Pitting Corrosion Potential Research Articles

On the behavior of nitrogen in a low-Ni high-Mn super duplex stainless steel

The present work describes an investigation on a new series of low-Ni high-Mn super duplex stainless steels (DSSs) 25Cr–2Ni–3Mo–10Mn–xN with nitrogen concentrations varying in the range between 0.37 and 0.50wt.%. It was observed that these alloys have a ferrite–austenite structure. Under the same heat-treatment conditions, the austenite shows a marked upward tendency with an increase in N content. Nitrogen delays the precipitation of σ phase. The increase in nitrogen enhances the yield strength (YS), ultimate tensile strength (UTS) and ductility as well as the pitting corrosion potential of the materials. The pitting corrosion occurs in the austenite phases in the case of low N content (0.37wt.%), but in the case of high N content (0.50wt.%) it happens in the ferrite phases.

In vitro study on Zr‐based bulk metallic glasses as potential biomaterials

With pure Ti and pure Zr as controls, the corrosion resistance, ion release behavior, and in vitro biocompatibility of Be-containing Zr₄₁Ti₁₄Cu₁₂Ni₁₀Be₂₃ bulk metallic glass (BMG) (LM1), Zr₄₄Ti₁₁Cu₁₀Ni₁₀Be₂₅ BMG (LM1b), and Be-free Zr₅₇Nb₅Cu₁₅.₄Ni₁₂.₆Al₁₀ BMG (LM106) were investigated in terms of electrochemical measurements in simulated body fluid (SBF) with pH value 7.4 and artificial saliva (AS) with pH value 6.3, and 3-[4,4-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay using L929 and NIH3T3 cells, aiming to assess the feasibility of Zr-based BMGs as potential biomaterial. It was found that LM1b showed superior corrosion resistance to LM106 and LM1 in both SBF and AS, and comparable with pure Ti and pure Zr. After 7200 s immersion, a two-layer structure oxide film was formed on LM1, LM1b, and pure Zr surfaces, while one-layer structure oxide film was formed on LM106 and pure Ti surfaces. The pitting corrosion potentials of LM1b were much higher than that of LM1, LM106, and pure Zr, resulting in very few ions releasing into the electrolytes. No Be ion could be detected but a little amount of Cu ion was detected for LM106, LM1, and LM1b after immersion in Dulbecco's modified Eagle's medium for 72 h at 37 °C. The indirect cytotoxicity results show that LM106, LM1, and LM1b extracts had no cytotoxicity to L929 and NIH3T3 cells. The direct cytotoxicity results show that cells could adhere well on the Zr-based BMG surface as in pure Ti and Zr. Lower cell proliferation rate of LM106 and LM1 is observed when compared with LM1b, which was found to be caused by Cu ion releasing rather than by Be ion.

Intergranular and Pitting Corrosion Susceptibilities of a Supermartensitic Stainless Steel Weldment

Abstract Degree of sensitization and pitting corrosion potential of a supermartensitic stainless steel weldment were measured and compared. An improvement in the degree of sensitization and in the ...

Corrosion behaviour of magnetron-sputtered Al 1−x–Mn x coatings in neutral saline solution

Al–Mn coatings with different contents (0–41 at.%) were deposited on glass slides by magnetron co-sputtering. These coatings were characterised, before and after immersion tests, by X-ray diffraction, scanning electron microscopy (SEM) and electron probe microanalysis. The electrochemical measurements in a neutral saline solution showed that the pitting corrosion resistance of Al–Mn coatings increased with increasing Mn content as the pitting corrosion potentials are progressively shifted towards positive values. The immersion tests reveal that for all Mn contents, Al–Mn coatings keep a sacrificial character compared with steel. For Mn content above 26 at.%, XRD analysis showed the formation of an amorphous phase. This structure would be responsible for the high increase of the hardness of Al–Mn coatings and of the stabilisation of their open circuit potentials during the 48 h immersion tests.

