Electrochemical behavior of Ni3Al-based intermetallic alloys in NaOH

The corrosion behavior of Ni₃Al-based intermetallic alloys in a 0.5 M NaOH solution was studied at 25 °C. The open circuit potential, cathodic and anodic potentiodynamic polarization, Tafel plots and linear polarization resistance measurements were used to characterize the corrosion behavior. For the Ni₃Al(B, Zr) alloy, potentiodynamic polarization curves showed a wide passive region that can be found between about ?0.220 V_SCE and 0.520 V_SCE. On the other hand, a narrow passive region, in the range of potentials from about ?0.180 V_SCE to 0.180 V_SCE, was observed for the Ni₃Al(B, Zr, Cr, Mo) alloy. Chromium, as an alloying element in the Ni₃Al(B, Zr, Cr, Mo) alloy, contributes to transpassive dissolution of the passive film at much lower anodic potentials and remarkably reduces the passivation region. The experiments indicated also that damaged passive films on alloys repairs itself and pits do not initiate. The surface of both alloys and passive films possess extremely high corrosion resistance in a studied solution. However, Tafel and linear polarization tests revealed that freshly exposed surfaces of the Ni₃Al(B, Zr) alloy exhibited better corrosion resistances than the Ni₃Al(B, Zr, Cr, Mo) alloy. Both methods, used for the determination of corrosion rates gave very similar results. The calculated corrosion rates are about 2.8 ·10^?3 and 6.0·10^?3 mm year^?1 for the Ni₃Al(B, Zr) alloy and B, respectively.     

Electrodeposition of zinc–nickel alloy by pulse plating using non-cyanide bath

Abstract

In this study, zinc–nickel electrodeposition was carried out in a sulphamate bath at pH 3–4 by pulse plating and the deposits obtained were characterised by measuring microhardness, surface roughness and by employing SEM, XRD, AFM techniques. The corrosion behaviour of the deposits was evaluated by potentiodynamic polarisation. The deposits obtained by pulse plating have an increased Ni content, thought to be responsible for an improved corrosion resistance.     

NiTi合金表面类金刚石膜的表面特征和腐蚀行为

采用等离子浸没离子注入和沉积（PIIID）法以C2H2为等离子源对NiTi合金进行表面改性。利用Raman光谱分析膜层结构。采用原子力显微镜和纳米压痕分析涂层前后NiTi的表面形貌和力学性能。利用电化学测试、扫描电镜和原子吸收光谱测试涂层前后基体的耐腐蚀性和Ni离子析出。结果表明：NiTi合金表面的膜层是类金刚石（DLC）；经过PIIID处理后，基体表面的粗糙度降低；纳米硬度得到提高；耐腐蚀性能获得明显改善；Ni离子析出得到有效的抑制。     

Corrosion behaviour of polycrystalline Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> thin films and its size effects

This study examines the effect of film thickness ranging from 230 to 404 nm on the corrosion resistance of Nb₂O₅ thin films grown by chemical solution deposition. The films were characterized to obtain the relationships between the deposition parameters and the most relevant physical properties (structural, surface morphology and corrosion resistance). From X-ray diffraction and XPS analyses we can conclude that the films were stoichiometric Nb₂O₅ and crystalline. The internal strain and morphology of the film changes as the number of layers increases indicating a thickness dependent grain size. The surface roughness, corrosion resistance were also affected by the film thickness. Electrochemical impedance spectroscopy (EIS) shows that the thicker film have higher passive and charge transfer resistance than the control samples. These results coating layer of Nb₂O₅ improves the corrosion resistance on an API 5L X80 steel alloy due to the formation of a film on the surface.     

Effects of Hf content and immersion time on electrochemical behavior of biomedical Ti-22Nb-xHf alloys in 0.9% NaCl solution

The aim of this study was to investigate the effects of Hf content and immersion time on the electrochemical corrosion behavior of the Ti-22Nb-xHf (x = 0, 2, 4, and 6 at%) alloy samples in 0.9% NaCl solution at 37 °C and neutral pH range, utilizing the potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. From the polarization curves, all these alloys exhibited typical passive behavior, which was indicated by a wide passive region without the breakdown of the passive films and low corrosion current densities. In addition, the values of the corrosion current densities and passive current densities decreased with increase in the Hf content. The EIS results, fitted by R_S(Q_PR_P) model, exhibited capacitive behavior (high corrosion resistance) with phase angles closed to −80° and high impedance values at low and medium frequencies, indicating the formation of a highly stable film on these alloys in the test solution. The resistance of the passive films improved with increase in the Hf content and immersion time. All these observations suggested a more noble electrochemical behavior of the Ti-22Nb-xHf alloys compared to the Ti-Nb binary alloy.     

