Potentiodynamic Polarization Curve Test Research Articles

Protection of N80 steel from erosion-corrosion of geothermal water by nanoparticle-modified expoxy resin coatings

In order to investigate the erosion-corrosion resistance of nano-SiO2/EP composite coating and TiO2/EP composite coating in a geothermal environment, the coatings were subjected to potentiodynamic polarization curve tests, AC impedance tests, weightlessness tests, under different immersion time in geothermal water. The micro-morphology of the coating after erosion-corrosion was observed to evaluate the protective effect of the modified EP coating on N80 steel. The result showed that the addition of nanoparticles can improve the corrosion resistance of EP coatings to a certain extent, and the optimum addition amount of nanoparticles is 3%. In geothermal water containing sand, the corrosion inhibition efficiency of EP coatings modified by nanoparticles was above 99.99% except for the 1 wt% SiO2/EP composite coating. When the nanoparticle content is 1 wt%, the protective effect of nano-SiO2/EP composite coating is better than that of TiO2/EP composite coating, but the protective effect is opposite when the nanoparticle content is 3% and 5%, respectively.

Effect of Tropical Marine Atmospheric Environment on Corrosion Behaviour of the 7B04-T74 Aluminium Alloy

In this work, the effects of the tropical marine atmospheric environment on the corrosion behaviour of the 7B04-T74 aluminium alloy were systematically investigated by using accelerated testing, together with corrosion kinetic analysis, microstructure observation, product composition analysis, and potentiodynamic polarization curve tests. The weight loss method was used for the corrosion kinetics analysis. The surface morphology and corrosion products transformation law were investigated by OM, SEM, EDS, and XPS. The electrochemical characteristics were studied using potentiodynamic polarization curves. The research indicated that the 7B04-T74 aluminium alloy has eminent corrosion resistance in the tropical marine atmospheric environment. Localized pitting corrosion occurred rapidly in the tropical marine atmosphere. In the later stage of corrosion, the corrosion of aluminium alloy did not become serious. Specifically, no obvious intergranular corrosion was found, which is related to the thermal treatment method. Corrosion products included Al(OH)3, Al2O3, and AlCl3, of which Al(OH)3 is the most notable.

Microstructure Evolution and Performance of Laser-Remelted Ti-6Al-4V Alloy

Herein, Ti-6Al-4V alloy was remelting by high-energy laser, the influence of laser energy density of mobile laser source on the evolution of solidification structure of Ti-6Al-4V alloy was studied, and the changes of relevant service performance of Ti-6Al-4V alloy after laser-remelting were explored. The results showed that there were four distinct regions: overheated zone, melting zone, heat-affected zone and substrate zone in Ti-6Al-4V alloy after laser remelting. The overheated zone and melting zone were dominated by primary α phase and secondary α phase, and a heat-affected zone was dominated by β phase. With the increase of laser energy density, the depth of molten pool and the range of melting zone in Ti-6Al-4V alloy increased, and the crystal phase distribution and grain size changed significantly. Laser-remelting Ti-6Al-4V alloy could still maintain a good passive state in the potentiodynamic polarization curve test, and the optimal laser power during remelting was 1200 W. This study proved that the crystal phase composition and grain size during the solidification process after laser-remelting were a key factor affecting the service performance of Ti-6Al-4V alloy.

Distribution of sulfate‐reducing bacteria in the crevice and its effect on the initial corrosion behavior of 2205 stainless steel in artificial seawater

AbstractIn the present study, the distribution and vitality of the sulfate‐reducing bacteria (SRB) inside the crevice were characterized by scanning electron microscopy and confocal laser scanning microscopy. Potentiodynamic polarization curve tests and electrochemical impedance spectroscopy were used to evaluate the corrosion resistance. Furthermore, a starvation experiment was conducted by controlling nutrients to investigate the effects of the crevices on the transportation of nutrients and the vitality of the SRB. The results demonstrate that it was more difficult for the SRB to enter the crevice, resulting in an incomplete biofilm formed on the surface. In addition, the insufficient supply of nutrients was also the reason for the low vitality of the SRB inside the crevice. Based on these results, it was inferred that the incomplete biofilm inside the crevice acted as a micro‐galvanic, thus making the corrosion rate of 2205 stainless steel in the initial crevice corrosion much more serious than that in the open system.