Study of Fe3Al Corrosion Behavior in Simulating Marine Biofilm Environment

Calcium Alginate is a kind of natural biopolymer which can be deposited on metal surfaces to form film. In this work, microbe film was simulated by Calcium Alginate gel, according to the natural structure and property of microbe film. Acetic acid, manganese dioxide, and sodium sulfide were added separately in sodium chloride solution to simulate different bacteria culture systems. The corrosion behavior of Fe3Al was investigated in simulating biofilm environment by open circle potential, polarization curves, and electrochemical impedance. Electrochemical results show that the passivating film formed immediately when Fe3Al electrodes exposed in simulated seawater. The corrosion process of Fe3Al in the medium with manganic sediment was mainly dominated by oxygen diffusion. In the simulated environment with acetic acid, the pitting corrosion potential on the surface of Fe3Al moved towards negative accompanied with the increasing concentration of chlorine ion and the decreasing value of pH. Simulated sulphate reduce bacteria (SRB) accelerated cathodic polarization process of Fe3Al surface, corrosion potential dropped sharply and the surface oxidative membrane broken when polarization potential reached −0.5 V, indicating that Fe3Al can be easier corroded by SRB than by other bacteria.

Electrochemical behaviour of Ti–Ni SMA and Co–Cr alloys in dynamic Tyrode’s simulated body fluid

The electrochemical behaviour of Ti-Ni shape memory alloy and Co-Cr alloys were investigated in dynamic Tyrode's simulated body fluid on a Model CP6 Potentiostat/Galvanostat. The results indicated that, for all alloys, the anodic dissolution and the pitting sensitivity increased with the flow rate of the Tyrode's solution increasing while the open-circuit potentials and pitting corrosion potentials decreased with the Tyrode's solution increasing. Pitting corrosion of Ti-Ni alloy was easier than Co-Cr alloys. Since the solution's flow enhanced oxygen transform and made it easy to reach the surface of electrodes, the plateau of oxygen diffusion control was diminished. All these indicated that the cathodic reduction and the corrosion reaction, which was controlled by the electrochemical mass transport process, were all accelerated in dynamic Tyrode's simulated body fluid.

In vitro corrosion and cytotoxicity on microcrystalline, nanocrystalline and amorphous NiTi alloy fabricated by high pressure torsion

Bulk nanocrystalline and amorphous Ni50.2Ti49.8 alloy samples were successfully prepared from commercial microcrystalline Ni50.2Ti49.8 alloy discs by high pressure torsion (HPT) technique. Then their corrosion resistance, surface wettability and cytotoxicity were further studied from the viewpoint of biomaterials. In both Hank's solution and artificial saliva, bulk nanocrystalline and amorphous Ni50.2Ti49.8 alloys showed significantly higher pitting corrosion potentials than that of microcrystalline Ni50.2Ti49.8 alloy. Meanwhile, the amount of Ni ion release after immersion in Hank's solution was minor, far below the threatening threshold of daily diet. Murine fibroblast and osteoblast cell lines were indirectly co-cultured with experimental sample extracts, indicating no cytotoxicity. Amongst all samples, the nanocrystalline Ni50.2Ti49.8 shows promising as best biomaterial candidate for its good combination of mechanical property, corrosion resistance and cytocompatibility.

Ａｌ‐Ｃｕ合金の耐孔食性に及ぼす強歪み加工ＥＣＡＰ処理の影響

Effects of equal-channel angular pressing (ECAP) on the pitting corrosion resistance of Al-Cu (AA2024) alloy with and without anodization were investigated using surface analysis and polarization curves in solutions containing 300 ppm or 0.6 mol·dm−3 of Cl−. The pitting corrosion potential and corrosion rate of Al-Cu alloy revealed no effect of ECAP on the pitting corrosion resistance of Al-Cu. The Al-Cu alloy contained such precipitates as Al2Cu, Al2CuMn and Al-Cu-Si-Fe-Mn intermetallic compounds, around which pitting corrosion occurred. Actually, ECAP pulverized these precipitates to decrease their size, but it had no effect on the pitting corrosion resistance of Al-Cu alloy because pitting corrosion occurred even around small precipitates of Al2Cu. In contrast, the time to initiate pitting corrosion of Al-Cu alloy while maintaining a constant potential of 1.2 V was longer with ECAP than without, indicating that ECAP improved the pitting corrosion resistance. Although the precipitates of Al2Cu and Al2CuMn disappeared because of oxidation during anodization, Al-Cu-Si-Fe-Mn intermetallic compounds were present and formed defects in anodic oxide films. Pitting corrosion of the anodized Al-Cu alloy occurred around the Al-Cu-Si-Fe-Mn precipitates. The improved pitting corrosion resistance of anodized Al-Cu alloy by ECAP appears to be attributable to the decreased size of the precipitates that initiate pitting corrosion.

