添加不同稀土元素对固体包埋法在 304 不锈钢表面制备 Ti / Cr-RE 双层涂层电化学性能的影响

目的选择合适的稀土制备Ti/Cr-RE双层涂层,提高不锈钢的耐腐蚀性能。方法采用两步粉末包埋法,先在304不锈钢表面渗Ti,再制备稀土改性Cr涂层,获得Ti/Cr-RE双层涂层。通过添加不同的稀土氧化物Y2O3和Ce O2,获得两种双层涂层,对比分析涂层的表面形貌、断面形貌及物相组成,利用电化学测试方法测定304不锈钢基体及两种Ti/Cr-RE双层涂层在3.5%(质量分数)Na Cl溶液中的电化学腐蚀性能。结果添加不同稀土元素钇、铈,都能在渗Ti不锈钢表面形成一层致密、连续的稀土改性渗铬层。在两种稀土元素改性的Cr涂层中,稀土元素分别与Cr,Fe,Ni,Ti形成了金属间化合物。304不锈钢基体的自腐蚀电位为-0.324 V,腐蚀电流密度为0.1363μA/cm2;钇改性铬涂层的自腐蚀电位为-0.341 V,腐蚀电流密度为0.2058μA/cm2;铈改性铬涂层则具有更高的自腐蚀电位(-0.263 V)及更低的腐蚀电流密度(0.030 86μA/cm2)。结论钇改性铬涂层不能提高304不锈钢基体的耐腐蚀性能,铈改性铬涂层可以明显提高基体的耐腐蚀性能。     

Study of a New Chromium-Free Conversion Coating Formed on ZnAl Alloy

BECAUSE OF A HIGHER CHEMICAL ACTIVITYzinc and zinc alloys(in bulk or in coating form)corrode rapidly in moist atmospheres recovering withwhite corrosion products—white rust and in acidicclimatic conditions becoming grey[l].So passivition orchemical conversion treatments is often needed fortheir corrosion protection.This is generally done bymeans of chromate treatment which offers a goodcorrosion inhibition.However,chromates are highlytoxic and carcinogenic[2]and their use can lead…     

几种不同材料在含硫介质中的腐蚀性

用失重法和恒电位极化法研究了45#碳钢、1Cr18Ni9Ti、304不锈钢和Ni-P合金镀层在含S介质中的腐蚀性.结果表明,低温条件下,S2-浓度变化对4种材料阴极极化和阳极极化影响较小,1Cr18Ni9Ti和304不锈钢的极化曲线相似,为典型的阴、阳极控制的电化学腐蚀过程,自腐蚀电位和自腐蚀电流相近;Ni-P合金镀层出现了钝化区;45#碳钢出现了阳极控制的扩散过程.温度升高,腐蚀速率增大,1Cr18Ni9Ti和304不锈钢的极化率变大,Ni-P合金镀层的钝化性能减弱, 1Cr18Ni9Ti、304不锈钢和Ni-P合金镀层均是含S介质中的耐蚀材料.     

LY12铝合金三价铈盐溶液中成膜工艺

利用浸渍法在LY12铝合金表面获得了金黄色的铈转化膜, 确定了常温稀土(铈)化学转化膜成膜工艺. 应用电化学方法和浸泡试验研究了铝合金铈化学转化膜的成膜动力学及转化膜在3.5%NaCl溶液中的耐蚀性能, 并与传统的Alodine处理工艺进行了比较. 采用表面分析技术分析了膜的成分并观察了膜的微观形貌. 结果表明, 本稀土处理工艺成膜工艺简单, 成膜速度快, 耐蚀性能略优于Alodine转化膜, 能有效地抑制铝合金的点腐蚀. SEM表明铝合金铈转化膜由许多球形颗粒和块状膜构成. EDAX能谱表明, 铈转化膜主要含有铈、氧和铝3种元素, 球形颗粒含有较高浓度的氧和铈.     

