Pulsed Electrodeposition for Preparing Nickel, Silver/Graphene Double-Layer Composite Coatings and Study on Friction Properties

A method for production of Sn–Sb–Cu alloy (babbitt) based composite coatings reinforced with micron-sized SiC and B4C particles on a steel substrate has been developed. A combined action of uniformly distributed high-modulus reinforcements and plastic matrix increases the strength and durability, reduces the wear rate, and significantly improves the antifriction properties of the coating. The surfacing rods based on B83 babbit containing reinforcing particles for arc welding of coatings on steel substrate were produced by the extrusion method. These rods were characterized by lack of porosity and discontinuities in the internal volume as well as by defect-free surface. The density and hardness of the rods are comparable with the same characteristics of the cast babbitt. Arc welding of coatings was performed in the AC mode with a non-consumable tungsten electrode in an argon atmosphere. Welding current I = 160–170 А, arc voltage U = 16–18 V, welding rate Vw = 4.2 m/h, and protective gas (Ar) flow rate VAr = 12–14 L/min. The structure and tribological properties of the composite rods and coatings deposited were investigated with the help of electron and optical microscopy methods and under dry sliding friction tribological tests. The size of SnSb intermetallic compounds in the rods after extrusion and in the coatings deposited was determined. It was found that the size of intermetallic phases decreased by a factor of two after introduction of SiC and B4C particles into the babbitt alloy. The results of wear tests show that reinforcing and modifying the structure of the surfacing rods by introduction of high-strength micron- and submicron-sized ceramic SiC and B4C particles improves the antifriction properties of surfaced composite coatings. The friction coefficient of the composite coating was the same throughout the load interval, while for the unmodified babbit coating its value was by two times higher than that for the composite coating under a load up to 39 N and 20% higher under loads greater than 39 N. The coatings with high-strength SiC and B4C particles have a low coefficient of friction (0.4) and a high coefficient of the friction process stability (0.8).

Fabrication and properties of hot-pressing sintered WC-Al2O3 composites reinforced by graphene platelets

With the rapid advances in science and technology, the core parts and techniques in tribosystems rely on solid-lubricating materials at wide temperature ranges for durability, especially for designing and producing materials with low friction coefficient and high wear resistance over wide temperature ranges. In this paper, a series of NiAl-Ag-Ta-Cr2O3 composite coatings with different contents of Ta and Ag were deposited by plasma spraying, and their tribological properties at RT-750°C under dry sliding conditions were investigated by a ball-on-disk tribometer. The friction products and compositions of worn surfaces at different temperatures were investigated. The deposited NiAl-Ag-Ta-Cr2O3 composite coatings exhibited excellent wear resistance at RT (10−7 mm3/Nm), while the friction coefficients were lower than 0.5 at RT to 750°C. The contents of Ta and Ag determined the mechanical properties of coatings and greatly affected the tribological properties by creating a tribo-film (lubricant film and glaze layer). NiAl-10Ag-5Ta-20Cr2O3 coating shows better tribological properties under all temperatures, while the wear rate is reduced to 5.58·10−6 mm3/Nm at 750°C, and the friction coefficient falls to 0.21 at 600°C. Excellent lubrication and wear resistance of composite coatings at high temperatures is mainly attributed to the Ag acting as the lubrication phase, and the top surface of the wear track being covered with a smooth glaze layer, which consisted of Ag, Ta2O5 Cr2O3, and AgTaO3. In addition, the lubrication mechanism of silver tantalate was also briefly discussed.

The x wt% graphene–Ti composites (x = 0, 0.2, 0.3 and 0.4) were obtained using the powder metallurgy method. The X-ray diffraction results demonstrated that the peak intensity of graphene increased monotonically with increasing graphene content. Furthermore, the number of grain boundary and interface between graphene and matrix increased as graphene increased, which led to a sharp rise of thermal resistances. The thermal conductivity and specific heat capacity of composites initially decreased drastically with addition of graphene, but then increased with increasing graphene content from 0.2 to 0.4 wt%. This phenomenon was connected with the graphene content and the characteristics of Ti matrix (pores, grain boundary and interface between graphene and matrix). The variation of the compressive strength of composites was attributed to the interaction effects of the average grain size of the Ti matrix (d m) and the volume fraction (V f) and aspect ratio (λ) of graphene.

