In this work, metal-based thermal barrier coatings (MBTBCs) for use in low heat rejection diesel engines have been produced, using high frequency induction plasma spraying (IPS) of iron-based nanostructured alloy powders. Important advances have been made over recent years to the development of ceramic-based thermal barrier coatings (TBCs) for diesel engines, but they are not yet applied in mass production situations. Besides the important economic considerations, the reliability of ceramic TBCs is also an issue, being associated with the difficulty of predicting their “in-service” lifetime. Through engineering of the nano/amorphous structure of MBTBCs, their thermal conductivity can be made as low as those of ceramic-based TBCs, with reduced mean free paths of the electrons/phonons scattering. In this work, nano/amorphous structured coatings were deposited by IPS using the following spray parameters: spraying distance (200mm), plasma gas composition (Ar/N 2 -85/15, by volume %), IPS torch power (25kW), and powder feed-rate (16g/min.). The structure and properties of the deposited layers were characterized through SEM (Scanning Electron Microscopy) observations. The thermal diffusivity (α) properties of the MBTBCs were measured using a laser flash method. Density (ρ) and specific heat (Cρ) of the MBTBCs were also measured, and their thermal conductivity (k) calculated (k =αρCp). The thermal conductivity of MBTBCs, with 7.5% total porosity, was found to be 1.22 W/m/K. The heat treatment study showed that phase transformation started at 650oC, and grain size growth from nano- to micron- scales occurred at around 1000°C under static exposure conditions. Thermal expansion coefficient (TEC) of MBTBCs was 15E-6 /K, which is close to the TEC of cast iron and thus, closer to the TEC values of aluminium alloys than are conventional TBCs. Fracture toughness of MBTBCs has also been assessed by use of Vickers hardness tests, with a 100 g load for 15 s, and the results show that there are no measurable crack developments around “indented” areas on all samples of MBTBCs tested.

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.

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.

Hot corrosion tests have been conducted on Ni- and Cr-based laser coatings, a high-velocity oxy-fuel (HVOF) sprayed coating and various wrought alloys covered with a synthetic salt of Na 2 SO 4 -V 2 O 5 and exposed at 650°C for 1000 h in air. Coating microstructures and reaction product layers were analyzed with scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The hot corrosion resistance of tested specimen was evaluated by measuring its mean thickness loss. Generally, wrought alloys, HVOF coating and Cr-based laser coatings suffered from selective corrosion beneath salt film, that is, distinct Cr-depleted layer was formed at alloy/salt interface. Cr-based laser coatings exhibited extended solid solubility and they transformed towards equilibrium condition. Cr-rich phases enriched further with Cr and they were prone to corrosion. Low diluted laser coatings and HVOF coating were more resistant to hot corrosion than commonly used industrial standard alloy, Nimonic 80A. Ni-based laser coating exhibited resistance equivalent to Cr-based coatings and superior to corresponding wrought alloy.

This work is devoted to the study of peculiarities of thermal sprayed coatings behavior under conditions of cavitation, as well as the elaboration of compositions of cavitation-resistant coatings and technology for their application with the aim of engine cylinders sleeves protection from cavitation-erosion destruction. The methods of arc metallization, flame and plasma spraying were used for coatings deposition. Powders of metal alloys and oxides, mechanical mixtures of nickel alloys with carbides, wires and flux-cored wires were applied as materials for thermal spraying. Method of magneto-striction vibration was used to determine the coatings cavitation resistance. A correlation between a bond strength of coatings and the character of their cavitation destruction was established. The best results were obtained in the case of using stainless steel wires and flux-cored wires using. Resistance of coated diesel engines sleeves was increased 1.6 times in comparison with sleeves without coatings. Semi-automatic line for arc metallization of diesel sleeves with a production of 600,000 sleeves per year was designed, build up and put into operation.

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.

Aluminum alloy has been gradually utilized in cylinder block instead of ferrous casting material for weight reduction in automobile industry these days. In order to acquire more weight reduction, a new liner-less technology - without cast iron liner used - is putting into practice in the fields of aluminum cylinder block and the target is for diesel engine. However, diesel fuel's impurity "sulfur" element and corrosive attack risk, such as sulfuric acid generated to the surface of liner is higher than gasoline fuel. Because of such disadvantage, wear and corrosion resistances applied to the inner cylinder-bore are required in order to achieve this liner-less aluminum cylinder block. This research is intended to accomplish both wear and corrosion performances using plasma thermal spray technology and to verify the feasibility of application to actual engine bore. A newly-developed ferrous powder (Fe-C-Ni-Cr-Cu-V-B alloy) revealed extremely excellent corrosion and wear resistances, compared with currently used bulk casting materials such as Fe-C-Si-B alloy and Fe-C-Si-Mo-B alloy for cylinder liner. For the last time, the new ferrous alloy powder was applied to actual engine bore by using Rota-Plasma spray coating. The experimental results with engine bore presented potential equivalent to current engine bore.

