Composite coatings using mixed alloy matrices reinforced with carbon-based solid lubricants as feedstock materials were prepared by atmospheric plasma spraying. The aim of the present study was to investigate the tribological characteristics of such coatings exploring potential benefits of CNTs as nano-additive to reduce friction and wear, improving lubrication conditions during operation in tribosystems, such as piston ring – cylinder liner systems. The chemical composition of feedstock materials and the thermal spray parameters during coatings deposition are correlated to friction coefficient and wear rate using pin-on-disk measurements. The developed coatings hybrid behaviour is studied. Co-based cermet as well as metal alloy anti-wear performance along with the promoted lubrication conditions during operation is revealed. The dependence of the developed coatings quality and performance on the characteristics of the feedstock powder is thoroughly discussed.

Self-fluxing alloys are an established thermal spray system in case of superimposed tribological and corrosive loads. A dense coating with high bonding strength can be formed by fusing. Such coating system represent the state of the art in valve technology. Diamond-like carbon (DLC) top coatings are used for friction-reduction. As an alternative approach, this study focuses on the possibility of incorporating solid lubricants in self-fluxing alloy coatings. This allows for higher local stress and failure tolerance as well as a reduced process chain. Molybdenum disulfide (MoS 2 ) was studied as solid lubricant in the self-fluxing alloy NiCrBSiFe. In this preliminary study, the optimization of the MoS 2 content with up to 10.0 wt% was performed in spark plasma sintered (SPS) bulk materials. The wear behavior under oscillating wear conditions was investigated. Besides the decrease in coefficient of friction (COF), the wear resistance was increased by incorporating MoS 2 . Furthermore, the distribution of the solid lubricants within the SPS bulk material and the influence of the production route were analyzed.

In this study, copper-doped bimodal WC-Co powders are applied to steel substrates by high-velocity oxyfuel spraying and the coatings are evaluated based on their microstructure and high-temperature wear performance. It is shown that the addition of copper reduces coating porosity without affecting the structure of the WC. It also inhibits the decomposition of WC and has a solid diffusion function. The friction coefficients and wear rates determined at different temperatures were found to be consistently low with minimum values being obtained at 450 °C. At high temperatures, the soft copper flows to the surface, forming a self-lubricating film that reduces friction and wear.

Adhesive-corrosion resistance is an important issue for the application life of solid lubricant coatings. With abundant metal droplets deposited on the surface of a solid self-lubricating coating, the coefficient of friction of the coating changes and results in adhesive wear. In this paper, a new method for evaluating the adhesive resistance for solid self-lubricating Ni-WSe2-BaF2·CaF2-Y-Ag-hBN coatings was reported. The microstructures and anti-adhesive characteristics under different angles of aluminum metal droplets obtained with an arc supersonic nozzle were investigated for high temperature solid self-lubricating coatings produced by plasma spray. The results demonstrate that the friction coefficient of Ni-WSe2-BaF2·CaF2-Y-Ag-hBN solid self-lubricant coatings is distributed between 0.086 and 0.299 at 25-800℃. The effect of molten metal drops on the coating adhesive-corrosion rate increases with the deposition angle. At 90°, the deposition rate of metal droplets on the coating and substrate surface is maximized, and the hexagonal boron nitride (hBN) self-lubricating coating deposition rate is only 58 mg/(cm2·s). This work demonstrates that hBN can effectively decrease the adhesive layer of the coating by the rate of the polishing and stripping.

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.

This study assesses the effect of yttrium additions on plasma sprayed MoS 2 /Ni-SiC-Y coatings produced from particle-reinforced composite powders. It is shown that the microstructure of the self-lubricating coatings improves with the addition of yttrium, resulting in increased hardness and cohesive strength. The tribological properties of the coatings were also studied, showing that the ideal amount of yttrium is 12 wt% based on wear loss measurements and that the fractal dimension of sliding wear debris depends on the friction load as well as the mass fraction of yttrium.