Investigation of effective parameters in improving corrosion resistance of silica coated stainless steel via sol–gel method

Abstract

The sol–gel method has been used to deposit oxide thin films. In the present study, silica was coated on 316L stainless steel substrate through sol–gel method via dipping process. Silica sol was made in a mixture of methyltriethoxysilane (MTES), tetraethyl orthosilicate (TEOS), pure water, absolute ethanol as solvent, nitric acid, and hydrochloric acid as catalysts. The corrosion resistance of samples was investigated in simulated body fluid by a potentiodynamic test and uniformity of the coating was evaluated by scanning electron microscope. We have assessed the effective parameters, such as wetting agent, number of layers, catalyst and different roughness of sublayers on corrosion properties of samples. The silica coating resulted in improvement of corrosion resistance of 316L stainless steel in body environment, and can be used as a proper coating on orthopaedic implants.     

Investigating the Significance of Bicarbonate with the Corrosion of High-Strength Steel in CO2-Saturated Solutions

This paper presents an electrochemical study on the corrosion behavior of API-X100 steel, heat-treated to have microstructures similar to those of the heat-affected zones (HAZs) of pipeline welding, in bicarbonate-CO₂ saturated solutions. The corrosion reactions, onto the surface and through the passive films, are simulated by cyclic voltammetry. The interrelation between bicarbonate concentration and CO₂ hydration is analyzed during the filming process at the open-circuit potentials. In dilute bicarbonate solutions, H₂CO₃ drives more dominantly the cathodic reduction and the passive films form slowly. In the concentrated solutions, bicarbonate catalyzes both the anodic and cathodic reactions, only initially, after which it drives a fast-forming thick passivation that inhibits the underlying dissolution and impedes the cathodic reduction. The significance of the substrate is as critical as that of passivation in controlling the course of the corrosion reactions in the dilute solutions. For fast-cooled (heat treatment) HAZs, its metallurgical significance becomes more comparable to that of slower-cooled HAZs as the bicarbonate concentration is higher.     

咪唑对钌化学机械抛光的影响

利用自制的抛光液,研究了在磷酸体系抛光液中咪唑(imidazole,C3H4N2)浓度和pH值对钌的抛光速率的影响。采用电化学分析方法和X射线光电子能谱仪(XPS)分析了缓蚀剂咪唑对腐蚀效果的影响;采用原子力显微镜(AFM)观察钌片表面的微观形貌。试验结果表明:金属钌在未加入咪唑的磷酸体系抛光液中,抛光速率最高为6.2nm/min,平均粗糙度(Ra)为10.7nm;而在抛光液中加入咪唑后,钌的抛光速率为3.9nm/min,平均粗糙度(Ra)降至1.0nm。咪唑的加入,虽然降低了金属钌的抛光速率,但提高了金属钌的表面质量。同时也促进了金属钌表面钝化膜的生成,降低了金属钌的腐蚀电流值,抑制了阴极反应。     

Influence of microstructure and roughness level on corrosion resistance of the austenitic stainless steel welded joint

The influence of microstructure and surface roughness of the X5CrNi18-10 austenitic stainless steel-welded joint on resistance to uniform, pitting, and intergranular corrosion, as well as on the stability of the passive film, was evaluated. The microstructure was revealed by optical microscopy and scanning electron microscopy, whereas surface topography and roughness levels were determined by atomic force microscopy. Corrosion characteristics were obtained by the electrochemical potentiokinetic reactivation method with double loop, electrochemical impedance spectroscopy method, as well as by potentiodynamic measurements. The degree of sensitization of heat-affected zone (HAZ) was significantly lower than the threshold value required for the occurrence of intergranular corrosion. However, HAZ showed a significantly greater tendency to pitting and uniform corrosion compared to weld metal and base metal. No effect of roughness levels (RMS from 3.6 to 54 nm) on the pitting potential value of the welded joint was observed (unlike in HAZ). The polished surface shows significantly higher corrosion resistance than the grinded surface. Generally, polishing improved corrosion resistance, especially in HAZ, which is very important because HAZ is a critical place for the occurrence of pitting and other types of corrosion.     

