Papers by Keyword: Composite Coating

Abstract: The Ni-P composite coatings onto 4043 aluminum alloy were prepared by electroless plating with nickel sulfate and sodium hypoposphite as raw material. The Ni-P composite coatings were heat-treated for 1 hour at 200°C, 300°C, 400°C, 500°C and 600°C, respectively. The tribological behaviour of the coatings was investigated on a vertical universal friction/wear tester under dry friction. The morphology and phase structure of the composite coatings were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), and the microhardness of the composite coatings were measured by Vickers diamond indenter. The results showed that the as-deposited coatings had smooth cellular pattern and amorphous structure, and the microhardness of the coatings reached the maximum at 400°C heat treatment, the reason is the formation of Ni3P alloy phase with increasing of the heat treatment temperature. The friction coefficient of coatings annealed at 400°C is the lowest. The wear loss was found to increase with corresponding increase in load and sliding speed. It was found that the wear mechanism of the as-deposited Ni-P composite coatings was dominated by adhesive wear and scuffing under the experimental conditions, but the wear mechanism of the coatings annealed at 400°C was scuffing.

Abstract: A kind of centrifugal casting plus in situ techniques of fabricating iron-based composite coating reinforced by tungsten carbide (WC) particles was developed. The experimental results show that the reinforcing particles were generated by reaction between dissolved tungten wires and carbon from gray cast iron molten. The composite coating mainly consists of primary WC carbides, some fine secondly WC carbides as the reinforcing phase and pearlite accompanied by negligible graphite flakes as the matrix. Compared with the unreinforced gray cast iron, the in situ synthesized WC particles can enhance the ultimate tensile strength and decrease elongation rate of the composite coating. Fracture morphology reveals that fracture mode of composite coating is brittle and ductile mixed fractures, the fracture mechanism of the composite is not only related with the introduction of reinforcement but also with the reduction of graphite flakes in the matrix

Abstract: A thick Fe-based amorphous and nanocrystalline composite coating was prepared by in-situ tungsten inert gas (TIG) cladding method. The results show that the cladding coating mainly consists of amorphous phase and nanocrystalline grains. The microstructure study shows that the Fe-based composite coatings have unique microstructure including nano-sized grains surrounded by nano-scale amorphous shell layer (encapsulated structure) and the homogeneously distributed dendrites/cellular crystals. The unique microstructure gives rise to the superior micro-hardness and wear resistance of the coating. The Fe-based coatings have great potential as promising wear-resistance structural materials used in electric power and cement industry.

Abstract: Multi-walled carbon nanotube (MWCNT)/Pb-Sn composite coatings and ordinary Pb-Sn alloy coatings were prepared by electrodeposition technique, respectively. The morphology images of the coatings in different growth time were observed by SEM at high and low magnifications. The results showed that composite coatings had a compacter and refiner surface than ordinary Pb-Sn alloy coatings; the addition of CNTs increased the number of crystal cores and changed the directions of crystal orientation, which resulted in a fine network structure.

Abstract: Fe–Al/Cr₃C₂ composite coatings produced from high-velocity flame spraying (HVFS) are Fe–Al intermetallic composite coatings with remarkable room-temperature and high-temperature properties. However, Fe–Al/Cr₃C₂ composite coatings have a Cr₃C₂ content of 50%. This causes the coatings to become porous and limits its room-temperature and high-temperature properties. In order to improve microstructure and properties of Fe–Al/Cr₃C₂ composite coatings, Fe–Al/Cr₃C₂RE, including Fe–Al/Cr₃C₂ and CeO₂, is sprayed by HVFS technology onto AISI 1020 steel. The properties including bonding strength and high-temperature corrosion-resistance of Fe–Al/Cr₃C₂RE composite coating are tested at 25°C and 650 °C. For comparison, two other materials, substrate AISI 1020 steel and Fe–Al/Cr₃C₂ composite coating, are tested under the same experimental conditions. The microstructures of the coatings are analyzed by scanning electronic microscopy (SEM), the cross-section morphology of Fe–Al/Cr₃C₂RE composite coating is analyzed by energy-dispersive spectroscopy (EDS), and the existing states of oxides are analyzed by transmission electron microscopy (TEM). The phases of the composite coating after corrosion are analyzed by X-ray diffraction (XRD). The results demonstrate that the properties of Fe–Al/Cr₃C₂RE composite coatings is better than that of either AISI 1020 steel or the Fe–Al/Cr₃C₂ composite coating. CeO₂ is a surface-active agent, and it significantly improves the microstructure and properties of Fe–Al/Cr₃C₂RE composite coating. CeO₂ improves the bonding strength of Fe–Al/Cr₃C₂RE composite coating by reducing the surface tension of droplet and enhancing its fluidity as well as wetting capacity on the surface of the substrate, decreasing the internal stress of coating.Adding CeO₂ to the coating produces Al₂O₃ and Cr₂O₃ oxide films, which protect the substrate AISI 1020 steel from corrosion more efficiently.