An improved strategy to synthesize graphite oxide with controllable interlayer spacing as coatings for anticorrosion application

AbstractA facile method to synthesize nanoscale graphene oxide (GO) with controllable interlayer spacing was carried out using two‐step oxidation process and much less acid to improve the efficiency of the oxidation. The X‐ray diffraction results demonstrated that GO had been successfully prepared from graphite because of disappearance of characteristic peaks of pristine graphite at about 2θ = 26.5° along with appearance of a sharp major peak of GO at about 2θ = 9.4°. The increased basal spacing d001of as‐prepared GO could reach as high as 9.39 Å, suggesting higher degree of oxidation than that prepared by the classical Hummers' synthesis, and characterization results from Fourier transform infrared spectrometer, X‐ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy further confirmed this conclusion. The influence of GO on anti‐corrosion performance of nanocomposite coatings composited with the 2,5‐dimethoxyaniline (DMA) conductive polymer was examined via potentiodynamic polarization curve tests in 3.5 wt% NaCl aqueous solution. The results demonstrated that the incorporation of GO significantly decreased the corrosion current density (icorr= 2.62 μA/cm2) in the case of GO‐PDMA coating, reflecting excellent physical isolation of GO and its synergistic effect with PDMA against the infiltration of water and corrosive electrolyte.

Fracture location transition in constant load tests of a NiCrMoV steel welded joint

The fracture location transition of the NiCrMoV steel welded joints induced by different tensile loads has been investigated through the constant load tests in 3.5 wt% NaCl at 180 °C. The mechanical properties of different zones in the welded joints were measured by the hardness measurement and localized tensile tests in air at room temperature. The corrosion properties were characterized by potentiodynamic polarization curve tests and scanning vibrating electrode technique (SVET) tests. The results reveal that the most susceptive corrosion zone and the weakest strength zone do not locate in same zone of the welded joint. This mismatch leads to the rupture locations of the welded joints change with the applied load in the constant load tests. For the applied load larger than or equal to 765 MPa, the rupture section locates in the middle of WM due to its weakest strength. But the fracture position shifts to the fusion zone for the applied load less than or equal to 760 MPa, which is attributed to stress corrosion cracking (SCC) originating from the pits under the combined effect of galvanic and stress-assisted corrosion.

Enhanced Galvanic Corrosion Phenomenon in the Welded Joint of NiCrMoV Steel by Low-Cycle Fatigue Behavior

The effect of microstructural changes on the corrosion of a NiCrMoV steel welded joint induced by low-cycle fatigue behavior in chloride solution has been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), potentiodynamic polarization curve tests and scanning vibrating electrode technique (SVET) tests. During the low-cycle fatigue tests, cyclic softening takes place in the three zones (base metal, BM/weld metal, WM/heat affected zone, HAZ) of the welded joint due to the decrease of dislocation density or the formation of low-energy structures. Compared to the as-received specimens, the corrosion potential of each zone in the low-cycle fatigue damage specimens moves to the positive direction and the corrosion current density decreases. The corrosion resistance of the individual zone increases, which is related to the reduction of dislocation density or the formation of low-energy structures. However, the difference of corrosion potential between base metal and weld metal in the low-cycle fatigue welded joints becomes lager, which means that the galvanic corrosion susceptibility of the low-cycle fatigue welded joint increases. This may be caused by the difference of microstructural changes in the various regions of welded joints during cyclic plastic deformation.

Wear and Corrosion Resistance of Al0.5CoCrCuFeNi High-Entropy Alloy Coating Deposited on AZ91D Magnesium Alloy by Laser Cladding.