This study investigates the effects of various reinforcement materials and solid lubricants on cold spray aluminum composite coatings. The wear resistance and friction coefficient of the coatings were very different with and without a reinforcement and solid lubricant. It was found that Al 2 O 3 greatly improves wear properties, Mo results in better dispersion hardening, and MoS 2 reduces the friction coefficient.

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.

This paper provides an overview of chemical vapor deposition (CVD) and atomic layer deposition (ALD) processes and the advantages they offer physical vapor deposition for the application of friction and wear coatings for micromechanical assemblies and components. It explains how hard and solid lubricant phases can be applied by these non-line-of-sight deposition methods, achieving nanoscale conformality and coating uniformity on buried surfaces and interfaces. It also discusses inherent disadvantages and explains how plasma excitation can be incorporated in either process to overcome material limitations.

In this work, mechanically alloyed Al–12Si/TiB 2 /h-BN composite powder was deposited onto an aluminum substrate by atmospheric plasma spraying. The results revealed that the mechanical alloying (MA) process has a significant effect on composite powder morphology and in-situ reaction intensity between the selective powders during plasma spraying. In addition, hexagonal boron nitride (h-BN) powder incorporated as a solid lubricant, which has excellent lubricating properties, decomposed into B and N and formed a solid solution after a long period of milling. More specifically, during plasma spraying a large amount of h-BN reacted with Al to form AlN. Unlubricated ball-on-disk testing ring was used to examine the anti wear performance of the coatings. The worn surfaces were examined using scanning electron and energy dispersive spectroscopy to elucidate the wear mechanisms operating at the sliding interface.

Abradable seals have been used in jet engines since the late 1960's. Today they are seeing applications in low pressure and high pressure sections of compressors as well as the high pressure turbine module of jet engines. Clearance control systems using abradable coatings are also gaining ever more attention in industrial and steam turbine applications. Thermal spraying is a relatively simple and cost effective means to apply abradable seals. Abradable coatings work by minimizing gaps between rotating and stationary components by allowing the rotating parts to cut into the stationary ones. Typically plasma and combustion spray processes are used for applying abradable coatings. The types of coatings employed in the HP turbine are zirconia based abradable material systems with polymer and, in some cases, solid lubricant additions such as hexagonal boron nitride. The coatings are designed to work at service temperatures of up to 1200°C. Types of matrix materials used in the low and high pressure sections of the compressor are aluminum-silicon, nickel and MCrAlY based systems. These compressor type systems typically also contain fugitive phases of polymer and/or solid lubricants such as hexagonal boron nitride or graphite. Operating temperature, depending on the material of choice, can be up to 750°C. Regardless of the specific application, fugitive phases and porosity are needed for abradable coatings. Polymers are used to create and control porosity in plasma sprayed coatings, a critical design requirement in adjusting abradability and erosion properties of thermal spray coatings. Combustion spray coatings generate porosity through the lower deposition velocities and temperatures compared to plasma and typically do not need polymer phases. Solid lubricants are added to help weaken the structure of thermal spray coatings and reduce frictional heating and material transfer to the blade.

A group of blended and spray dried solid lubricants with the same nominal composition were deposited by atmospheric plasma spraying (APS). The wear resistance of two coatings formed at room temperature and 350°C was evaluated using a rig test to simulate actual application conditions. The results showed that the blended powder coating showed inferior mechanical and tribological properties due to its non-uniform microstructure, which were induced by the differences in the physical and thermophysical properties of each constituent phase. However, the nanostructured spray-dried feedstock coating showed a better wear resistance due to its lower porosity, higher hardness and higher bond strength. In addition, the friction coefficient decreased with an increase of the Ag fraction and the uniformity of the Ag solid lubricant in the coating.