Abstract: The MoS₂ powders was coated with Al₂O₃ ratio varying 5wt.% to 50wt.% content. Ni–MoS₂/Al₂O₃ composite coatings were prepared by means of pulse electrodeposition in a nickel-plating bath containing MoS₂/Al₂O₃ powder to be co-deposited. The dependence of surface morphology, microhardness and tribological properties of the composite coatings was investigated in relation to the Al₂O₃ ratio in MoS₂/Al₂O₃ powder. The results demonstrate that the coating co-deposited with MoS₂/50wt.%Al₂O₃ showed a compact and fine granular surface morphology; the highest microhardness and wear resistance. The hardness of Al₂O₃ is responsible for this improvement.

Abstract: In the present work, ultra-fine Al₂O₃/ZrO₂-MgO-CeO₂ powders were used as the starting materials to produce Al₂O₃-ZrO₂ composite coatings on 45# carbon steel by flame spray. The ultra-fine Al₂O₃/ZrO₂-MgO-CeO₂ powders were prepared via the co-precipitation method accompanied a crushing sintering process. The microstructure, the phase compositions and the bond strength of the crushed sintered powders and the corresponding composite coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and a tensile bond strength tests respectively. It was found that the phase composition, the surface topography and the coating adhesion were different from the difference kinds of coatings. Results indicated that the phase composition of the flame sprayed ceramic coatings consisted of tetragonal-ZrO₂, cubic-ZrO₂, ZTA (zirconia toughened alumina) and γ-Al₂O₃, with a small amount of α-Al₂O₃, and that bond strength values attained 45.1 MPa for 42.6wt.% Al₂O₃/57.4wt.% Mg_0.13Ce_0.1Zr_0.77O_1.87 coating.

Abstract: The influence of MoS₂ lubrication phase on the tribological properties of the Ni₆₀A/MoS₂ composite coating was conducted on UMT-2 micro-wear testing machine (USA), discussing the self-lubricating effect and mechanism. The result shows that with the increasing content of MoS₂, the friction coefficient of the coating which changed with the increasing content of the MoS₂ presents firstly decreases then increases, and the value reach the minimum when the quality percent of MoS₂ wrapped with Nickel is 35%. Low-friction property of the Ni₆₀A/MoS₂ composite coating is due to the forming of MoS₂ lubricating film in friction surface. The decreasing of the friction coefficient of the coating is in proportion to the coverage area of MoS₂ lubricating film.

Abstract: A composite coating was prepared on Ti-6Al-4V surface by the combination of nitriding, Mo-sputtering and sulfurizing treatments. The microstructure and phase constituent of the composite coating were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Furthermore, the cross-sectional hardness gradient of the coating was determined. The results revealed that the composite coating consisted of Ti, Mo, MoS₂, TiN and transition layer and the grain size of the sulfides formed on the coating surface were different with treatment temperature. The examination of the cross-sectional hardness of the composite coating revealed that the coating was an ideal tribological surface.

Abstract: To improve the mechanical product hardness, wear resistance and corrosion resistance, Fe-SiC composite plating process and properties have been studied. By using self-made asymmetric AC - DC power supply and adding SiC in ferrous chloride bath, the high performance Fe-SiC composite coatings are prepared by electrodeposition method. The effect of Phase, composition and SiC particle content on the surface morphology, structure, hardness, wear resistance and corrosion resistance of Fe-SiC composite coatings are studied. The process parameters of Fe-SiC composite plating are optimized. The results show that the micro-cracks in composite coatings will reduced and the hardness, wear resistance and corrosion resistance will increased by adding SiC particles under the condition of optimum process.