Surface treatment of Cf/Al composites with immersion in aqueous solution containing Ce ions for corrosion barrier

In this study, Ce‐rich coating is investigated as corrosion inhibitor of carbon fibers reinforcement aluminum matrix (Cf/Al) composites. The coatings are obtained by immersion in aqueous solution containing Ce(NO₃)₃ onto composite surface, whereas the Ce‐rich coating process produces a coating with highly heterogeneous nature of the surface, but micro‐cracked layer with “dry‐mud” morphology. The coatings were composed of Ce‐rich nano‐particles, Ce‐rich particles with a sphere‐like morphology, which are agglomerated particles with diameter 4 ～ 8 nm and piled up for this coating. TEM observation for Ce conversion coating of the corresponding ring‐like SAED patterns could not be matched to any of the previously reported structures of cerium compounds. Results of high‐resolution XPS spectra of Ce3d obtained for Ce conversion coating show that the Ce3d spectra has several components with binding energies characteristic of Ce³⁺ and Ce⁴⁺. The Ce‐rich coating process produces effective corrosion protecting of Cf/Al composites, which is verified by electrochemical measurement results. The R_t values of coated sample are higher than those of uncoated sample, this confirms the better corrosion resistance of coating obtained after immersion treatment for Cf/Al composites.     

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.     

Ce 盐封孔对 SiCp/ Al 复合材料表面 Ni-P 镀层的影响

为提高SiCp/Al复合材料的耐腐蚀性能,先化学镀镍,再沉积稀土封孔,讨论了稀土溶液主盐Ce(NO3)3浓度和沉积时间对镍-稀土多层膜耐蚀性能的影响。结果表明:化学镀镍的SiCp/Al复合材料在室温下沉积稀土时,采用Ce(NO3)3含量1 g/L、成膜时间2 h的条件获得的多层膜耐蚀性最好,其腐蚀电位为-0.48mV,腐蚀电流密度为3.54×10-8A/cm2;稀土在膜层中以Ce的氧化物颗粒堆积状态存在,起到了封孔的作用;膜层中的镍磷合金呈多晶态,而稀土含量少,未能测出;稀土溶液浓度越高,沉积速度越快,而在相同浓度下,膜层厚度随着时间的延长而增加,越厚则膜层结合力越差。     

Effect of Ti3SiC2 content on the corrosion behavior of Al/Ti3SiC2 composite coatings

The purpose of this study was to investigate the electrochemical corrosion properties of flame-sprayed Al and Al/(5, 10, 15)% Ti₃SiC₂ coatings in a 3.5% NaCl solution. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used for analyzing the microstructural characteristics of the coatings. For examining the corrosion behavior of the coatings, a potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) were used. After the potentiodynamic polarization test, the SEM micrograph of coatings indicated that Ti₃SiC₂ particles played a significant role in pitting corrosion. The results of potentiodynamic polarization tests revealed that Al/Ti₃SiC₂ coating is nobler than that of the pure aluminum coating. On the contrary, the addition of Ti₃SiC₂ particles reduced the process of thickening the passive layer. The results of the EIS tests demonstrated that the presence of Ti₃SiC₂ particles significantly enhances the corrosion resistance of the coatings.     

Corrosion behavior of porous Ti3SiC2 in nitric acid and aqua regia

Porous Ti₃SiC₂ with high purity was synthesized using TiH₂, Si and C powders with mole ratio of Ti to Si to C being 3:1.2:2 by reactive synthesis method. The corrosion behaviors of porous Ti₃SiC₂ in nitric acid and aqua regia were investigated by immersing test. Scanning electron microscope (SEM), X-ray diffractometer (XRD), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS) were used to analyze the morphology, compositions and element contents of the samples before and after corrosion to determine the corrosion product and corrosion mechanism. The mass loss values of porous Ti₃SiC₂ are 26.9 and 132.5 μg/cm², respectively after immersing in nitric acid and aqua regia for 600 h. The results indicate that Ti₃SiC₂ transforms to Ti₅Si₃ which has better corrosion resistance in nitric acid and aqua regia with mass loss values of 9.34 and 7.06 μg/cm² under the same immersing time, respectively. The dramatic dissolution of porous Ti₃SiC₂ in the acids is due to its special microstructure.     

