Recent studies have shown that graphene can improve the tribological performance of materials by lowering the coefficient of friction and increasing wear resistance. In this present work, the authors evaluate an inductively coupled plasma process that synthesizes graphene nanoflakes in-flight and uniformly deposits them on metallic substrates. The quality of the graphene flakes was characterized and coating surface friction was measured using a ball-on-three-plates tribometer. Test results showed that graphene nanoflake coatings reduced the coefficient of friction of steel from 0.6 to less than 0.2.

Due to good performance in abrasive and sliding wear and enhanced oxidation behavior, coatings based on Co-Cr-W alloys are widely used in industrial applications, where the material is exposed to high temperature. Within the scope of this study, a Co-based alloy similar to commercial Stellite 6, which additionally contains 20.6 wt.% of vanadium, was deposited by Twin Wire Arc Spraying (TWAS). Multi-criteria optimization using statistical design of experiments (DoE) have been carried out in order to produce adequate coatings. The produced coatings have been analyzed with respect to their tribological behavior at elevated temperatures. Dry sliding experiments were performed in the temperature range between 25°C and 750°C. Oxide phases were identified in the investigated temperature range by X-ray diffraction (XRD) using synchrotron radiation. The V-doped Stellite-based coating possesses a reduced coefficient of friction (COF) of about 0.37 at elevated temperatures (above 650°C), which was significant lower when compared to conventional Stellite 6 coating that serves as reference. In contrast, both produced coatings feature a similar COF under room temperature. X-ray diffraction reveals the formation of cobalt vanadate and vanadium oxides above 650°C. The formation of vanadium oxides exhibits the ability of self-lubricating behavior, thus leading to enhanced tribological properties.

NiCrBSi is a material generally used in wear-resistant coatings. In order to improve the tribological properties of atmospheric plasma-sprayed NiCrBSi coatings, Molybdenum (Mo) was incorporated into the NiCrBSi coatings to reduce the friction coefficient and wear rate under dry and oil-lubricated conditions. In this paper, Mo-NiCrBSi composite coatings with Mo content of 5, 10, 20 and 30 wt.% were deposited on stainless steel substrates respectively by atmospheric plasma spray. X-ray diffraction, optical microscopy and scanning electron microscopy equipped with energy dispersive spectroscopy were utilized to investigate the phase structure and surface morphology of the composite coatings. Reciprocating friction tests were conducted to measure the friction coefficients and 3D optical microscopy was used to depict the wear track profiles. The results showed that the 30 wt.% Mo-NiCrBSi coating exhibits the best tribological performance. In addition, MoO 2 and MoS 2 films were formed in the friction process under dry condition and oil-lubricated condition respectively.

Wear-resistant cobalt–based alloy (Stellite 12) coatings deposited by plasma transferred arc (PTA), commonly used to protect critical mechanical components in harsh environments, were modified by addition of hard ceramic particles (TiC) and solid lubricant compounds (MoS 2 and CaF 2 ) to improve the overall tribological performance. In this preliminary study, microstructural, microhardness and tribological analyses were carried out to assess: a) the feasibility of PTA deposition of thermally sensitive phases characterised by very low density; b) the effect of the addition of a mixture of soft and hard phases on the coating hardness; c) the effect of the modified composition in terms of wear resistance; d) the effect of the addition in terms of lubrication (friction coefficient and produced heat). Results showed that: a) an appropriate pre-consolidation of feedstock materials can be effective in preserving the heat-sensitive phases within the microstructure of PTA deposits; b) the addition of a total amount of 5% wt. of solid lubricants and reinforcing carbides produced a limited decrease in the coating hardness (about 13%) and an evident improvement in terms of friction coefficient but, on the other hand, a remarkable reduction (about 30%) in wear resistance. Further investigation will be addressed to optimize the composition of modified feedstock to counteract the softening effect of lubricant phases without depressing the self-lubrication behaviour.

Cryomilled Cu-Al powder and the Cu/Al mixture were sprayed onto aluminum substrate using the cold spraying process. This study focused on the wear properties of the nanocrystalline (NC) Cu-Al coating in comparison to its coarse-grained (CG) Cu/Al counterpart. The results showed that the as-sprayed deposit presented a dense microstructure. Investigations on the worn surface of the NC coating revealed that the plastic deformation with grooves and some debris were prominent with no visible cracking. Nanocrystalline Cu-Al coating showed a good wear resistance with a low friction coefficient. The enhancement of the wear properties of the NC Cu-Al was attributed to the grain refinement and the superior hardness.

