Surface Volta Potential Research Articles

Study of the corrosion mechanism of Mg–Gd based soluble magnesium alloys with different initial texture states

Abstract In order to clarify the influence of different initial texture states on the corrosion mechanism of soluble Mg alloy materials, the as cast and after extruded + perforated (EP) deformed Mg–Gd based soluble magnesium alloys are investigated by the microstructure, surface morphology, surface volta potential, immersion test and electrochemical measurement separately. The results indicate that: the rate of corrosion of the as cast Mg–Gd based soluble magnesium alloy can reach 43.85 mg/cm2/h at 93 °C in a 3 wt% KCl solution, while after EP deformation the rate of corrosion is greatly reduced to only 8.37 mg/cm2/h. Combined with the microstructure analysis, it is concluded that the EP deformed destroyed the coarse reticulated second phase in the as cast structure, which reduced the micro-electrocouple corrosion effect of the second phase. Finally, the corrosion mechanism models for different initial texture states are established through the analysis of microstructure and corrosion morphology, respectively. It is found that the microscopic corrosion mechanism of the as cast Mg–Gd based soluble magnesium alloy is mainly intercrystalline corrosion, which is a superposition of micro-electrocouple corrosion and Mg matrix dissolution. While the microscopic corrosion mechanism of the EP deformed is mainly intracrystalline corrosion, which is manifested as pitting corrosion.

Selective alloying of pure aluminum with varying amounts of magnesium using friction stir processing for improved mechanical and corrosion-resistant properties

This study investigates the effects of adding different amounts of Mg to the surface of pure Al substrate using friction stir processing (FSP) technique to prepare Al–Mg solid solutions. For this purpose, machined grooves on the surface of the pure Al plates were filled by bulk Mg blocks and FSPed to form Al–Mg solid solution layers with ∼2.0, 4.5, and 33.9 at.% Mg. The chemical composition, microstructure, and surface Volta potential of the surface alloyed layers were studied by SEM/EDS, XRD, and SKPFM, respectively. The results revealed that incorporating Mg into the Al substrate causes a considerable refinement of the microstructure, resulting in a significant increase in Vickers hardness number from 25 to 208.4 HV (∼734% increase). As the Mg content in the alloyed layer increased, a transition from a single-phase solid solution structure to a dual-phase structure was observed. Based on the potentiodynamic polarization results, it is evident that the corrosion resistance of the single-phase alloyed layer can match that of marine-grade aluminum alloys.

Metallurgical manipulation of surface Volta potential in bimetals and cell response of human mesenchymal stem cells

Bioelectricity plays an overriding role in directing cell migration, proliferation, differentiation etc. Tailoring the electro-extracellular environment through metallurgical manipulation could modulate the surrounding cell behaviors. In this study, different electric potential patterns, in terms of Volta potential distribution and gradient, were created on the metallic surface as an electric microenvironment, and their effects on adherent human mesenchymal stem cells were investigated. Periodically and randomly distributed Volta potential pattern, respectively, were generated on the surface through spark plasma sintering of two alternatively stacked dissimilar metals films and of a mixture of metallic powders. Actin cytoskeleton staining demonstrated that the Volta potential pattern strongly affected cell attachment and deformation. The cytoskeletons of cells were observed to elongate along the Volta potential gradient and across the border of adjacent regions with higher and lower potentials. Moreover, the steepest potential gradient resulting from the drastic compositional changes on the periodic borders gave rise to the strongest osteogenic tendency among all the samples. This study suggests that tailoring the Volta potential distribution and gradient of metallic biomaterials via metallurgical manipulation is a promising approach to activate surrounding cells, providing an extra degree of freedom for designing desirable bone-repairing metallic implants.

Localized Corrosion of Stainless Steel Triggered by Typical Inclusions in NaCl Solution: Oxy-Sulfide and MnS.

The localized corrosion behavior of stainless steel (SS) induced by typical inclusion such as MnS and oxy-sulfide in NaCl solution was investigated by immersion tests and microelectrochemical tests. Oxy-sulfide consists of an internal polygonal oxide part and an external sulfide part. The surface Volta potential of the sulfide part is always lower than that of the surrounding matrix, as in the case of individual MnS, while the potential of the oxide part is indistinguishable from that of the surrounding matrix. Sulfides are soluble, while oxides are almost insoluble. Oxy-sulfide exhibits a complex electrochemical behavior in the passive region, which can be attributed to its complex composition and multi-interface coupling effects. It was found that both MnS and oxy-sulfide increase the susceptibility of the local area to pitting corrosion.

