Structures of ceramics coatings on steel fabricated by hot-dipping and micro-arc oxidation

Firstly, an aluminum coating was produced metallurgically on mild steel by hot-dipping, then an aluminum oxide coating was formed self-growingly from the aluminum coating by micro-arc oxidation treatment. The structures of the composite coatings were investigated by means of SEM, TEM and XRD. The results show that the composite coating consists of three layers which are Fe-Al alloy, aluminum coating and aluminum oxide orderly outward from the steel substrate. There are amorphous phases, k-Al2O3 and θ-Al2O3 mainly in the aluminum oxide.

Hot-Dip Coating of Lead-free Aluminum on Steel Substrates with Ultrasonic Vibration

Hot-dip coating has been practically employed in manufacturing zinc alloy coated steel sheets.However,it is difficult to coat aluminum alloy on a bulky steel substrate without sufficient preheating,because a rapidly solidified layer containing gas babbles is formed on a substrate surface.A variety of iron-aluminides are also formed at the interface of a steel and aluminum hot-dip coating system,which is the main difficulty in joining of steel with aluminum.Ultrasonic vibration was applied to a steel substrate during hot-dip coating of aluminum alloy to control a rapidly solidified layer and a brittle reaction layer.Hot dipping of columnar steel substrates into molten aluminum alloy （Al-2.7 mass fraction Si-4.6 mass fraction Sn） was carried out through the use of a Langevin oscillator with resonant frequency of 19.5 kHz.The application of ultrasonic vibration is quite effective to control a rapidly solidified layer and a surface oxide layer from a substrate surface by the sonocapillary effect based on a cavitation phenomenon,so that the intimate contact is achieved at the beginning of hot-dip coating.The application of ultrasonic vibration to hot-dipping is effective to control a reaction layer with less than 5 #m in thickness.An impact test exhibits that the good adhesive strength is approved in hot-dipped aluminum coatings with a thin reaction layer of approximately 5μm.

Analysis of Coating Microstructure of Hot-Dip Aluminum of Deformed Low-Carbon Steel Containing Rare Earth

The coating microstructure of hot-dip aluminum (HDA) of deformed low-carbon steel containing RE was analyzed by metallography microscopy, TEM and XRD, and the forming mechanism was also discussed. The results show that, the Fe_2Al_5 phase, on whose subcrystal boundaries, Al particles with the size of 7～30 μm existing on parallel linear are, grows a strong orientation. And the spread activation energy of Al is 155.22 kJ·mol -1. In addition, the effects of deformation on coating microstructure of hot-dip aluminum and the function of RE were preliminarily analyzed.

Effect of Pb content on the surface topography and corrosion resistance of hot dip Zn-Al-Mg coatings

In this study,the effect of Pb content on the surface morphology and salt spray corrosion resistance of hot dip Zn-AI-Mg coatings was investigated. The results showed that the coating surface easily formed small grains of zinc spangle structures and that the salt spray con＇osion resistance of the coating decreased when Pb content was greater than 0.01%. The microstructure and energy dispersive spectrum analysis of surface and cross-sectional areas was performed by scanning electron microscopy. Pb content present in the coating was analyzed by glow discharge spectrum. The results showed that the distribution of Pb in the coating was not uniform. The Pb content was segregated on the surface and at the cross-section of the Zn-A1-MgZn2 ternary eutectic structure,especially,on the surface of the Zn-A1-MgZn2 ternary eutectic structure.

Electrochemical Properties of Poly(ethylene oxide)(PEO) Doped TiO_2-PEO Films Prepared by Sol-gel Dip Coating Technique

PEO modified Ti02 -PEO organic-inorganic hybrid thin films were prepared via, sol-gel dipping process on glass substrate pre-coated with ITO. The preparation parameters were studied. Electrochemical and optical properties of the films were characterized by cyclic voltammetric response and visible transmittance. X-ray diffraction (XRD) was used to determined the crystalline structure of the gel. The results show the sols added with PEO have acceptable stable periods for practical use. The PEO modified optical transitivity of the hybrid films has heavy effects on the crystallization of TiO2 during structural evolution because of the interaction between PEO and Ti02 . PEO-TiO2 films have better electrochemical activity than the TiO2 equivalent behaved as higher Li + insertion/extraction current density and cyclic reversibility.

