Self-lubricating Coatings Research Articles

Study on the effect of TiC/B on the performance of laser cladding in-situ fabricating wear-resistant self-lubricating coatings

To improve the wear resistance of IN718, coatings containing the self-lubricating phase h-BN were prepared and the coating properties were analyzed in relation to the variation of laser power. The results show the TiC added to the cladding powder partially decomposes and in-situ fabricates new reinforcing phases TiN, B4C, etc. The lubricating phase h-BN was in-situ fabricated by adding B into the powder. As the laser power increased from 1.6 kW to 2 kW and 2.5 kW, eutectic microstructures of high melting point reinforcing and lubricating phases were observed. Due to the decomposition of TiC and in-situ fabricated of TiC2, TiN and B4C concentrations changing with the laser power, the surface hardness of the coatings prepared at 2.5 kW was the highest at 391.03HV0.5. Which is 1.096 and 1.108 times of 1.6 kW and 2 kW. At room temperature, the coating fabricated by 2 kW has the highest average friction coefficient of 0.537. This is because the self-lubricating phase h-BN is a high-temperature lubricating phase and the wear surface has a low oxide content, and is influenced by the hardness of the coating. At 500°C, the coating fabricated with 2.5 kW has the lowest average friction coefficient due to the best synergistic effect of the lubricating and reinforcing phases at 0.376. The 2.5 kW coating has the best wear resistance, with wear rates 0.69 and 0.54 times at room temperature and 0.82 and 0.8 times at 500°C of 1.6 kW and 2 kW. The wear mechanism at room temperature is abrasive wear, and at 500°C is mainly a combination of h-BN and oxide synergistic lubrication.

Effect of coated graphene on friction and wear properties of nickel-based self-lubricating coatings prepared by laser cladding

Graphene is an ideal material for improving the self-lubricating properties of coatings, but the high-energy laser beam can damage graphene during the laser cladding process. Therefore, in this paper, amorphous silicon dioxide (SiO2) is used to surface coat graphene particles to obtain silica-coated graphene with core-shell structure (G@SiO2). By adding niobium carbide (NbC) as the ceramic reinforcing phase and G@SiO2 nanoparticles as the solid lubricant in Ni60, a self-lubricating composite coating was prepared on the surface of 45 steel matrix by laser cladding technology. It is shown that G@SiO2 can promote the grain refinement of NbC in the coating. On the other hand, the addition of G@SiO2 promotes the generation of hard phase of chromium carbide, which together with NbC improves the hardness of the material. The maximum microhardness of the composite coating was 946 HV, which was 302.7% higher than that of the 45 steel base material. The lowest coefficient of friction value of the coated material was 0.25, and the lowest wear amount was 2.45 × 106 μm3. Compared with the composite coating without added G@SiO2, the coefficient of friction of the coated material with the addition of G@SiO2 was reduced by 50% and wear amount was reduced by 62%.

Strong-bonding self-lubricating nickel-matrix coatings at a wide temperature range

The weak bond strength that affects self-lubricating coatings across a wide temperature range severely limits their application on the surfaces of high-temperature mechanical parts. To solve this problem, the strong-bonding self-lubricating NiCrAlY-Ag-BaF2/CaF2 coatings were produced by detonation spraying. The as-sprayed coatings exhibit high bond strengths of 65 – 75 MPa by controlling the formation of semi-molten state particles and in-situ oxides. The composite coating with 10 wt% fluoride eutectic and 20 wt% Ag shows the favorable tribological properties at a wide temperature range from room temperature to 900 °C. The combined effects, including the formation of the lubricating Ag film, the synergistic lubricating effect of BaF2/CaF2 and CaCrO4 formed by tribo-chemistry at high temperature, tribo-glaze of oxides, and tribo-transfer film, contribute to favorable lubrication at a wide temperature range.

Processes and Properties of Self-Lubricating Coatings Fabricated on Light Alloys by Using Micro-Arc Oxidation: A Review

A self-lubricating coating is a kind of coating formed on the surface of the material by various processes that can self-replenish lubricating substances during the friction and wear process. This paper presents a comprehensive review of the processes and properties of self-lubricating ceramic coatings developed through Micro-arc Oxidation (MAO) on light alloys, including aluminum, magnesium, and titanium. Three technical approaches for the preparation of self-lubricating coatings via MAO are recapitulated. The structures and properties of the self-lubricating coatings prepared by each technical route are compared and analyzed, and the future development tendency of this field is also anticipated.

