One of the main levers to reduce CO2 emissions in cars and trucks is mass and friction reduction, which is often achieved through the use of special coatings. The aim of the present work was to develop metal-ceramic-lubricant composite coatings with the best combination of wear, seizure, fatigue, and thermal resistance. Metal-based coatings incorporating hard particles and solid lubricants were cold sprayed onto steel substrates and the relationship between coating microstructure and tribology was studied. To meet the demanding tribological requirements of heavily loaded engines, the interfaces between the different components were optimized by selecting appropriate feedstock powders and assessing a wide range of process parameters. Alumina-reinforced bronze composite coatings were made from powders with different morphologies. Aggregated ceramic powders were found to be more beneficial in terms of wear than massive powders, and graphite was found to be effective for reducing seizure.

Cold spraying of automotive engine blocks requires a gun adaptation for inner diameter spraying with a very short nozzle. In this work, 316L coatings are sprayed with such a gun and the behavior of particles impacting aluminum and stainless steel surfaces is studied in order to understand the factors that affect coating adhesion and cohesion. Correlations between spraying parameters and coating properties were investigated via design of experiments and the effect of process parameters on deposition efficiency and coating thickness was optimized for mass production. Post-process honing was also employed as part of the study and smooth coatings with small pores were obtained.

The aim of this work is to develop and assess an eco-friendly carbon-based composite coating for piston ring applications. The coatings were produced from sugarcane waste and Mo, NiCr, and CrC powders using high-velocity oxyfuel spraying and thermal chemical vapor deposition. SEM-EDS and XRD analysis confirms the presence of carbides and oxides that cause coating hardness to increase with increasing temperature. At 550 °C, under a 20 N load with a sliding velocity 0.3 m/sec, the friction coefficient of the coating was found to be 0.2, the wear value was 130 μm, and friction force was 4N. The results indicate that the friction and wear properties of the coatings improve with increasing temperature due to the formation of tribo-oxidative films and the effects of graphitization associated with the presence of carbon.

In times of duality of combustion engine and electric motor propulsion the automotive industry is developing both powertrain systems. Weight reduction and enhancement of efficiency plays a vital role in the conception of combustion engine for passenger cars. The thermal spray technology therefore is trend-setting as it achieves both aims. GROB-WERKE have, as reported previously, developed and integrated their GTS (GROB Thermal Spray) process for steel deposits in aluminum cylinder bores into their production lines. Further effort was now made to improve performance and versatility. The application of measurement and simulation technics hand in hand with extensive experimental investigation in spray deposit diagnostics as well as plasma and particle jet analysis led to highly developed and advanced deposit microstructure and cylinder bore topographies. Complex and extensive CFD (Computational Fluid Dynamics) simulation of the gas and particle flow gave the thermal spray process the highest performance, efficiency and product cleanliness.

Several surface preparation techniques are being used like grit blasting, HP water jet roughening as well as mechanical roughening for the preparation of Aluminum cylinder bore surfaces before a thermal spraying can be applied. However, in case of spray-repaired CI cast iron engine blocks the conventional mechanical roughening processes - using cutting inserts with small dovetail-undercut geometry - are not applicable due to the high hardness and high material toughness. Therefore such CI engine blocks are bored oversize in order to remove the bore wear damage and subsequently this rough-machined surface is coated by a NiAl-bond coating material in order to provide sufficient bond strength for the functional top coating material. In this paper it will be demonstrated that the 2-step spray-repair process can be replaced by a single-step process by using a new diamond-roll-roughening method. This process leads to significant higher bond strength values than the conventional process, including the bond coating material. PAT Adhesion test results as well as microstructural cross sections of coated cylinder bores will be presented. The principle of the roll-roughening process is outlined. In addition it will be shown that different mechanical roughening methods can be combined to obtain high bond strength values for spray-repaired aluminum blocks which require a higher coating thickness to compensate for the depth of the original mechanical bore activation.

Nowadays combustion engines are the most common way to impel vehicles. Thereby losses occur, due to cooling, exhaust gas and friction. Modern engines roughly dissipate 8% of the chemical energy stored in the fuel because of friction in different tribological systems. The highest potentials for optimisation can be found in the tribological system of inner surface of combustion chamber and piston ring. Besides friction, corrosive stress of inner surface of combustion chamber increases e.g. due to the utilization of auxiliary systems such as Exhaust-Gas-Recovery. In order to save energy, reduce emissions and enhance the lifetime of combustion engines innovative coating material systems need to be developed, especially for inner surface of combustion chamber. This study focuses on the development of innovative iron based materials for combustion chamber application using Plasma Transferred Wire Arc (PTWA) and Rotating Single Wire Arc (RSW) technologies. In order to improve the wear and corrosion resistance boron and chromium are added into the feedstock material. After deposition, different honing topographies are manufactured in order to evaluate their influence on the tribological behavior. Furthermore, electro-chemical corrosion tests are conducted by using an electrolyte simulating the exhaust gas concentrate. In conclusion an optimised coating material deposited by PTWA and RSW and improved surface topographies can be combined.

A390 alloy is a hypereutectic aluminum alloy with attractive mechanical properties at high temperature, good wear resistance and appropriate thermal properties making it challenging candidate material for automotive and aerospace applications. Currently, this alloy is widely used in automotive industry engine components production. In case of engine blocks, fatigue strength and wear resistance are the main cause of failure. Generally, the surface properties of aluminum alloys, in particular as hardness and wear resistance concerns, are insufficient to fulfill some requirements. Nowadays, there is an increasing interest toward the study and the development of innovative protective coatings suitable to enhance the wear resistance of such alloys. The goal of this paper is to develop appropriate protective coatings for A390 aluminum alloy enhancing its wear resistance. The study has been carried out to characterize the morphological, mechanical and wear resistance properties.

