• Journal of the Korean Vacuum Society
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• v.4 no.S2
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• pp.58-63
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• 1995

Plasma spray has attracted attention as an effective method for obtaining protective coatings. In this paper, the physical, mechanical and thermal properties of coatings are reviewed. The microstructural features of the coatings are described. The relationship between the properties of coatings and their microstructure is also discussed. Plasma sprayed coatings are used to reduce wear and improve thermal protection on a large number of components in various industries. In some cases, the conditions of application are very aggressive and therefore the resulting maintenance costs are expensive. Improved coating materials and appropriate properties of coatings are the most promising ways to solve these problems[1,2]. The optimum coating properties depend on the microstructure of coatings[1-5]. In this paper, some ceramic coatings frequently used in industries were reported. The physical, mechanical and thermal properties of ceramic coatings are reviewed. The microstructure features of coatings are addressed. The relationship between the microstructure of coatings and their properties are discussed.

• Corrosion Science and Technology
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• v.2 no.5
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• pp.207-211
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• 2003

The weather resistance of five coatings systems based on alkyd, chlorinated rubber, epoxy, polyurethane and fluoropolymer were studied by natural exposure test and accelerated test. The coatings were exposed at Hanoi station with urban industry atmosphere and at Baichay station with marine atmosphere. The degradation of coatings was evaluated by gloss measurement and surface analysis by scanning electronic microscopy. The results obtained show that among coatings tested the gloss of polyurethane and fluoropolymer coatings remained highly and those of alkyd, chlorinated rubber and epoxy coatings were very low after two years of atmospheric exposure. Under accelerating conditions the gloss of fluoropolymer coatings remained highly after 80 cycles of testing. By comparison with accelerating test in UV-condensation chamber the conditions at atmospheric stations are more aggressive.

• Corrosion Science and Technology
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• v.15 no.5
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• pp.209-216
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• 2016

In the present study, chitosan based self-healing anticorrosion coatings were prepared by layer by layer (lbl) addition of chitosan (Ch) and polyvinyl butyral (PVB) on mild carbon steel substrate. Chitosan coatings exhibited enhanced coating stability and corrosion resistance in aggressive environments by the application of a PVB top layer. Chitosan layer in the lbl coatings have been modified by using glutaraldehyde (Glu) and silica ($SiO_2$). Performance of different coatings was tested using electrochemical impedance spectroscopy and immersion test. The best anticorrosion performance was observed in case of 10 % Ch_$SiO_2$_PVB coatings, which withstand immersion test over 25 days in 0.5 M salt solution without visible corrosion. 10 % Ch_$SiO_2$ coatings without the PVB top layer didn't last more than 3days. Application of PVB top layer sealed the defects in the chitosan pre-layer and improved its hydrophobic nature as well. Raman spectra and SEM of steel surfaces after corrosion study and removal of PVB_Ch/Glu_PVB coatings showed a passive layer of iron oxide, attributing to the self-healing nature of these coatings. Conducting particle like graphene reinforcement of chitosan in the lbl coatings enhanced corrosion resistance of chitosan coatings.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.206-212
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• 1998

The water permeation in protective coatings, which may greatly influence the corrosion protective property of these coatings, was studied using the electrochemical impedance spectroscopy technique. During the absorption of water in protective coatings immersed in electrolyte solution, the change of coating capacitance with concentration of electrolyte was determined from impedance measurements. When water absorption or desorption of coatings occured by exposing the coatings to electrolyte solutions of different concentration, increase in impedance caused by desorption of water was found to be higher in the case of thicker film. The amount of water absorbed in coatings changed with concentration of electrolyte. The water taken up in coatings from the solution of lower electrolyte concentration was deserted by contact with the solution of higher concentration. The uptake of water in protective coatings varied depending on the type of coating ingredient especially binder.

• Corrosion Science and Technology
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• v.21 no.1
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• pp.41-52
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• 2022

Herein, we report polyvinyl butyral composites coatings containing various loadings of 72-h bath sonicated hexagonal boron nitride particles (5 ㎛) to enhance barrier properties of coatings. Barrier properties of coatings were determined in 3.5 wt% NaCl after different time periods of immersion via electrochemical techniques such as open circuit potential, electrochemical impedance spectroscopy, and potentiodynamic polarization test. Coatings containing sonicated hexagonal boron particles exhibited improved corrosion resistance for longer periods of immersion compared to neat coating. We also discussed effects of hexagonal boron nitride on healing properties of polyvinyl butyral. Coatings containing 1.0 wt% loading of sonicated hexagonal boron nitride showed improved long-term barrier properties than coatings with other compositions. The presence of hexagonal boron nitride also affected the healing properties of polyvinyl butyral coatings besides their barrier properties. Such improved barrier properties of composites coatings were attributed to the high aspect ratio, plate-like shape, and electrically insulated nature of the filler.

