Passive Potential Range Research Articles

Experimental investigation of comprehensive performance by tailoring the proportion of late transition metals in quinary Fe-Co-Ni-Si-B amorphous alloys

We fabricated the Fe-Co-Ni-Si-B multi-principal element alloys by vacuum melt-spinning method. The effects of late transition metals proportion in quinary alloy ribbons on the formation, phase structure, thermal stability, microhardness, corrosion resistance and soft magnetic properties were investigated. The melt-spun structure consists of an amorphous single phase for all the specimens. The surfaces of glassy ribbons are rather flat and flawless and the average surface roughness is 0.351 nm or below. The initial crystallization temperature (Tx) and supercooled liquid region (ΔTx) of alloy system decrease by degrees with increasing Co and Ni content, showing the maximum values of 753.0 K and 60.0 K for Fe60Co10Ni10Si6B14 alloy. But the glass transition temperature (Tg) seems to barely change and maintain approximately 692.0 K. All the as-received alloy ribbons exhibit good bending ductility and acceptable Vickers microhardness ranging from 671 to 785 HV0.5. The amorphous alloy ribbons present a gradually wide passive potential range (ΔE) with the decrease of Fe content, but the corrosion current density (Icorr) becomes larger. The smallest Icorr value is 1.785 μA·cm-2 for Fe60Co10Ni10Si6B14 alloy and the widest ΔE value is about 0.272 V for Fe26Co27Ni27Si6B14 alloy. The saturation magnetization of these glassy alloys reduces from 165.0 to 112.0 emu/g as the Fe content decreases. Meanwhile, the coercivity also changes from 14.25 to 6.70 A/m. This paper offers a brand-new perspective to understand the role of late transition metals on the various physicochemical properties of quinary Fe-Co-Ni-Si-B amorphous alloys.

An experimental study and Monte Carlo simulation about the polyaniline coating dopants impact on long-time corrosion resistance of 304 SS

Here, the polyaniline (PANI) films doped with CH3COO–, HSO4-, NO3–, H2PO4-, and NaSO4- were formed by anodic electrodeposition on the 304 SS surface to improve the durability of the protective passive film and reducing the penetration rate of corrosive species. To provide the best dopant for corrosion protection of 304 SS in a NaCl medium, various experimental and theoretical evaluations have been carried out. The most durable PANI coating in the 3.5 wt.% NaCl solution was the PANI/CH3COOH, with a 102–fold increase in its charge transfer resistance after 20 days of immersion (Rct = 5.6 × 105 kΩ.cm2). The salt spray results confirmed preventing the formation of corrosion pits/products after 20 days when doped-PANI covered the 304 SS surface. Potentiometric analysis shows that PANI/CH3COOH, in the presence of chloride ions, brings the potential of 304 SS into the passivation potential range (potential shift from −100 mV to + 200 mV). PANI/CH3COOH also had the strongest surface adsorption with an energy of ∼−19 kcal/mol. The increase in corrosion resistance of the PANI/CH3COOH sample is due to the strengthening of the oxide layer at the interface between the coating and the substrate and to the corrosion barrier effect of the PANI film.

Superior corrosion resistance of high-temperature Ir–Ni–Ta–(B) amorphous alloy in sulfuric acid solution

In this work, the corrosion behaviors and underlying mechanisms of high-temperature Ir-based amorphous alloys in an acidic solution were investigated systematically. The Ir-Ni-Ta-B amorphous alloy exhibits a crevice corrosion behavior with a superior corrosion resistance characterized by a low passive current density and a wide passive potential range. It is found that the high-exchange current density of H+ and H2 couple on the metalloid constituent can accelerate the active precipitation of passivation elements, leading to rapid formation of passive film. In sulfuric acid solutions, the formed passive film containing Ir, Ta5+ and Ni3+ oxides significantly increase the corrosion resistance.

