface roughness. The microstructure of the coatings achieved with the different systems as well as the resulting adhesion and cavitation erosion resistance are compared. These results are also compared with the performance of standard WC-CoCr coatings.

Previous investigations of thermal spraying processes have shown that the relations between process parameters and the objective measurements are very complex. An approved approach to control complex processes is the application of Neural Networks (NN). Thus, Neural Networks have been designed to control the process of APS and HVOF spraying. Feed forward Neural Networks (Multi Layer Perceptron, MLP) are used. They are able to control a process. The way to train the Neural Network is to conduct as many experiments as possible, this is the major difficulty for the industrial use of Neural Networks. To save time and money DoE (Design of Experiments) is used to create an optimal experimental plan for the training. For testing the implementation of Neural Networks coatings are sprayed with APS, using DoE. The Neural Networks are combined with the particle flux imaging (PFI) tool. In future this combination will be able to provide an open loop control for thermal spray processes. The Neural Networks will be integrated with the software of the PFI-unit in order to create an easy to handle and affordable process control device. First experiments have been done with the APS process by spraying ZrO 2 onto steel substrates. Afterwards the porosity of the coating was correlated to the recorded images and to the process parameters.

The number of parameters influencing the plasma spraying process is very high. Only a part of these parameters can be controlled online; some of them such as gas flows, current, voltage and spraying distance can be controlled easily, others such as particle temperature and velocity can only be controlled with substantially higher effort. As differences from parameter values preinstalled or given at the start of the process, the noise factors affect the coating properties in different ways and show big effects on the coating quality. Nevertheless there is only little knowledge about the significance of several noise factors and about the influence of small process parameter fluctuations on the coating properties. Because some of these noise factors such as plasma torch degradation cannot be avoided, the aim of this work is to determine the sets of coating parameters, where the influence of noise factors is minimized. This should be achieved by using online diagnostic tools, that afford the observation of fast and easy controllable process characteristics. On the other hand process errors shall be identified in an early process stage using appropriate diagnostic methods.

In modern jet engines, the efficiency of the compressor stages is highly dependent upon the clearance between housing and rotating compressor blades. To control the over-tip leakage, abradable coating systems are applied on the housing. In the high pressure compressor they typically consist of a thermal sprayed multiphase material, comprising a metal matrix combined with a dislocator and/or a solid lubricant as well as a defined level of porosity. In this study, novel material systems have been sprayed via the plasma and flame spray process and compared to reference materials. Resulting microstructures have been analyzed as well as important coating characteristics evaluated, including coating hardness and erosion resistance. Furthermore rig tests were performed to analyse the coatings abradability behaviour under different operation conditions of the compressor.

Especially, composites of aluminium metal foams are of high potential for lightweight applications in automotive, aerospace and general engineering because of their excellent ratio of low weight and high stiffness. To fulfill the industrial need for these new materials as soon as possible, a new integrated manufacturing process concept has been developed and studied at our institute. The new “easyFoam-process” concept consists of four basic steps: production of semi-finished parts via the powder metallurgical route, forming of the foamable semi-finished part into a near net shape by extrusion or any standard aluminium-forming process, coating of the surface by thermal spraying and foaming by inductive heating. Thus it’s feasible to provide a fast, continuous and efficient production of metal foam composites with highly reproducible properties, resulting in eminent advantages over current techniques for foam sandwich production in terms of degree of anisotropy, statistical spread in foam properties and production economy. This process is also the only one being able to produce a graded pore structure in symmetrical parts of PM-aluminium foams. The thermally sprayed coatings serve simultaneously as mould and as future multifunctional coating. In this paper, some results of our first study in coating the foamable Al-tubes and inductive heating the coated parts are presented.

The efficiency of gas turbines is highly dependent upon the clearance between compressor housing and rotating blades. Abradable seal coatings are employed to minimize the clearance and control the over-tip leakage by allowing the blade tips to cut into the coating and herewith implementing a method of self-adjustment. These coatings consist of a thermally sprayed multiphase material, comprising a metal matrix, a dislocator and a defined level of porosity. Thermally sprayed abradable linings aim at a well balanced profile of properties relevant for the application as abradable seals. Amongst others these include: abradability, ageing resistance, corrosion and oxidation resistance as well as surface finish and bond strength to substrate materials. Due to the high demands in aircraft industry, the coating properties also have to match strict requirements with regards to quality control. Hence the spraying process has to be stable and well controlled. In this work, an APS sprayed abradable coating was sprayed with different sets of parameters and analysed by an on-line diagnostic system. The coating microstructure and properties were evaluated and related to the diagnostic results.

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.