Due to the demand for improved fuel economy as well as increased safety features, weight reduction is one of the major aims in the automotive industry. Future lightweight automotive components for the next car generation will probably use lots of magnesium alloy. These will form galvanic couples with other materials and may induce phenomena accelerating the corrosion rate of automotive components. The materials used were magnesium alloy AZ31B and several types of cold sprayed coating. The relative performance of each cold sprayed corrosion preventive compounds (CPC) was assessed in combination with the materials under several different electrochemical and accelerated corrosion tests. Baseline data for AZ31B with no CPC applied was also collected. CPC characteristics and properties are also included and discussed. The studies on bare Mg/Steel couples validated accelerated corrosion but found that CPC cold sprayed coatings mitigate corrosion rates. Thus Mg/Fe interfaces with defect-free cold sprayed coatings CPC can prevent buildup of corrosion products and reduce galvanic corrosion of automotive components.

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.

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 application of thermal coatings in cylinder bores is depending on above all functionality, process reliability and economy of pre treatment of the substrate surfaces. Different removing processes like water jetting or sand blasting are increasingly substituted by mechanical machining. Thereby great importance is attached to functionality and degree of automation. For an assured engine function, high bond strength is required. The roughening process as a modified cutting machining meets the requirements of modern production lines. Removing overspray after thermal coating by a water jetting process, is a further contribution for a higher automation degree. The final machining of sprayed surfaces is effected by a multi stage honing process. The composite structures of thermal coated layers call for high performance diamond abrasives. The finished functional cylinder surface comprehends cavities of thermal coated layer and smooth honing pattern. The technological description of roughening and honing, the process components as well as the machining results will be presented. Pre and post treatment are essential processes, which enable the application of high performance thermal coating materials in friction optimized combustion engines.

This study compares the tribological performance of HVOF and HVSFS coatings applied to gray cast iron and aluminum cylinder liners. Five different materials, including Fe alloy, FeCrMo, CrC-NiCr, NiCrBSi, and WC-Co, were sprayed using a conventional HVOF torch operated by a six-axis robot while the liners were manipulated by means of a rotary table. A similar setup was used to spray TiO 2 -TiC coatings, but the gun was modified for nano-sized particles in a suspension fed axially into the combustion chamber. Coating microstructures were examined using optical and SEM imaging and friction and wear properties were determined through oscillating friction wear tests. The results obtained are compared to state-of-the-art cylinder liners.

Widely studied in the 1980s, the insulation of pistons in engines aimed at reducing the heat losses and thus increasing the indicated efficiency. However, those studies stopped in the beginning of the 1990s due to NOx emission legislation, and also due to acceptable oil prices. Nowadays, with the improvement of exhaust after treatment systems (Diesel Particulate Filter, Selective Catalytic Reduction, and Diesel Oxidation Catalyst) and engine technologies (Exhaust Gas Recirculation), there are more trade-offs for NOx reduction. Besides, the fast rise of the oil prices tends to come back to insulation technologies in order to save fuel. This paper deals with the realization of a 1 mm thick plasma sprayed thermal barrier coating with a graded transition between the topcoat and the bondcoat on top of a serial piston for heavy-duty truck engines (11L displacement – Exhaust Gas recirculation – Single Stage Turbocharger with Variable Geometry Turbine and intercooler). The effects of the insulated pistons on the engine performance are also discussed.

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.

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.

New advanced thermal spray technology allows providing wear resistant coatings on the cylinder surface of aluminum or magnesium engines. The obtained special surface topography after the finishing allows to decrease significantly the coefficient of friction and to decrease the fuel consumption of an amount of 2 to 4%. Engine tests on diesel and gasoline engines have confirmed the value of this technology regarding the aspect of energy saving. This coating technology is introduced since 5 years in Europe by the manufacturing of high power diesel and gasoline engines respectively. The combination of different MMC coating materials allows the development of new specific solutions for each type of engine. Coatings with improved corrosion resistance and abrasion resistance were also developed and are available now. A brief overview on other applications of thermal spraying in the automotive industry will be also given. The MMC coating shows interesting perspectives for its use in diesel engines equipped with EGR systems to reduce the wear of the cylinder bores.

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.

Since about the year 2000, cast aluminum automobile engine blocks have been coated in production lines using internal plasma spraying technology. Using this approach, the coefficient of friction between the cylinder wall and the piston assembly can be reduced to 30% and oil consumption is reduced of a factor two in comparison with cast iron. The extremely low wear rate of the friction elements increases engine life and reduces maintenance costs. The fuel consumption of the cars can be reduced from 2 to 4% in the case of gasoline and diesel engines. The coating costs are strongly dependent on production volume. For high volume production, the costs can be similar to those for cast iron liners. This paper reviews results from laboratory and field tests evaluating the performance and cost efficiency of plasma sprayed engine block liners.

Diesel engine development is continuously progressing: light vehicle diesel (LVD) engines are gaining in popularity in Europe and therefore we see a steady improvement in power performance and fuel consumption going along with increased loading of the power-cylinder components. Moreover, heavy-duty (HD) engines for trucks are facing stricter environmental legislation leading amongst other technologies to the introduction of exhaust gas recirculation (EGR). Whatever reduced emission technology will be applied, they all will significantly influence the engine tribology. This paper is dedicated to describing modern piston ring coating technologies to face the future diesel engine demands. The paper mainly focuses onto modern piston ring coating technology such as hard particle reinforced chrome plating, HVOF spraying and PVD. In particular, it will be discussed how thermal spray coatings need to be designed to find their position among established or future coating technologies of the competition.