Stress corrosion cracking of X80 steel heat-affected zone in a near-neutral pH solution containing Bacillus cereus

Bacillus cereus (B. cereus) is observed to have varying effects on the stress corrosion cracking (SCC) sensitivity of different microstructures in the simulated heat-affected zone (HAZ) of X80 steel. At open circuit potential (OCP), the SCC sensitivity of different microstructures increased from 3.40–7.49% in an abiotic medium to 10.22–15.17% in a biotic medium. At −0.9 V (SCE), it increased from 22.81–26.51% to 35.76–39.60%. The increment in SCC sensitivity upon exposure to B. cereus was highest in the coarse-grained HAZ (7.68 and 16.79% at OCP and −0.9 V, respectively), followed by the intercritical and fine-grained HAZs. Owing to differences in the phase composition, grain boundary type, dislocation density, and surface volta potential, the initial adhesion number and position of B. cereus in the microstructure of the HAZ were differed, resulting in different sensitivities to SCC.

Towards understanding Shewanella algae-induced degradation of passive film of stainless steel based on electrochemical, XPS and multi-mode AFM analyses

The degradation of the passive film of stainless steel caused by Shewanella algae was investigated through electrochemical tests, X-ray photoelectron spectroscopy and atomic force microscopy (AFM). The dynamic mode and the nano manipulation mode of AFM were adopted to obtain the 3D topography of cell/passive film interfaces and to manipulate cell movement, respectively. The surface Volta potential scanning by tapping-amplitude modulation mode and the conductivity tests by PeakForce-TUNA mode of AFM revealed the electron injection phenomenon from S. algae cells into adjacent passive film, which promoted the reduction of Fe3+ compounds and accelerated the degradation of passive film.

Graphene coated copper in a one-year atmospheric corrosion and color preserving challenge

A one-year atmospheric corrosion study was conducted to evaluate the performance of transparent single-layer (SLG) and multilayer graphene (MLG) coating as a protective coating on copper substrate against atmospheric corrosion and color changing. Employing the CIE−L*a*b* color space, it was shown that the transparent SLG and MLG coatings can maintain the pure color of copper before exposure to the atmosphere. However, after 15 days the color change (∆E) in the SLG-coated copper (SLG/Cu) was found to be more than that in the bare copper. A scanning Kelvin probe (SKP) was used to measure the surface potential as well as corrosion behavior. The observed decrease of average surface Volta potential of SLG/Cu, from -312 mV to -830 mV, was supposed to be caused by corrosion and electron transfer during galvanic cell formation. Further examinations by Raman spectroscopy, OM, and AFM measurements were logically correlated with those from SKP. Moreover, it was revealed that the surface voltaic potential for MLG-coated copper (MLG/Cu) remains constant along one-year atmospheric exposure. The presented results strongly prove that the MLG coating could be considered an anti-corrosion coating that can fully preserve the color of copper metal after exposure to the environment for at least a year.

Research on corrosion mechanism of microstructure on low alloy steel in humid atmosphere

The corrosion process of low-alloy steels with three different microstructures in a humid atmosphere was systematically studied in this paper. Scanning electron microscope (SEM), transmission electron microscope (TEM), scanning Kelvin probe force microscope (SKPFM) and electrochemical measurement were conducted to characterize the microstructure, surface Volta potential and corrosion kinetic parameters of different phase. Confocal laser scanning microscope (CLSM) and X-ray diffraction (XRD) were utilized to characterize morphology and composition of rust layer. The results show that the volt potential of the substrate surface has a linear relationship with the corrosion kinetic parameters, and the structure with small micro-area potential difference and low average potential has better corrosion resistance. The ferrite in the dual phase will preferentially dissolve as an anode to form a crater, which will be filled with corrosion products, resulting in an uneven diffusion of oxygen and thus the formation of a concentration polarization. Dual phase steel will form a poorly protective rust layer, which causing the corrosion resistance analysis to be inconsistent with the final corrosion rate results.