Tribocorrosion Resistance of Dental Implant Alloys—Assessment of cp-Ti, Ti6Al4V, and NiCr in Neutral and Acidified Saliva

Saliva is a potentially aggressive environment due to the presence of acids, chloride, and pH variation, thus the dental implant system can be subjected to corrosion in this medium. Due to masticatory loads during chewing, the joint of implant rehabilitation is subjected to relative micromovements among components leading to a microgap formation and wear. Furthermore, dissimilar alloys in contact at joint interface of dental implant system can potentially drive to electrochemical galvanic couple occurrence. Torque relaxation can be enhanced by corrosion caused by the infiltration of saliva in the microgap. This study aimed to evaluate the influence of saliva and its pH variations on corrosion and tribocorrosion of alloys employed in dental implant system. NiCr, cp-Ti, and Ti6Al4V alloys were evaluated through electrochemical tests in artificial saliva at pH 3.0 and 6.0. The possible occurrence of the galvanic couple for a 3:1 area ratio and their effects were also verified by electrochemical measurements. SEM and confocal microscopy were used for the analysis of worn surfaces. Corrosion polarization tests did not indicate the potential occurrence of galvanic corrosion in saliva. NiCr was more susceptible to localized corrosion and more resistant to tribocorrosion in acidified and neutral artificial saliva than titanium-based alloys. Coupled alloys did not present differences in tribocorrosion performance when compared to each isolate alloy in neutral saliva, pH 6.0. For pH 3.0, Ti6Al4V remained on a passive potential range during sliding when coupled to NiCr, while the other materials were not affected by the galvanic couple condition.

Comparative EIS study of titanium-based materials in high corrosive environments

Electrochemical impedance spectroscopy (EIS) is a technique relatively complex and modern that owes its existence to the emergence of electronic circuits. In this work, the behaviour in HCl 20% of three materials, Ti, Ti-15 Mo and Ti-15Mo-5Al fabricated by laser beam melting, was analysed using EIS. Impedance spectra have been obtained at various potentials, from open circuit potential to +2.0 V vs. Ref. Once the profiles of the impedance spectra were analysed, the experimental data were adjusted to an equivalent electrical model. Two models of equivalent circuits were presented: at Ecorr simple circuit is used while in the passive potential range an equivalent circuit with 2-time constants was used for fit the experimental data. It was concluded that titanium and studied titanium alloys undergo spontaneous passivation due to the oxide film formed on their surface in the reducing acid solution.

Comparative EIS study of titanium-based materials in high corrosive environments

Electrochemical impedance spectroscopy (EIS) is a technique relatively complex and modern that owes its existence to the emergence of electronic circuits. In this work, the behaviour in HCl 20% of three materials, Ti, Ti-15 Mo and Ti-15Mo-5Al fabricated by laser beam melting, was analysed using EIS. Impedance spectra have been obtained at various potentials, from open circuit potential to +2.0 V vs. Ref. Once the profiles of the impedance spectra were analysed, the experimental data were adjusted to an equivalent electrical model. Two models of equivalent circuits were presented: at Ecorr simple circuit is used while in the passive potential range an equivalent circuit with 2-time constants was used for fit the experimental data. It was concluded that titanium and studied titanium alloys undergo spontaneous passivation due to the oxide film formed on their surface in the reducing acid solution.

Passive Film Properties of Bimodal Grain Size AA7075 Aluminium Alloy Prepared by Spark Plasma Sintering.