Cerium chemical conversion coatings for corrosion protection of stainless steels in hot seawater environments

In order to replace the hazardous chromate‐based surface treatment, a new cerium chemical conversion coating was developed on 316L stainless steel through a mixed solution of hydrated cerium nitrate, citric acid, and hydrogen peroxide. The chemical composition was characterized by energy‐dispersive spectroscopy, X‐ray photoelectron spectroscopy and atomic force microscope. The dense conversion coating is composed of CeO₂ with a small amount of Ce₂O₃ and has small grain size lower than 50 nm. Its thickness is about 47.4 nm as determined by spectroscopic ellipsometry analysis. Potentiodynamic polarization was used to study the corrosion behavior of the coatings in the concentrated artificial seawater at 72 °C. In comparison with the conventional nitric acid‐chromate passivated specimens, the cerium conversion coatings show much higher pitting potentials. It is suggested that the cerium conversion treatment is more effective than the nitric acid‐chromate passivation to improve the pitting resistance of 316L stainless steel used in the hot seawater environments.     

304不锈钢在H2S介质条件下的应力腐蚀

用电化学测试及慢应变速率拉伸试验（SSRT）方法对304不锈钢在饱和H2S溶液和NACE标准溶液中的应力腐蚀行为进行研究.结果表明,Cl-能显著降低304不锈钢在饱和H2S溶液中的腐蚀电位和点蚀电位,增加点蚀倾向,并降低抗H2S应力腐蚀能力.     

LY12 Al合金铈转化膜的研究

确定了Al合金常温稀土(铈)化学转化膜工艺.并用电 化学法、扫描电镜研究了其成膜过程、耐蚀性,分析了化学成分和形貌.结果表明,工艺简 单,成膜速度快,耐蚀性好.添加剂有效促进了铈的转化处理.     

Cerium-tannic acid passivation treatment on galvanized steel

A novel cerium-tannic acid passivation treatment was performed on galvanized steel. The corrosion resistance of cerium-tannic passivated samples was tested by dropping test with 0.5 wt.% CuSO₄ aqueous solution. The mass loss per unit area of passivated samples was measured after the corrosion in 0.5 mol/L NaCl + 0.005 mol/L H₂SO₄ at room temperature for 96 h. The electrochemical behaviors of cerium, tannic acid, and cerium-tannic acid passivated samples on galvanized steel in 0.5 mol/L NaCl solution were investigated by polarization curves and electrochemical impendence spectra. The corrosion equivalent circuit was established according to the impedance characteristics. The results show that cerium-tannic acid treated samples exhibit better corrosion resistance than the sole cerium or tannic acid treated samples under the same condition. The mechanism of synergistic effect for cerium-tannic acid passivation on galvanized steel was discussed.     

Evaluation of the corrosion resistance of iron boride coatings obtained by paste boriding process

An evaluation of corrosion resistance of boride coatings in AISI 304 steel was carried out. Formation of iron boride layers (FeB and Fe₂B) at the material surface was obtained by paste boriding process. Boron paste thicknesses of 4 and 5 mm were applied to the steel surface. A thermochemical treatment, for each boron potential, was carried out at temperatures of 1173, 1223 and 1273 K; with exposure times of 4 and 6 h. Corrosion resistance of the borided samples was evaluated by the electrochemical techniques of open circuit and polarization resistance with a 0.1 M solution of NaCl. Dependence between the polarization resistance and the experimental parameters is observed. The results show that the corrosion resistance is maximized with a treatment time of 4 h and a boron paste thickness of 4 mm.     

