Papers by Keyword: Coating

Abstract: The effects of different negative voltages on micro-arc oxidation coating fabricated on ZK60 Mg alloy were investigated under two steps increasing mode of 280-360V. The microstructure, coating thickness and corrosion resistance of coatings were evaluated by scanning electron microscopy (SEM), energy disperse spectroscopy (EDS), microscope with super-depth of field and electrochemical impedance spectroscopy (EIS). Current-time responses during MAO process were also analyzed combined with coating characteristic. The results reveal that higher negative voltage helped to develop a compact, smooth, thicker and better corrosion-resistant coating. The coating with maximum thickness of about 20.2μm formed under negative voltage of 20V exhibits higher impedance value and the best corrosion resistance.

Abstract: Proposed an accuracy estimation method combined thin films section of hot disk thermal constants analyzer and Fourier transform formula, saves the requirement that heat capacity must be given in advance when use anisotropic model hot disk thermal constants analyzer to test the thermal conductivity of materials with coating. Use the anisotropic model of hot disk thermal constants analyzer and heat transfer experiment to testify the accuracy of this method.

Abstract: Double-coated Mg powders with a chloride and a polymer such as HTPB(hydroxy-terminated polybutadiene),NC(nitrocellulose),PVB(polyvinylbutyral) were fabricated by physical vapor deposition and solvent evaporation,respectively.The influence of the addition and the species of the first and second coating agents on the water reaction characteristics was investigated. The results show that both the hydrogen release during the reaction with water and the reaction rate increases distinctly with the increase of the chloride.Compared with those of the raw Mg powders and Mg powders coated with the chloride, the initial reaction temperature of the double-coated Mg powders increases to different extent.Moreover,the initial reaction temperature has an increase trend with the increase of the addition of coating agents.

Abstract: The research relates to a method for preparing an in-situ crosslinked polymer coating. It has excellent solubility in aqueous alkaline solution, but didnt dissolve in general organic solvents and water. The crosslinked polymer coating was made through the reaction of a copolymer derived from diacetone acrylamide (DAAM) and ethacryloyloxyethyl-carbazochrome-p-toluenesulfonamide (MCTS) with a crosslinking agent, isonicotinyl hydrazide. The two components were dissolved in 3-methoxypropanol to prepare the coating solution, which was then coated to a grained and anodized aluminum substrate and dried at 120 °C for 5 min to obtain the crosslinked coating. There exists intermolecular hydrogen bond between the pyridine ring of isonicotinyl hydrazide and the sulfonamide group of the MCTS unit of the copolymer. The reaction between the hydrazide group and the carbonyl group during the drying process generated the hydrazone bond, resulting in the crosslinked polymer coating. The intermolecular hydrogen bond and the covalent bond render the coating insoluble in most organic solvents. However, the hydrogen bond was readily broken down when the coating was exposed to aqueous alkaline solution due to the ionization of the sulfonamide group, causing rapid dissolution of the coating. The coating was also used as the under-layer for the preparation of a double-layed CTP plate. The performance of the double-layed CTP plate was preliminarily studied.

Abstract: Si-Ti coatings were prepared on the surface of T-222 alloy by fused slurry method at different temperatures (1425-1500°C). Microstructure and composition of the coatings were characterized and analysed through scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), energy dispersive X-ray spectrometry (EDS) respectively. The coating fabricated at 1450°C exhibited excellent structure compatible with high temperature oxidation resistance. Its surface is relatively smooth with few holes and cracks and the main phase on the surface is (Ti, Ta)Si that possesses outstanding corrosion resistance. Moreover, the cross-sectional structure of the coating is smooth and compact which can effectively prevent O₂ from permeation. The isothermal oxidation behaviors in pure O₂ atmosphere at 1500°C for 2h finally demonstrate that the optimum coating temperature is 1450°C.

Abstract: This work elucidated corrosion resistance of the electrodeposited MgO/calcium phosphate (Ca-P/MgO) films on titanium (Ti). The microstructure, phase composition, and corrosion resistance of the films were studied. Results revealed that The Ca-P/MgO composite coatings were rough and inhomogeneous, the upper layer was floral-like crystals or flakes agglomerates morphology, and the lower layer was needle-like crystals which were mutually cross linked. The coating was very dense, and the content of Mg was about 0.3 wt%. Potentiodynamic polarization test manifested that the Ca-P/MgO-coated surface exhibited superior corrosion resistance than the bare titanium.

Abstract: In the present work, Cr₂O₃-Al₂O₃-Cr coatings are prepared on Q235 steel by aluminothermic process based on Cr₂O₃ Al system, using Cr₂O₃ as diluents while a small quantity of Fe₂O₃ to reduce reaction temperature. The results showed that after treated at 650oC for 30minutes, homogenous Cr₂O₃-Al₂O₃-Cr coatings can be prepared on Q 235 steel by aluminothermic process with the powders mixture with weight ratio of Cr₂O₃: Fe₂O₃: A1 equal to 4: 0.3: 1.12, while coatings prepared by mixture with superfluous aluminum are fragmentary. Surface hardness of the coatings prepared with superfluous Cr₂O₃ is about 23.9GPa while that of the coatings prepared with superfluous Al is about 10.9 GPa and large scatter of 13.7% in hardness.