The bimodal-grain-size 7075 aluminium alloys containing varied ratios of large and small 7075 aluminium powders were prepared by spark plasma sintering (SPS). The large powder was 100 ± 15 μm in diameter and the small one was 10 ± 5 μm in diameter. The 7075 aluminium alloys was completely densified under the 500 °C sintering temperature and 60 MPa pressure. The large powders constituted coarse grain zone, and the small powders constituted fine grain zone in sintered 7075 aluminium alloys. The microstructural and microchemical difference between the large and small powders was remained in coarse and fine grain zones in bulk alloys after SPS sintering, which allowed for us to investigate the effects of microstructure and microchemistry on passive properties of oxide film formed on sintered alloys. The average diameter of intermetallic phases was 201.3 nm in coarse grain zone, while its vale was 79.8 nm in fine grain zone. The alloying element content in intermetallic phases in coarse grain zone was 33% to 48% higher than that on fine grain zone. The alloying element depletion zone surrounding intermetallic phases in coarse grain zone showed a bigger width and a more severe element depletion. The coarse grain zone in alloys showed a bigger electrochemical heterogeneity as compared to fine grain zone. The passive film formed on coarse grain zone had a thicker thickness and a point defect density of 2.4 × 1024 m−3, and the film on fine grain zone had a thinner thickness and a point defect density of 4.0 × 1023 m−3. The film resistance was 3.25 × 105 Ωcm2 on coarse grain zone, while it was 6.46 × 105 Ωcm2 on fine grain zone. The passive potential range of sintered alloys increased from 457 mV to 678 mV, while the corrosion current density decreased from 8.59 × 10−7 A/cm2 to 6.78 × 10−7 A/cm2 as fine grain zone increasing from 0% to 100%, which implied that the corrosion resistance of alloys increased with the increasing content of fine grains. The passive film on coarse grain zone exhibited bigger corrosion cavities after pitting initiation compared to that on fine grain zone. The passive film formed on fine grain zone showed a better corrosion resistance. The protectiveness of passive film was mainly determined by defect density rather than the thickness in this work.

Impact of rare earth compounds on corrosion of aluminum alloy (AA6061) in the marine water environment

The impact of rare earth compounds (CeCl3 and Ce2(SO4)3) on the corrosion inhibition of aluminum alloy (AA6061) in 3.5% NaCl solution was elucidated using polarization, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) and complemented with EDX and SEM examination. The addition of either CeCl3 or Ce2(SO4)3 to the blank chloride solution, decreases the corrosion current and causes a widening of the passive potential range between corrosion potential (Ecorr) and pitting potential (Epit). The data confirmed that CeCl3 and Ce2(SO4)3 act as corrosion inhibitors. It was found that the inhibition performance of Ce2(SO4)3 are higher than that of CeCl3. In the presence of Ce2(SO4)3 and CeCl3, the AA6061 surface is well protected, in which the surface of AA6061 was smoother and the corroded areas obviously diminished. The results suggest that the existence of Ce2O3/Ce(OH)3 conversion coat on the electrode surface enhances the charge and mass barrier leading to the reduction in corrosion rates of the AA6061 alloy.

Effect of cold rolling on the microstructural, magnetic, mechanical, and corrosion properties of AISI 316L austenitic stainless steel

This study has evaluated the effect of different levels of cold rolling (from 0 to 50%) on the microstructural, magnetic, and mechanical properties and the corrosion behavior of 316L austenitic stainless steel in NaCl (1 mol/L) + H2SO4 (0.5 mol/L) solution. Microstructural examinations using optical microscopy revealed the development of a morphological texture from coaxial to elongated grains during the cold-rolling process. Phase analysis carried out on the basis of X-ray diffraction confirmed the formation of the ferromagnetic α′-martensite phase under the stresses applied during cold rolling. This finding is in agreement with magnetic measurements using a vibrating sample magnetometer. Mechanical properties determined by tensile and Vickers microhardness tests demonstrated an upward trend in the hardness-to-yield strength ratio with increasing cold-rolling percentage, representing a reduction in the material’s work-hardening ability. Uniform and localized corrosion parameters were estimated via potentiodynamic polarization corrosion tests and electrochemical impedance spectroscopy. In contrast to the uniform corrosion, wherein the corrosion current density increased with increasing cold-working degree because of the high density of microstructural defects, the passive potential range and breakdown potential increased by cold working, showing greater resistance to pit nucleation. Although pits were formed, the cold-rolled material repassivation tendency decreased because of the broader hysteresis anodic loop, as confirmed experimentally by observation of the microscopic features after electrochemical cyclic polarization evaluations.