Preparation and corrosion resistance of titanium–zirconium–cerium based conversion coating on 6061 aluminum alloy

This paper aims to develop a chromium-free chemical conversion coating with good corrosion resistance. A novel chemical conversion coating was prepared on 6061 aluminum alloy by dipping in the treatment solution containing titanium/zirconium based-ions and sodium metaphosphate and cerium nitrate hexahydrate as additives. The morphology and composition of the conversion coatings were observed by scanning electron microscopy and energy dispersive X-ray spectroscopy. The microarea structure of conversion coatings at different formation stages was analyzed by electron probe microanalyzer. The electrochemical polarization curve revealed that the corrosion potential of the conversion coating was −0.577 V and the corrosion current density was 0.1148 μA/cm². The equivalent circuit fitted by AC impedance showed that the film resistance reaches 68,140 Ω. The formation of coating preferentially grows on the Al (Fe) Si intermetallic to form oxides of Ti and Zr; then TiO₂ formed by a higher concentration of Ti⁴⁺ gradually covered ZrO₂. Ce³⁺ could adsorb on the intermetallic compound, the hydrolysis of which causes the local pH of the solution to decrease and promotes the aluminum alloy dissolved.     

Effect of gelatin additions on the corrosion resistance of cerium based conversion coatings spray deposited on Al 2024-T3

The corrosion resistance of cerium based conversion coatings on Al 2024-T3 was improved by the addition of a water soluble gelatin to the coating solution. Auger electron spectroscopy depth profiling showed that coatings deposited from solutions containing 800-3200 ppm gelatin were ~ 400 nm thick, while coatings deposited from solutions with 0-200 ppm gelatin were ~ 850 nm thick. The thinner coatings exhibited reduced surface cracking and spalling. Open circuit potential measurements during deposition showed that adding gelatin to the coating solution resulted in a more negative and stable potential with increasing gelatin concentrations. Visually, increasing gelatin concentrations promoted the formation of stable bubbles that covered panel surfaces, which limited transport of cerium species to the surface and decreased the deposition rate. X-ray diffraction analysis revealed that only coatings deposited from solutions containing 400-3200 ppm gelatin could be converted to CePO₄H₂O during post-treatment, potentially improving the corrosion resistance compared to coatings deposited from solutions without gelatin.     

硫脲对 304 不锈钢镀镍层抗腐蚀性能的影响

目的研究硫脲对电镀镍层形貌、晶型、晶粒尺寸以及抗腐蚀性能的影响。方法在添加和不添加硫脲两种条件下,对304不锈钢进行电镀镍。通过XRD和SEM对比镀层的晶相结构、晶粒尺寸和微观形貌,通过Tafel曲线和EIS电化学阻抗谱对比分析样品的抗腐蚀性能。结果添加硫脲前后,镍镀层的择优生长方向从200晶面转变为111晶面,晶粒平均尺寸从60.2 nm减小为20.7 nm。由于硫脲吸附在金属表面,阻滞了溶液中金属离子放电,从而提高了阴极极化作用;同时,硫脲分子吸附在晶体生长的活性点上,有效抑制了晶体生长;因此,镍晶粒得到细化。关于腐蚀性能,镀镍304不锈钢的耐腐蚀性能最好,其次是304不锈钢基体,最差的是含硫镀镍304不锈钢。结论硫脲能够改变镍镀层晶体的择优取向,并且细化晶粒。硫脲影响电镀镍层抗腐蚀性能的机理是:阴极吸附的硫脲通过电化学还原产生H2S,进一步与Ni2+反应生成Ni S,Ni S再与富集的Ni反应生成Ni3S2。随着电镀的进行,Ni3S2被更多地沉积在镍镀层的表面,降低了镍层表面钝化膜的致密性;而且,Ni3S2与镍层存在电势差,故易发生原电池腐蚀。此外,晶粒细化导致晶界和晶面的缺陷增加,也使得腐蚀加速。故镀液中加入硫脲,镀层的耐腐蚀性能大大降低。     

Improvement in corrosion resistance of magnesium coating with cerium treatment

Corrosion protection afforded by a magnesium coating treated in cerium salt solution on steel substrate was investigated using open circuit potential, polarization curves, and electrochemical impedance spectroscopy (EIS) in 0.005 M sodium chloride solution (NaCl). The morphology of the surface was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The cerium treated coating was obtained by immersion in CeCl3 solution. The results showed that the corrosion resistance of the treated magnesium coating was improved. The corrosion potential of the treated coating was found to be nobler than that of the untreated magnesium coating and the corrosion current decreased significantly. Impedance results showed that the cerium treatment increased corrosion protection. The improvement of anti-corrosion properties was ataibuted to the formation of cerium oxides and hydroxides that gave to a physical barrier effect.     