Corrosion performances of a Nickel-free Fe-based bulk metallic glass in simulated body fluids

The corrosion performance of a Nickel-free Fe-based bulk metallic glass (BMG), Fe 41Co 7Cr 15Mo 14C 15B 6Y 2 alloy, in Hank’s solution with pH value 7.4 and artificial saliva solution with pH value 6.3, was investigated by electrochemical techniques, aiming to assess the feasibility of Fe-based BMG as potential biomaterial. It was found that Fe 41Co 7Cr 15Mo 14C 15B 6Y 2 BMG shows superior corrosion resistance in both simulated body fluids (SBF). The EIS analysis and cyclic polarization measurements indicated that the Fe 41Co 7Cr 15Mo 14C 15B 6Y 2 BMG has larger polarization resistance value than that of 316L SS. The pitting corrosion potentials of Fe 41Co 7Cr 15Mo 14C 15B 6Y 2 BMG are much higher than that of the 316L SS, resulting in very few ions releasing into the SBFs while a significant amount of Ni and Fe ions release was found for 316L SS under the same condition.

Influences of Aging Precipitation on Corrosion Resistance of 18Cr-18Mn-2Mo-0.77N HNS

Influences of aging precipitation of Cr2N and Chi (χ) phases on the resistance to pitting corrosion and intergranular corrosion of 18Cr-18Mn-2Mo-0.77N high nitrogen steel (HNS) as a type of fundamental and structural materials were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern and electrochemical methods. Intergranular, cellular Cr2N and χ phases precipitate gradually along grain boundaries and inward grains. The volume fraction of precipitation presents a C-curve with a nose temperature of 850°C during 2h aging treatment. The solution-treated (ST) HNS exhibits the highest pitting corrosion potential because of high nitrogen content in steel, and especially no precipitation. The pitting corrosion resistance of aged HNS decreases because of the formation of aging precipitation which results in the depletion of Cr and Mo in the matrix. The pitting corrosion potentials firstly decrease then increase as the same tendency as the amount of precipitation expect 850°C and 900°C. Double loop electrochemical potentiokinetic reaction (DL-EPR) results show that the change tendency of IGC susceptibility is well consistent with the amount of precipitation of aged HNS for 2h at various temperatures. With prolonging the aging time at 850°C, aged HNS presents more obviously intergranular sensitization due to the formation of aging precipitation which results in the depletion of Cr and Mo.

Electrochemical and acoustic emission studies of aluminum pitting corrosion

The potentiodynamic and acoustic emission studies were carried out in a typical three-electrode electrochemical cell. The working electrode was prepared from aluminum alloy 1050A. Cyclic polarization and acoustic emission investigations of pitting corrosion were carried out simultaneously. On the basis of acoustic and potentiodynamic (cyclic polarization) investigations pitting corrosion potential was determined and compared.

Inhibition of Pitting Corrosion of Aluminum Bronze in Sodium Chloride Solution

Abstract The pitting corrosion of aluminum bronze (Cu-6%Al) has been investigated in sodium chloride (NaCl) solution of different concentrations. Potentiodynamic anodic polarization and galvanic current-time measurements were carried out. The pitting corrosion potential, Epit, shifts to more negative values and the induction period for initiation of pitting corrosion becomes shorter with the increase of NaCl concentrations. The effect of increasing additions of different organic compounds on the pitting corrosion of the alloy in 0.5 M NaCl solutions was studied. It was found that the presence of these organic compounds in increasing concentrations shifts the Epit to more positive values and the induction period becomes shorter. The inhibitory effect of the organic compounds greatly depends on the molecular structure and size of the compound, the number of adsorption centers, and the electron density on these adsorption centers. The sulfur-containing organic compounds has the highest inhibitory effect.