• Journal of Welding and Joining
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• v.17 no.4
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• pp.53-59
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• 1999

Amorphous alloys have also been called glassy alloys or non-crystalline alloys. They are made by the rapid solidification. The solidification occurs so rapid that the atoms are frozen in their liquid configuration. There are unique magnetic, mechanical, electrical and corrosive behaviors which result form their amorphous structure. In the study. amorphous coatings were manufactured with Ni-Cr-B-Si powders by flame spray. Measurement of hardness, were resistance, corrosion resistance and observation of microstructures and XRD, DSC were performed to investigate characteristics of amorphous coatings. The experimental results obtained as follow: 1) Amorphous powders could not be manufactured with the spraying in the spraying in the liquid nitrogen. But, amorphous coatings could be manufactured with the rotation cooling method by liquid nitrogen. In the fabrication of amorphous coatings, major factor was the rapid cooling by rotation of the substrate. 2) Hardness of coatings was obtained Hv 960 by formation of amorphous phase. But, wear resistance decreased. That was due to porosity in the coatings by the rapid cooling. 3) In the case of corrosion resistance, amorphous coatings were superior to air-cooled coatings. That was due to formation of amorphous phase. 4) After amorphous coatings were heat-treated at 520℃ for 1hr. hardness increased 80% and wear resistance increased 30% comparing with air cooled coatings. These were due to crystallization of amorphous phase and decrease of porosity by heat-treatment.

• Journal of the Korean institute of surface engineering
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• v.46 no.6
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• pp.242-247
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• 2013

Zr-Al-N coatings were synthesized by the hybrid coating system combining arc ion plating and DC magnetron sputtering from a Zr and an Al target in argon-nitrogen atmosphere, respectively. By changing the power applied on the Al cathodes, the Zr-Al-N coatings with various Al contents were deposited. The microstructure and chemical compositions of the Zr-Al-N coatings were studied by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM). With increasing of Al content in the coatings, the solid solution (Zr, Al)N crystallites were observed in the Zr-Al-N coatings. The nanohardness of the Zr-Al-N coatings exhibited a maximum value of 42 GPa for the Zr-Al (7.9 at.%)-N, and decreased with further increase in Al content in the coatings. The oxidation and corrosion behavior of the Zr-Al-N coatings revealed better properties compared than those of ZrN coatings due to the formation of a solid solution.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.17-17
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• 2012

Magnesium alloys exhibit many attractive properties such as low density, high strength/weight ratio, high thermal conductivity, very good electromagnetic features and good recyclability. However, most commercial magnesium alloys require protective coatings because of their poor corrosion resistance. Attempts have been made to improve the corrosion resistance of the Mg alloys by surface treatments, such as chemical conversion coatings, anodizing, plating and metal coatings, are commonly applied to magnesium alloys in order to increase the corrosion resistance. Among them, chemical conversion coatings are regarded as one of the most effective and cheapest ways to prevent corrosion resistance. In this study, zinc phosphate conversion coatings on various Mg alloys have been developed by selecting proper phosphating bath composition and concentration and by optimizing phosphating time, temperature. Morphology, coatings composition, corrosion resistance, adhesion and its formation and growth mechanism of the zinc phosphate conversion coatings were studied. Results have shown some attractive properties such as simplicity in operation, significantly increased corrosion protective property. However, adhesions between coatings and substrate and also between coatings and paint are still not satisfied. Resolving the problems and understanding the mechanism of phosphating process are targets of our study.

• Journal of the Korean institute of surface engineering
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• v.50 no.6
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• pp.460-464
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• 2017

As increasing thermal efficiency of the gas turbine, the performance improvement of thermal barrier coatings is also becoming important. Ytrria stabilized zirconia(YSZ) is the most popular materials for ceramic top coating because of its low thermal conductivity. In order to enhance the performance of thermal barrier coatings for hot sections in the gas turbine, suspension plasma spraying was developed in order to feed nano-sized powders. YSZ coatings formed by suspension plasma spraying showed better performance than YSZ coatings due to its exclusive microstructure. In this research, two YSZ coatings were deposited by suspension vacuum plasma spraying at 400 mbar and 250 mbar. Microstructures of YSZ coatings were analyzed by scanning electron image(SEM) on each spraying conditions, respectively. Crystalline structure transformation was not detected by X-ray diffraction. Thermal conductivity of suspension vacuum plasma sprayed YSZ coatings were measured by laser flash analysis. Thermal conductivity of suspension vacuum plasma sprayed YSZ coatings containing horizontally oriented nano-sized pores and vertical cracks showed $0.6-1.0W/m{\cdot}K$, similar to thermal conductivity of YSZ coatings formed by atmospheric plasma spraying.

• Journal of the Korean institute of surface engineering
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• v.43 no.6
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• pp.283-288
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• 2010

Ni-$TiO_2$ nano composite coatings were fabricated using pulse current electrodeposition technique at 100 Hz pulse frequency with a constant 50% pulse duty cycles and reference was taken with respect to the direct current (dc) electrodeposition. The properties of the composite coatings were investigated by using SEM, XRD, Wear test and Vicker's microhardness test. Pulse electrodeposited composite has exhibited enhancement of (111), (220), and (311) diffraction lines with an attenuation of (200) line. The results demonstrated that the microhardness of composite coatings under pulse condition was significantly improved than that of pure nickel coating as well as dc electrodeposited Ni-$TiO_2$ composite coatings. Wear tracks have shown the less plastic deformation in pulse plated composite. Coefficient of friction was also found to be lower in pulse plated composite coatings as compared to dc plated composite coatings.