Modern thermal spray equipments and diagnostic tools give a lot of relevant process data. Currently only single process parameters (e.g. particle temperature) are recorded and analysed in order to keep the parameters constant. However, even this simple kind of process control is not state of the art in every spray shop. The issue of this publication is the development of a method for prediction of material- and component-properties for thermal spraying. This method will allow an offline process control of the complex coating process. For the development of this kind of process control numerous experiments will be been carried out with both HVOF- and APS-processes using the Particle-Flux-Imaging diagnostic tool (PFI). The PFI-system is the basis for the process control to be developed. In comparison to other diagnostic tools it is easy to handle and cheaper. The set up of experiments and the data evaluation were carried out by means of statistical DOE [1]. The first series of experiments were designed to determine the significant interrelations between these influencing parameters. Based on the results from the first series of experiments, the significant parameters were further manipulated during spraying the second series of experiments The correlation between the coating properties (hardness, porosity) and the main influencing parameters are the basis for the creation of an offline process control.

Die-casting moulds are subjected to severe conditions of cyclical thermal and mechanical loads, as well as chemical and mechanical wear. Dies mostly fail due to a combination of wear mechanisms. Heat checking, erosion, melt corrosion and soldering often lead to complete die failure. Ceramic plasma-sprayed coatings have a great potential for die protection, since they are chemically inert, and show high form stability at elevated temperatures. Furthermore, they show good resistance against thermal shock due to the porous state of the coated layer and low Young’s modulus. In the present study, the influence of hot isostatic pressing on thermal fatigue resistance of plasma spraying coatings is investigated. Thermal and thermomechanical tests were applied to characterise their ability to protect dies. The coatings were evaluated by residual stress measurements, metallography, hardness test and X-ray diffraction.

This paper presents selected research results of the DFG founded project group, consisting of four institutes focusing on diagnostic methods in thermal coating processes. The aim of this group is to characterize the Atmospheric Plasma Spraying (APS) process by means of diagnostic methods so that – based on the requirement profile of the coating – appropriate adjusting of the process parameters can be realized. For this purpose, different diagnostic tools like Particle Shape Imaging, Laser Doppler Anemometry, Schlieren Technique, Particle Image Velocimetry, Enthalpy Probe, DPV 2000 and Thermography were qualified and adjusted to each other. Most of the results presented in this article are limited to the area close to the substrate which is difficult to handle with diagnostic methods. Additionally, new achievements concerning nozzle design and system enhancements are introduced.

Wear and friction properties of aluminium titanate, zirconium silicate and magnesium zirconate atmospheric plasma sprayed ceramic (APS) coatings in contact with 100Cr6 steel were investigated under dry sliding conditions as a function of high temperature. The tribological tests were performed at different temperatures varying from 20 °C up to 800 °C using an High Temperature Ball on Disk Tribometer. The wear scar diameters of the 100Cr6 steel ball were measured by optical micrograph. The cross sections of the worn ceramic coated disks were determined with a Laser Profilometer. Results show that as a result of the higher temperature (up to 400 °C), the material yields more readily (softening effects ) and so adhesion is the dominant wear mechanism. For hybrid bearing, operating temperature of about of 200 °C must therefore be avoided.

The application of wear resistant coatings onto the wall of aluminium engine cylinder bores by thermal spray have seen much development over the last 10 years, with regards to both equipment design and also to the material system used. While the technology has been successful in allowing the implementation of aluminium engine blocks into mass production, there is still room for improvement. One area that can be improved is the preparation of the substrate material in order to allow a good adhesion of the thermal spray coating. Grit blasting, a traditional preparation technique, is undesirable for a mass production environment due to the risk of the assembly areas becoming contaminated with grit. Therefore, an alternative method has been sought that can offer a suitable bond strength without introducing potential risks in the manufacture line. In this study, NiAl bond coats were sprayed onto aluminium substrates using the Plasma Transferred Wire Arc (PTWA) coating system developed by Ford Motor Company. A variety of surface preparation techniques, including traditional and some more novel methods, were used and analysed with respect to bond strength, ease of application and cost.

The number of parameters and noise factors that influence the plasma spraying process is huge, with over 200 known. Today, only a few parameters such as gas flow rate, current, voltage, spraying distance and substrate roughness can be controlled. In recent years, several particle diagnostic systems have been developed, which give the chance to control processes much better than at present. These techniques are now close to being introduced in industrial applications. In addition to the in-flight particle properties, the surface temperature of the substrate has a large influence on the coating quality. Statistical methods are widely used to quantify the influences of the particle and substrate characteristics. Neural networks provide a greater capability to analyse particle characteristics and substrate temperature data for coating quality control. In this work, the analysis of comprehensive process data and coating characteristics using neural networks is investigated and compared to established design of experiments (DOE) statistical methods.