Effect of surface Volta potential of Cr‐containing steel on uniform corrosion and pitting corrosion

AbstractThe corrosion behavior of 5.5%Cr–8.5%Cr steels in a CO2 environment was studied. To clarify the effect of Volta potential on uniform corrosion and pitting corrosion, weight loss test, electrochemical measurement, scanning electron microscope, energy dispersive spectrometer, confocal laser scanning microscope, and scanning Kelvin probe force microscope were conducted. The results show that there is a linear relationship between the surface potential of the steel substrate and the self‐corrosion potential. The increase of the Cr content reduces the surface potential and increases the self‐corrosion potential, reducing the thermodynamic tendency of corrosion. The Al‐oxide inclusions show lower potential than the substrate, and their sensitivity to pitting corrosion is affected by the potential difference with the substrate. The larger the potential difference, the easier it is tantamount to induce pitting corrosion.

Effect of Temperature and Composition on Corrosion Behavior of Medium Cr Steel in a Salt Solution Containing CO2

In this paper, the corrosion behavior of three kinds of medium Cr low C steels in the simulated service environment of the transport pipeline was investigated through accelerated corrosion experiments, and the corrosion resistance mechanism of these experimental steels at different temperatures was investigated by electrochemical means. Finally, the reasons for the difference in corrosion behavior were analyzed from the grain boundary and surface Volta potential. The results show that as the temperature rose, the corrosion rate of the 5Cr specimen increased sharply and the corrosion type developed from slight general corrosion to severe general corrosion. The 7Cr specimen was less sensitive to temperature, and the type of corrosion changed from slight general corrosion to local corrosion. Finally, the 9Cr specimen was not sensitive to temperature, and the type of corrosion was always local corrosion. 5Cr steel could form a protective product film at 30°C. As the temperature rose, the protective ability of the product film decreased, and the matrix dissolved easily. The film of 7Cr and 9Cr samples had not yet precipitated and the matrix was difficult to dissolve at 30°C. However, the matrix dissolved easily at 50°C, and the product film had formed, which played a major role. At 70°C, the protective effect of the product film decreased, and the gap between the 7Cr and 9Cr samples began to appear. The increase of Cr content helped to refine grains and increased the proportion of low-angle grain boundaries. At the same time, the increase of Cr element helped to increase the maximum Volta potential of the experimental steel and increased the Volta potential difference. As a result, the test steel was shown to be resistant to uniform corrosion, but it also increased the risk of pitting corrosion.

Degradation mechanism of 6063 aluminium matrix composite reinforced with TiC and Al2O3 particles

The degradation mechanism of 6063 aluminium matrix composites reinforced with TiC and Al2O3 particles was investigated by microstructure characterization, electrochemical experiments, scanning Kelvin probe force microscopy (SKPFM) and density function theory (DFT) calculation. The addition of the TiC and Al2O3 particles refines the grain structure of the composite material and increases the content of AlFeSi phase at the grain boundary. The surface Volta potential of AlFeSi (653 mV) was higher than that of the matrix alloy and Cl− is more easily adsorbed on the surface of AlFeSi phase rather than on TiC particles and AlMgSiCu phase. The strong absorption energy between Cl− and the AlFeSi phase will destroy the surrounding oxide film and cause the pitting corrosion around the AlSiFe phase. Therefore, the adding of TiC and Al2O3 particles reduces the corrosion resistance of the composite material.

Effect of ultrasonic shot peening duration on microstructure, corrosion behavior and cell response of cp-Ti

Surface mechanical attrition treatment (SMAT) of metallic biomaterials has gained significant importance due to its ability to develop nano structure in the surface region. In the present study, the microstructural changes and corrosion behavior of the commercially pure titanium (cp-Ti), following different durations of ultrasonic shot peening (USSP) has been investigated. cp-Ti was shot peened for different durations from 0 to 120 s and the treated samples were examined for microstructural changes in the surface region, cell viability and corrosion behavior. Cell viability was considerably increased after USSP for 60–120 s, exhibiting maximum for the 90 s of USSP. The passivation tendency was also improved with peening duration up to 90 s, however, it declined for longer duration of USSP. The beneficial effects of USSP may be attributed to nano structuring in the surface region and development of higher positive potentials at the USSP treated surface. Transmission Electron Microscope (TEM) examination of the USSPed surface revealed dislocation entanglement and substructure. Also, higher surface volta potential was observed over the USSPed sample exhibiting better cell proliferation. The present work is corollary to previous work of the group and mainly discusses the role of USSP duration, as a process parameter, on the cell viability and corrosion resistance of cp-Ti.