Mechanical properties and corrosion resistance of pulse electrodeposited Ni-B/B4C composite coatings

MAX phase containing Ti-Al-(C, N) composite coatings is promising in marine engineering due to the improved tribocorrosion performance of titanium alloys. Therefore, novel Ti-Al-(C, N) composite coatings were prepared in this study using laser cladding on TC4 substrate. Electrochemical performances of as-obtained composite coatings were then analyzed under static and dynamic conditions in an artificial seawater environment, and their tribocorrosion behaviors and corrosion–wear synergism mechanism were examined by a tribocorrosion test system. The results showed that the existence of self-lubricating phases Ti2AlC and Ti2AlN in composite coatings and the corrosion products with a certain lubrication effect generated during the friction process kept the average friction coefficient at a low level. With the increase of load, the mechanical failure of the passive film in the friction process was enhanced, the adsorption of corrosive medium on the surface of the passive film led to its active dissolution, and the wear volume increased from 1.45 × 10−2 to 3.24 × 10−2 mm3. The corrosion of composite coatings in artificial seawater was not extensive, and volume loss caused by tribocorrosion was mainly determined by wear behavior. In sumary, the coatings exhibited good bearing capacity in the marine environment, thereby showing broad prospects for marine equipment applications.

Graphene-reinforced aluminum matrix composites prepared by spark plasma sintering

Ni–Co–Al2O3 composite coatings were prepared by pulsed electrodeposition and electrophoresis–electrodeposition on aluminum alloy. The content of Al2O3 particles of the Ni–Co–Al2O3 composite coating prepared by electrophoresis–electrodeposition was significantly higher than the composite coating prepared by pulsed electrodeposition. The composite coating prepared by electrophoresis–electrodeposition exhibited a better anti-wear performance than that prepared by pulsed electrodeposition. The morphology, composition and microstructure of the composite coatings were determined by means of X-ray diffractometer (XRD) and scanning electron microscopy (SEM). The hardness and friction properties of the samples were tested on the microhardness tester and the friction and wear loss tester respectively.

Optimization of pulsed electro co-deposition for Ni-B-TiN composites and the variation of tribological and corrosion behaviors

Graphene and its derivatives are widely recognized as effective reinforcements due to their unique mechanical, thermal and lubrication performance. Incorporation of these reinforcements into polyamide-imide (PAI) coating matrix has shown significant potential for improving the tribological performance. Here, the mechanisms underlying the tribological improvement enabled by graphene oxide (GO) are investigated via frictional experiments and molecular dynamics simulations. It was found that the coefficient of friction (COF) of PAI coating is reduced upon the addition of GO over the range of 100–400 MPa and 20–100 mm/s, with a maximum reduction of ~25% achieved at 200 MPa and 60 mm/s. Simulations reveal that the friction reduction arises from strong adhesion interactions between the embedded GO sheets and PAI molecular chains, which inhibit the shear-induced mobility of the chains during the friction process. This mechanism enables a further reduction in the COF of the GO/PAI composite coating by increasing the interfacial adhesion through the tailored modulations of surface morphology and chemistry of the GO sheets. These findings pave the way for advancing the rational design and application of graphene-based composite coatings with highly improved tribological performance.

Enhanced tribological properties of Y/MoS2 composite coatings prepared by chemical vapor deposition

Si3N4/TaC composite MAO coatings were fabricated by microarc oxidation (MAO) on a Ti–6Al–4V (TC4) alloy in a phosphate-based electrolyte containing Si3N4/TaC mixed particles. The influence of the amount of Si3N4/TaC particles on the microstructure, composition, tribological behavior, and corrosion properties of the MAO coatings has been investigated. Morphological research of the MAO coatings was carried out using scanning electron microscopy (SEM), with the surface porosity analyzed by ImageJ software. X-ray diffraction (XRD) was used for the detection of the phase characteristic of the MAO coatings, and an abrasive wear test and electrochemical measurements were conducted in the artificial seawater solution by the ball-on-disc friction tester and the electrochemical workstation, respectively. The results showed that Si3N4/TaC particles could be successfully incorporated into the composite coatings, and the addition of Si3N4/TaC particles greatly reduced the porosity of the coatings, thus improving both tribological and corrosion properties of the composite MAO coatings. The composite MAO coating with the addition of 1 g/L Si3N4 + 0.5 g/L TaC particles showed the best tribological property and the optimum corrosion properties.