Effect of conducting composite polypyrrole/polyaniline coatings on the corrosion resistance of type 304 stainless steel for bipolar plates of proton-exchange membrane fuel cells

A bilayer conducting polymer coating composed of an inner layer of polypyrrole (Ppy) with large dodecylsulfate ionic groups obtained by galvanostatic deposition, and an external polyaniline (Pani) layer with small SO 4 2− groups obtained by cyclic voltammetric deposition was prepared to protect type 304 stainless steel used for bipolar plates of a proton-exchange membrane fuel cell. The corrosion performance of the bare and coated steel in 0.3 M HCl was examined by electrochemical impedance spectroscopy, polarization and open-circuit potential measurements. The experimental results indicated that both the composite Ppy/Pani coatings and the single Ppy coatings increased the corrosion potential of the bare steel by more than 400 mV (saturated calomel electrode), and increased the pitting corrosion potential by more than 500 mV (saturated calomel electrode). The bilayer coatings could reduce the corrosion of the alloy much more effectively than the single Ppy coatings, serving as a physical barrier and providing passivity protection, with acceptable contact resistance.

The electrochemical behavior and surface analysis of Ti 50Ni 47.2Co 2.8 alloy for orthodontic use

Objectives The aim of this study was to investigate the electrochemical behavior of Ti 50Ni 47.2Co 2.8 alloy in deaerated artificial saliva solutions with binary NiTi alloy as reference and to characterize the composition and structure of the passive film after polarization tests. Methods The corrosion behavior of NiTiCo alloy was systematically studied by open circuit potential, potentiodynamic and potentiostatic techniques. The surface characterization after anodic polarization tests were demonstrated by XPS. The electrolytes were maintained at 37 °C by immersing the test cell in water bath. 500 mV vs. SCE was applied on the samples for potentiostatic tests. The metal ions concentration was measured by ICP/OES. Results Potentiodynamic and potentiostatic tests results showed that the corrosion behavior of NiTiCo was similar to that of NiTi alloy. With the increase of pH value of the electrolytes, both corrosion potential ( E corr) and pitting corrosion potential ( E b) decreased. XPS results revealed that the outmost passive film consisted mainly of TiO 2 which were identical with that of NiTi alloy. The Ni ion release amount of NiTiCo was very close to that of NiTi alloy as examined by ICP/OES. Neither Ti nor Co ion was detected due to the detection limitation. Significance The corresponding relationship between corrosion behavior and pH value of the artificial saliva should be taken into consideration during the application of orthodontic wires. The addition of Co had little effect on the corrosion behavior of NiTi as well as the formation of the passive film.

Mechanical and corrosion properties of dc magnetron sputtered Al/Cr multilayers

Mechanical and corrosion properties of Al/Cr multilayer coatings deposited by dc magnetron sputtering are investigated and compared to pure Al and Cr coatings. The objective of this study is to increase the mechanical properties of sacrificial Al-based coatings. The results indicate that mechanical and corrosion properties depend on the architecture organisation. The reduction of the layer thickness allows an increase of the coating hardness. The nanolayer architecture leads to a “hard and tough” material compared to the other architectures. Moreover, the intrinsic corrosion resistance is enhanced, as the corrosion and the pitting corrosion potentials are progressively shifted towards positive values. The nanolayer coating presents the highest intrinsic corrosion resistance but multilayer and nanolayer Al/Cr coatings become nobler than the steel substrate. The corrosion resistance of the coated steel is then strongly dependent on the microscopic coating defects which act as preferential pathways for the corrosive solution. So the nanolayer architecture organisation improves the mechanical properties but does not permit to conserve the sacrificial behaviour of the aluminium based coating, which is harmful for the corrosion protection of coated steel.

Extremely high pitting resistance of NiTi shape memory alloy thin film in simulated body fluids

In this paper the corrosion behavior of NiTi thin films fabricated by sputtering from Ni and Ti targets has been studied by cyclic potentiodynamic polarization tests in Hank's and Ringer's solution at 310 K. For comparison, bulk NiTi Shape Memory Alloy (SMA) has also been studied to elucidate the different corrosion behavior of bulk and thin film material. The electrochemical experiments reveal that thin film NiTi SMA has comparable corrosion current density ( i corr), much higher pitting corrosion potentials and wider passive range than the bulk NiTi. We show that NiTi SMA vapour deposited thin films are less susceptible to pitting corrosion than the bulk.