Fabrication of ZrO_2/Mo-Si/Ni Functionally Graded Material by Dip-Coating

A slurry dip-coating technique was developed for fabrication of Zr02/Mo-Si/Ni functionally graded material (FGM)on the stainless steel substrate. The rheological behavior of ZrO2-Ni-ethanol slurry was characterized by viscositytest. The amount of polyvinyl butyral (PVB) additives, which served as the dispersant and binder in ZrO2-Ni-ethanolslurry, was optimized. The results showed that the characters of mixed slurries with added 9 vol. pct (relativelyto total powders) MoSi2 powders prepared by mechanical alloying changed little. The stainless steel substrate wascoated several times by dipping in the slurries, and followed by drying in air every dipping. After debinding in Arin graphite die, the coated FGM plate was finally hot pressed at 1300℃ for 1 h under the pressure of 5 MPa in Arin the same die. Microstructural observations of the sintered FGM specimens revealed that the graded layers wereformed on the stainless steel substrate, in which no cracks were observed.

Influence of Sn Low Doping on the Morphological, Structural and Optical Properties of ZnO Films Deposited by Sol Gel Dip-Coating

In this work, Undoped Zinc Oxide (ZnO) and Sndoped Zinc Oxide (ZnO:Sn) films have been deposited by sol-gel dip coating method, where the Sn/Zn atomic ratio was 3% and 5% in the solution. The effects of Sn incorporation on morphological, structural and optical properties of ZnO films were investigated. The Scanning Electron Microscopy (SEM) showed that the morphological surface of the films was affected by Sn low doping. The X-Ray Diffraction (XRD) patterns showed that all films have polycrystalline structures, and the doping incorporation has not lead to substantial changes in the structural characteristics of ZnO films. The crystallite size was calculated using the well-known Scherrer’s formula and found to be in the range of 23 - 40 nm. The measurements from UV-Visible Spectrophotometer (U-Vis) indicated that the highest average optical transmittance in the visible region was related to Undoped ZnO film, then the optical band gap and Urbach energy values of thin films were calculated. The X-Ray Photoelectron Spectroscopy (XPS) has demonstrated that Sn is incorporated in ZnO lattice.

Comparative Study of Structural, Optical and Electrical Properties of SnO₂Thin Film Growth via CBD, Drop-Cast and Dip-Coating Methods

Tin oxide (SnO2) thin films were deposited on glass substrate by Chemical Bath Deposition (CBD), Drop-Cast and Dip-Coating method. The thin films were post-annealed at 500°C for 2 hours. The structural, optical, and electrical properties of the SnO2 thin films were investigated by using XRD, FTIR, SEM, EDX, UV-Vis spectroscopy, and Electrometer experiment. The XRD patterns of SnO2 thin films deposited on glass substrate by CBD method, Drop-Cast method and Dip-Coating method showed cubic, tetragonal and amorphous structures respectively. The FTIR spectrum exhibited the strong presence of SnO2 with the characteristic vibrational mode of Sn-O-Sn. The SEM analysis was observed that the surface morphology of the thin films toughly depends on the deposition methods of the SnO2 thin films. EDX measurement confirmed that the thin films are the composition of Tin (Sn) and Oxygen (O2). The optical band gap of SnO2 thin films deposited by CBD method, Drop-Cast method and Dip-Coating method is found to be 3.12 eV, 3.14 eV and 3.16 eV respectively. Thin films deposited by Dip-Coating method showed the highest band gap. The electrical results confirmed that the SnO2 thin films are good conductors and pursued Ohm’s Law. These properties of the SnO2 thin films brand are appropriate for application in solar cell assembly, gas sensor devices and transparent electrodes of panel displays.