The crushed and rounded ferroboron (FeB) powders of Fe-18.8B-0.2C-0.5Si-0.8Al (wt %) were deposited onto an aluminum substrate by thermal spraying methods to improve its tribological properties. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties like graphite were incorporated to the iron boride powders as solid lubricant by sintering process and high energy ball milling technique which allows homogeneous distribution of solid lubricants in a hard metallic matrix to obtain protective coatings with low friction coefficient. As-sprayed coatings are composed of mainly h-BN and FeB, iron matrix supersaturated with boron owing to the rapid solidification of molten droplets flattened on a substrate. The friction and wear behaviors of each coating were evaluated using ring-on-disk type wear tester under paraffin base oil condition in air atmosphere. Preliminary results revealed that iron boride powder with h-BN powder (5 wt.%) is an applicable method to produce a protective composite coating against friction and wear.

In many aeronautical applications such as in the fan blade / disk dovetail notch, two parts made up of a titanium alloy are in contact and relative motion between them can occur. Titanium alloys like Ti-6Al-4V are promising candidates for tribological application because of their low weight and high specific strength. However, because of the poor tribological behavior of Ti-6Al-4V under self-mating conditions, modification of the surface has become imperative. In this work, we report on the fretting wear of plasma sprayed Cu-Ni- In along with MoS 2 solid bonded lubricant and Ti-6Al-4V. Substrate coated pins were tested against a flat plate of Ti- 6Al-4V alloy. The effect of temperature and frequency on fretting wear of Cu-Ni-In, the composite coating and Ti-6Al- 4V was investigated. Wear properties of the coatings and substrate were evaluated. The morphologies of the worn surfaces and surfaces beneath the worn surfaces were characterized with the help of an optical microscope, scanning electron microscope, electron probe micro analyzer and energy dispersive spectroscopy. Results showed that the composite coating exhibited better fretting resistance than the Cu-Ni-In plasma sprayed coating with no additive. It also exhibited lower surface roughness and a lower coefficient of friction than Cu-Ni-In or Ti-6Al-4V under the same testing condition. Therefore, the use of MoS 2 solid bonded coating scan be considered as one of the possible simple and cheap approaches for reducing fretting wear.

Generally, the surface of a substrate is roughened by blasting in pretreatment thermal spraying. Since some of the grit remains on the substrate surface, sprayed coating and the adhesion property characteristics are degraded. However, it seems that there is almost no research on this problem. In this study, residual grit is quantitatively evaluated, and a technique for reducing grit is proposed. For residual grit reduction, a solid lubricant was used, and applied to the surface of a substrate or grit; reduction of residual grit was confirmed. After blasting with solid lubricant, it remained on the substrate surface, which could be removed by heating the substrate.

Water atomized cast iron powder of Fe-2.17C-9.93Si-3.75Al (in wt%) were deposited onto an aluminum alloy substrate by atmospheric DC plasma spraying to improve its tribological properties. Pre-annealing of the cast iron powder allows to precipitate considerable amounts of graphite structure in the powder. However, significant reduction in graphitized carbon in cast iron coatings is inevitable after plasma spraying in air atmosphere due to the in-flight burning and the dissolution into molten iron droplets. Hexagonal boron nitride (h-BN) powders which have excellent lubricating properties like graphite were incorporated to the cast iron powder as solid lubricant by sintering process (1300 °C) to obtain protective coatings with low friction coefficient. The performance of each coating was evaluated using ring-on-disk type wear tester under paraffin base oil condition in air atmosphere. Conventional cast iron liner which has flaky graphite embedded in pearlitic matrix was also tested in similar conditions in order to make a comparison. Sections of worn surfaces and debris were characterized and wear behaviour of plasma sprayed coatings are discussed.

