Thermal spraying is a complex physical process consisting of three main sub-systems: flame/plume generation, powder/flame/plume interaction and coating build-up. While mathematical and CFD models provide valuable insight about the individual modules of a thermal spray process, it is very difficult to gain overall insight of the whole process and dependencies between different inputs and outputs using mathematical and CFD analysis, due to very complex and interconnected nature of the thermal spray process. In this work, a sophisticated experiment has been conducted to collect enough data for the sake of developing data-driven model of a plasma spray process. Metco 204 powder feedstock material and F4 gun have been used. An optimized number of data samples has been chosen by applying common industrial input parameters in the experiment. The developed neural network model is able to predict the coating quality parameters with acceptable average accuracy of above 90% on test data by considering all relevant measurement error deviations of the process analysis methods. A sophisticated user-interface has been developed to enable the use of the model for coating parameter development as well as the designing recipe for target coating characteristics. The developed model can be used for different purposes: parameter development, off-line coating quality control, and eventually adaptive coating control.

A conventional GTV K2 kerosene fuel HVOF spraying system has been modified with the aim to achieve process conditions comparable to cold gas spraying concerning the average particle velocities and surface temperatures in the spray distance. The employed measurements include the use of expansion nozzles that have been optimized for supersonic conditions up to a Mach number of 2.5 and the use of combustion chambers with reduced critical diameters that provide increased combustion chamber pressures up to 1600 kPa. Copper powders with different size fractions and oxygen content are sprayed with the novel HVOF technology. Coatings are analysed concerning their microstructure, oxygen content and electrical conductivity. In-flight particle velocities and surface temperatures are determined by the GTV NIR Sensor. Results are compared with those obtained for cold gas spraying using identical powders. The new HVOF technology permits the production of copper coatings that show similar levels of porosity, oxygen content and electrical conductivity like cold gas sprayed coatings. Also aluminium powder has been sprayed successfully with the novel technology. In-flight particle velocities can be almost as high as in modern cold gas spraying systems. Coatings are analysed and show a microstructure comparable to cold gas sprayed coatings.

In an effort to inhibit a climate change, the European Union has decided to reduce the CO 2 emissions by approx. 30% by year 2020, as compared to the level of emissions in year 1990’s. In general, traffic is responsible for 20% of all CO 2 emissions and 84% of those emissions result specifically from road traffic. In accordance with the present targets of the CO 2 emission reduction the automotive industry has to meet strict regulations. The strict emission goals can only be reached by weight reduction of the vehicle and by an improved efficiency of engine and drive train. Close to 50% of the friction losses in a combustion engine result from the interaction between the piston ring and the cylinder bore surface. Therefore the cylinder bores as well as the piston rings were coated with new, low-friction materials. The friction behaviour was characterized in linear reciprocating tribometer-test in order to identify the best combination of bore and ring coatings.

According to the present state of the art “in situ, real-time control systems” are absolutely necessary in modern applications within the field of Thermal Spray technology with regard to the quality and reproducibility of thermal spray coatings for a wide range of industrial applications. Compared with the already existing diagnostic systems and their algorithms which are developed on the basis of CCD cameras, an algorithm can be developed for in situ, real-time control systems, which possesses a by far closer physical approach for the determination of the particle characteristics due to the measurement principle. Thus, about 300 particles can be detected per millisecond as well as average particle velocities within the range of 30 - 1200 m/s and average particle surface temperatures between 700 - 3000 °C can be determined. A statistical distribution of approximately 3000 particles is considered for the computation of the online measured average particle velocities and surface temperatures. The accuracy of the measurement determines the use of an online process control during Thermal Spray processes.