热镀锌层柠檬酸改进型铈盐转化膜的生长机理

将热镀锌钢板浸入含有25 g/L Ce(NO3)3·6H2O、4~6 g/L H2O2(30%)、15~20 g/L H3Cit的处理液中,在70℃下处理10 s~240 min,从而在其表面获得铈盐转化膜。采用中性盐雾试验(NSS)和电化学极化曲线来分析膜层耐蚀性能,确定最佳成膜时间范围。采用扫描电镜(SEM)观察膜层的微观形貌,利用能谱仪(EDS)、X射线光电子能谱仪(XPS)、红外吸收光谱仪(IR)分析膜层的化学组成。结果表明:处理时间为10 min左右的铈盐转化膜耐腐蚀性能最优,最佳工艺条件下得到的铈盐转化膜的耐蚀性能与铬酸盐转化膜的相当;随着处理时间的延长,膜的厚度增加,膜层的裂纹变宽;处理时间超过10 min后膜层逐步产生脱落,耐腐蚀性能也随之降低;转化膜的生长过程中,前期以柠檬酸铈吸附膜的沉积为主,后期以Ce(OH)3/Ce2O3及Ce(OH)4/CeO2的沉积占主导。     

Wetting of molten Sn-3.5Ag-0.5Cu on Ni-P(-SiC) coatings deposited on high volume faction SiC/Al composite

The wetting of molten Sn-3.5Ag-0.5Cu alloy on the Ni-P(-SiC) coated SiC_p/Al substrates was investigated by electroless Ni plating process, and the microstructures of the coating and the interfacial behavior of wetting systems were analyzed. The SiC particles are evenly distributed in the coating and enveloped with Ni. No reaction layer is observed at the coating/SiC_p/Al composite interfaces. The contact angle increases from ～19° with the Ni-P coating to 29°, 43° and 113° with the corresponding Ni-P-3SiC, Ni-P-6SiC and Ni-P-9SiC coatings, respectively. An interaction layer containing Cu, Ni, Sn and P forms at the Sn-Ag-Cu/Ni-P-(0,3,6)SiC coated SiC_p/Al interfaces, and the Cu-Ni-Sn and Ni-Sn-P phases are detected in the interaction layer. Moreover, the molten Sn-Ag-Cu can penetrate into the Ni-P(-SiC) coatings through the Ni-P/SiC interface and dissolve them to contact the SiC_p/Al substrate.     

Effect of heat treatment on pitting corrosion resistance of 6061 Al/SiC<Subscript>P</Subscript> composite coated by the cerium oxide film in 3.5 N NaCl solution

One of the main drawbacks of 6061 Al/SiC_P composite is its poor pitting corrosion resistance in the aggressive environment containing chloride ions, such as seawater, for example. The present article deals with the investigations of effects of aging on the corrosion behavior of 6061 Al/SiC_P composite and of the heat treatment on the pitting corrosion resistance of 6061 Al/SiC_P composite coated by cerium oxide prepared by chemical bath technique. Potentiodynamic polarization test was used to study the corrosion behavior of cerium oxide coatings in 3.5N NaCl solution. The microstructure of cerium oxide was examined by scanning electron microscopy (SEM) and the formed phases were identified by X-ray diffraction (XRD). The pitting corrosion resistance of the cerium oxide coating was found to be improved after heat treatment at 300°C for 30 min.     

Thermal conductive properties of Ni-P electroless plated SiCp/Al composite electronic packaging material

Electroless plated SiC_p/Al composites with a high thermal conductivity are required for electronic packaging application. In this paper, in-plane thermal conductive properties of SiC_p/Al composites with and without electroless plated Ni-P coatings are compared, and influence of various characteristics of Ni-P coatings are investigated. It is found that in addition to thickness of the coatings, phosphorus concentration and microstructure of the plated layers also influence the thermal conductive properties of plated composites. Based on the results, it is suggested that a low phosphorus concentration and a properly tailored crystalline microstructure of the Ni-P coatings, together with a reasonable choice of coating thickness, may contribute to optimization of thermal conductive properties of the composite material.     