Effect of heat treatment conditions on the passivation behavior of WE43C Mg–Y–Nd alloy in chloride containing alkaline environments

Mg–Y–Nd alloy (WE43C or Elektron 43) is a heat treatable magnesium wrought alloy that can be used up to 250 °C for aerospace application. This alloy has excellent mechanical properties (UTS: up to 345 MPa at room temperature) and improved corrosion resistance. Electrochemical passivation studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of chloride from 0 to 1000 ppm. The passive potential range typically extended to more than 1.5 VAg/AgCl. The transpassive potential was not dependent on the heat treatment condition of the alloy when the chloride concentration increased up to 500 ppm. However, pitting protection potential varied with the heat treatment condition when the chloride addition was 500 ppm or more. The specimen surface was analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy to understand the passivation behavior of this alloy. The passivated surface of the WE43C specimens indicated that the surface layer consisted of MgO, Mg(OH)2, and rare earth oxide phases, and the heat treatment conditions did not significantly affect the composition of the surface film.

Electrodeposition of nickel-based composite coatings from a sulfamate electrolyte

Nickel-based composite coatings modified with carbon nanotubes were electrodeposited from a sulfamate electrolyte. The functional properties (friction coefficient, protective power) of these coatings were compared to those of electrodeposited nickel coatings without dispersed phase. Incorporation of carbon nanotubes into nickel coatings leads to a 1.40–1.45-fold decrease in the sliding friction coefficient and to a 1.35–1.40-fold increase in the width of the passive potential range.

Threshold Chloride Concentration for Passivity Breakdown of Mg–Zn–Gd–Nd–Zr Alloy (EV31A) in Basic Solution

Mg–Zn–Gd–Nd–Zr alloy (EV31A) is a heat-treatable magnesium (Mg) cast alloy that can be used up to 200 °C for automobile and aerospace applications. This alloy has excellent mechanical properties (ultimate tensile strength: 280 MPa at room temperature, and ~230 MPa at 200 °C) and improved corrosion resistance. Electrochemical corrosion studies were conducted on this alloy under different heat treatment conditions in 0.1 M NaOH solution with the addition of 0–1000 ppm of chloride. The alloy showed excellent passivity in the 0.1 M NaOH solution. The passive potential range typically extended to more than 1.2 VAg/AgCl. The transpassive potential was observed to be dependent on heat treatment condition of the alloy. More than 80 ppm of chloride was required to induce passivity breakdown in any heat treatment condition. Peak aging at 200 °C for 16 h imparted better resistance for localized corrosion than other heat-treated conditions. The alloy in the as-received condition showed the highest passivation kinetics due to its smaller grain size that possibly increased the diffusion of reactive elements to form protective oxide. The passive film of the EV31A alloy showed n-type semiconductivity with a charge carrier density of ~2 × 1021 cm−3 with no chloride addition. The charge carrier density increased with chloride addition in the electrolyte which could be correlated with the susceptibility to localized corrosion.

Comparison of Corrosion Resistance for 304 and 316 Stainless Steel in the Simulated Primary Circuit of PWR

Corrosion resistance of 304 SS after Al3+ addition process was investigated and compared with that of 316 SS by weight loss, corrosion rate and potentiodynamic polarization analysis. Al3+ addition process in high temperature water can reduce the oxidation of 304 SS, slow down the corrosion rate and enlarge the passive potential range. The corrosion resistance of 304 SS after Al3+ expansion process is better than that of 316 SS. This may give a new way for corrosion protection and lower the structural material cost for many nuclear power station.