Preparation and Electrochemical Properties of Trivalent Chromium Coating on 6063 Aluminium Alloy

Chromium (Cr3+) conversion coating was prepared on 6063 aluminium alloy using chromic potassium sulfate and phosphoric acid. Tafel polarization curves and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical properties of the coating formed under different conditions. The optimum conditions were obtained as following: temperature was 30-40 ℃, deposition time 9 min, the pH was adjusted to 2.0-3.0, the KCr(SO4)2 and H3PO4 concentrations were controlled within 15-25 g·L-1 and 10-20 g·L-1, respectively. The polarization result showed that the coating had more positive corrosion potential (Ecorr) and pitting corrosion potential (Epit), and lower corrosion current density (icorr), indicating that the coating formed under the optimum conditions had better corrosion resistance. To explain the electrochemical properties of the coating, a simple equivalent circuit was designed. Electrochemical parameters of EIS, such as the resistance (Rcoat) and capacitance (Ccoat), the charge transfer resistance (Rct) and double layer capacitance (Cdl), were obtained by fitting the EIS plots. The results of EIS were in good agreement with those of Tafel polarization curves.

SUS304 ステンレス鋼のスパッタエッチングによる円錐状突起物の生成および表面の腐食挙動

The sputter etching of SUS304 stainless steel specimens was carried out, and the formation and growth processes of conical protrusions was investigated. In addition, the polarization behavior of the specimens in 3.5%NaCl aqueous solution and the surface morphology after the polarization test were examined. At an early stage of the sputter etching, the conical protrusions form mainly along grain boundaries. However, with increase in the sputter etching time the protrusions form also within the grains. With further increase in the sputter etching time, some protrusions grow largely and the entire surface is covered by the huge conical protrusions and the irregular small ones around them. The outer layer of the huge protrusion contains larger chromium but smaller nickel amount than matrix, and the interior has almost the same composition as the matrix. This means that the protrusion has a shell structure. For the specimen with short time sputter etching, the corrosion potential becomes nobler and the pitting corrosion potential becomes smaller, while the passive current density is smaller than those of non-sputter-etched specimen. In these specimens, the corrosion occurs preferentially along grain boundaries and around protrusions in grains. For the specimen with long time sputter etching, where the entire surface is covered by protrusions, the pitting corrosion potential increases and the corrosion progresses mainly from the interior of the specimen leaving the surface layer with many protrusions. In some cases, only the outer layer of the shell remains separately as a result of the corrosion of the interior and root of the huge protrusion.

The electrochemical behavior and surface analysis of Ti49.6Ni45.1Cu5Cr0.3 alloy for orthodontic usage

The aim of this study was to investigate the electrochemical behavior of Ti(49.6)Ni(45.1)Cu(5)Cr(0.3) (TiNiCuCr) alloy in artificial saliva solutions with a wide rage of pH values and to characterize the surface passive film after polarization tests. This article represents the ideal, static environment and associated electrochemical response and comparison values. The corrosion behavior of TiNiCuCr alloy was systematically studied by open circuit potential, potentiodynamic, potentiostatic, and electrochemical impedance techniques. Potentiodynamic and potentiostatic test results showed that the corrosion behavior of TiNiCuCr was similar to that of NiTi alloy. Both corrosion potential (E(corr)) and pitting corrosion potential (E(b)) showed a pH-dependent tendency that E(corr) and E(b) decreased with the increase of the pH value. X-ray photoelectron spectroscopy results revealed the composition of the passive film consisted mainly of TiO(2) with a little amount of Ni oxides (NiO/Ni(2)O(3)) that was identical with NiTi alloy. Besides Ni, a Cu enriched sub-layer was also found. The nickel ion release rate showed a typical time-related decrease as examined by ICP/OES. In conclusion, the addition of Cu and Cr had little effect on the corrosion behavior of NiTi or on the composition and the structure of the passive film.

Pitting Corrosion Behavior of Sintered SUS444 Stainless Steel in MgCl<sub>2</sub> Solution

The pitting corrosion behavior of sintered SUS 444 stainless steels (P/M specimens) with different kinds of porosity ratios of 13.3, 9.11 and 6.88 % was studied in an aqueous solution containing MgCl2 compared with a conventionally processed SUS 444 stainless steel(I/M specimen). The pitting corrosion potential decreased almost linearly as porosity ratio increased, and the I/M specimen showed the best resistance against the initiation of pitting corrosion. The pitting corrosion morphology by SEM observation showed that more small pits were observed on the specimen with larger porosity ratio while less number but larger diameter pits were observed on the specimen with smaller porosity ratio, and it was also confirmed that the I/M specimen had the least number but the largest and deepest pits.