A typical high-pressure fuel pump for direct injection (DI) engines operates with fuels such as petroleum-based hydrocarbons that have inherent lubricating properties. However, environmental requirements put the thrush to use cleaner fuels that don’t contain lubricants and consequently an increasing abrasion problem presents with the surface of high-pressure fuel pump for direct injection engines. To alleviate this problem, the alternative solution is to promote wear and corrosion resistance of DI engines by applying high-lubricity coatings onto surfaces of engine components such as pump plungers. In this work, self-lubricating nanocomposites with nano-Al 2 O 3 /TiO 2 matrix and Fe 3 O 4 additive as solid lubricant was the first applied. The nanocomposites had been fabricated into lubricant coatings with a single layer or a functionally graded structure in plasma spray process. Tribological test results for the nanocomposite coatings demonstrated 4 times increase in sliding wear resistance and 3-5 times increase in abrasive wear resistance in under the tested conditions. The lowest coefficient of friction about 0.18 was measured on the nanocomposite coating with an optimal Fe 3 O 4 content in pin-on-disk test in ethanol. Based on morphologies and wear behavior analyses, the wear mechanism was proposed for the nanocomposites. The nanocomposite coatings have exhibited the advantages of cleavability, chemical stability, low friction and high wear resistance, and will have a potential for various applications that require high lubricity at ambient and elevated temperature.

In this work, HVOF sprayed hard metal multi-component Cr 3 C 2 -25Ni+10 vol-% solid lubricant coatings were prepared by HVOF spraying. CaF 2 , BN, MnS and WS 2 were used as solid lubricants. Powders were prepared by the spray drying and sintering method. This method produces homogeneous and spherical powders. Powders were sprayed with DJH 2600 HVOF-system. Microstructures, phase structures and compositions of powders and coatings were analysed with optical microscope, scanning electron microscope with EDS-analysator and x-ray diffractometer. The particle size distributions of sintered powders were determined by laser diffractometer. The amount of retained solid lubricant in the sprayed coatings was evaluated by EDS and compared to that in the spray powder. This study showed that spray drying and sintering method is a preferable method for manufacturing multi-component solid lubricant containing thermal spray powders. In sintering processes, solid lubricant phases remained in powders except for the Cr 3 C 2 -25Ni+10vol-%WS 2 -powder. Also, after HVOF spraying, coatings contained solid lubricants.

Thermal sprayed (HVOF) cermet coatings (WC-17Ni) with and without solid lubricant (PTFE) were deposited on steel disks for sliding wear evaluation using the ball on disk configuration. Alumina (Al 2 O 3 ) balls were slid against coated disks. The coated disks were ground and lapped to roughness of 0.3µm Ra and 0.05µm Ra respectively. A significant reduction in the average coefficient of friction was observed when solid lubricant was incorporated into the cermet coating. There were reductions in average coefficients of friction from 0.84 to 0.55 for ground disks and from 0.65 to 0.48 for lapped disks. These represented reductions in coefficient of friction of 34.5% and 26% by incorporating solid lubricant into the ground disks and lapped disks respectively. The inclusion of solid lubricant in the coating also resulted in significant reduction in the average specific wear rate for both the ball and disk. Abrasive wear was the predominant wear mechanism observed on the worn samples’ surfaces using optical microscopy. A conceptual wear mechanism with the introduction of solid lubricant into the cermet composite coating was proposed. A hypothesis on the formation of lubricating PTFE films on contacting surfaces during sliding wear was supported with elemental mapping by Scanning Electron Microscopy/Energy Dispersion X-ray (SEM/EDX) analysis of worn ball surfaces after sliding against disk counterfaces deposited with composite cermet coating containing solid lubricant. The EDX mapping showed a homogenous distribution of fluorine element across the surfaces analyzed.

This paper describes the production of self-lubricating chromium carbide-nickel coatings using the HVOF spraying process. The present work deals with the preparation of Cr 3 C 2 -Ni + CaF 2 multicomponent powders and to spray them with a minimum loss of the CaF 2 solid lubricating phase. The powders are processed by atomization with subsequent sintering and qualification processes. The microstructure of the powder and resulting layers is characterized by SEM. The content of calcium fluoride in the sprayed layer is determined using the EDS method and compared with its content in the spray powder. Wear resistance is measured using a rubber wheel tester. Paper includes a German-language abstract.