Up to now no coating systems are marketable in the field of direct hot extrusion, which provide both surface protection of the parts being in contact to the billet (i.e. container and die), and a significant reduction of the frictional losses being induced by the billet passing along the container walls. To dispense the use of lubricants and to enhance the usable forming capacity of the process, different oxide ceramics were given in one suspension and plasma sprayed. The aim is to reach a mixing of the feedstock to obtain deterministic solid solutions of the oxide phases which show a reduction of their coefficient of friction under dry sliding conditions. To reach this goal the high surface-to-volume ratio of feedstock with primary particle sizes below 100 nm was used. By means of X-ray diffraction it could be proven, that the desired phases could be synthesized. The coatings showed a considerable lowering of their frictional coefficient in tribological testings against 100Cr6 in the region of the operation temperatures for the hot extrusion of aluminium alloys. Besides the experimental work the fundamentals of the mixing process of different oxides regarding crystallographic aspects are discussed.

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.

Nanostructured materials are of particular scientific interest because of their physical and mechanical properties, which are superior to those of conventional materials. They are more widely used in various industrial applications mainly due to decreasing production costs. The work is concerned with a study of the tribological properties of a HVOF sprayed composite of nanostructured WC12Co mixed with nanostructured Fe 3 O 4 , having the properties of solid lubricant. The coatings were sprayed by means of a Hybrid Diamond Jet system. A T-01 ball on disc tribological tester was used to study their resistance to wear and determine the coefficient of friction on the basis of friction force obtained in the course of continuous measurement at a set load. Result of investigations were compared with properties of coatings sprayed with standard WC12Co/ Fe 3 O 4 . The microstructures and compositions of the nanostructured powders and coatings were analyzed by scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray analysis. Their phase composition was studied using a Bruker D8 Advance diffractometer.

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.

The combination of thermally sprayed hard coatings with a polymer based top coat leads to multilayered coating systems with tailored functionalities concerning wear resistance, friction, adhesion, wettability or specific electrical properties. The basic concept is to combine the mechanical properties of the hard base coating with the tribological or chemical abilities of the polymer top coat suitable for the respective application. This paper gives an overview of different types of recently developed multilayer coatings and their application in power transmission under dry sliding conditions. State of the art coatings for dry sliding applications in power transmission are mostly based on thin film coatings like DLC or solid lubricants, e.g. MoS 2 . A new approach is the combination of thin film coatings with combined multilayer coatings. To evaluate the capability of these tribological systems, a multi-stage investigation has been carried out. In the first stage the performance of the sliding lacquers and surface topography of the steel substrate has been evaluated. For this purpose case-hardened steel substrates were laser textured and coated with different sliding lacquers. In the following stage thermally sprayed hard coatings were tested in combination with different sliding lacquers. For this test stage steel samples were coated with oxide ceramics, metal alloys and hard metals by high velocity flame spraying (HVOF) and high velocity suspension flame spraying (HVSFS). After a grinding process several types of sliding lacquers were applied by air spraying on the coated specimens. Wear resistance and friction coefficients of combined coatings were determined using a twin disc test-bed.

Babbitt surfacing is used in tribological applications because of its low friction coefficient. Thermal spray surfacing and pouring are two widely used production processes for Babbitted parts. This paper presents a comparative analysis of structures and friction properties of Sn-Sb-Cu Babbitt layers produced by these techniques. The sprayed Babbitt coatings were produced by arc spraying of 1.6 and 3 mm diameter wire.

HVOF sprayed coatings are widely used to improve the service life of machines components. Influence of spraying parameters and different kinds of materials on coatings properties have been investigated in many works. Our investigations concern properties of HVOF sprayed two tungsten carbide coatings after applying electrospark deposition process (ESD). After finishing microstructure of sprayed coatings were changed by applying tungsten carbide electrode. Changes of microstructure and properties of the sprayed and post ESD process coatings were analysed with a scanning microscope JOEL JSM-5400. The element distribution was analysed with a microprobe ISIS 300 Oxford Instruments whereas phase composition was analysed by diffractometer D8 Advance (BRUKER). The roughness of coatings was measured with Talysurf-4, whereas Matuzawa MMT-X3A was used to study changes of their hardness. Ball on disc tester and dry abrasive rubber wheel tester were applied to estimate coefficient of friction and wear resistance of sprayed coatings before and after EDM process.

