This paper presents an assessment of the properties of three thermal sprayed coatings for a thermal barrier applied to the piston head of an internal combustion engine. Coating (1) has a topcoat of Al 2 O 3 and a bond coat of Ni-Cr. Coating (2) has a topcoat of YSZ and a bond coat of CoNiCrAlY. Coating (3) is 316 stainless steel. The investigators conducted thermal cycle tests and tensile pin tests, and evaluated the thermal barrier effect of the coatings. The results showed that coating (3) had no cracks or delamination after the thermal cycle test, while coatings (1) and (2) had partial cracks and delamination. Coating (2) had the highest adhesion strength, and its thermal barrier property was better than that of coatings (1) and (3). In terms of cost and overall evaluation, coating (3) was considered the most reasonable and appropriate thermal sprayed coating for the piston head application.

Thermal barrier coatings (TBCs) are widely used to insulate the combustion chamber of internal combustion engines to improve their performance efficiency, reduce pollution, and protect the metals from high temperature oxidation. In this work, a TBC coating composition of 80% zirconium oxide and 20% gadolinium oxide (GdPSZ) was prepared in the laboratory and plasma spray coated on the combustion chamber of single-cylinder diesel engines. An engine performance test was conducted for both the baseline (uncoated) engines and the coated engines. The coatings in the combustion chamber of the engines were found to be well adhered after 300 hours of rigorous testing. A significant reduction in smoke density was observed, especially at higher loads, for the coated engines. However, the coated engines exhibited a 2-6% reduction in volumetric efficiency and an increase in brake-specific fuel consumption compared to the uncoated engines. The results for other performance parameters are also discussed.

The HVOF sprayed wear resistant hardmetal coatings with favourable sliding properties are suitable for increasing the lifetime of sliding applications, such as pistons of combustion engines, pumps and other hydraulic devices. In practice, the coatings face the problem of their interaction with other media, in the case of sliding wear usually lubricants. In the paper, the friction properties of five different HVOF sprayed coatings are evaluated by pin-on-disk test according to ASTM G-99 under dry and lubricated conditions and lubricated block-of-ring test according to ASTM G77. Several types of lubricants designed for combustion engines were used to compare their influence on coatings sliding wear behavior. Based on the results, the suitability of coatings for the application on the engines parts is discussed and the effect of counterpart material and different types of lubricants on the coefficient of friction and coatings wear rate is analyzed. It was confirmed, that the CrC-based coating are more suitable for the application under the condition corresponding to combustion engines, e.g. elevated temperature and steel counterpart, than the WC-based coatings. From the group of CrC-based coatings, the superior behavior was observed at the CrC-CoNiCrAlY coating, the matrix material of which offers further enhancement of the sliding wear behavior.

In rocket engine combustion chambers the cooling channels are subjected to extremely high temperatures and environmental attack. Because of the good heat conduction the inner combustion liner is made of copper. Thermal and environmental protection can be provided by Thermal Barrier Coating Systems. The performance of an APS-sprayed standard coating system for nickel based substrates (NiCrAlY and YPSZ) on copper substrates is investigated. Because mechanical and thermal properties (e.g. the coefficients of thermal expansion) of the two substrates are different, known failure mechanisms for nickel based substrates can not be directly transferred to the new application. Thermal cycling and laser shock testing is performed to identify possible failure mechanisms. The laser shock setup consists of a high-power diode laser (3kW) and realizes surface temperatures of up to 1500°C. Furthermore, it is possible to realize high thermal gradients inside the specimen, similar to those in real service. Delamination of the thermal barrier coating at the interface between bond coat and substrate is observed. Usually, this interface is not failing in standard applications, which gives an important hint for further research. Furthermore, FEM analysis confirms that stresses are maximal at this interface.

To meet new regulations and specifications for internal combustion engines, new approaches to significantly decrease fuel consumption and emissions are needed. The deployment of tribologically functional coatings applied by supersonic flame spraying represent a promising technology for achieving these targets. Thermally sprayed coatings can help in improving efficiency of internal combustion engines by reducing the internal friction and improving the durability and wear resistance of the engine’s cylinder wall thereby facilitating extreme engine downsizing concepts. Thermal spraying is also capable of processing highly corrosion resistant materials like alloys and ceramics to enable the safe utilization of biofuels in modern combustion engines. In addition, specific surface structure of thermal spray coatings, including their intrinsic porosity, shows the benefit of reducing the friction by sustaining hydrodynamic friction even in spots with low relative movement, e.g. top and bottom dead center. On top, the open surface porosity can reduce the oil consumption and thereby decrease the polluting emissions of internal combustion engines. The thermally sprayed coatings were applied using HVOF and HVSFS processes deploying various materials, including novel nanostructured powders. The coated cylinders and engines have been compared to state-of-the-art components with respect to friction coefficient, wear and oil consumption.

