In this study, two high-Cr stainless steel feedstocks and a post-spray honing process are evaluated for potential use on cylinder running surfaces in passenger car engines. The two materials, X12 CrNi 25-4 and X6 Cr17, were deposited by plasma transferred wire arc (PTWA) spraying on aluminum cylinder bore surfaces that were mechanically roughened prior to coating. The coatings were then honed to a mirror finish using progressively finer diamond tools. Coating surfaces were analyzed by SEM and REM imaging, roughness profiles were recorded, and coating hardness and porosity were measured. The results are presented and discussed along with recommendations for additional work.

Since 2000, cast iron-liners have been replaced in several engine projects by Fe-based thermally sprayed coatings in the bores of a light metal crankcase. In contrast to cast in liners the linerless versions of these Al-crankcases are very demanding with regard to the porosity and tensile strength in the areas around the bores. The casting porosity has to be diminished to maximum pores smaller than 1mm² due to the roughening procedure, either mechanical roughening (MR) or high power water jet roughening (WR), in order to prevent either tool failure (MR) or widened pores (WR). At Nemak Dillingen these challenges are met by the Core Package Process (CPS), offering the advantages of a highly flexible casting design and a nearly unlimited choice of the cast alloy. These boundaries enable the production of lightweight crankcases made of the strong and creep resistant Al-Si-Cu based secondary alloy A319. The high quality of the cylinder bore surface is achieved by a carefully designed thermal household of the solidifying casting. The cylinder chill form a stable and sound shell in the very beginning of solidification, whereas feeding takes place from the sidewall structure of the crankcase. At the same time, specially designed chills for the bearing seat enable a very short solidification time, the resulting properties are crucial for highly loaded diesel engines. After casting and machining, the crankcases have been mechanically roughened and coated with 0.8 % C-Steel. The coatings and the interface between the coating and the casted Al-substrate have been investigated by means of light microscopy regarding the interlock between coating and substrate and the near-surface porosity of the cast metal.

Hypoeutectic AlSi engine blocks of modern passenger cars are generally equipped with cast iron liners in order to provide cylinder running surfaces that meet the tribological requirements. A very promising alternative to the use of cylinder liners lies within the application of thermally sprayed coatings onto the walls of cylinder bores as friction partners for the piston rings. This work describes the development of a novel iron based wire feedstock as well as its application by the Plasma Transferred Wire Arc internal diameter coating system. The material developed within the frame of this work leads to partially amorphous coatings with embedded nanoscale precipitations if processed by thermal spraying. The coatings were applied onto the inner diameters of test liners made of Aluminium EN AW 6060 and onto cylinder bore walls of in-line 4 cylinder engines. All substrates were mechanically roughened in order to obtain high bond strengths of the sprayed coatings. The coatings microstructure was analysed by light optical microscopy, hardness measuring by transmission electron microscopy. Furthermore the oil storage capacities of the honed surfaces were determined.

MCrAlY materials are widely used as bond coats for thermal barrier coatings on turbine blades. The aim of this work is to improve mechanical properties and wear resistance of thermal sprayed NiCoCrAlY-coatings by strengthening the coating with hard phase particles. In order to retain the effect of the dispersion reinforcement at high temperatures, the use of temperature-stable oxide hard phases such as ZrO 2 is necessary. To realise this new material structure, the high energy ball milling process is applied and analysed. With this process it is possible to achieve a homogeneous distribution of the oxide hard phases in the NiCoCrAlY matrix. The mixture ratio between NiCoCrAlY and ZrO 2 was varied between 5 wt-% and 10 wt-% ZrO 2 . The influences of the milling time of the high energy ball milling process on the distribution of the hard phases in the metal matrix were analysed. After spraying with a HVOF system the mechanical properties of the coatings are measured and compared with conventional NiCoCrAlY coatings.

In modern jet engines, the efficiency of the compressor stages is highly dependent on the clearance between blade tip and casing. In order to improve efficiency of gas turbines (i.e. areo engines as well as land based gas turbines), the gap between the rotating turbine blades and casing has to be minimized. Any increase in the gap results in power loss. Abradable coatings permit a minimization of the clearance and control of the over-tip leakage by allowing the blade tips to cut into the coating. Thermal sprayed abradable coatings 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, surface finish and bond strength to substrate materials. In this work, abradable coatings consisting of a multiphase material, comprising a metal matrix in addition to a solid lubricant as well as a defined level of porosity, were developed using the Triplex Pro 200 (Sulzer Metco, Wohlen, Switzerland) in order to increase the reproducibility and deposition efficiency. Additionally the influence of the process parameters on coating characteristics such as porosity, hardness and, resulting from this, coating erosion properties and abradability was investigated.

HVOF-sprayed carbide based coatings such as WC/Co or Cr 3 C 2 /NiCr are industrially well established for wear and corrosion protection applications. Due to their high carbide content of typically 75 wt.-% and more, they are providing a very high hardness and excellent wear resistance. Unfortunately costs for matrix materials like Ni or Co underlie strong fluctuations and are significant higher compared to iron. Therefore an alternative concept to the conventional carbides is based on TiC-strengthened low cost Fe-base materials, which are already in use for sintering processes. Depending on the carbon content the Fe-base material can additionally offer a temperable matrix for enhanced wear behaviour. Within this study the sprayability of TiC-strengthened Fe-powders with a gaseous and a liquid fuel driven HVOF-system has been investigated. The resulting coatings have been analysed with respect to microstructure, hardness and phase composition and compared to galvanic hard chrome, HVOF-sprayed and remelted NiCrBSi and HVOF-sprayed Cr 3 C 2 /NiCr (80/20) coatings as well as sintered Fe/TiC reference materials. Furthermore the Fe/TiC coatings have been heat treated to proof the retained temperability of the Fe-matrix after thermal spray processing. For determination of wear properties tribometer tests have been conducted. Currently the corrosion resistance of the sprayed Fe/TiC coatings is investigated as well the wear behaviour in a practical hydraulic test bench.