In order to improve the wear and corrosion resistance of an AZ91D magnesium alloy substrate, an Al0.5CoCrCuFeNi high-entropy alloy coating was successfully prepared on an AZ91D magnesium alloy surface by laser cladding using mixed elemental powders. Optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction were used to characterize the microstructure of the coating. The wear resistance and corrosion resistance of the coating were evaluated by dry sliding wear and potentiodynamic polarization curve test methods, respectively. The results show that the coating was composed of a simple FCC solid solution phase with a microhardness about 3.7 times higher than that of the AZ91D matrix and even higher than that of the same high-entropy alloy prepared by an arc melting method. The coating had better wear resistance than the AZ91D matrix, and the wear rate was about 2.5 times lower than that of the AZ91D matrix. Moreover, the main wear mechanisms of the coating and the AZ91D matrix were different. The former was abrasive wear and the latter was adhesive wear. The corrosion resistance of the coating was also better than that of the AZ91D matrix because the corrosion potential of the former was more positive and the corrosion current was smaller.

The plasma pretreatment influence on corrosion behavior of Ion Vapor Deposition (IVD) of aluminum coating

PurposeThe purpose of this study is to investigate the effect of plasma pretreatment on the corrosion and adhesion behavior of Al coating deposited on iron steel by ion vapor deposition (IVD).Design/methodology/approachAr plasma sputtering was carried out for 0, 5, 10 and 15 min, and then IVD Al coating was performed. Surface free energy measurements were conducted on the plasma-sputtered surfaces. Cross-sectional observations were carried out on the coating/substrate interface by using scanning electron microscopy. Corrosion resistance of the deposited films was characterized using potentiodynamic polarization curve test and electrochemical impedance spectroscopy (EIS).FindingsResults demonstrated that surface free energy values were increased by increasing the sputtering time before coating process. The corrosion current density of the IVD Al coating deposited after 15 min Ar plasma pretreatment is three orders of magnitude lower than that of steel ST37 substrate. The EIS tests confirm the excellent anticorrosive properties of the Al-coated specimens.Originality/valueWith the increase in the plasma pretreatment time, coating adhesion would ameliorate because of the presence of plasma, which makes substrates a better place for Al ions to set and prevent any gap between coatings and substrates. This fact can be attributed to an increase in the surface free energy and reduction of contact angle of substrate exposed to plasma pre-treatment.

In Situ Electrochemical Behavior of Aluminum Chemical Mechanical Polishing at Low Down Pressure in Environmentally Friendly and Weakly Alkaline Slurry

The lower pressure tendency in chemical mechanical polishing (CMP) process requires a lower adhesive inhibitor with environmentally friendly corrosion properties to replace the conventional benzotriazole (BTA) inhibitor for aluminum (Al) CMP. Open circuit potential test, potentiodynamic polarization curve test, linear sweep voltammetry and potential drop investigated by in-situ electrochemical mechanical polishing (ECMP) platform were used to reveal the controlled evolution process of corrosion inhibitor films at low pressure during Al CMP. The comparison between BTA and 1,2,4-triazole (TAZ) shows that TAZ has lower current density, wider potential inhibition interval, and high planarization efficiency, although TAZ has lower adhesion on Al surface. Finally, the surface roughness of Al after CMP with TAZ in weakly alkaline slurry at pressure of 1 psi was observed by atomic force microscopy (AFM) with a value of 0.19 nm. This studies demonstrated that the conventional BTA can be replaced by environmentally friendly corrosion inhibitor TAZ, which is a promising alternative candidate to the Al CMP at low down pressure.

Microstructure and mechanical properties of friction welded AISI 1040/AISI 304L steels before and after electrochemical corrosion

Abstract The aim of the present study is to investigate the effect of welding parameters both on the electrochemical corrosion behavior and tensile strength of pre- and post-electrochemical corrosion of friction welded dissimilar steels. The microstructural changes of AISI 1040/AISI 304L friction welded couples and also parent materials were analyzed by using scanning electron microscopy. The electrochemical behaviors of AISI1040/AISI304L joints were comparatively investigated by potentiodynamic polarization curve test and by electrochemical impedance spectra. Moreover, tensile strength experiments were carried out determining the behavior of friction welded joints of pre- and post-electrochemical corrosion and results indicated that the maximum tensile test value of the dissimilar welded pre-electrochemical corrosion was higher than those of post-electrochemical corrosion and was also very close to AISI 1040 parent material value.