Effect of Continuous Annealing Temperature on Microstructure and Properties of Ultra-Purified Ferritic Stainless Steel

Effect of continuous annealing temperature on mechanical properties, formability, work hardening rate, texture, and corrosion resistance of ultra-purified ferritic stainless steel is analyzed by means of tensile test, electron back scattering diffraction, and electrochemical tests. The results show that with the increase of continuous annealing temperature during 850–940 °C, tensile strength and yield strength of the tested steel reduce and then rise slightly and decrease at last. Elongation increases sharply with the rise of continuous annealing temperature and then kept approximately constant. At 910 °C, the best formability and comprehensive performance are obtained, and the strength and elongation achieve best comprehensive performance. The grains near the {111} orientation grow up selectively. The higher continuous annealing temperature, the more obvious the tendency of growing and thus the more the γ fiber texture content. The low energy and low ∑ CSL grain boundaries composed of textures are the reasons why the corrosion resistance of specimen presents the changing trend similar to texture orientation. With the increases of continuous annealing temperature, the passive potential range and the stability of the surface film first increase and then decrease, while the pitting corrosion potential first decrease slightly and then increase sharply.

Inhibition Mechanism of Phosphate Ions on Chloride-Induced Crevice Corrosion of Alloy 22

Alloy 22, a nickel-based alloy that belongs to the Ni-Cr-Mo family, shows an outstanding corrosion resistance in most environments. Alloy 22 was extensively studied regarding its crevice corrosion behavior both in pure chloride solutions and in solutions containing other ions such as nitrate, sulfate, and carbonate/bicarbonate. Electrochemical tests were performed to study uniform and localized corrosion of Alloy 22 in a deaerated aqueous solution of 1 M NaCl and 1 M NaCl with different amounts of phosphate additions at 90°C and at pH near neutral. Results show that the addition of phosphate to the solution increased the length of the passive potential range. Moreover, results from two type of electrochemical tests showed that the addition of 0.3 M phosphate and higher completely eliminated the susceptibility of Alloy 22 to crevice corrosion. The excellent inhibitive effect of phosphate is comparable to that of nitrate already reported in the literature. Elemental analysis of the corroded area suggests th...

The electrochemical behaviour of 316L austenitic stainless steel in Cl− containing environment under different H2S partial pressures

In oil–gas production environments, presence of H2S–Cl− can induce deterioration of the passive film, leading to pitting corrosion of stainless steels. In this paper, by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and capacitance measurements (Mott–Schottky analysis), the electrochemical behaviour of AISI 316L austenitic stainless steel was investigated in Cl− solutions under different H2S partial pressures (from 0 to 1.0bar). The results indicated that presence of H2S in Cl− solution can accelerate both the cathodic and anodic current density, leading to a metastable passive state in higher passive potential range, changing the semiconductor behaviour from p-type to n-type, increasing its susceptibility to corrosion. XPS analysis was employed to characterize the surface film after potentiostatic polarization, whose results provide good evidences for the electrochemical measurements.

Effect of FeCO3 Supersaturation and Carbide Exposure on the CO2 Corrosion Rate of Carbon Steel

The effect on corrosion of carbon steel of varying bicarbonate (HCO3−) and ferrous ion (Fe2+) concentrations in carbon dioxide (CO2) purged in 1 wt% sodium chloride (NaCl) and 50 wt% monoethylene glycol (MEG, C2H6O2) solutions was studied. The iron carbide (Fe3C) in the steel was exposed by pre-corrosion to explore its role in the iron carbonate (FeCO3) film formation process at pH-stabilized conditions. The corrosion layers formed ranged from being protective and showing passive behavior (corrosion potential approximately −0.5 V vs. silver/silver chloride [Ag/AgCl]) to being non-protective despite highly supersaturated solutions and long exposure times. The corrosion rate and potential development are discussed based on thermodynamic, kinetic, and electrochemical principles. The corrosion potential increased sharply after a protective FeCO3 film was established, indicating passivation. New reaction mechanisms are proposed at these high potentials, which are more anodic than that obtainable by H+ reduction. Dissolved Fe3C and magnetite (Fe3O4) are important factors in this passive potential range.