Improving corrosion resistance of aluminium metal matrix composites using cerium sealed electroless Ni–P coatings

Abstract

A conversion coating treatment using cerium salts was developed for the surface sealing of electroless nickel–phosphorus (Ni–P) coatings on carbon fibre reinforced aluminium (Cf/Al) composites. The corrosion resistances of uncoated and coated materials (i.e. the Ni–P coating, the Ce conversion coating and Ce sealed Ni–P coatings) were evaluated in 3·5 wt-%NaCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy. Ce sealed Ni–P coating showed the highest corrosion resistance and clearly improved the overall corrosion resistance of Cf/Al composites. Thus, the Ce sealed Ni–P coating had no obvious microcracks that were generally evident in the more conventional Ce conversion coatings. This is presumed to occur because the electroless nickel surface is relatively homogeneous, compared with the Cf/Al composite surface on which different local coating thicknesses would encourage increased microcrack formation. X-ray photoelectron spectroscopy analysis showed that the Ce conversion coating mainly contained both Ce³⁺ and Ce⁴⁺ species; however, Ce⁴⁺ species were the dominant oxidation state on Ce sealed Ni–P coatings.     

Influence of curing temperature, silica nanoparticles- and cerium on surface morphology and corrosion behaviour of hybrid silane coatings on mild steel

This work is aimed at developing and investigating silane based organic-inorganic hybrid coatings possessing unique properties, which can be used to improve the performance of steel structures subjected to marine corrosion. These silane based sol-gel coatings were prepared by dip coating planar samples of mild steel in solution of an organically modified silica sol made from hydrolysis and polycondensation of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) in acid catalysis condition. Crack-free coatings were obtained on curing at 200 °C. On increasing the curing temperature to 400 °C, however, cracks developed in the plain organic-inorganic hybrid coatings. This observation was consistent with the visual observations where appearance of the coated specimen changed from colourless metallic to brownish grey on curing from 200 °C to 400 °C temperature. The coatings were further modified using SiO₂ nanoparticles and cerium. The effect of change in the - temperature as well as - composition on the microstructural properties of the coatings was determined using optical microscopy, scanning electron microscopy and atom force microscopy. Additionally, Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR/FTIR) was carried out to show the formation of the Si-O-Si structural backbone of the hybrid material with the organic CH₃ group incorporated into the silica network. The corrosion protection performance of these coatings was examined using potentiodynamic polarisation technique and electrochemical impedance spectroscopy in aerated 3.5 wt.% NaCl solution. The polarization curves and corrosion resistance as measured by the bode plots suggested that the plain hybrid coatings offer good protection against corrosion. However, the SiO₂ and cerium modified nano hybrid coatings exhibited superior performance to that displayed by plain hybrid coatings.     

Wear and corrosion resistance of CoCrNi composite coatings by laser cladding

Two kinds of CoCrNi composite coatings, CoCrNiMo and CoCrNiMoBC, were prepared by laser cladding on the base metal of 304 stainless steel. The wear and corrosion properties of the coatings were studied by wear tests and electrochemical tests. Results show that the addition of B₄C promotes the generation of the ceramic phase, and therefore improving the microhardness of the coating and enhancing its wear resistance, while simutaneously keeps its excellent corrosion resistance. Energy dispersive X-ray spectrometry analysis shows that the chromium distribution in the two coatings is relatively uniform, which is beneficial for corrosion resistance. Scanning Kelvin probe microscopy results reveal that the potential difference between dendrites and interdendrites is only 20 mV, which leads to a relatively low driving force for galvanic corrosion. Observation through the atomic-scale high-resolution transmission electron microscopy shows that the fundamental reason for the high wear and corrosion resistance of the coating is the excellent coherent interface between the two phases, which reduces the interface energy and potential difference and thus improving its corrosion resistance.