A conventional GTV K2 kerosene fuel HVOF spraying system has been modified with the aim to expand the applicable range of process conditions in order to also cover the presently existing gap between conventional HVOF and cold gas spraying. Different measures have been applied in order to reduce heat transfer and increase momentum transfer to spray particles. Increase of momentum transfer results both in reduced particle temperature as a consequence of reduced dwell time in the hot flame area and high particle velocities. In detail expansion nozzles with conical shape that provide improved expansion of combustion gases, combustion chambers with reduced critical diameters that provide increased combustion chamber pressures and the injection of coolant media water and / or nitrogen into the combustion chamber are applied. The effect of modified spraying conditions on the process characteristics and coating properties have been studied for a variety of materials. Besides copper, titanium alloys and MCrAlYs also WC/Co(Cr) and Cr 3 C 2 /Ni20Cr have been sprayed and respective coatings have been analysed concerning their microstructure, gas content, microhardness and wear resistance. In particular a moderate increase of oxygen content in dense titanium alloy coatings compared to the powder feedstock from 0.41 to 0.59 wt.-% proves the high potential of the undertaken measures to expand the application field of HVOF spraying. Thereby existing systems only need relatively small modifications to achieve this expansion.

Titanium exhibits very good corrosion resistance property because of the formation of very dense oxide coating. Especially the good corrosion against Cl- solution for titanium material makes it wide applications in sea industry. It is very difficult to deposit titanium coating under atmospheric condition due to the strong affinity with oxygen and nitrogen especially in high temperature plume. Except the expensive LPPS process, much attention has been paid to the newly developed cold spraying. Unfortunately the stringent requirement for the starting power and low production efficiency limit the application of the cold spraying. A modified HVOF process was developed by reducing the outlet diameter of chamber and by directly introducing water into chamber, therefore lower plume temperature and higher chamber pressure than conventional HVOF process can be achieved. Attempts to deposit Titanium coating were carried out, and immersion of Titanium coated A3 steel into artificial seawater was performed in order to evaluate the density of as-sprayed Titanium coating. The results showed that dense Titanium coating could be obtained after parameter optimization and very few corrosion spot was observed on the surface of Titanium coated A3 steel after immersion into artificial seawater for 120 h.

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.

For deposition of protective coatings different coating techniques are available. Usually, detailed evaluation of various deposit types and materials is necessary for selection of the best suited coating for specific application fields and demands. Subject of this work are thermally sprayed functional coatings applied as wear (and corrosion) protective layers. Examination of different optimized thermal spray coatings, i.e. HVOF sprayed WC/Co(Cr) and Cr 3 C 2 /NiCr coatings, conventional flame sprayed and fused self fluxing alloy coatings reinforced by hardmetal and APS sprayed oxide Al 2 O 3 /TiO 2 and Cr 2 O 3 coatings, is done in comparison to thick hard chromium platings. Two abrasive wear tests featuring wear by lose abrasive particles are carried out. These impart dry wear conditions according to ASTM G65 (Rubber Wheel test) and wear by abrasive suspensions according to ASTM G75 (Miller test). The work also contains evaluation of newly developed HVOF torch components permitting increased combustion gas, and therefore also particle, velocities concerning the benefit in terms of coating properties. Exemplary evaluation of the new components influence on velocity and temperature of spray particles is carried out by comparative SprayWatch analyses. Both the influence on the coatings microstructure and the wear performance are studied. Coating microstructure is evaluated qualitatively by optical and scanning electron microscopy and the micro hardness HV0.3 is measured. Worn surfaces are studied by SEM in order to deduce wear mechanisms.

The combination of excellent mechanical, thermal and chemical properties of silicon carbide (SiC) and titanium carbide (TiC) has made these materials very attractive both for structural ceramics applications and for thermal sprayed coatings. To suppress oxidation and to avoid the formation of silicides during spraying of SiC-based composites, feedstock spray powders have been developed containing 32 wt.-% of an alumina-yttrium ceramic binder matrix. The spray powders are prepared by spray-drying and sintering (a&s). Also, TiC-based composite spray powders showing the same matrix material and content have been developed and produced. Thermal spray processing of the described powders by atmospheric plasma spraying (APS) using an F6 APS torch and high velocity oxygen fuel spraying (HVOF) with the Top Gun G acetylene torch is carried out. Both the produced coatings and feedstock powder are characterized by optical microscopy, X-ray diffractometry (XRD) and scanning electron microscopy (SEM) including energy dispersive X-ray analyses (EDXS).