Plasma Spraying NiCoCrAlY-Cr2O3-AgMo Coatings: Fabrication and Tribological Mechanisms

The increasing demand for high-performance aircraft engines has led to a greater emphasis being placed on advanced sealing coating technologies. Developing long-life, self-lubricating, and wear-resistant coatings is of significant research value. This study focuses on the fabrication of a novel self-lubricating and wear-resistant NiCoCrAlY-Cr2O3-AgMo composite coating. This coating was deposited onto a GH4169 substrate utilizing plasma spraying. Scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) methods were employed to characterize the elemental composition and microstructure of the fabricated NiCoCrAlY-Cr2O3-AgMo composite coating. Microhardness measurements across the coating cross-section indicated a gradual increase in hardness from the GH4169 substrate to the NiCoCrAlY-Cr2O3-AgMo coating. The average hardness of the GH4169 substrate was 413.92 HV0.2, while the CoNiCrAlY bonding layer region exhibited an average hardness of 467.60 HV0.2. The NiCoCrAlY-Cr2O3-AgMo coating itself demonstrated an average microhardness of 643.22 HV0.2. Room temperature friction tests indicated that the average coefficient of friction (COF) of the GH4169 substrate was 0.665. In contrast, the NiCoCrAlY-Cr2O3-AgMo coating exhibited a significantly lower average COF of 0.16, representing a 75.94% reduction compared to the uncoated GH4169 substrate. High-temperature friction tests were conducted at 400 °C, 500 °C, and 600 °C, indicating average COF values of 0.438, 0.410, and 0.268, respectively, for the NiCoCrAlY-Cr2O3-AgMo coating. Specifically, at 600 °C, the formation of a lubricious NiMoO4 tribofilm on the coating surface was observed. This tribofilm effectively reduced the wear rate of the GH605 pin to 2.78 × 10−6 mm3/N·m, highlighting the potential of the NiCoCrAlY-Cr2O3-AgMo coating to reduce wear in high-temperature sliding contact applications.

Structure, mechanical, and tribological properties of Ag2CrO4 high-temperature oxide coatings

In this research, a series of Ag2CrO4 high-temperature self-lubricating oxide coatings were prepared by reactive radio frequency magnetron sputtering under different argon-oxygen flow ratio (Ar:O2 ratio) conditions. Effects of the gas flow ratio on phase composition, coating morphology, high temperature treatment in air atmosphere, mechanical and tribological properties are studied. A low Ar:O2 flow ratio is beneficial for the formation of Ag2CrO4 phase. At high temperature treatment, formation of surface Ag particle and volatility and decomposition of the Ag2CrO4 phase are observed, and the volatility and decomposition of the coating are slight at temperatures below 500 °C. When the Ar:O2 ratio is 1:1, the coating shows exceptional comprehensive performance, it is dense with a smooth surface, excellent toughness and bond strength, and the lowest wear rate and coefficient of friction, which is 0.14 mm3/10−3N∙m and 0.35 respectively. The coating can function as a lubricant in temperature environments of 500 ℃ and below, demonstrating practical application value.

Friction and wear properties of D-gun sprayed CrFeNiAl0.3Ti0.3-Ag-SrSO4 high entropy alloy matrix self-lubricating coating at elevated temperature

CrFeNiAl0.3Ti0.3-10 wt% Ag-(10−30) wt% SrSO4 high entropy alloy matrix self-lubricating coatings were fabricated using detonation spray technique and tribological characteristics of CrFeNiAl0.3Ti0.3-10 wt% Ag-(10−30) wt% SrSO4 coatings were explored from 25 to 1000 °C. The Ag and SrSO4 lubricants have good compatibility with CrFeNiAl0.3Ti0.3 matrix phase. The bond strength and hardness of CrFeNiAl0.3Ti0.3-Ag-SrSO4 coatings are 30 ∼ 65 MPa and 461 ∼ 535 HV, respectively. Meanwhile this coating exhibited good tribological performance across the wide temperature range and achieved the lowest friction coefficients of 0.29 ∼ 0.49 and wear rates of 2.68 ∼ 11.82 × 10−5 mm3/Nm when SrSO4 content is 10 wt%. Between 25 and 600 °C, SrSO4 and Ag lubricants, can effortlessly create complete lubricating films, preventing three-body wear and plastic deformation. At 800 and 1000 ℃, SrSO4 inflicts a significant impact on the formation of the oxide tribo-layer. When SrSO4 content is 10 wt%, it is feasible to form a compacted oxide layer containing SrCrO4, SrAl2O4 and SrTiO3, reducing the friction and wear. With further increasing SrSO4 content to 20 wt% and 30 wt%, the excessive SrSO4 leads to a detrimental on the compactness of oxide tribo-layer, increasing the friction and wear.

