热喷涂Zn-Ni复合涂层在海水中的腐蚀行为研究

利用喷雾干燥法制备了不同Ni含量的团聚型Zn-Ni复合粉末,并在此基础上用氧乙炔火焰喷涂工艺制备了Zn-Ni复合涂层。通过动电位极化和电化学阻抗测试,并结合SEM、EDS和XRD分析,研究涂层在海水介质中的防护性能和腐蚀机理。结果表明：涂层的自腐蚀电位稳定值在-0.98~-0.95 V,Ni可起到稳定Zn(OH)₂,抑制其向疏松ZnO转化的作用,腐蚀产物的堆积使得涂层电阻R_c和电荷转移电阻R_t不断增大,腐蚀电流不断减小;不同Ni含量涂层的耐蚀性存在明显差异,其中Ni含量为20 mass%的涂层耐蚀性能最好。     

Corrosion properties of in situ laser remelted NiCrBSi coatings comparison with hard chromium coatings

This study aims at evaluating the effect of an in situ laser remelting treatment of NiCrBSi coatings, deposited by plasma spraying. Life Cycle Assessment (LCA) method was used to estimate the environmental impacts of coating processes. It was demonstrated with this LCA that the in situ remelting process was clean. Microstructural results were also evaluated. A good metallurgical bond was formed at the remelted coating interface. Scanning electron microscopy observation revealed also that laser treatment induces a change of the microstructure from lamellar to columnar dendritic. The dependence between the microstructure of NiCrBSi coatings, which was modified by laser treatment, and corrosion resistance has been evaluated by potentiodynamic polarization curves. Results show that, the corrosion resistance was increased because of a finer structure and higher densities of the coatings, but corrosion mechanisms occurring in all cases were different. From the electrochemical experiments in NaCl solution it can be deduced that laser remelting of as-sprayed coatings does not affect their corrosion rate. Corrosion evolves due to a progressive penetration of the electrolyte through the disturbed structure of the as-sprayed samples, whereas the substrate surface of remelted coating is not reached, because of a higher density. But ClMO intermediate species were formed on the surface, because Cl⁻ can destroy the protective film on the coating. The hybrid plasma/laser process was cleaner than hard chromium plating and its corrosion behavior is superior too.     

Zn,Al 合金涂层在膨润土中的加速腐蚀实验研究

采用高速电弧喷涂技术在16MnR钢基体上制备Zn,Al合金涂层,针对其实际应用环境,设计并通过模拟洞室膨润土填埋环境的加速腐蚀实验对涂层的耐腐蚀性能进行研究。结果表明:随着加速腐蚀时间的延长,Zn,Al系合金涂层的腐蚀速率降低;Zn,Al系合金涂层对16MnR钢的防护作用明显,起到了牺牲阳极的阴极保护作用;与Zn涂层和Zn-Al合金涂层相比,Al涂层表现出较优的耐腐蚀性能。     

淫羊藿苷含量对Mg/UMAO/CS/IC涂层性能的影响

为了研究淫羊藿苷含量对镁/超声微弧氧化/壳聚糖/淫羊藿苷（Mg/UMAO/CS/IC）涂层性能的影响,并提高纯镁的耐蚀性,采用电泳沉积（EPD）和UMAO技术在纯镁基体上制备Mg/UMAO/CS/IC涂层。采用扫描电子显微镜（SEM）、X射线衍射（XRD）、原子力显微镜（AFM）和傅立叶变换红外光谱（FTIR）对涂层的特征进行分析。对不同样品在模拟体液中进行了电化学阻抗和动电位极化的腐蚀行为研究。结果表明：当IC含量为0.4 g/L时CS/IC层具有较好的封孔效果。添加不同IC含量的Mg/UMAO/CS/IC涂层均由Mg、MgO、CS和Mg₂SiO₄组成。不同IC含量涂层的自腐蚀电流密度（i_corr）比Mg至少都低一个数量级,能为镁基底提供更有效的保护。IC含量为0.4 g/L时Mg/UMAO/CS/IC涂层的耐蚀性更好,自腐蚀电流密度（1.667×10^-6 A/cm²）最小。Mg/UMAO/CS/IC涂层可有效解决纯镁在临床骨内固定应用上降解过快的问题。     

Effect of plasma surface treatment and heat treatment ambience on mechanical and corrosion protection properties of hybrid sol-gel coatings on aluminum