Electrochemical corrosion behavior of biomedical Ti–22Nb and Ti–22Nb–6Zr alloys in saline medium

The aims of this study were to investigate the effects of Zr addition and potentiodynamic polarization on the microstructure and corrosion resistance of Ti–22Nb and Ti–22Nb–6Zr alloy samples. The corrosion tests were carried out in 0.9% NaCl at 37 °C and neutral pH value, utilizing the OCP, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. The results of XRD and optical microscopy indicated that the addition of Zr stabilized the β phase, which plays a crucial role in the corrosion resistance improvement of the Ti–22Nb–6Zr alloy. From the polarization curves, it can be seen that the alloys exhibited a wide passive region without the breakdown of the passive films and also low corrosion current densities. In addition, the values of the corrosion current densities and passive current densities decreased with the addition of 6 at% Zr into the Ti–22Nb alloy. The EIS results of these two alloy samples after 1‐h immersion in 0.9% NaCl solution, and being fitted by R_S(Q_PR_P) model, suggested that the corrosion resistance of the passive films improved with the addition of Zr and only a single passive film formed on the surfaces. However, two time constants were observed for the Ti–22Nb and Ti–22Nb–6Zr alloy samples after potentiodynamic polarization, the spectra of which can be fitted using the R_s(Q_o(R_o(Q_bR_b))) model. In addition, the corrosion resistance of the two alloy samples was reinforced significantly because of polarization when compared to the immersed samples. All these observations suggested a nobler electrochemical behavior of the titanium alloys with the addition of Zr element and after polarization.     

Corrosion of 316L stainless steel in ionic liquid working fluids used for absorption heat pumps or refrigerators

Abstract

The corrosion behaviour of 316L stainless steel (316L ss) in aqueous solutions of ionic liquid 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]) with different contents of water was investigated by scanning electron microscopy (SEM), potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). The results indicate that 316L in aqueous solutions of ionic liquid [EMIM][DEP] shows an obvious surface passivation, a broad passive region and low corrosion current densities. It also has better corrosion resistivity than in 0?177 M LiBr aqueous electrolytes. Furthermore, in order to explain the corrosion mechanism in two working fluids, the Van der Waals volume of ions and the interaction energies of ion pairs were calculated based on the density functional theory (DFT) in quantum chemistry combined with gradient corrected functional using Gaussian 09.     

Eis and XPS study of surface modification of 316LVM stainless steel after passivation

The effects of surface finish, nitric acid passivation and ageing in air on corrosion resistance of 316LVM stainless steel in 0.5% H₂SO₄ have been investigated by EIS, potentiodynamic polarization measurements and XPS. The results indicate that a smoother surface exhibits to a higher corrosion resistance. The effectiveness of the passivation treatment strongly depends on nitric acid concentration, passivation time and temperature. The passivation treatment significantly increases the corrosion resistance due to a high Cr content in the passive film and increased film thickness. Ageing after passivation increases the corrosion resistance whereas ageing before passivation has little effect.     

The comparison of the corrosion resistance of advanced ferromagnetic stainless steels by Mott–Schottky approach

Ferromagnetic stainless steels (SSs) have been investigated as potential candidates for dental prosthesis applications in replacement of magnetic attachments made of noble and expensive alloys. In order to be used as biomaterials, their corrosion resistance has to be appropriate. The corrosion resistance of passive materials is related to the characteristics of the passive film formed and their properties might be investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and Mott–Schottky approach. The corrosion resistance and the capacitance of the passive films formed on PM2000, DIN 1.4575, and 17‐4 PH advanced SSs during 2 days of immersion in a phosphate buffered saline solution (PBS), at 25 °C and pH 7.0 were studied by electrochemical techniques. A commercial alloy Dyna EFM was also analyzed for comparison reasons. The results showed that films on tested materials behave as both n‐type and p‐type semiconductors and the PM2000 presented the highest corrosion resistance among all of them.     

Characterization of roughness and pitting corrosion of surfaces modified by blasting and thermal oxidation

The blasting process generates a renewed surface on the surface of metallic biomaterials with a different topography and a different chemical composition. The impact of particles on the metallic surface increases both the surface roughness and susceptibility pitting corrosion. The aim of this work is to smoothen the sharp edges of blasted Ti6Al4V alloy surfaces by means of oxidation treatment and the evaluation of their susceptibility to pitting corrosion after this thermal oxidation. Oxidation treatments were performed at 500 and 700 °C for 1 h on samples blasted with SiO₂/ZrO₂ and Al₂O₃ particles. Compositional, microstructural and topographical characterization of the blasted surfaces were carried out by scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX), and atomic force microscopy (AFM). The surface reactivity and corrosion behaviour of the samples were assessed by scanning Kelvin probe (SKP) and by anodic polarization curves. The susceptibility to pitting corrosion of the Ti6Al4V blasted surfaces becomes higher as roughness increases. The oxidation treatment of the Ti6Al4V blasted surfaces causes the presence of nuclei of oxides that cover the area free of particles, especially in the samples treated at 700 °C, giving rise to a higher micro-nano roughness. The presence of the oxide, covering the blasted Ti6Al4V, decreases the surface reactivity leading to a lower passive current and wider pasivation region, decreasing the susceptibility to pitting corrosion.     