     

Electrochemical corrosion behavior of plasma sprayed Al2O3‐13%TiO2 coatings in aqueous hydrochloric acid solution

One kind of conventional and two kinds of nanostructured Al₂O₃‐13%TiO₂ coatings were prepared by plasma spray process. The phase composition and microstructure of coatings were examined by means of scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to investigate the corrosion behavior of coatings in aqueous hydrochloric acid solution. The results showed that nanostructured coatings had superior corrosion resistance compared to conventional Metco 130 coating. The corrosion resistance of coatings was mainly related to their microstructure and defects density. The EIS measurement for long time immersion in hydrochloric acid solution revealed that the corrosion resistance of coatings decreased with the increasing of immersion time. During the immersion period, electrochemical corrosion mainly occurred on the carbon steel substrate under NiCrAl coatings. In addition, the Al₂O₃‐13%TiO₂ coatings were also failed during corrosion in aqueous hydrochloric acid solution.     

Study of Cerium and Lanthanum Conversion Coatings on AZ63 Magnesium Alloy Surface

采用扫描电子显微镜,X射线能谱,Tafel极化曲线和电化学阻抗谱法研究了铈镧转化膜对AZ63镁合金耐蚀性能的影响。结果表明,铈和镧的复合转化膜比单一稀土膜的表面更加均匀致密,对镁合金的耐蚀性有明显改善。双稀土转化膜的缓蚀效果随着浸泡成膜时间的增长而增加。延长时效时间有助于铈和镧的进一步氧化,耐蚀性能先增后减,时效48 h膜层的耐蚀效果最好。     

Corrosion resistance of cerium‐based chemical conversion coatings on AA5083 aluminium alloy

In this paper the effect of several parameters, such as temperature, time of immersion, cerium ions and hydrogen peroxide concentration, pH of the conversion solution, on the composition and morphology of the conversion layer are investigated as well as on its corrosion resistance in chloride environments. The cerium‐based chemical conversion coatings ennobles the corrosion potential and inhibits both the cathodic and anodic reactions rate. Using a cerium (III) chloride solution a not homogeneous coating is obtained and agglomerates with a “dry‐mud” morphology of mixed cerium‐aluminium oxide are deposited above the cathodic intermetallic particles, while using a cerium (III) nitrate solution the coating is more uniform but thinner than that obtained with cerium (III) chloride. Solution temperature below 50°C and time of immersion of 10 minutes produces a coating with better corrosion resistance.     

Effect of porosity sealing treatments on the corrosion resistance of high-velocity oxy-fuel (HVOF)-sprayed Fe-based amorphous metallic coatings

High-velocity oxy-fuel-sprayed FeCrMoMnWBCSi amorphous metallic coatings were sealed with sodium orthosilicate (Na₃SiO₄), aluminium phosphate (AlPO₄), and cerium salt sealants. The microstructure of the sealed coatings was characterised by scanning electron microscopy, energy dispersive spectrometer, and X-ray diffraction. Corrosion behaviour was examined using electrochemical methods of potentiodynamic polarisation, cyclic polarisation, electrochemical impedance spectroscopy, and Mott-Schottky tests. The results indicated that the uniform corrosion resistance of the three sealed coatings was enhanced greatly, and the passive current densities were decreased by one order of magnitude after the sealing treatments. The AlPO₄ sealant can penetrate the coatings by no less than 50 μm and enhance their hardness, which exhibited a more uniform corrosion resistance, fairly good pitting corrosion resistance, and can be applied in long-term corrosive and/or abrasive environments. The cerium salt-sealed coating showed better pitting corrosion resistance but inferior corrosion resistance in the local regions of micro-cracks, which was practically used for temporary corrosion protection. The Na₃SiO₄-sealed coating showed better uniform corrosion resistance and inferior pitting corrosion resistance, which can be applied in short-term corrosion environments. The stability of the passive film affected the corrosion behaviour of the sealed coatings. The AlPO₄-sealed coating performed better as a protective passive film during the long-term immersion test for a lower defect concentration and a more protective passive film.