Hybrid sol-gel coatings derived from a base catalyzed hydrolysis of tetraethylorthosilicate and methyltriethoxysilane were deposited on aluminum substrates by a dip coating technique. Some of the coatings were deposited on substrates whose surfaces were pre-treated using atmospheric-air plasma prior to coating in order to study the effect of surface activation by plasma pre-treatment. The coated substrates were heat treated in different ambiences like air, flowing N₂ and vacuum to see the effect of heat treatment ambience on the properties of the coatings. Characterization of the coatings after heat treatment was carried out with respect to coating thickness, pencil scratch hardness, adhesion, water contact angle and their microstructure. Corrosion testing for all the coatings was carried out by electrochemical polarization measurements as well as electrochemical impedance spectroscopy in 3.5% NaCl solution for 1 h exposure time to investigate on their corrosion resistance. Coating thicknesses ranging from 1 μm-5 μm were obtained by varying the withdrawal speeds. Heat treatment in a controlled atmosphere with low oxygen content was seen to improve the hydrophobicity of coated surface, as measured by water contact angles (20^o — air; 71^o — N₂; 95^o — vacuum), thereby improving the corrosion resistance. Surface pre-treatment using open-air plasma was seen to improve the adhesion of the sol-gel coatings thus making it possible to obtain adherent and thick coatings in a single dip coating process. Both the methods of processing the coatings reduced the corrosion rate of aluminum from 1.95 mpy to 0.004 mpy in case of coatings densified in nitrogen and to 0.00068 mpy for coatings deposited on a plasma treated substrate and densified in air.     

Improving the corrosion performance of epoxy coatings by chemical modification with silane monomers

In this communication, commercial epoxy resins were chemically modified with various silane monomers under the catalysis of organotin compound, aiming to enhance the corrosion resistance of epoxy coatings on 2024-T3 aluminum substrates. Immersion studies conducted in 3.5 wt.% NaCl solution showed that the coating capacitance (C_c) decreases significantly after the silane modification, as measured by electrochemical impedance spectroscopy (EIS), indicating the higher resistance to water permeation. EIS measurements also indicated an enhancement in protectiveness of silane-modified epoxy coatings against substrate corrosion, which was characterized by higher charge transfer resistances (R_ct) and lower double layer capacitance (C_dl) at substrate/electrolyte interface. The adhesion of epoxy coatings was also found to improve after the modification with silane components. The best performance was observed for coating system modified by 3-glycidoxypropyltrimethoxy silane (GPTMS).     

16MnR低合金钢在KOH溶液中的腐蚀行为

研究了16MnR低合金钢在不同浓度KOH溶液中的腐蚀行为和腐蚀速率,并利用电化学测试对16MnR钢腐蚀过程中的电化学行为特征进行了研究。结果表明：随着KOH浓度的增大,16MnR钢的自腐蚀电位和极化电阻变低,自腐蚀电流密度变大,维钝电流密度也有所增加,腐蚀速率变大;电化学阻抗谱分析所得结论与线性极化和动电位极化的结果相一致。扫描电镜观察表明：在浸泡腐蚀实验中,16MnR钢表面的腐蚀程度随KOH浓度的增大而越来越严重,能谱分析表明该腐蚀产物主要为Fe₂O₃。     

Korrosionsverhalten von Hybridschichtsystemen

Corrosion behaviour of hybrid coating systems Potentiodynamic methods were used to investigate the corrosion protection value of various hybrid coating systems. Combinations of galvanic chromium and electroless nickel interlayers with titanium nitride and chromium nitride coatings produced by sputterion-plating method were tested. Anodic polarization curves show that corrosion resistance is strongly connected with the microdefects present in the coatings. The coating system consisting of chromium nitride with electroless nickel as an interlayer exhibits excellent corrosion resistance properties in 1N H₂SO₄ solution. The reason for this behaviour is presented and discussed in detail.     

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.     

Corrosion and Wear Behaviors of Cr-Doped Diamond-Like Carbon Coatings

A combination of plasma-enhanced chemical vapor deposition and magnetron sputtering techniques has been employed to deposit chromium-doped diamond-like carbon (DLC) coatings on stainless steel, silicon and glass substrates. The concentrations of Cr in the coatings are varied by changing the parameters of the bipolar pulsed power supply and the argon/acetylene gas composition. The coatings have been studied for composition, morphology, surface nature, nanohardness, corrosion resistance and wear resistance properties. The changes in I _D /I _G ratio with Cr concentrations have been obtained from Raman spectroscopy studies. Ratio decreases with an increase in Cr concentration, and it has been found to increase at higher Cr concentration, indicating the disorder in the coating. Carbide is formed in Cr-doped DLC coatings as observed from XPS studies. There is a decrease in sp ³/sp ² ratios with an increase in Cr concentration, and it increases again at higher Cr concentration. Nanohardness studies show no clear dependence of hardness on Cr concentration. DLC coatings with lower Cr contents have demonstrated better corrosion resistance with better passive behavior in 3.5% NaCl solution, and corrosion potential is observed to move toward nobler (more positive) values. A low coefficient of friction (0.15) at different loads is observed from reciprocating wear studies. Lower wear volume is found at all loads on the Cr-doped DLC coatings. Wear mechanism changes from abrasive wear on the substrate to adhesive wear on the coating.     