Abstract: Micron-sized WC-CrCNi powder (WC-metal powder, WC 68%, C 0.56%, Cr 21% Ni 6%) was coated onto magnetic shaft material Inconel718 (In718) surface using HVOF thermal spraying equipment for the improvement of the surface properties of the shaft. During the HVOF coating, metal carbides, such as WC and Cr₇C₃ decomposed to W₂C, metals and free carbon. The free carbon and the excesively sprayed oxygen formed carbon oxide gases and thus produced pores and voids in coating. The optimal coating process (OCP) that produced the lowest coating surface porosity and the highest surface hardness was determined by the Taguchi experimental program of nine processes for four spray parameters with three levels. Coatings with porosity 1.20±0.1% and hardness 1150±60 Hv were prepared using optimal coating processes. The coating was porous, but the hardness was improved approximately three times from 400±10 Hv (In718) to 1150±60 Hv (coating). Friction coefficients (FC) of the coating were lower compared with In718 at both 25°C and 450°C. FC decreased with increasing temperature from 25°C to 450°C for both In718 and the coating. Wear depths of coatings were smaller than those of In718 at both 25°C and 450°C. For the improvement of the surface properties and durability of the magnetic shaft, HVOF WC-CrCNi power coating was recommended.

Abstract: Ground and satin stainless steel surfaces are often applied to lend various products a characteristic high-quality appearance. Examples can be found in interior and exterior architecture, passenger elevators, public ticket machines and cover panels of white goods. In everyday use the visual appearance of these products is impaired by soiling. Especially on the surfaces of household appliances fingerprints tend to accumulate. On satin stainless steel parts the cutaneous sebum sticks to the brush marks. Thus extensive cleaning effort is required. Since several years the manufacturers of stainless steel offer satin stainless-steel sheet metal equipped with thin clear coatings for this application. The clear coating fills the brush marks and also causes a better wetting behavior and optimal cleaning properties. In this regard, the term easy-to-clean surface is common.The manufacturers face the challenge of applying a very thin clear coating with an index of refraction adjusted to the satin stainless steel surface and the cutaneous sebum. Thus, ideally the coating should not be distinguishable, concerning haptic and optic properties. The thickness of these coatings amounts to a few micrometers. Therefore, the heat transfer coefficient of the surface only varies minimally and the surface does not feel painted. The advantageous wetting behavior and the slightly differing reflection properties of the clear coating contribute to reducing the adhesion and conspicuousness of fingerprints significantly. Because of these attributes the term anti-fingerprint coatings is used.A further prerequisite for the application of anti-fingerprint coatings in high-quality parts is a good scratch resistance. Therefore, nanoparticle-reinforced coating systems are applied. Typically hard particles like SiO₂ or Al₂O₃ are used. In addition to this, a curing procedure by ultraviolet radiation combined with a suitable solvent-free coating system can be used. This further improves the hardness and scratch resistance of the coating. Due to these requirements the clear coatings are applied in a coil-coating procedure. Consequently, the final painted sheets have to be processed to the respective sheet metal part. Common forming processes for white goods’ panels are bending and crash forming. After forming the final processor does not spend any effort on varnishing or curing on-site which leads to special cost savings in comparison to a piecework coating.The required performance characteristics of the anti-fingerprint coating allow no compromises concerning the coating system with regard to the formability. During forming operations damage is caused to the clear coating in the form of crack formation and delamination. Due to the optical properties of coating systems specifically adjusted to ground stainless steel surfaces, the defects in the clear coating are difficult to identify precisely. However, the properties of the final painted sheet metals’ surface are impaired. This also includes the corrosion resistance which must be taken into account especially for stainless steel applications, e.g. in the kitchen area or in outdoor applications.On the one hand this paper deals with experimental analyses for the identification of the defects caused to an anti-fingerprint clear coating by forming operations. The elaborated procedure is used to identify cracks and delamination due to bending operations. In the experiments mandrel bending specimens of the coated stainless steel sheet metal are formed. Due to different bending radii the intensity of cracks and delamination in the coating varies. But the orientation of the bending edge towards the grinding direction also influences the damage intensity and the damage characteristics. These specimens are also examined in a salt spray test to determine the influence of the different coating damages on the corrosion resistance of the stainless steel substrate. In comparison, the same stainless steel sheet metal material without clear coating is tested simultaneously. The comparison demonstrates the influence of the coating and the deformation-induced damages. On the other hand, to examine the damages as a result of a typical forming process a simplified oven panel is manufactured in a crash forming tool. The front side of the panel remains flat and shows no strains. But along the sharp bending radius, which is typical for the design of high-quality white goods’ applications, cracks in the clear coating can be observed. The experimental results show an influence on the coating damages resulting from the use of a deep draw foil. Furthermore, the forming tool features a heating device and panels are formed at higher temperatures with an effect on the coating damages.

Abstract: Mechanical surface treatments like machine hammer peening and deep rolling can substitute an essential part of the manual polishing time in the conventional process chain of die and mold production. However, the increasing use of high strength steels in the automotive industry and the associated wear of deep drawing tools require further wear-protection methods. In this context it is still unknown if hammer peened and deep rolled surfaces can ensure a sufficient adhesive strength of a coating. Therefore, in the present work different coatings are applied on hammer peened and deep rolled surfaces. Finally, the wear behavior is examined in the strip drawing test. The evaluation of the experimental results proves the potential for an industrial application of the mechanically treated and coated tools.