Effect of pattern coating thickness on characteristics of lost foam Al-Si-Cu alloy casting

An experimental study on lost foam casting of an Al-Si-Cu alloy was conducted. The main objective was to study the effect of pattern coating thickness on casting imperfection and porosity percentage as well as eutectic silicon spacing of the alloy. The results showed that increasing slurry viscosity and flask dipping time influenced the casting integrity and microstructural characteristics. It was found that thinner pattern coating produced improved mould filling, refined microstructure and higher quality castings containing less porosity.

Formation and structure of composite coating of HDA and micro-plasma oxidation on A3 steel

Composite coatings were obtained on A3 steel by hot dipping aluminum(HDA) at 720 ℃ for 6 min and micro-plasma oxidation(MPO) in alkali electrolyte. The surface morphology, element distribution and interface structure of composite coatings were studied by means of XRD, SEM and EDS. The results show that the composite coatings obtained through HDA/MPO on A3 steel consist of four layers. From the surface to the substrate, the layer is loose Al2O3 ceramic, compact Al2O3 ceramic, Al and FeAl intermetallic compound layer in turn. The adhesions among all the layers are strengthened because the ceramic layer formed at the Al surface originally, FeAl intermetallic compound layer and substrate are combined in metallurgical form through mutual diffusion during HDA process.Initial experiment results disclose that the anti-corrosion performance and wear resistance of composite coating are obviously improved through HDA/MPO treatment.

Heat Transfer during the Solidification of Hot Dip Aluminizing Coating

Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity.Although the pulling speed is one of the most important parameters to control the coating thickness of aluminizing products,however,there are few publications on the mathematical modeling of pulling speed during the hot dip process.In order to describe the correlation among the pulling speed,coating thickness and solidification time,the principle of mass and heat transfer during the aluminizing process is investigated in this paper.The mathematical models are based on Navier-Stokes equation and heat transfer analysis.Experiments using the self-designed equipment are carried out to validate the mathematical models.Specifically,aluminum melt is purified at 730 ℃.The Cook-Norteman method is used for the pretreatment of Q235 steel plates.The temperature of hot dip aluminizing is set to 690 ℃ and thedipping time is set to 3 min.A direct current motor with stepless speed variation is used to adjust the pulling speed.The temperature change of the coating is recorded by an infrared thermometer,and the coating thickness is measured by using image analysis.The validate experiment results indicate that the coating thickness is proportional to the square root of pulling speed for the Q235 steel plate,and that there is a linear relationship between coating thickness and solidification time when the pulling speed is lower than 0.11 m/s.The prediction of the proposed model fits well with the experimental observations of the coating thickness.

热浸镀Zn-Al-Mg镀层在模拟湿热海洋大气环境中的腐蚀行为研究

目的 为详细研究热浸镀Zn-Al-Mg镀层在模拟湿热海洋大气下的腐蚀行为及作用机理,同时为热浸镀Zn-Al-Mg镀层在湿热海洋大气环境中服役提供数据参考。方法 采用腐蚀失重、XRD、SEM、电化学等测试方法对热浸镀Zn-Al-Mg镀层在模拟湿热海洋大气环境下的腐蚀行为进行研究。结果 腐蚀产物主要由Zn_(5)(OH)_(8)Cl_(2)·H_(2)O组成,腐蚀一段时间后,发现少量ZnO、Zn_(5)(OH)_(6)CO_(3),腐蚀产物具有与锌腐蚀类似的层状结构,1 848 h呈“三明治”型,相比于上下两层暗色物质,中层亮色腐蚀产物富集更多的Cl元素。热浸镀Zn-Al-Mg镀层腐蚀速率大体随时间延长呈上升趋势,只在672~840 h腐蚀速率下降,对比镀锌在模拟环境和锌在湿热大气环境中的腐蚀,热浸镀Zn-Al-Mg镀层在模拟湿热海洋大气中表现出较好的耐蚀性。结论热浸镀Zn-Al-Mg镀层在模拟湿热海洋大气下腐蚀产物演变与腐蚀过程中Mg的参与有关。腐蚀672~840h阶段腐蚀速率下降的原因与腐蚀产物中ZnO的减少和Zn_(5)(OH)_(8)Cl_(2)·H_(2)O占比增加有关。对比镀锌在模拟环境和锌在湿热大气环境中的腐蚀,预测热浸镀Zn-Al-Mg镀层在严酷湿热海洋大气中仍具有较高的耐蚀性,可以优先考虑作为湿热海洋环境的建设用材。