(SiC/AlN)2 multilayer film as an effective protective coating for sintered NdFeB by magnetron sputtering

SiC/AlN and (SiC/AlN)2 multilayer films with a well-arranged bilayer structure and a four-layer structure are prepared respectively on NdFeB substrates by a magnetron sputtering method. Crystal phase and microstructures of the SiC/AlN and (SiC/AlN)2 films are investigated using x-ray diffraction (XRD), field-emission scanning electron microscope (FESEM) and atomic force microscope (AFM). It is observed that the surface of the (SiC/AlN)2 four-layer film is much denser and smoother than that of the SiC/AlN bilayer film. Corrosion behaviors of the NdFeB substrates coated with SiC/AlN and (SiC/AlN)2 films as well as the bare NdFeB substrate are evaluated by potentiodynamic polarization curve tests. It is revealed that the lateral growth structures developed in interfaces are favorable for an enhanced corrosion resistance. Corrosion current densities of the (SiC/AlN)2 coated NdFeB measured in acid, alkali and salt solutions are 2.796 × 10−9, 3.65 × 10−6, and 2.912 × 10−6 A cm−2, respectively, which are much lower than those of the bare NdFeB and the SiC/AlN coated NdFeB.

Mussel-inspired functionalization of PEO/PCL composite coating on a biodegradable AZ31 magnesium alloy

The rapid degradation of magnesium-based implants in physiological environments in vivo not only will quickly deteriorate their mechanical strengths but will also lead to a severe change of the micro-environment around the implants, which may cause the final failure of magnesium-based implants. In this work, a polycaprolactone (PCL) layer was prepared to seal the plasma electrolytic oxidization coating (PEO) to form a PEO/PCL composite coating on a biodegradable AZ31 magnesium alloy, followed by further surface functionalization with polydopamine. The in vitro degradation behaviors of the bare AZ31 alloy and coated samples were evaluated in a simulated body fluid (SBF) using the potentiodynamic polarization curve test and the static immersion test. The bioactivity of the samples was investigated using the SBF soaking test. The cytocompatibility of all samples was evaluated using the cytotoxicity test and analysis of the adhesion and proliferation of osteoblast cells (MC3T3-E1) directly cultivated on the sample surface. The results showed that the PCL layer successfully sealed the pores of the PEO coating, and then the polydopamine layer formed on its surface. The in vitro degradation tests showed that the PEO/PCL composite coating improved the corrosion resistance of the AZ31 alloy in SBF with a more positive corrosion potential and a lower corrosion current density. Due to the protection of the PEO/PCL composite coating, the surrounding environment showed nearly no influence on the degradation of the coated sample, which led to no obvious local alkalization and hydrogen evolution. Moreover, compared with the AZ31 alloy and PEO coating, the PEO/PCL composite coating was more suitable for cell adhesion and proliferation. After further surface functionalization by polydopamine, the corrosion resistance of the composite coating was maintained, while its bioactivity was significantly enhanced with a large amount of hydroxyapatite (HA) formed on its surface after immersion in SBF. The initial cell adhesion and spread were also improved by the polydopamine. By further immobilizing polyhexamethylene biguanidine (PHMB) onto the coating surface via the assistance of polydopamine, good antibacterial ability was obtained. This feasible method for fabricating a cytocompatible and antibacterial composite coating on a biodegradable AZ31 alloy may be promising in implant applications due to the osteointegration and anti-infection properties of these materials post operation.

Anticorrosive property of Al coatings on sintered NdFeB substrates via plasma assisted physical vapor deposition method

An Al coating was achieved on NdFeB substrate via plasma assisted physical vapor deposition method. The coatings were treated with trivalent chromium passivation and were characterized by a scanning electron microscope equipped with an energy dispersive spectrometer. The adhesive strength between the coatings and NdFeB substrates was evaluated by tensile test. The coatings achieve much higher adhesive strength (25.7MPa) than that of Al coating without plasma assistance. The anticorrosive property of the coatings was studied by electrochemical impedance spectroscopy, neutral salt spray and potentiodynamic polarization curve tests. The corrosion current density of the passivated Al coated NdFeB specimens is 0.2205μA·cm−2, which is two orders of magnitude lower than that of bare NdFeB substrates. Also, the NSS and EIS tests confirm the excellent anticorrosive properties of the Al coated NdFeB specimens with plasma assisted physical vapor deposition method.