Deposition of thick TiAlN coatings on 2024 Al/SiCp substrate by Arc ion plating

Aluminum-matrix composites with particulate SiC ceramic reinforcements (Al/SiC_p) have received much attention for space and aircraft propulsion applications. It is imperative to deposit thick hard coatings on these composites for protection. TiAlN coatings with a Ti interlayer were deposited by arc ion plating (AIP) on 2024 Al/SiC_p substrates at various nitrogen flow rates. It was found that when the nitrogen flow rate is increased from 100 sccm to 250 sccm, the deposition rate decreases, the coating hardness increases and the adhesion strength decreases. Based on the above results and the principle of gradient materials, the thick gradient TiAlN coatings with a Ti interlayer were successfully deposited on a 2024 Al/SiC_p substrate to a thickness of 60 μm by continuously increasing the nitrogen flow rate during deposition. Such an achievement can be attributed to the gradient distribution of elements, hardness, and stresses across the coating thickness.     

Degradation behaviour of ZrO2-Ni/Al gradient coatings in molten Zn

In order to improve the corrosion resistance of metallic materials in molten zinc, ZrO₂-Ni/Al gradient coatings were sprayed on the surface of the Fe-0.35-0.44 wt.% C steel. The corrosion behaviour and corrosion mechanism of the ZrO₂-Ni/Al gradient coatings in molten zinc were studied. The ZrO₂-Ni/Al gradient coatings on the surface of steels prolonged the lifetime of samples and changed the corrosion behaviour of the samples in molten zinc. The lifetime of the ZrO₂-Ni/Al gradient coatings immersed in molten zinc at 620 °C is 28 days, which is 4 times as long as that of the general ZrO₂ coatings. The ZrO₂-Ni/Al gradient coatings were corroded in molten zinc at 620 °C, which was caused by zinc atom diffusing along the crystal boundary and pores of the ZrO₂-Ni/Al gradient coatings, and reacting with Ni/Al particle in the ZrO₂-Ni/Al gradient coatings. The corrosion mechanism of the coatings in molten zinc at 620 °C was crystal boundary corrosion, pitting corrosion and reaction corrosion.     

镁合金等离子喷涂Al/Al_2O_3涂层的耐腐蚀性能

采用等离子喷涂技术在AZ31镁合金表面制备Al/Al_2O_3复合涂层,测试了镁合金及表面喷涂有Al/Al_2O_3复合涂层的镁合金试样的极化曲线,研究了没有涂层、经封孔处理和未经封孔处理的喷涂有复合涂层的镁合金三种试样在浸泡腐蚀和5%NaCl盐雾腐蚀情况下的耐腐蚀性能及其腐蚀行为.结果表明,经封孔处理的Al/Al_2O_3复合涂层镁合金试样在上述腐蚀条件下的耐腐蚀性均优于镁合金和涂层未封孔处理的试样,在浸泡试验中未封孔处理的涂层试样比镁合金腐蚀更加严重,在盐雾试验中却优于镁合金.     

Preparation and characterization of Ce-silane-ZrO2 composite coatings on 1060 aluminum

In order to improve the property of traditional Ce-based conversion coatings, Ce-silane-ZrO₂ composite coatings were successfully prepared on 1060 aluminum. The microstructure, chemical element composition and corrosion resistance of Ce-based conversion coatings and Ce-silane-ZrO₂ composite coatings were investigated by SEM, AFM, XPS and EIS analyses. Stacking structure of the composite coating can be observed. The inner layer of the composite coatings mainly consists of oxide and hydroxide of Ce(III), and the silane network is composed of the outer layer together with a small amount of Ce(IV) hydroxide. By adding silane and ZrO₂ nanoparticles into Ce-based conversion coatings, the porosity and the micro cracks of the coatings decrease apparently accompanying with the improvement of the corrosion resistance.     