Sr元素含量对Zn-2.0%Al-1.2%Mg镀层的微观组织与耐蚀性的影响

为了进一步研究微量合金元素对镀层微观组织的调控以及耐蚀性能的影响机理,采用双镀法在Q235钢板上制备Zn-2.0%Al-1.2%Mg-x%Sr(x=0、0.03%、0.06%、0.09%、0.12%,质量分数)镀层,通过扫描电子显微镜(SEM)、X射线衍射仪(XRD)、5%NaCl浸泡实验等方法探究Sr元素含量对Zn-2.0%Al-1.2%Mg镀层的微观组织与耐蚀性的影响。结果表明:添加适量的Sr元素,可以有效细化Zn-2.0%Al-1.2%Mg镀层表面凝固组织中的初生η-Zn相,引导生成Zn/Al/MgZn_(2)三元共晶组织,使中间合金层中FeAl_(3)-Zn_(x)柱状晶变得更加致密。当Sr的添加量为0.09%时,镀层表面凝固组织的细化效果最为明显,中间合金层最薄且致密,此时镀层的浸泡腐蚀速率最低,耐蚀性最好。

Structure of Micro-nano WC-10Co4Cr Coating and Cavitation Erosion Resistance in NaCl Solution

Cavitation erosion （CE） is the predominant cause for the failure of overflow components in fluid machinery. Advanced coatings have provided an effective solution to cavitation erosion due to the rapid development of surface engineering techniques. However, the influence of coating structures on CE resistance has not been sys- tematically studied. To better understand their relationship, micro-nano and conventional WC-10Co4Cr cermet coat- ings are deposited by high velocity oxygen fuel spray- ing（HVOF）, and their microstructures are analyzed by OM, SEM and XRD. Meanwhile, characterizations of mechan- ical and electrochemical properties of the coatings are carried out, as well as the coatings＇ resistance to CE in 3.5 wt % NaC1 solution, and the cavitation mechanisms are explored. Results show that micro-nano WC-10Co4Cr coating possesses dense microstructure, excellent mechanical and electrochemical properties, with very low porosity of 0.26 4-0.07% and extraordinary fracture toughness of 5.58 4-0.51 MPa.m1/2. Moreover, the CE resistance of micro-nano coating is enhanced above 50% than conventional coating at the steady CE period in 3.5 wt % NaC1 solution. The superior CE resistance of micro- nano WC-10Co4Cr coating may originate from the unique micro-nano structure and properties, which can effectively obstruct the formation and propagation of CE crack. Thus,a new method is proposed to enhance the CE resistance of WC-10Co4Cr coating by manipulating the microstructure.

稀土元素对桥梁缆索用热浸镀Zn-10Al镀层钢丝耐蚀性能的影响

通过双镀法制备Zn-10Al-xRE(x=0.05,0.08,0.11,0.14,0.17)五种热浸镀锌铝镀层,并利用中性加速盐雾试验、电化学实验及扫描电子显微镜(SEM)分析其腐蚀形貌及耐蚀性能。结果表明,五种镀层在中性加速盐雾试验下,可保证基体在120d以内不被腐蚀,而纯锌镀层在30d时已经出现红锈,证明Zn-10Al-xRE的耐蚀性能可达到纯锌镀层4~5倍。Zn-10Al-xRE镀层钢丝的耐蚀性能随稀土含量的上升先升高再降低,添加0.08%RE的Zn-10Al镀层耐蚀性最好。用SEM对120d盐雾试验下的镀层钢丝进行观察,可以看出纯锌镀层的腐蚀产物较为疏松,Zn-10Al-xRE的腐蚀产物较为致密,Zn-10Al-xRE中腐蚀产物大约分为韧窝状、球状及针片状,耐蚀性能最好的Zn-10Al-0.08RE镀层中含有大量韧窝状腐蚀产物。