TiO2 and TiO2-graphene composite films were prepared by a simple drop casting method using titanium diisopropoxide and graphene precursor. The structural analysis of the films was done by X-ray diffraction which indicate presence of anatase phase of TiO2 along with the appearance of graphene peak in TiO2-graphene composite film. The morphology of the films was studied by scanning electron microscopy from which graphene sheets incorporated in TiO2 nanoparticles can be seen. Absorbance study by UV-Visible spectroscopy indicate an increase in absorbance of TiO2-graphene films in visible region. Spectroscopic ellipsometry study shows an increase in refractive index of TiO2- graphene films in comparison to TiO2 films which may be due to increase in crystallinity of TiO2-graphene films. Optical absorbance study done on TiO2 and graphene solution with different concentration of graphene shows an increase in extinction coefficient with increase in graphene content in TiO2 measured at 632 nm. This indicates an increase in absorption of TiO2 with increase in Graphene content which can be useful for visible light absorption applications.

The paper studies the possibility of forming composite metal-ceramic (Sv-08G2S-О-Al2O3) and metal-carbide (Sv-08G2S-О-TiC) electric arc sprayed coatings using a hardening phase in the form of powder particles in a free form. For this, a modernized cap of the spray head of an EM-14M electric arc spray gun was used, equipped with a unit for continuous powder feed supply. A laboratory batch of samples was obtained in various technological modes of spraying. Microstructures of the deposited coatings are investigated using a scanning electron microscope. It has been established that composite coatings are characterized by a lamellar structure and a rather low porosity from 8 to 12% (depending on the deposition mode and the hardening phase content), and phase particles of different shades are well differentiated in the structure. The phases were identified by their microhardness indicators. It has been established that the microhardness of the metal matrix (Sv-08G2S-О) is 1.88GPa, ceramic Al2O3 particles ‑ 17.1GPa, TiC particles‑ 31GPa. The influence of the technological parameters of spraying, namely: current, voltage and powder consumption on the content of the hardening phase in the structure of the composite electric arc coatings has been investigated. It was found that when using the maximum values of technological parameters (current 160A, voltage 35V and powder consumption 35 g/min), the maximum content of the hardening phase in the coatings is obtained: 10.3% Al2O3 in metal-ceramic and 25.6% TiC in metal-carbide. The significantly higher maximum TiC content in comparison with the Al2O3 content in composite coatings is explained by the high density of carbide and, as a consequence, the increased velocity of these particles in the high-temperature heterophase jet. Experimental studies of the influence of the content of the strengthening phase in composite coatings on their bond strength to the substrate have been carried out. It is shown that the maximum value of the bond strength of metal-ceramic coatings is 30 MPa and corresponds to the Al2O3 content of 8.7%. As for metal-carbide coatings, the maximum bond strength value of 32 MPa was obtained with a carbide phase content of 18.4%. At the same time, the bond strength of the convention coating sprayed of Sv-08G2S-О wire is 26 MPa. An increase in this characteristic for composite coatings is explained by the additional activation of the sprayed surface by unmelted solid particles of Al2O3 and TiC. It is shown that the decrease in bond strength with an increase in Al2O3 content to 10.3%, and TiC to 25.2% is explained by a significant decrease in the actual contact area of the coating with the substrate.

To improve the wear resistance of the surface of the cotton picker spindle, a Ni-Co-ZrO2 composite coating with different ZrO2 nanoparticle concentrations was prepared using electrodeposition technology on the micro surface of spindle hook teeth, and the morphologies of the surface and cross-section, element contents, grain sizes, microhardness and friction coefficients of the Ni-Co-ZrO2 composite coating were obtained; a simulated wear test was conducted based on the independently developed spindle hook tooth wear device, and the morphologies and elemental distributions of the composite coating before and after wear were obtained; the effects of different ZrO2 nanoparticle concentrations (0, 2, 4, 6, 8 g/L) on the morphology, element content, grain size, microhardness, friction coefficient and wear resistance of the coating were discussed. The test results indicated that compared with Ni-Co coatings, Ni-Co-ZrO2 composite coatings featured a more compact coating structure, a greater coating thickness, and a smaller grain size. The presence of ZrO2 nanoparticles led to further improvement of the coating’s microhardness, friction coefficient and wear resistance. When the mass concentration of ZrO2 nanoparticles reached 4 g/L, the microhardness of Ni-Co-ZrO2 composite coating reached the maximum value, 545.4 Hv0.1, and the friction coefficient decreased to 0.06. At the same time, in the simulated wear test, the composite coating with this concentration had the smallest wear area and the highest wear resistance.