A new challenge in the transport systems concerns with improving efficiency. Thermal swing coatings are interesting candidates for internal combustion engines due to their potential to reduce cooling requirements and increase efficiency. K 2 Ti 6 O 13 (KTO) thermal barrier coatings (TBCs) were prepared by atmospheric plasma spraying through powder structure design and optimization of deposition conditions. The thermophysical properties of plasma-sprayed KTO deposits and their effect on the thermal swing have been investigated. Their thermal conductivities were tested by a laser flash method and the thermal performance of the coatings was further examined by thermal swing test. The phases, nominal chemical compositions and microstructure of KTO deposits were characterized by X-ray diffraction (XRD) and scanning electron microscopy combined with energy dispersive spectrometry (SEM-EDS). The results indicated that the chemical composition change occurs to the coatings resulting in a deviation from nominal stoichiometry due to chemical reactions between the plasma gas and particles. The thermal conductivity of the coating is very sensitive to the coating compositions, and the coating prepared using porous powder under pure argon presents a single K 2 Ti 6 O 13 phase and high porosity, and the lowest thermal conductivity of 0.85 W/m·K.

The development of thermal barrier coatings (TBCs) for diesel engines has been driven by the potential improvements in engine power and fuel efficiency that TBCs represent. TBCs have been employed for many years to reduce corrosion of valves and pistons because of their high temperature durability and thermal insulative properties. There are research programs to improve TBCs wear resistance to allow for its use in tribologically intensive areas of the engine. This paper will present results from tribological tests of ceria stabilized zirconia (CeSZ). The CeSZ was applied by atmospheric plasma spray process. Various mechanical and thermal properties were measured including wear, coefficient of thermal expansion, thermal conductivity, and microhardness. The results show the potential use of CeSZ in wear sensitive applications in diesel applications. Keywords: Thermal Barrier Coating, Diesel Engine, Wear, Thermal Conductivity, and Thermal Expansion

For more than two decades researchers have been working on thermal barrier coatings to improve the performance of diesel engines. However, these coatings have still not achieved widespread application in conventional diesel engines. The original motivation for this work was the improvement of fuel economy, since even a few percent improvement would result in huge savings in the transportation industries, but the coatings also effect exhaust emissions, component wear, and the sensitivity of engines to fuel quality. Wear at high temperatures, where conventional lubricants are not effective, is a serious problem in low heat rejection engines. Ceramic materials such as thermal barrier coatings in cylinder liners must have an acceptable wear rate and coefficient of friction. In this work we compare the wear behaviour of nanostructured thermal spray zirconia coatings with conventional zirconia coatings. First, process parameters that allowed the nanoparticles present in the feedstock powder to be retained in the coating were found. Then pin on disc wear tests of the two types of coatings were carried out at room temperature. The coating containing retained nanoparticles exhibited a lower coefficient of friction and less wear loss under discontinuous testing than the conventional coating.

Increasing the combustion temperature in diesel engines is an idea which has been pursued for over 20 years. Increased combusting temperature can increase the power and efficiency of the engine, decrease the specific fuel consumption, CO and (possibly) the NOx emission rate. At the same time, TBCs should protect the metallic substrate against the corrosive attack of fuel contaminants (Na, V, and S). The most common system used is Yittria Partially Stabilized Zirconia (Y-PSZ). However, in diesel engines Y-PSZ TBCs have not met with wide success. To reach the desirable temperature of 850-900°C in the combustion chamber from the current temperature of 350- 400°C, a coating with a thickness of at least 1mm is required. This introduces different considerations than in the case of turbine blade coatings, which are on the order of 100µm thick. The design of a multilayer coating employing relatively low cost materials with complementary thermal properties is described. Numerical models were used to optimize the thickness for the different layers to yield the minimum stress at the operating conditions while achieving the desired temperature gradient. Abstract only; no full-text paper available.

Partially stabilized zirconia (8Y2O3-ZrO2) coatings were studied as thick thermal barrier coatings (TTBCs) for diesel engine applications. To improve the hot corrosion resistance of TTBCs the 1 mm thick yttria stabilized zirconia coating was densified with aluminum phosphate based sealant. Combined with better hot corrosion resistance other benefits obtained with sealing treatment are improved adhesion as well as increased mechanical properties of the ceramic layer. Three aluminum phosphate based sealants were investigated with varying viscosity level. Different sealant viscosities were used to optimize the level of sealant penetration into the coating. Sealant penetration and the violence of the reaction were determined by XRD, SEM/EDS and optical microscopy. The hardness profile from bond coat to the surface of the top layer was determined. Coating microstructure and phase structure were characterized by optical microscopy and by X-ray diffraction. Microhardness and porosity were determined. Residual stress states were measured by X-ray based stress analyzer. Bond strength of the coatings was determined with tensile test equipment. To simulate the diesel engine combustion conditions, hot corrosion tests were performed for the sealed TTBCs. Hot corrosion resistance of the coating was tested in isothermal exposure of 60Na2SO4 - 40V2O5 melt for 48 hours at 600 °C.