Saving energy is a major concern in every aspect of the economy, especially in the automotive and aerospace industry. The use of lightweight materials is one way to reduce weight of moving parts and thus energy consumption. Research activities to improve the porosity on the one hand, and the coating properties like wear and corrosion resistance on the other hand, show the potential of a hybrid coating process. The creation of thermal-sprayed coatings and a laser post-treatment enable a minimization of porosity and an improvement of wear properties. Different coating materials (e.g. Al-Si alloy) have been investigated regarding microstructure, hardness, wear- and corrosion protection.

Carbon fibre reinforced carbon (CFC) composites have been more and more used in different industrial areas as high temperature materials. Some application examples are CFC components in modern furnaces for heat-treatment and brazing. Because CFC components can react with metallic materials when they contact each other, diffusion barrier coatings are essentially important for such CFC components. The aim of the project IGF 14.880 N “Thermally sprayed diffusion barrier coatings for CFC components in high temperature applications” is to develop diffusion barrier coatings by thermal spraying technology. In the project, different coating systems have been developed and investigated regarding the coating build-up, coating microstructure, bonding, thermal shock resistance and diffusion barrier function. The research results reveal that some developed coating systems are suitable for applications in furnaces. In the present paper, some research results of this project are reported.

One of the most popular test methods for the evaluation of thermally sprayed coatings and substrate pre-treatment is the bond strength test in accordance to the standard EN 582 (in Europe) or ASTM C633-79 (in the U.S.). An interlaboratory test, carried out in 2003, has shown that bond strength tests of samples that were joined by different institutions in accordance to DIN EN 582 lead to bond strength values that varied by the factor 2, even if the same adhesive was used. The test not only made clear that the adhesives used to join the loading block to the substrate block but also many other parameters have a tremendous influence on the results of the bond strength tests. It was also clarified that the DIN standard needs to be supplemented in order to improve the comparability and the reproducibility of the bond strength test results. The first aim of this work was to identify the influencing parameters by carrying out Failure Mode and Effect Analyses (FMEA) together with namable institutions. Based on these results, a work instruction based on the DIN standard will be composed in order to avoid its weak spots. Later, a second interlaboratory test will be carried out to evaluate the quality of the work instruction.

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.

Demands on functional coatings with high dimensional accuracy and high surface quality has led to increasing interest in processing of very fine powder grades in a particle size range < 25 µm. Fine powders are not only showing a distinct potential for application of thin and dimensionally accurate coatings, but are also very promising for the production of dense and homogeneous coatings with improved mechanical properties. The large specific surface of fine powders is allowing for relatively low thermal energy levels that are introduced into the process. Nevertheless this also requires a very sensitive temperature control, to prevent overheating of the particles. The reduction of the thermal energy level is resulting in significant advantages particularly for the usability of the HVOF process for coating of inner diameters. Within this work in-flight particle properties of ultrafine carbide powders were analyzed. The studied HVOF process allows the adjustment of a broad parameter range by utilization of a hydrogen stabilized liquid fuel combustion process. A conventional straight nozzle type as well as a curved nozzle for internal spraying was studied. For a further assessment of the potential of ultrafine carbide powders also spray trials with a plasma spraying system have been made.

Process optimization and innovative material applications gain more and more interest under the aspect of continuously increasing functional and structural demands on thermal sprayed coatings. With the cascaded triple arc plasma gun generation, the atmospheric plasma spraying process was advanced by delivering enhanced plasma stability and, associated with this, higher deposition efficiency. The TriplexPro 200 is the latest version of a three cathode plasma spraying system on the market and offers distinctly higher particle velocities, due to its advanced nozzle design. As a result of the higher particle velocities, lower particle oxidation and higher coating density can be realized. In order to increase the corrosion protection of metallic coatings and the thermal properties of TBCs, the aim of the work performed is a parametric study to deposit advanced coating systems for high temperature applications.

After having established an offline process control based on the optical process diagnostic system PFI (Particle Flux Imaging) the process robustness has been increased by experimental identification of the impact of the noise factors „electrode wear“ and „injector wear“ in the APS process. Neural networks were used for implementing a process controller into a GTV APS process control center. In combination with the PFI system a tool was installed in the process center that is able to predict coating quality by analyzing some characteristics of the plasma and the particle plume. The neural network can be trained for all applications and all feedstock materials. An offline controller is instructing the operator through a desktop in order to train the network. The training, that means the monitoring of the process through different parameter setups and its reactions, is generated and executed automatically. Due to the fact that controlling the process parameters cannot influence every aspect of the coating quality, noise factors have to be regarded. For the APS process the electrode wear and the injector wear were identified as the most influencing noise factors. Both were analyzed by means of Design of Experiment (DOE) and long-term monitoring (200 hrs). The samples were characterized by light microscopy and different coating test methods that were chosen with respect to the coatings functions (e.g. wear resistance). The result of this work is a set of parameters that are as robust against both noise factors as possible and that are adapted to certain changes by a neural network process control.

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.

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.

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.

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.