Effects of Ce, La and Ba addition on the electrochemical behavior of super duplex stainless steels

The effects of rare earth metal (REM: Ce, La) and Ba addition on aqueous corrosion properties of super duplex stainless steels (SDSS) were investigated by electrochemical tests and surface analyses. The results of potentiodynamic test indicated that the passive range increased by the addition of Ce, La, and Ba, indicating increased relative resistance to localized corrosion. The EIS measurements showed that the Ce-La-Ba-bearing alloys exhibited higher R_ct and R_p values than the Ce-La-Ba-free alloy at the passive and breakdown states. Furthermore, the additions of REMs and Ba together promoted the formation of dense chromium-enriched passive film.     

Microstructure and corrosion resistance of vanadium films deposited at different target-substrate distance by HPPMS

High power pulsed magnetron sputtering（HPPMS）, a novel physical vapor deposition technology, was applied to prepare vanadium films on aluminum alloy substrate in this paper. The influence of target–substrate distance（Dt–s）（ranging from 8 to 20 cm） on phase structure, surface morphology, deposition rate, and corrosion resistance of vanadium films was investigated. The results show that the vanadium films are textured with a preferential orientation in the（111） direction except for that fabricated at 20 cm. With Dt–sincreasing, the intensity of（111） diffraction peak of the films decreases and there exists a proper distance leading to the minimum surface roughness of 0.65 nm. The deposition rate decreases with Dt–sincreasing. All the V-coated aluminum samples possess better corrosion resistance than the control sample. The sample fabricated at Dt–sof 12 cm demonstrates the best corrosion resistance with the corrosion potential increasing by 0.19 V and the corrosion current decreasing by an order of magnitude compared with that of the substrate. The samples gain further improvement in corrosion resistance after annealing, and if compared with that of annealed aluminum alloy, then the corrosion potential of the sample fabricated at 20 cm increases by 0.415 V and the corrosion current decreases by two orders of magnitude after annealed at 200 °C. If the annealing temperature further rises to 300 °C, then the corrosion resistance of samples increases less obviously than that of the control sample.     

碳化对模拟混凝土孔溶液中HRB335钢腐蚀行为的影响

应用电化学阻抗谱、循环伏安与动电位极化等方法研究了碳化后模拟混凝土孔溶液pH值的变化对钢筋腐蚀电化学行为的影响.结果表明,随着pH值的下降钢筋表面钝化膜的稳定性与耐蚀性不同程度地降低.当模拟液pH值为12.5与11.5时,钝化膜的稳定性处于因pH值降低导致的钝化膜溶解与表面沉积物CaCO3或含钙氧化物CaFe2O4等耐...     

The correlation between the properties of the passive film on 304L steel and its susceptibility to SCC in chloride media

Certain physico-chemical properties of passive films formed in hot concentrated NaCl, CaCl₂ and MgCl₂ on 304L steel were investigated in order to elucidate their effect on susceptibility to SCC. The resistance to pitting corrosion and suceptibility to SCC was found to be correlated. The resistance to pitting corrosion is discussed on the basis of composition and surface condition of passive films determined by AES methods and the dielectric response of the metal-passive film-electrolyte system as a function of frequency.     

The influence of tin and silver as microstructure modifiers on the corrosion rate of Pb–Ca alloys in sulfuric acid solutions

The effect of microstructure modifiers, Sn and Ag, on the corrosion rate of commercial Pb–Ca alloy in H₂SO₄ electrolyte was investigated by the potentiodynamic polarization and by the weight loss corrosion rate measurement at the open circuit potential. The effect of microstructure modification of the Pb–Ca alloy, provoked by the alloying with tin and silver as well as by the proper thermo‐mechanical treatment, is recorded by optical microscopy. The weight loss experiments have shown three‐ to five‐fold decreases in the corrosion rate of ternary Pb–Ca–Sn and quaternary Pb–Ca–Sn–Ag alloys, compared to the results for primary Pb–Ca alloy. It is largely in accordance with the results of potentiodynamic polarization measurements that showed comparable decrease in the passive current density of the modified alloys. The obtained results are discussed in terms of the synergetic effect of the addition of modifiers and the thermo‐mechanical treatment on to the Pb–Ca alloy microstructure refinement, and accordingly the increase in their corrosion resistance.     

Influence of pH on electrochemical properties of passive films formed on Alloy 690 in high temperature aqueous environments

Passive films formed on Alloy 690 in different pH solutions at high temperatures were studied by potentiodynamic polarization, Auger electron spectroscopy, thermodynamic diagrams and the Mott–Schottky relation. The chemical compositions and electronic structures of the passive films were found to be strongly pH-dependent. In alkaline solutions, a secondary passivation was clearly observed on potentiodynamic polarization curves. The passive films were a mixture of Cr₂O₃ and FeCr₂O₄ below the flat band potential of nickel oxide and were NiFe₂O₄ above this potential. Electronic structure models, describing the electrochemical properties of the passive films, are proposed and discussed.