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.

Zirconia based, 8Y 2 O 3 -ZrO 2 and 22MgO-ZrO 2 thick thermal barrier coatings (1000µm), were studied with different sealing methods for diesel engine applications. Aim of the sealing procedure was to improve hot corrosion resistance and mechanical properties of porous TBC coatings. The surface of the TTBCs was sealed with two different methods, phosphate based sealing treatment and laser glazing. The thickness of the densified top layer in all cases was 50-400µm. XRD analysis showed some minor phase changes and reaction products caused by phosphate based sealing treatment and some crystal orientation changes and phase changes in laser-glazed coatings. The porosity of the outer layer of the sealed coating decreased in all cases, which led to increased microhardness values. The hot corrosion resistance of TTBCs against 60Na 2 SO 4 - 40V 2 O 5 deposit was determined in isothermal exposure at 650°C for 200 h. Corrosion products and phase changes were studied with XRD after the test. Short-term engine test was performed for the reference coatings (8Y 2 O 3 - ZrO 2 and 22MgO-ZrO 2 ) and for the phophate sealed coatings. Engine tests were performed at the maximum load of the engine and it was aimed to evaluate the thermal cycling resistance of the sealed coatings. All the coatings passed the engine test, but some vertical cracks were detected in the phosphate sealed coatings.

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.

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.

This paper provides an overview of thermal spray activities in Finland, Sweden, Norway, and Denmark. In Finland, thermal spray technology has widest use in pulp and paper processing, protecting various types of rolls and cylinders. In Sweden, the technology is of great importance in the manufacture of aero engines and industrial gas turbines. In Norway, thermal spraying is widely used in offshore applications, including subsea oil drilling enterprises, and in Denmark, thermal spraying is used in boilers, maritime diesel engines, and for wear resistance of machine tool components. Development and innovation in thermal spray technology in northern Europe is dominated by research conducted in Finland and Sweden, followed by Denmark and Norway.

The future demands of diesel engines require new options for low-friction and wear-resistant materials in order to increase efficiency and achieve environmentally sound solutions. Efforts are made to improve the performance and reduce the weight of engine blocks by coating the Aluminium cylinder bores with thermal-spray processes. Thus beside other means today nanocrystalline coatings are currently discussed, which should allow for the desired combination of structural, productional, and topographical properties. Beside sufficient tribological properties it is important that the composite (base material and coating) allows for an elongated endurance under cyclic mechanical and thermal stresses. In this work a four-point-bending test was used to examine deleterious failure mechanisms during fatigue such as spalling of the coating or delamination from the substrate. Therefore various thermally sprayed coatings were bent in tension and compression. The results were analysed in relation to the coating microstructure.

In the present study, yttria-partially-stabilized zirconia (YSZ)/Al 2 O 3 coatings, which are used for jet engines, gas turbines and diesel engines were coated with thermal barrier coatings (TBCs) to provide high thermal resistance, reduce the metal surface temperatures, and increase component durability. The effect of alumina addition from 0 to 80 wt% on the properties of plasma sprayed YSZ coatings was investigated. The coatings were produced using a METCO 3MB plasma spray gun on stainless steel and graphite substrates. Scanning electron microscopy (SEM) was used to analyze the microstructures of the coated samples. The microhardness was investigated depending on the alumina contents. Vickers hardness on cross section of coatings was observed to increase with the increase in alumina mixing ratio. The presence of alumina phase commonly improves the mechanical properties of YSZ.

The experimental results of developing tribological surface coatings for high temperature application are presented. The primary focus of this work was in the area of high output advanced, low heat rejection (LHR) diesel engines, where high temperature lubrication between the piston ring and the cylinder liner wall surface is essential. The target temperature focused upon in our research is an operating top ring reversal temperature of approximately 1000° F. The technology developed typically involves treating a porous thermal spray coating with chemical binders improving coating strength and integrity and eliminating open porosity to form an almost monolithic appearing coating. The effectiveness of the densification through the coating thickness was studied. It has been shown that densification process improves mechanical properties and dramatically extends coating wear resistance. Good results were obtained using densified plasma spray Iron oxide (hematite) for a cylinder liner coating versus plasma sprayed Tribaloy T 800 for piston ring. Single Cylinder LHR engine test successfully demonstrated the feasibility of this tribological pair for the possible future applications.