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.

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.

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.

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.

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.

This paper reports morphological study of coatings microstructure performed on two selected reference abradable materials: AlSi-hBN and NiCrAl-Bentonite. Scanning Electron Microscopy (SEM) was used to obtain adequate micrographs for analysis. The porosity and non-metal particles morphology was assimilated to elliptical inclusions within the metallic matrix. Accordingly, they were described by means of three different geometrical parameters related to the shape, size and orientation distribution, allowing additional statistical analysis on the coatings.

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.

Nanostructured materials have a high potential to improve properties of thermal spray coatings. High-energy ball milling is an effective process to produce dispersion-strengthened powders with a homogenous nanoscale microstructure and superior mechanical properties compared to unstrengthened material. Because of the relatively low temperatures and heat flux during HVOF spraying, the microstructure of the powder particles can be maintained in the coating. In this study Al 2 O 3 - dispersion-strengthened NiCr powders were synthesised by high-energy ball milling, using optimised milling parameters. Thermal spray coatings were produced using the HVOF process. The improvement of the tribological behaviour and the potential for technical applications were evaluated. The study shows the favourable impact of mechanically alloyed MMCs on the tribological behaviour of HVOF coatings on the basis of an Al 2 O 3 -strengthened NiCr powder