Protection Performance of Plasma Sprayed Al_(2)O_(3)-13 wt%TiO_(2) Coating Sealed with an Organic-inorganic Hybrid Agent

An organic-inorganic hybrid sealing agent was fabricated and used in the plasma sprayed Al_(2)O_(3)-13 wt%TiO_(2)coating,and conventional silicone agent was also used for comparison.Protection performance of the coatings was comprehensively evaluated based on both anti-corrosion and anti-biofouling properties.The results reveal that the sealing treatment is remarkably useful to decrease the porosity of the coating,and the porosity of the coating sealed with the hybrid agent is only 0.035%.Immersion corrosion test and Tafel polarization test reveal that the sealed coating with the hybrid agent exhibits a better corrosion resistance by compared with the coating sealed with silicone agent.The corrosion current density i_(corr) of the hybrid agent sealed coating is only 0.7×10^(-6)A·cm^(-2).Moreover,anti-biofouling tests both in the outdoor analogue hydraulic environment and in the natural marine environment prove that the mentioned novel coating presents a better combination of corrosion resistance and anti-biofouling property by compared with the other coatings,and it could be used as a protection of metal components in the marine environment.

ELECTROCHEMICAL CORROSION BEHAVIOR OF HOT DIP COATING IN ARTIFICIAL SEAWATER

The corrosion behavior of a zinc-baased alloy (compared with that of pure zinc) coating was studied in this research on the electrochemical corrosion behavior of hot dip coating in artificial seawater. The electrochemical parameters of these two hot dip coatings were measured by the galvanostatic method and accelerated corrosion test. The two coatings showed uniform corrosion, but the corrosion of the pure zinc coating was actively sustained continuously. The corrosion of the zinc-based alloy coating was very slow because of the formation of a stable anti-corrosion membrane. The corrosion mechanisms of these two coatings were also compared by the weak polarization curve fitting method. The corrosion of the zinc-based alloy coating is typical of that in natural passive corrosion system.

Effect of Dip Coating Process on the Performance of Graphene/Spandex Yarn Strain Sensor

This study presented the effect of the concentration of graphene in the dispersion,the type of polyvinyl alcohol(PVA)and the surfactant on the sensing properties of dip-coated graphene/spandex yarns as resistance strain sensors.Experimental results showed that the addition of styrene-acrylic emulsion surfactant facilitates the dispersion of graphene and then improves the conductivity and sensing performance,and the sensitivity is up to 91.The conductivity and sensing properties of graphene/spandex yarns at 2%graphene dispersion are better than those at 1%graphene dispersion.When the conductive yarn treated by 2%graphene dispersion is stretched to 50%,the sensitivity is up to 29,the repeatability is good,and the hysteresis is low.In terms of the binding agent,PVA as a high alcoholysis and large polymerization decreases the sensitivity,repeatability as well as the hysteresis.

Effect of Mischmetal on Oxidation Resistance of 55Al－Zn Alloy Hot Dip Coating

The effect of mischmetal addition on high temperature oxidation resistance of 55wt% Al43.4 wt% Zn-1 .6wt% Si alloy hot-dip coatings has been investigated. It is found that rare earth addition improves high temperature oxidation resistance of the coatings. The oxidation tests at 800℃, 100 h and 1000℃, 50 h show that the coating with addition of 0. 1 % RE has the best properties. The morphology of oxide scale and element distribution of coating section were analysed by SEM, EPMA and XRD. It is indicated that mischmetal addition improves the adhesion between oxide scale and coating substrate, and spalling resistance of the scale is also improved with the addition of RE. Additionally, RE controls the degeneracy speed of Al-content in the coatings and inhibits the growth of Fe-Al intermetallic compound. For this reason, higher Al-content is kept in all the coatings with RE addition.