Study of structure and corrosion resistance of Fe-based amorphous coatings prepared by HVAF and HVOF

Fe-based amorphous coatings with a composition of Fe_49.7Cr₁₈Mn_1.9Mo_7.4W_1.6B_15.2C_3.8Si_2.4 have been prepared on a mild steel substrate by High velocity air fuel (HVAF) and High velocity oxygen fuel (HVOF) processes. The microstructure and corrosion resistance in 3.5 wt.% NaCl solution of the coatings prepared by the two processes were comparatively studied. It was found that the two coatings exhibit dense structure with the porosity of 0.4% and compact bonding with the substrate. However, HVOF coating contains higher oxygen content than HVAF coating, resulting from the formation of significant oxide contours between the partially melted particles in HVOF process. Electrochemical polarization tests and electrochemical impedance spectroscopy (EIS) analysis indicate that the HVAF coating has better corrosion resistance than the HVOF coating. The preferential corrosion along the oxide contours thus providing efficient diffusion channels for electrolyte accounts for the poor corrosion resistance in HVOF coating. The present results demonstrate that HVAF with less cost can be a promising spray process to fabricate the Fe-based amorphous coating for industrial applications.     

Microstructure, spallation and corrosion of plasma sprayed Al2O3–13%TiO2 coatings

The electrochemical corrosion behaviours of the steel substrates coated with three different plasma sprayed Al₂O₃–13%TiO₂ coatings were studied in this paper. The three kinds of Al₂O₃–13%TiO₂ coatings were conventional ME coating, nanostructured NP coating and NS coating. There were micro cracks, laminar splats and straight columnar grains in ME coating. For the two nanostructured coatings, the laminar microstructure and columnar grains were not obvious. The NP coating had the highest hardness and spallation resistance. Electrochemical corrosion behaviour of the three coatings was mainly investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in aqueous Na₂SO₄ solution.     

Pulse electroplating of Ni-W-P coating and its anti-corrosion performance

Ni-W-P coatings were electrodeposited on copper substrates by pulse electroplating. Effects of electrolyte pH (1-3), temperature (40–80 °C), average current density (1–7 A/dm²) and pulse frequency (200–1000 Hz) on deposition rate, structure and corrosion resistance performance of Ni-W-P coatings were studied by single factor method. Surface morphology, crystallographic structure and composition of Ni-W-P coatings were investigated by means of scanning electron microscopy, X-ray diffractometry and energy dispersive X-ray spectroscopy, respectively. Corrosion resistance performances of Ni-W-P coatings were studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 3.5% NaCl solution (mass fraction) and soil-containing solution. It was found that the pulse electroplated Ni-W-P coatings have superior corrosion resistance performance and the electroplating parameters significantly affect the structure and corrosion resistance performance of Ni-W-P coatings. The optimized parameters of pulse electroplating Ni-W-P coatings were as follows: pH 2.0, temperature 60 °C, average current density 4 A/dm², and pulse frequency 600 Hz. The Ni-W-P coating prepared under the optimized parameters has superior corrosion resistance (276.8 kΩ) and compact surface without any noticeable defect.     

Effects of Substitution of Fe by Mischmetal on Formation and Properties of Arc-Sprayed AlSi-Based Amorphous Coating

The influence of a partial substitution of Fe with Mischmetal [Ni₆₀RE₄₀ (wt.%), RE: rare earth including Ce; La; Nd and Pr] on the glass formation ability (GFA), mechanical properties and electrochemical corrosion behavior of arc-sprayed AlSiFe-based amorphous coatings has been investigated. It is revealed that partial substitution of Fe by Mischmetal slightly debases the GFA and mechanical properties of the AlSiFe amorphous coating because of the selective oxidation of RE elements. With Mischmetal substitution, the amorphous fraction, onset crystallization temperature and microhardness of the coating decrease to 64.3%, 306 °C, and 338.7 Hv₁₀₀, respectively. Compared with a crystalline aluminum alloy and coating, the coating with Mischmetal substitution still has a prominent wear and corrosion resistance. The relative wear resistance of the coating with Mischmetal substitution is about 2.5 times than that of the 6061-Al alloy under the same dry sliding testing condition. In 0.6 M NaCl aqueous solution, the coating with Mischmetal substitution manifests a lower I_corr, higher E_corr and E_p values in polarization curves and bigger fitted R_ct value in EIS plots than does the as-sprayed crystalline Al coating.     