Degradation processes in Al/SiCp/MgAl2O4 composites prepared from recycled aluminum with fly ash and rice hull ash

The degradation characteristics of Al/SiC_p/spinel composites prepared with fly ash (FA) and rice hull ash (RHA) under environmental conditions were investigated. Composite specimens were prepared with recycled aluminum via reactive infiltration in the temperature range 1050–1150 °C for 50–70 min and, in argon atmosphere at a pressure slightly above that of the atmospheric pressure. Results reveal that although both FA and RHA help in preventing SiC_p dissolution and the subsequent chemical degradation of the composites, due to the interaction of native carbon in FA with liquid aluminum, FA‐composites are susceptible to corrosion via Al₄C₃. Moreover, this phase accelerates the degradation process and increases the damage severity. The primary corrosion mechanism in both types of composites is attributed to microgalvanic coupling between the intermetallic Mg₂Si and the matrix. Accordingly, an appropriate control of the Si/(Si + Mg) molar ratio in the aluminum alloy hinders the Mg₂Si corrosion mechanism in both types of composites and a proper FA calcination prevents chemical degradation in FA composites.     

Effect on Corrosion Resistance of Ce-Rich-Sealed Ni-P Coatings on Cf/Al Composite Surface

In this study, Ni-P coatings and sealing of the coatings by Ce-rich solution on Cf/Al composite surface for enhanced corrosion resistance are investigated. The corrosion resistance of uncoating sample in 3.5 wt.% NaCl solution was investigated and a comparison with Ni-P and Ce-sealed Ni-P coatings is given. Effect of Ce-sealing on Ni-P coating is discussed. The results of electrochemical measurements of corrosion performance of Cf/Al composites show that sealing of Ni-P coatings with Ce-rich solution can improve the corrosion resistance. The Ce-rich-sealed Ni-P coating has higher corrosion resistance than the coating without Ce, and the electroless plated Ni-P coating on composite surface has higher corrosion resistance than the bare sample, as evidenced by EIS and potentiodynamic polarization measurements. The microstructure of the Cf/Al composites and the two kinds of coatings (i.e., Ni-P coating and Ce-sealed Ni-P coating) were examined by scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. The Ce-sealed Ni-P coatings on Cf/Al composite surface have a total thickness of ~11 μm of which 10 μm is the thickness of the Ni-P coating and ~1 μm is the thickness of the Ce-rich sealing. It shows that the selected area electron diffraction ring pattern of Ce-rich sealing on Ni-P plated composite is consistent with Ce₆O₁₁ or CeO₂. X-ray photoelectron spectroscopy results show that Ce⁴⁺ was the dominant oxidation state for Ce-rich sealing on Ni-P plated composite. The Ce-sealing treatment on Ni-P coating has improved the corrosion resistance over and above the corrosion resistance offered by the Ni-P mono-coating to the bare substrate.     

Effect of SiO2:Na2O molar ratio of sodium silicate on the corrosion resistance of silicate conversion coatings

Passivation treatment by sodium silicate solution is considered as an alternative to chromium chemical conversion treatment to improve the corrosion resistance of hot-dip galvanized (HDG) steels. In this paper, a transparent silicate coating was formed on the surface of HDG steel by immersing in sodium silicate solution with SiO₂:Na₂O molar ratio in the range from 1.00 to 4.00. The parameter about the SiO₂:Na₂O molar ratio of silicate solution has been discussed using corrosion resistance and surface morphology. Tafel polarization, electrochemical impedance spectroscopy (EIS) measurements and neutral salt spray (NSS) test show that silicate coatings increase the corrosion resistance of HDG steels. From the results obtained, it is deduced that the optimum SiO₂:Na₂O molar ratio is 3.50. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD), and reflectance absorption infrared spectroscopy (RA-IR) show that there are no obvious differences of the chemical composition and structure in various silicate coatings. The silicate coatings mainly consist of zinc oxides/hydroxides, zinc silicate and SiO₂. However, atomic force microscopy (AFM) images reveal that the surface of silicate coatings with a molar ratio of 3.50 is more compact and uniform than other silicate coatings.     

