Impedance spectroscopy studies of electroless Ni–P matrix,Ni–W–P,Ni–P–ZrO2, and Ni–W–P–ZrO2 coatings exposed to 3.5% NaCl solution

Ni–P matrix, ternary Ni–W–P and Ni–P–ZrO₂ coatings, and quaternary Ni–W–P–ZrO₂ coatings were deposited using electroless method from a glycine bath. Their corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) for various immersion times in a 3.5% NaCl solution. From among the investigated coatings, the ternary Ni–W–P coatings show the highest resistance to corrosion in the first hour of exposure to the 3.5% NaCl medium. An addition of ZrO₂ adversely affects the performance of both the Ni–P coatings and the Ni–W–P coatings. For all the coatings, including the ones containing tungsten, a marked decrease in pore resistance (R_por) over time is observed. This means that their corrosion resistance and capacity to protect the substrate decline. On the other hand, after 24 h immersion in the 3.5% NaCl solution the Ni–W–P coating shows the highest low‐frequency impedance modulus (|Z|_{f = 0.01 Hz}). As regards corrosion resistance, the Ni–P coatings and the Ni–W–P coatings perform best.     

Comparative study on corrosion protection properties of electroless Ni‐P‐ZrO2 and Ni‐P coatings on AZ91D magnesium alloy

Electroless Ni‐P‐ZrO₂ and Ni‐P coatings on AZ91D magnesium alloy were prepared, and their corrosion protection properties were compared in this paper. The potentiodynamic curves and electrochemical impedance spectroscopy (EIS) of the coated magnesium alloy in 3.5% NaCl solution showed that the corrosion performance of Ni‐P‐ZrO₂ composite coating was superior to that of Ni‐P coating. The same conclusion was obtained with salt spray and immersion tests. The corrosion morphologies of two kinds of coatings with various immersion time intervals in 3.5% NaCl solution indicated that most corrosion products concentrated on the nodules boundaries of Ni‐P coating and blocked corrosion pit was the main corrosion form. For the Ni‐P‐ZrO₂ coating, tortuous nodules boundaries were not the weak sites of the coating and corrosion initiated from the nickel phosphor alloy around the nanometer powders. Open corrosion pits occurred on the composite coating surface, and the coating was corroded gradually. Thus, the Ni‐P‐ZrO₂ coating exhibited better corrosion protection property to magnesium alloy substrate than Ni‐P coating.     

Corrosion resistance of electrodeposited RE-Ni-W-P-SiC composite coating

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Synthesis and passivation behavior of electroless Ni–P‐CNT composite coating

Carbon nanotubes (CNTs) have high chemical stability, unique hollow nanotube structure, and are believed to be ideal materials for fabricating composites. In this study, Ni–P and Ni–P‐CNT composite coatings were fabricated by electroless plating. Scanning electron microscopy was used to characterize the coatings. The corrosion behavior of Ni–P and Ni–P‐CNT coated samples were evaluated by polarization curves and electrochemical impedance spectroscopy in 3.5 wt% NaCl and 0.1 M H₂SO₄ aqueous solutions at room temperature. The results indicated that incorporation of CNTs in the coating significantly increased corrosion resistance. The role of CNTs in improvement of corrosion resistance of the coating was also discussed.     

Corrosion protection of epoxy coatings containing ZSM‐5 zeolites on Mg–Li alloys

The epoxy composite coatings are developing towards nontoxic and environmentally friendly in the field of corrosion protection. In this study, ZSM‐5 zeolites were chosen as fillers and added to the epoxy coatings on the Mg–Li alloy surface. The effect of ZSM‐5 zeolites on the corrosion properties of epoxy coating was investigated. The results show that the epoxy coating doped with ZSM‐5 zeolites can improve the corrosion protection of the substrate. In particular, the epoxy coating loaded with 0.5% ZSM‐5 zeolites provides enough protection of the alloy against corrosion.     

Corrosion behavior of nanostructured Ni‐Si3N4 composite films: A study of electrochemical impedance spectroscopy

Ni‐Si₃N₄ nanocomposite films with both the consecutive Ni crystallites and dispersed Si₃N₄ particles in the nanometer range have been fabricated using DC electroplating technique, and characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X‐ray diffraction (XRD). The corrosion resistance of the Ni‐Si₃N₄ nanocomposite film has been compared to that of pure Ni coating through polarization. Meanwhile, the corrosion process of Ni‐Si₃N₄ nanocomposite film in neutral 3.5% NaCl solution has been investigated using electrochemical impedance spectroscopy (EIS). The results show that the Ni‐Si₃N₄ nanocomposite film is more resistant to corrosion than the pure Ni coating. The corrosion of Ni‐Si₃N₄ nanocomposite film is controlled by electrochemical step, and the whole corrosion process is divided into two sequential stages. The main corrosion type of Ni‐Si₃N₄ nanocomposite films in neutral 3.5% NaCl solution is pitting.     

不同颗粒致密度WC-10Co-4Cr涂层的耐腐蚀性能

在300 M钢表面上,利用超音速火焰喷涂技术将两种不同颗粒致密度的WC-10Co-4Cr粉末制成涂层.利用扫描电镜、X射线衍射仪、显微硬度计分析涂层的微观组织,通过极化试验和浸泡试验分析涂层的耐腐蚀性能.结果表明,高颗粒致密度粉末制备的WC-10Co-4Cr涂层孔隙率为1.52％,是低颗粒致密度粉末制备涂层的1.95倍;在3.5％ NaCl溶液中,高颗粒致密度粉末制备涂层的耐蚀性较差,腐蚀电流密度是低颗粒致密度粉末制备涂层的2.67倍.低颗粒致密度粉末制备的涂层孔隙率低,对基体的保护性较好.     