Microstructure, mechanical properties and tribological properties of NiCrAlY-Ag-SrF2 self-lubricating coatings by detonation spraying

Self-lubricating coating is used to solve the problem of insufficient lubrication and failure of mechanical transmission parts at high temperature. In this work, we designed a NiCrAlY-Ag-SrF2 coating through the synergistic lubricating effect of a novel SrF2 lubricant and Ag, and the reinforcing action of in-situ formed oxides. The results showed that the NiCrAlY-Ag-10 wt% SrF2 coatings have high bond strength (60 MPa) and hardness due to the low porosity and production of in-situ oxides. From room temperature (RT) to 900 °C, the friction coefficient and wear rate of the coating are 0.29 − 0.47 and 1.03 × 10−5 − 6.74 × 10−5 mm3/N·m, respectively. This reveals that SrF2 can be employed as an alternative to high temperature lubricants, and the coatings achieve lubrication effect at a wide temperature range.

PSF@PAO40 microcapsules enhanced epoxy resin coating toward anti-wear/corrosion performance

Microcapsules-enhanced coating emerges as the times require since the traditional organic coating hardly realizes the long-term protection of metal materials. Herein, PSF@PAO40 microcapsules (PPs) were prepared via Poly α-olefin 40 (PAO40) encapsulated within Polysulfone (PSF) shell using solvent evaporation method. Then self-lubricating composite coatings were fabricated by introducing PPs into epoxy resin (EP). The coating structure was characterized using X-ray microtomography (CT), and its relationship with anti-wear/corrosion performance was explored. Compared to pure EP coating, the composite coatings with 10 wt% PPs demonstrated an 87.9 % reduction in friction coefficient and 84.5 % reduction in wear rate. Additionally, the lowest frequency impedance (|Z|0.01 Hz) increased by 1 order of magnitude. Superior anti-wear/corrosion performance of the composite coatings is primarily attributed to the three-dimensional network distribution structure of PPs, which facilitate continuous lubrication and provide a physical barrier against corrosive media.

Research of the effects of laser power variation on the properties of laser cladding Ni45/Cr3C2/MoS2 self-lubricating wear-resistant coatings on the surface of 300M ultra-high-strength steel

Research of the effects of laser power variation on the properties of laser cladding Ni45/Cr3C2/MoS2 self-lubricating wear-resistant coatings on the surface of 300M ultra-high-strength steel

Tribological properties of atmospheric plasma sprayed Cr3C2–NiCr/20% nickel-coated graphite self-lubricating coatings

Using atmospheric plasma spraying technology, Cr3C2–NiCr (CN)and Cr3C2–NiCr/20 % Nickel-coated graphite (CG) composite coatings were successfully deposited on 304 stainless steel substrates, with three different spraying distance parameters designed to optimize the experiment. The study investigated the influence of nickel-coated graphite on the structure, hardness, porosity, and friction-wear performance of the composite coatings. Wear mechanisms were investigated based on analyses of morphologies and chemical states of the worn surfaces of the CG composite coatings. Our results demonstrate that the CG coating exhibits lower friction coefficients, ranging from 0.24 to 0.28, than that of the CN coating. The incorporation of nickel-coated graphite leads to formation of a solid-lubricating film at friction interface, lowering friction and wear. What's more, presence of nickel-coated graphite mitigates brittleness of the CN coating, as is deemed important for improving abrasion resistance of the coatings.

Effect of Nb particles on the microstructure and tribological properties of laser cladding Ni60/Ag(Cu)/nanoNi/h-BN composite coatings

Nickel-based self-lubricating composite coatings (Ni60/Ag(Cu)/nanoNi/h-BN) with different amounts of Nb were manufactured by laser cladding on the surface of 42CrMo steel. The effects of carbide forming element Nb on the microstructure evolution and tribological properties of the composite coatings were investigated. The results show that Nb is easily precipitated at grain boundaries and reacts with carbon to form the in-situ synthesized phase NbC. The grains were refined and rich substructures appeared inside, which improved the strength and hardness of the coatings. The average microhardness of the coatings with 5.5 wt% Nb addition reaches 731.5HV0.2, which is 192.1HV0.2 higher than that of NCA0(0 wt%), and 3.17 times that of the substrate. Compared to NCA0, the average friction coefficient and wear rate of NCA3 decreased by 38.1% and 30.6%, respectively. The solid lubricant formed a lubricant film during wear, and the fine grains facilitated oxidation wear, resulting in the formation of oxidation film. The lubricant film, oxidation film and the increase in hardness together improved the tribological properties of the coating.