Corrosion resistance of cold-sprayed Ta coatings in very aggressive conditions

This study deals with the corrosion behaviour of high-pressure cold-sprayed Ta coatings, compared with Ta bulk material and inert-atmosphere plasma-sprayed Ta coatings. Electrochemical polarization and electrochemical impedance spectroscopy measurements are carried out in 1 M KOH solution; immersion tests are performed in 1 wt.% HF solution, and the resistance to high-temperature oxidation and molten salt attack is evaluated by hot corrosion tests. Moreover, the effect of substrate material (steel, Al and Cu) on the coating formation is investigated using FESEM.     

Improvement of the oxidation and wear resistance of pure Ti by laser cladding at elevated temperature

NiCrBSi and NiCrBSi/WC-Ni composite coatings were produced on pure Ti substrates by the laser cladding technology. Thermal gravimetric (TG) analysis was used to evaluate the high temperature oxidation resistance of the laser cladding coatings. The friction and wear behavior was tested through sliding against the Si₃N₄ ball at elevated temperatures of 300 °C and 500 °C. Besides, the morphologies of the worn surfaces and wear debris were analyzed by scanning electron microscopy (SEM) and three dimensional non-contact surface mapping. The results show that the microhardness, high temperature oxidation resistance and high temperature wear resistance of the pure Ti substrates are greatly increased. For the pure Ti substrate, the wear behavior is dominated by adhesive wear, abrasive wear and severe plastic deformation, while both laser cladding coatings, involving only mild abrasive and fatigue wear, are able to prevent the substrates from severe adhesion and abrasive wear. In particular, the laser cladding NiCrBSi/WC-Ni composite coating shows better high temperature wear resistance than the NiCrBSi coating, which is due to the formation of a hard WC phase in the composite coating.     

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.     

Colonization of Bacteria on the Surfaces of Cold-Sprayed Copper Coatings Alters Their Electrochemical Behaviors

Copper coatings were fabricated on stainless steel plates by cold spraying. Attachment and colonization of Bacillus sp. on their surfaces in artificial seawater were characterized, and their effects on anticorrosion performances of the coatings were examined. Attached bacteria were observed using field emission scanning electron microscopy. Electrochemical behaviors including potentiodynamic polarization and electrochemical impedance spectroscopy with/without bacterial attachment were evaluated using commercial electrochemical analysis station Modulab. Results show that Bacillus sp. opt to settle on low-lying spots of the coating surfaces in early stage, followed by recruitment and attachment of extracellular polymeric substances (EPS) secreted through metabolism of Bacillus sp. The bacteria survive with the protection of EPS. An attachment model is proposed to illustrate the bacterial behaviors on the surfaces of the coatings. Electrochemical data show that current density under Bacillus sp. environment decreases compared to that without the bacteria. Charge-transfer resistance increases markedly in bacteria-containing seawater, suggesting that corrosion resistance increases and corrosion rate decreases. The influencing mechanism of bacteria settlement on corrosion resistance of the cold-sprayed copper coatings was discussed and elucidated.     

Improving of Corrosion Behavior of Al 7075 by Applied Titania–<Emphasis Type="Italic">Benzotriazole</Emphasis> Nanostructured Coating with Sol Gel Method

Nowadays, self-healing coatings display high abrasion resistance and bond strength. Application of these coatings are reckoned the most common and the most economic method for restoration and protection against corrosion by which metal structures durability is enhanced. The major role of a self-healing hybrid coating in corrosion inhibition is to supply materials for controlling types of corrosion. In this paper, titania–Benzotriazole nanostructured coating has been applied to substrate Al 7075 by using the sol–gel process and immersion method. The bonds existing in the hybrid coating, structure and morphology and coating corrosion behavior have been studied using Fourier transform infrared spectroscopy (FTIR), GIXRD, atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and impedance electrochemical test, respectively. The obtained results are indicative of generating a homogeneous, uniform, crack-free titania–Benzotriazole nanostructured coating associated with excellent optimization of corrosion resistance at 2.8% Benzotriazole.     

Electrochemical Behavior and Stress Corrosion Sensitivity of X70 Steel Under Disbonded Coatings in Korla Soil Solution

The corrosion of X70 pipeline steel under a model disbonded coating was studied in a simulated solution of Korla soil by combining in situ electrochemical measurements at different locations in the crevice and stress corrosion cracking (SCC) sensitivity analyses in the corresponding simulated environments. The results from electrochemical impedance spectroscopy showed that the corrosion product resistance R _t and charge transfer resistance R _ct of X70 steel first increased and then decreased with increasing distance from the opening of the crevice in the disbonded coating. Scanning electron micrographs showed that pitting in the crevice became more severe at deeper locations in the crevice. Slow strain rate tests showed that the lowest SCC sensitivity of X70 steel was found at 15 cm away from the opening, and the highest SCC sensitivity was at the end of the crevice.