Corrosion characteristics of the wrought Ni‐Cr‐Mo alloys

This paper concerns the wrought, nickel‐chromium‐molybdenum (Ni‐Cr‐Mo) alloys, a family of materials with a long history of use in the chemical process industries. Their attributes include resistance to the halogen acids and resistance to pitting, crevice attack, and stress corrosion cracking in hot, halide salt solutions. The purpose of this paper is to characterize the performance of the Ni‐Cr‐Mo alloys in several key chemicals, using iso‐corrosion diagrams. These indicate the expected corrosion rates over wide ranges of concentration and temperature. Furthermore, the differences between individual Ni‐Cr‐Mo alloys, and their behavior relative to the stainless steels are defined. The data indicate benefits of both a high chromium content and a copper addition, as used in Hastelloy® C‐2000® alloy.     

Electrochemical corrosion behavior of electroless Ni–P coating in NaCl and H2SO4 solutions

Electrochemical corrosion behavior of electroless Ni–P coating in NaCl and H₂SO₄ solutions were studied by potentiodynamic polarization curves and electrochemical impedance spectra techniques, as well as the corrosion morphology was characterized. The results indicate that electroless Ni–P coating with about 25 µm is stable in 30 days immersion in NaCl solution. Although it was corroded with prolonged immersion days, the corrosive medium has not penetrated through the coating. During the H₂SO₄ concentration ranging from 5 to 10%, the corrosion current density of electroless Ni–P coating increased due to the intensified anodic dissolution process; in 15% H₂SO₄ solution, electroless Ni–P coating shows obvious anodic passivation effect.     

纯铜热化学反应热喷涂陶瓷/渗铝复合涂层耐蚀性研究

采用火焰喷涂技术在铜基体表面先后喷涂渗铝层和陶瓷涂层,并加热保温,制备成铜基陶瓷/渗铝复合涂层。用XRD和SEM对涂层进行组织结构分析和形貌观察,并测试涂层的硬度、抗热震性和耐蚀性。结果表明,复合涂层中有Cu9Al4、Cu5Zn8、Cu3Ti等新相生成;渗铝层部分有γ2相（Cu9Al4）析出且涂层与基体结合紧密;复合涂层的硬度为82～87 HRE,其耐热震次数可达50次以上;复合涂层封孔后的耐酸蚀能力提高到基体的16倍,耐盐蚀能力提高到基体的25倍;极化试验表明,复合涂层抗电化学腐蚀能力显著增强,其耐蚀性能远优于纯铜渗铝层和单纯陶瓷涂层。     

Corrosion resistance of the anti‐sulfide steel in the CO2/H2S containing solutions

The present work primarily investigates the corrosion characterization of the common P110 steel and the anti‐sulfide P110SS steel in CO₂‐containing solution with or without hydrosulfuric acid (H₂S) at 70 °C. The electrochemical techniques such as potentiodynamic polarization sweep and electrochemical impedance spectroscopy (EIS) were used to disclose the differences of the corrosion mechanisms between both P110 and P110SS steels in CO₂‐containing solution with various additions of H₂S. The EIS data fitted by ZsimpWin software were analyzed and discussed. The experimental results indicated that H₂S could accelerate and also inhibit the corrosion attack according to the changes of corrosive environments.     

Study on particle distribution,microstructure and corrosion behavior of Ni‐Al composite coatings

Watt's baths containing different amounts of Al powder were used to electroplate the pure Ni and Ni–Al composite coatings. Surface morphology, microstructure of the samples and particle distribution in the coatings were studied using optical microscope, SEM, EDX and XRD. The results showed that the electroplated sample in the bath containing 40 g.L^?1 Al has the maximum particle and the best particle distribution. Evaluation of microstructures demonstrated that Al particles change the microstructure of Ni from coarse‐columnar to fine‐granular structure due to providing new nucleation sites and stopping columnar growth of Ni grains. Corrosion measurements revealed that Ni‐Al coatings have lower corrosion resistance than pure Ni probably due to formation of active‐passive cells and weak bandings between Al particles and Ni substrate.     

Performance of cold sprayed Ni‐20Cr and Ni‐50Cr coatings on SA 516 steel in actual industrial environment of a coal fired boiler

Power plants are one of the major industries suffering from severe erosion–corrosion (E‐C) problems resulting in substantial losses. One way of tackling this problem is by the use of thermal spray coatings. In the current investigation a new emerging technique i.e. cold spray coating process was used to deposit Ni‐20Cr and Ni‐50Cr powder on SA 516 (grade 70) boiler steel. The bare as well as the coated steels were subjected to cyclic experimental studies, in the superheater zone of a coal fired boiler. Weight change, thickness loss, XRD, FE‐SEM/EDS and X‐ray mapping techniques were used to analyse the eroded‐corroded specimens. The uncoated steel showed weight gain after exposure in the actual boiler environment, whereas, for the coated steels there was initial weight loss followed by negligible weight change. Based upon thickness loss data the cold‐sprayed Ni‐50Cr coating was found to provide better E‐C resistance than the Ni‐20Cr coating.