The Green Lubricant Coatings Deposited by Physical Vapor Deposition for Demanding Tribological Applications: A Review

The emergence of nanotechnology and surface engineering techniques provides new opportunities for designing self-lubricant coatings with enhanced properties. In recent years, green coating technologies have played a vital role in environmental preservation. This article mainly reviews five typical types of self-lubricant coatings including MoN coatings, VN coatings, WN coatings and TMN (Transition Metal Nitride) soft-metal coatings, and DLC (Diamond-like Carbon) with lubricant agents deposited by PVD (Physical Vapor Deposition) for the demanding tribological applications, which is the latest research into the green lubricant coatings. Furthermore, it is of great significance for designing the green self-lubricant coatings to adapt the demanding tribological applications to meet the industrial requirements.

Laser cladding Ni60 @ WC/ Cu encapsulated rough MoS2 self-lubricating wear resistant composite coating and ultrasound-assisted optimization

This research aims to broaden the scope of self-lubricating wear-resistant coatings for applications in diverse industries such as automotive, metallurgy, power, and aerospace. Employing laser cladding technology, we successfully fabricated high-performance self-lubricating ceramic composite coatings. A comprehensive investigation was conducted to understand the inhibitory effect of Cu on the thermal decomposition of MoS2, and the study systematically explored the relationship between powder composition, coating structure, and organizational properties. The mechanisms behind friction reduction and wear resistance were unveiled, shedding light on the formation of the MoS2 self-lubricating protective film. Research findings reveal that during the laser cladding process, Cu and Ni undergo solid solution, resulting in the formation of the Cu–Ni alloy phase and crystal refinement. The MoS2 aggregation area exhibits a fine dendritic structure, while the dispersion area showcases coarse dendritic and cellular crystals. The addition of Cu and MoS2 influences the content of the MxCy phase and the thermal decomposition of MoS2. The incorporation of Cu increases the average coating hardness, whereas MoS2 addition decreases it; nevertheless, the Cu/MoS2 coating hardness is enhanced by at least 6.4 %. Cu significantly improves the coating's wear resistance, with a relatively smaller impact on friction reduction. MoS2 functions as a friction-reducing phase during wear, effectively preventing the peeling of hard phases and reducing the friction coefficient. Cu is uniformly distributed in the coating, experiencing solid solution strengthening, reducing adhesive region areas, and minimizing wear debris generation. MoS2, although unevenly distributed, forms intermittent lubricating films on the surface. The lubricating film of the Cu/MoS2 coating remains stable, preventing mutual contact of the friction surface and concurrently reducing the friction coefficient and wear amount. While the study successfully prepared a self-lubricating ceramic coating with excellent wear resistance, some surface quality defects persist. Further optimization of the preparation method was achieved through ultrasound-assisted technology.

Static- vs Impact-Ice-Shear Adhesion on Metals and a Self-Lubricating Icephobic Coating

To characterize the performance of icephobic coatings for aerospace applications, various shear-based techniques have been used. Generally, these techniques are conducted in conjunction with comparison tests on metals. In this study, a review of the various approaches for measuring adhesion for static and impact ice for metal and icephobic surfaces was done. This review indicated that many details of the test conditions either varied significantly among studies or were omitted. To address this uncertainty, new measurements were taken to examine in-situ ice-shear-adhesion strength for impact and static ice with various surfaces, using a consistent icing-research-tunnel facility with well-characterized and detailed test conditions. The results for the two different metals tested revealed a significantly higher ice adhesion for static ice compared to that for impact ice. However, the tested self-lubricated icephobic coating significantly reduced ice adhesion strength for both impact and static ice and this performance was retained after multiple icing tests. Based on the methodology review and the current experimental study results, it is recommended that future ice adhesion studies fully characterize the following: the apparatuses for shear measurement, which include protocols and procedures used; the surface chemistry and roughness; the thermal conditions of the air, water, and surface; and for impact ice, the droplet conditions such as velocity and size in order to ensure repeatability within a study and comparison across studies.