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.

The blast erosion-resistance properties of HVOF thermal spray Cr 3 C 2 type coating system and aluminized material were examined to improve erosion-resistance of turbine housings of compressors used in turbochargers for marine diesel engines. As a result, the erosion life of aluminized material is as same as that of the substrate, on the other hand the erosion life of thermal sprayed coating is ten times of that of the substrate. Therefore, erosion life of turbine housing can be extended by the surface treatment procedure. This technology is applicable to actual products.

The proposed work describes recent efforts to develop metastable Al-Fe-V-Si coatings for internal-combustion engine applications with higher mechanical properties at high operating temperatures. To do so, the metastable solid powder alloy was engineered from rapid solidification technique (namely gas atomization). The metastable alloy powder was deposited using the Cold Spray process in order to produce protective coatings on top of existing parts. The critical velocity, above which Cold Spray deposition takes place, was successfully achieved and Al-Fe-V-Si coatings were produced. The microstructure of the feedstock powder was retained in the coatings produced, showing the potential of the Cold Spray process to produce metastable coatings for internal combustion engine applications.

In the last decade 3D-CFD has been successfully established for three-dimensional simulations of fluid flow, mixture formation, combustion and pollutant formation in internal combustion engines. In direct injected engines, the accuracy of simulation results and hence their contribution to design analysis and optimization strongly depends on the predictive capabilities of the models adopted for simulation of the injector flow, spray formation and propagation characteristics. The original KIVA-3V code uses the droplet collision algorithm of O’Rouke for calculating collisions in Lagrangian spray simulation. The modified KIVA-3V code includes no-time-counter (NTC) method which is proposed by David P. Schmidt (2000). The NTC method of calculating spray droplet collisions is both faster and more accurate than the current standard method of O’Rouke. In this work an original and a modified version of KIVA-3V multi-dimensional CFD code is used to simulate the spray resulting from the injection of diesel fuel. Numerical results from original and modified KIVA-3V are compared to experimental data and also results obtained from Fire code.

Aluminium-based plain bearings for gasoline internal combustion engines are traditionally manufactured by casting and rolling, followed by forming and boring. The application places severe demands on the bearing material and a combination of properties such as fatigue, seizure and wear resistance are required. These properties are achieved by using a multi-phase material comprising of a distribution of tin in an aluminium alloy matrix. HVOF has been investigated as an alternative process for bearing manufacture and as a route to producing novel bearing materials with microstructures that cannot be achieved using the conventional casting route. The work reported describes the use of different HVOF spraying systems and powder types to develop aluminium-tin based coatings for advanced bearing applications. The coatings are described in terms of microstructure characteristics. The fatigue performance of the advanced sprayed bearings is compared with conventional cast bearings.

Atmospheric Rheo-Spraying (ARS) using the HVOF process enables injection-molded structures and thick-film coatings from steels and from high-temperature Ni-based alloys with layer thicknesses down to the centimeter. The ARS process control is based on the thermal spraying of particles in the solid state at a maximum average speed of more than 600 m/s. The coating consolidation to porosity values below 1% occurs through the particle impact with high kinetic energy. Because of the low particle oxidation, the mechanical properties of the heat-treated injection-molded structures are comparable to those of forged alloys. In this paper, ARS injection molding is successfully implemented in combination with an innovative manufacturing technique in rocket engine technology to produce a model composite combustion chamber with a thermally sprayed internal pressure jacket. Paper includes a German-language abstract.

This paper investigates the stability of molybdenum base silicides, which are located in combustion chambers and in an endothermic environment, for use in radiant tubes for heat treatment. The subject matter was plasma-sprayed molybdenum disilicide, pentamolybdenum trisilicide, hot-pressed molybdenum disilicide, and molybdenum disilicide composites containing SiC and silicon nitride reinforcements. Results of the investigation show that the oxidation resistance of plasma sprayed molybdenum disilicide can be detrimentally effected due to the silicon loss that occurs during the high temperature plasma spray process. Paper includes a German-language abstract.