Surface working of 304L stainless steel: Impact on microstructure, electrochemical behavior and SCC resistance

Abstract The effect of surface working operations on the microstructure, electrochemical behavior and stress corrosion cracking resistance of 304L stainless steel (SS) was investigated in this study. The material was subjected to (a) solution annealing (b) machining and (c) grinding operations. Microstructural characterization was done using stereo microscopy and electron back scattered diffraction (EBSD) technique. The electrochemical nature of the surfaces in machined, ground and solution annealed condition were studied using potentiodynamic polarization and scanning electrochemical microscopy (SECM) in borate buffer solution. The stress corrosion cracking resistance of 304L SS in different conditions was studied by exposing the samples to boiling MgCl2 environment. Results revealed that the heavy plastic deformation and residual stresses present near the surface due to machining and grinding operations make 304L SS electrochemically more active and susceptible to stress corrosion cracking. Ground sample showed highest magnitude of current density in the passive potential range followed by machined and solution annealed 304L SS. Micro-electrochemical studies established that surface working promotes localized corrosion along the surface asperities which could lead to crack initiation.

Effect of Titanium on the Precipitating Behavior of Inclusions and Corrosion Resistance of Niobium Stabilized 409 Ferrite Stainless Steel

In order to investigate the effect of titanium addition on the precipitating behavior of inclusions and corrosion resistance of niobium stabilized ferrite stainless steel, experiments were conducted in a high frequency vacuum induction furnace for smelting titanium and niobium stabilized ferrite stainless steel in argon atmosphere, and the composition, morphologies and size of inclusions in the samples were investigated. Precipitating behavior of the inclusions and intergranular corrosion resistance of the samples were analyzed by CSLM. Corrosion resistance of the steel in 2% NaHSO3 solution was tested by using electrochemistry comprehensive test instrument. The results show that inclusions in the as cast steel mainly are rectangle TiN, TiC, NbC and complex inclusions with TiN or TiC as core packed by NbC, and their size is about 1~5μm. There are a few nearly spherical complex inclusions with Al-Mg-Si-Ti-O as core packed by TiN, TiC, NbC or their complex inclusions. The spherical inclusions become rectangle with the increase of titanium addition, and the quantities of inclusions which size is larger than 5 μm increase. Precipitates increase during heat treated and grain size of the steel becomes a little smaller with the increase of titanium content in the steel. The grain boundary of the steel becomes stabilization and intergranular corrosion resistance enhances with the increase of titanium content in the steel according to the online analysis results. Passivation current density of the steel becomes smaller and passive potential range becomes wider in 2% NaHSO3 solution at 30°C with the increase of titanium content in the steel which indicates corrosion resistance of the steel being enhanced.

Aging and Electrochemical Behaviour of 7017 Al-Zn-Mg Alloy of Various Tempers

Artificial aging behaviour of a 7017 Al-Zn-Mg alloy was studied by hardness measurement. The electrochemical behaviour of various alloy tempers, such as under-, peak-, and over-aged, have been evaluated by measuring variation of open circuit potential (OCP) with time and potentiodynamic polarization study in different environments. All the alloy tempers were tested in 3.5 wt. % NaCl solution at neutral (pH 7), at acidic (pH 1) and at alkaline (pH 12) conditions. It has been observed that the OCP values of the alloy tempers shifted toward noble direction with the increase of aging time in 3.5 wt. % NaCl solution. The polarization curves are more or less similar in shape exhibiting only active region in neutral (pH 7) and in acidic (pH 1) conditions, but an active-passive region at alkaline (pH 12) condition. The electrochemical parameters; Ecorr, Icorr, passive potential range (Ep) and passive current (ip), obtained from potentiodyanamic polarization curves for the alloy tempers in acid, neutral and alkaline solution; depend on the alloy tempers and the pH of the solution as well. Attempts have been made to explain the observed electrochemical behaviour of the alloy tempers, which is influenced by the microstructure, presence and distribution of second phase precipitates, accessed by DSC and XRD techniques.