High‐temperature corrosion behavior of some post‐plasma‐spraying‐gas‐nitrided metallic coatings on a Fe‐based superalloy

The objective of the present study is to propose a cost‐effective process for modifying commercially available coatings by gas nitriding using commonly available equipment and starting materials. Al–Cr and Ti–Al metallic coatings were deposited on Superfer 800H (Fe‐based superalloy) using a plasma spray process. Then the gas nitriding of the coatings was done in the lab and the parameters were optimized after conducting several trials on plasma‐sprayed‐coated specimens. Characterization and high‐temperature corrosion behavior of coatings after exposure to air and molten salt at 900°C were studied under cyclic conditions. Techniques like XRD, SEM/EDX, and X‐ray mapping analysis were used for the characterization of the coatings and analysis of the oxide scale. Both the coatings successfully protected the substrate and were effective in decreasing the corrosion rate when subjected to cyclic oxidation (Type‐I hot corrosion) at 900°C for 50 cycles in air and molten salt (a salt mixture of Na₂SO₄–60%V₂O₅ dissolved in distilled water). Based on the findings of the present study, the coatings under study are recommended for tapplications to super‐heater and reheater tubes of boilers and all those surfaces that face fireside corrosion, such as fluidized beds, industrial waste incinerators, internal combustion engines, gas turbines or steam turbines, to provide protection against degradation in these environments. The cost of the product/process is approximately Rs. 0.62 per mm² in case of Al–Cr coating and Rs. 1.86 per mm² in case of Ti–Al coating.     

Corrosion resistance of Mg−Al LDH/Mg(OH)2/silane−Ce hybrid coating on magnesium alloy AZ31

An environmentally-friendly hybrid coating on AZ31 magnesium alloy substrates was reported. The synergic effect was studied on Mg−Al-layered double hydroxide Mg−Al LDH/Mg(OH)₂-coated AZ31 magnesium alloy via an in-situ steam coating process and a subsequent combined surface modification of bis-[triethoxysilylpropyl]tetrasulfide (BTESPT) silane and Ce(NO₃)₃. The microstructure and composition characteristics of the hybrid coatings were investigated by means of X-ray diffraction (XRD), scanning electronic microscopy (SEM), Fourier transform infrared spectrophotometry (FT-IR) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the coated samples was evaluated by potentiodynamic polarization (PDP), electrochemical impedance spectrum (EIS) and hydrogen evolution rate during immersion in 3.5 wt.% NaCl solution. The results show an improved corrosion resistance of the alloy in the presence of BTESPT silane and Ce(NO₃)₃. This is most likely due to the synergistic effect of steam coating and silane coating to enhance the barrier properties of hybrid coating. In addition, the formation mechanism and anti-corrosion mechanism of coatings were discussed.     

铈盐对铝合金的缓蚀机理研究

应用分离电解池(the split cell)技术将阴阳极分离,通过测定因溶液中氧含量改变和添加CeCl3导致两电极之间的净电流的变化,研究了CeCl3对B95超强铝合金在0.1 mol/L NaCl溶液中腐蚀行为的影响,并用扫描电子显微镜(SEM)和X射线能量散射谱(EDS)表征电极表面的形貌特征,结合其它电化学技术如电位-时间曲线、极化曲线等手段,对Ce盐缓蚀机理作了深入探讨.结果表明,经Ce盐处理的B95超强铝合金表面可形成一层不均匀分布的转化膜,成膜动力学包括铝合金的溶解及随后的成膜两个过程;铝合金Ce化学转化膜主要由Ce、O、Al组成;3.5%NaCl溶液全浸试验表明添加CeCl3后腐蚀率可降低数百倍,铝合金的耐蚀性能大大提高,CeCl3表现为一种优良的铝合金缓蚀成膜剂.     

Effect of thermal cycling on the expansion behavior of Al/SiCp composite

The coefficient of thermal expansion (CTE) and accumulated plastic strain of the pure aluminum matrix composite containing 50% SiC particles (Al/SiC_p) during thermal cycling (within temperature range 298–573 K) were investigated. The composite was produced by infiltrating liquid aluminum into a preform made by SiC particles with an average diameter of 14 μm. Experiment results showed that the relationship between the CTE of Al/SiC_p and temperature is nonlinear; CTE could reach a maximum value at about 530 K. The theoretical accumulated plastic strain of Al/SiC_p composites during thermal cycling has also been calculated and compared with the experimental results.