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.

One of the most effecting parameters for the wire arc spraying with the regard to the properties of the sprayed coatings is the flow characteristic of the atomizing gas. Depending on the nozzle inner contour at the entrance of the torch, the atomizing gas is emanating the nozzle as a non-adjusted supersonic gas jet, either under- or over expanded. Thus, a convergent-divergent nozzle with a bell-shaped divergent exit is designed in order to generate a completely expanded atomizing gas flow inside the nozzle without any shock nodes in the emanating gas jet. The influence of the flow characteristic of the atomizing gas (air) on the droplet velocity is investigated by Laser- Doppler-Anemometry measurements. The coating quality is characterised with regard to the surface roughness and porosity.

Two new inner contours of de Laval nozzles (V70, V21) for F4 torch, which have already successfully been established for the Atmospheric Plasma Spraying (APS) are investigated for application under Vacuum Plasma Spraying conditions (VPS). Studies have been performed with regard to power efficiency, sound level and arc voltage fluctuations as well as coating quality and deposition efficiency for use of CoNiCrAlY powder as feedstock material. The results are compared to the commonly used standard VPS nozzle. CFD calculations and enthalpy probe measurements of plasma gas velocity and temperature distribution in the centreline of the supersonic plasma jets are carried out in order to get insight in the basic dependencies.

Detailed studies concerning influence of microstructural features on the resistance of different thermal spray coatings against dry abrasive wear (Taber Abraser test) and oscillating wear (ball on disk configuration) are carried out. Besides WC and Cr 3 C 2 based cermet coatings produced by a triple cathode APS system with axial powder feed and by HVOF systems using kerosene fuel also APS Cr 2 O 3 and Al 2 O 3 coatings are tested. At the example of WC/CoCr coatings the influence of carbide size and content, powder size fraction, powder manufacturing process and spraying process parameters is studied. For APS Al 2 O 3 investigations concerning the influence of powder feed rate and nozzle geometry of single cathode APS torch are imparted. Oscillating wear tests are performed using alumina and hardened steel balls as counter bodies. Coatings are characterized concerning phase composition and residual stress state by means of XRD. Additionally microstructure is evaluated by SEM investigations and micro hardness is measured. Guidelines for manufacturing of thermal spray coatings fitting the specific demands of the two applied wear conditions are deduced.

An optimised de-Laval-type-contour for the Atmospheric Plasma Spraying (APS) with respect to the thermal and deposition efficiency as well as to the arc voltage fluctuations and the sound level of the plasma torch is presented. Investigations of the plasma gas dynamics and two different feedstock materials (Al 2 O 3 (fused and crashed) and Cr 2 O 3 (agglomerated and sintered)) have been done to promote the industrial utilization of convergent-divergent nozzles for the APS.

A modified Laval-like-contour for a convergent-divergent nozzle is presented for the Atmospheric Plasma Spraying (APS). The influence of the nozzle design on the thermal and deposition efficiency as well as on the arc voltage fluctuations and the sound level of the plasma torch are investigated and compared with former investigations. The improvements of the quality of DC-Plasma sprayed Al 2 O 3 coatings by the nozzle design is shown by the coating porosity, adhesive and breakdown strength. A 2D-model presents the gas dynamics inside the nozzle. The intention of this study is to promote the industrial application of convergent-divergent nozzles for the APS in conjunction with the optimisation of the plasma gas dynamics.

This paper investigates the influence of nozzle design on the quality of Al 2 O 3 coatings produced by atmospheric plasma spraying. It compares the thermal and deposition efficiency of different plasma guns along with the porosity and adhesion strength of the resulting coatings. The intent of the study is the application of convergent-divergent nozzles as an economic alternative to the nozzles typically used for atmospheric plasma spraying. Paper text in German.