Interaction between Sodium Molybdate and FSWed Weld of 5083 Effected by Temperature

Similar welds composed of 5083 were produced by friction stir welding. In the solution of 0.2 M NaHSO3 and 0.6 M NaCl, with the addition of a given concentration sodium molybdate as the inhibitor, the electrochemical corrosion behaviors of the friction stir welds (FSW) and 5083 were comparatively investigated by potentiodynamic polarization curve tests and electrochemical impedance spectra (EIS) for different test temperatures (herein, 25°C,30°C,35°C,40°C). The results indicated that at 30°C, the anti-corrosion property of 5083 FSW weld and parent material was superior to those of the other temperatures.

Interaction between Sodium Molybdate and FSWed Wled of 5083 Effected by Time

Similar welds composed of 5083 were produced by friction stir welding. In the solution of 0.2 M NaHSO3 and 0.6 M NaCl, with the addition of a given concentration sodium molybdate as the inhibitor, the electrochemical corrosion behaviors of the friction stir welds (FSW) and 5083 were comparatively investigated by potentiodynamic polarization curve tests and electrochemical impedance spectra (EIS) at the ambient temperature for different test periods. The results indicated that : with the extension of period, the inhibition efficiencies (IE) for both the weld and 5083 base materials enhanced, at the same period, the inhibition efficiency (IE) for the weld was beyond that for 5083 base materials, sodium molybdate may be thought of as an effective inhibitor for 5083 aluminum alloy, the interaction between inhibitor and weld is stronger than that between inhibitor and base materials.

Inhibition Effect of Sodium Molybdate on Friction Stir Weld of 5083 in Aqueous Solution

Similar welds composed of 5083 were produced by friction stir welding. In the solution of 0.2 M NaHSO3 and 0.6 M NaCl, the electrochemical corrosion behaviors of the friction stir welds (FSW) and 5083 were comparatively investigated by static weight loss experiments and potentiodynamic polarization curve tests at the ambient temperature. The results indicated that the average corrosion rate of the weld was less than that of 5083. Then, sodium molybdate was added to the corrosive solution and its effect on the corrosion behaviors of the weld and parent metal was comparatively assessed. The inhibition efficiency (IE) for the weld was beyond that for 5083 base materials, sodium molybdate may be thought of as an effective inhibitor.

Microstructures and electrochemical behaviors of the friction stir welding dissimilar weld

By using optical microscope, the microstructures of 5083/6082 friction stir welding (FSW) weld and parent materials were analyzed. Meanwhile, at ambient temperature and in 0.2 mol/L NaHS0 3 and 0.6 mol/L NaCl solutionby gravimetric test, potentiodynamic polarization curve test, electrochemical impedance spectra (EIS) and scanning electron microscope (SEM) observation, the electrochemical behavior of 5083/6082 friction stir welding weld and parent materials were comparatively investigated by gravimetric test, potentiodynamic polarization curve test, electrochemical impedance spectra (EIS) and scanning electron microscope (SEM) observation. The results indicated that at given processing parameters, the anti-corrosion property of the dissimilar weld was superior to those of the 5083 and 6082 parent materials.

Comparison of the Electrochemical Behaviors Among 5083/6082 Friction Stir Welding Dissimilar Weld and Parent Materials

At the ambient temperature, in the 0.2 M NaHSO3 and 0.6 M NaCl solution, by gravimetric test, potentiodynamic polarization curve test and electrochemical impedance spectra (EIS), the electrochemical behavior of 5083/6082 friction stir welding dissimilar weld and two parent materials were comparatively investigated. The results indicated: at the given processing parameters, the anti-corrosion ability of the dissimilar weld was superior to those of the 6082 and 5083 parent materials.