Enhanced tribological performance of TiO2-hBN/CNT double-layer coating by CNT-assisted plasma electrolytic oxidation with nanoparticles addition

Hexagonal boron nitride (h-BN) is considered a very promising anti-friction material, however, how to assemble them densely and uniformly on metal surfaces remains a challenge. In this study, CNT-assisted plasma electrolytic oxidation (PEO) with the addition of h-BN nanoparticles was employed to create a double-layer coating on titanium alloy, demonstrating exceptional tribological characteristics. The CNTs not only acted as lubricating phases to improve the anti-friction performance but also as additives to facilitate the transition from the nanocomposite coating to the double-layer coating. The later stage of the PEO process with CNT doped in the electrolyte produces an interesting sudden rise in current density, which generates strong and dense discharge that facilitates the deposition and sintering of h-BN. As a result, the double-layer coating has a higher adhesion and hardness as well as more h-BN nanoparticles incorporated into the coating compared to coatings without CNTs-assisted deposition. Further, the double-layer coating exhibits a lower friction coefficient (∼ 0.11), attributed to the high release rate of h-BN under shear to form a lubrication film in conjunction with CNTs on the contact surface. The simple technique offers a novel approach to fabricating self-lubricating ceramic coatings on light alloys, which has huge potential for application in the anti-friction materials field.

Friction and wear properties of wide-velocity range high-energy plasma sprayed CuSn–NiCr solid self-lubricating coatings under heavy load

As one of important copper-based solid self-lubricating coatings, the low wear resistance of Cu–Sn coatings greatly limits its application in some heavy-duty cases. In the present work, two types of CuSn–NiCr composite powders designed by electroless plating (E-CN) and mechanical mixing (M − CN) methods, respectively. The friction and wear properties of wide-velocity range high-energy plasma sprayed CuSn–NiCr coatings were studied. The results suggested that, the fracture toughness of E-CN and M − CN coatings increased by 1.38 times and 1.55 times compared with as-sprayed Cu–Sn coatings, and the wear rate decreased by 29 % and 50 % correspondingly. Due to the tribofilm formation and micro-pores storage effect, the M − CN coating with 10 wt% addition ratio of Ni–Cr phase exhibited the lowest friction coefficient and the smallest wear rate. With the increase of Ni–Cr phase, the wear mechanism was transformed from adhesive to abrasive, and accompanied by fatigue step-shaped spallation. Friction and wear model of the CuSn–NiCr coatings was divided into rapid, stable and declining stages.

STRUCTURE AND PROPERTIES OF SELF-LUBRICATING COPPER-NICKEL-GRAPHITE COATING FABRICATED USING COLD SPRAY

Application of self-lubricating Cu-matrix coatings is an attractive way to provide high electrical conductivity and wear performance in contact friction pairs in various areas of modern engineering. In the present work, the structure and properties of self-lubricating copper-nickel-graphite coating deposited on copper substrate using high-pressure cold spray were studied for the first time. The coating was fabricated by spraying dendritic copper and flaked nickel-coated graphite powders mixed in a ratio 70/30 wt.%, which ensured the formation of a lamellar structure. The obtained coating exhibited an attractive combination of hardness (108.8 HV1), coefficient of friction (0.34) and electrical conductivity (43.8 % IACS), which open prospects for its electrical applications.

Study of Design and Microstructure Properties of Laser Clad Multiphase Coupled Nickel-Based Self-Lubricating Coatings

Study of Design and Microstructure Properties of Laser Clad Multiphase Coupled Nickel-Based Self-Lubricating Coatings

Quality control of NiCr-Cr3C2-hBN@Ni coating on thin-walled GH4169 alloy surface prepared by plasma spraying

As equipment lightweight trends progress, thin-walled structures have seen extensive application in critical aerospace components. Nevertheless, the aero-engine tail nozzle flaps are exposed to the harsh operating conditions of high-temperature friction, so there is an urgent requirement to prepare wear-resistant, self-lubricating coatings with a wide range of temperatures for their protection. Due to the poor rigidity and weak strength of thin-walled workpieces and complex forms of structural stresses, the processing is extremely difficult. In order to solve the thermal deformation problem of coating workpieces prepared by spraying on the surface of thin-walled workpieces, the effects of spraying path, cooling airflow, and spraying interval on the thermal force field of thin-walled workpieces to prepare NiCr-Cr3C2-hBN@Ni coating are investigated in this study using finite element simulation. As a result, the deformation and stress of thin-walled workpieces can be minimized by adding back-side cooling air during the spraying process and moving the cooling air with the gun in a set interval, with the maximum warpage and maximum stress being less than 2.366 mm and 0.177 GPa, respectively. During the spraying process by simulating the optimum spraying process, no significant warpage of the substrate occurred and the coating was sprayed with uniform thickness. Typically, the thickness error rate is 16.7 %, and the coating hardness reaches 15–20 GPa, with excellent tribological properties in a wear rate of 10−5 mm3·N−1·m−1 and 10−6 mm3·N−1·m−1, which protects the workpiece effectively.