HVOF spraying was used to prepare coatings from mechanical blends of Cr 3 C 2 -25NiCr and NiCrBSi powders. The aim of the work was to study the influence of addition of a metallic phase on tribological properties of the coatings in sliding conditions. Tribological properties of the coatings were characterised under dry sliding. Addition of NiCrBSi decreased the coefficient of friction in high temperature, pressure and sliding speed.

Babbitt is used at tribology applications according to its low friction coefficient. Thermal spraying and pouring are widely used production processes of Babbitted parts. Comparative analysis of structure and wear properties of Babbitt layers produced by these technologies was done. Examples of typical arc sprayed Babbitted part's applications which were done at Mashprom are represented.

This study investigates the tribological properties of two HVOF-sprayed tungsten carbide coatings, each with a different content of cobalt, which were subjected to electrical discharge machining (EDM). It was found that the electrospark deposition of WC8Co over the HVOF-sprayed WC12Co and WC17Co coatingsresults in the formation of a homogeneous layer of tungsten carbide with a low cobalt content. The EDM layer is well bonded with the HVOF-sprayed coating as confirmed by the gradual change in the content of the elements in the coating and layer. The friction coefficients obtained for the two coatings with the EDM layer are very similar as their composition, microstructure, hardness, and surface roughness are approximately the same.

In this study, two metallic powders, Ni-20Cr and Ni3Al, were plasma sprayed on stainless steel substrates in order to compare their sliding wear properties. The coatings exhibited typical splat morphology prior to wear testing. After wear testing, the coatings were again examined along with an uncoated substrate. It was concluded that although either coating can effectively reduce the wear rate of 309 stainless steel, the Ni3Al coating is a better choice.

In this study, micro and nanostructured alumina coatings were plasma sprayed on steel substrates using different combinations of spraying parameters. Test results show that the nanostructured coatings have lower hardness, a lower friction coefficient, and higher wear resistance than microstructured alumina coatings.

In this study, suspension plasma spraying is used to produce self-lubricating titanium oxide coatings. Certain nonstoichiometric titanium oxide phases, called Magneli phases, exhibit a reduction in friction under dry sliding conditions at elevated temperatures. These phases, however, tend to undergo crystal changes during thermal spraying, resulting in the loss of their good friction behavior. In this work, the goal is to stabilize these phases with suitable lattice substitutions for Ti 4+ . The resulting phases are shown to be homologous to Ti n O 2 n -1 , but have the advantages of a three-component system, making them more thermally stable with a broader area of formation.

For years, special attention has been paid to study and to develop innovative copper alloys and composites, with improved mechanical behaviour in respect to pure copper and preserving its excellent electrical and thermal properties. In this work different copper/alumina blends have been prepared and then deposited by cold spray at different gas carrier temperatures. The deposition efficiency and the content of embedded alumina have been determined by means of image analysis using SPIP software. Optimized deposition temperature results 450°C: the coatings exhibit compact, pore-free microstructure and very low oxidation. Microhardness and friction coefficient have been evaluated of both pure copper and composite coatings. An increase of microhardness from 65HV 0.015 to 150HV 0.5 has been observed while a progressive reduction of friction coefficient as a function of alumina content has been reported. Further characterizations to determine thermal and electrical properties of copper/alumina composites are in progress.

In this paper, tin-bronze/TiN and tin-bronze/quasicrystal (AlCuFeB) composite coatings were fabricated by cold spray process. Microstructures and microhardness of coatings were characterized. Ball-on-disc dry sliding wear tests were conducted in an ambient condition to examine the tribological performance of the composite coatings. The results show that the microhardness and densities of composite coatings increase significantly compared to those of the pure tin-bronze coating. The friction coefficients of coatings decrease with the introduction of reinforces. Furthermore, the tin-bronze/quasicrystal composite coating yields a lower friction coefficient and wear rate compared to the bronze/TiN coating. The tribological mechanisms were discussed.