Correlation of surface Volta potential with galvanic corrosion initiation sites in solid-state welded Ti-Cu bimetal using AFM-SKPFM

This study aims to correlate the microstructure and Volta potential distribution of Ti-Cu welded bimetal to its corrosion initiation sites, using AFM-SKPFM, and SEM-EDS. Local melted zones with Ti-Cu intermetallic precipitates in weld interface and in Cu matrix showed different Volta potential values in comparison with those of Ti and Cu regions. SKPFM revealed that Cu region has a higher Volta potential than that of Ti region. AFM and microstructural images after immersion in corrosive media proved the presence of a galvanic cell. Corrosion mainly extends on Cu side due to the increasing growth of Ti passive film.

Iron hydrogenation under atmospheric corrosion. Studies using a scanning vibrating microscope

A scanning vibrating capacitor (SVC, Kelvin probe) is used to study hydrogenation of iron and steel under the conditions of atmospheric corrosion. It is shown that hydrogen that forms in the course of corrosion or under cathodic polarization diffuses through the membrane and interacts with its opposite side, causing a decrease in the surface Volta potential. It is proposed that atomic hydrogen reduces Fe3+ ions in the passive film. It is shown that the SVC technique is informative for registration of local regions of hydrogenated metal at very low hydrogen flow into steel.

Retraction Note: Investigation of coating delamination on steels by surface topography and Volta potential difference

Corrosion-induced delamination of an epoxy coating on the AISI/SAE 1045 carbon steel was studied under a humid atmospheric condition (temperature of 25 °C, one standard atmospheric pressure, and relative humidity of 90 %) by the technique of scanning Kelvin probe force microscopy (SKPFM). Surface-polished 1045 samples were first cold coated with the epoxy and then subject to the atmospheric corrosion under the humid atmospheric condition. At specified time intervals, surface Volta potential of the samples was measured using the SKPFM over the dry surface of epoxy coating. The map of Volta potentials demonstrated high contrasts among three characteristic zones: intact steel-epoxy interface, delaminated interface, and interface with active corrosion, which based on a rigorous calibration procedure were then linked to the actual corrosion potential of the steel (measured using a potentiostat w.r.t. a saturated calomel electrode). The SKPFM was found to be able to provide a mean of direct and nondestructive detection of early active corrosion and coating delamination of steels at a submicroscopic resolution, which outperformed the conventional electrochemical techniques for such purposes.

Effects of surface states on the oxidation behavior of 316LN stainless steel in high temperature pressurized water

Nuclear grade 316LN stainless steel with different surface states are prepared: electropolished and ground to 240 grit. Surface topography, surface Volta potential distribution, and nanohardness distribution on cross‐sectional surface are investigated, respectively. Oxide films on the ground and electropolished samples after immersion in high temperature pressurized (HTP) water for 0.1, 168, and 366 h were studied using various methods. Distinct from electropolished surface, the ground surface is featured by a rugged surface and a heterogeneous distribution of surface Volta potential. A thicker (∼28 µm) cold‐worked layer was introduced by grinding. More crystallites were precipitated on the ground surface, resulting from the existence of high‐energy sites with higher residual strain and higher electrochemical activity and a less protective inner layer. The oxidation rate was reduced by electropolishing and a thinner oxide film was formed, due to the formation of a more protective oxide film with higher content of chromium (Cr). The mechanism of oxide film formation was further discussed.

Stressed Corrosion of an Austenitic Stainless Steel Studied by Scanning Kelvin Probe Force Microscopy

Under the ambient temperature (25°C) and pressure (one Standard Atmospheric Pressure) conditions, surface Volta potential of an austenitic stainless steel was measured using the Scanning Kelvin Probe Force Microscopy (SKPFM) to study its stressed-related corrosion behavior in a 0.5 M chloride solution. In an oxygen and water regulated environment (using a glovebox), the steel shows a map of Volta potentials with high contrasts among the different grains and grain boundaries, which was then linked to the actual corrosion potential (w.r.t. a saturated calomel electrode) based on a rigorous calibration procedure. Corrosion behavior of the steel under tensile stress was then compared to that of the same sample under no tensile stress in light of the measured Volta potential, which was found to be sensitive to the level of applied tensile stress, although the tested stainless steel in general is known for its high corrosion-resident capability. According to this study, surface Volta potential measured by SKPFM can be used as a high-accuracy indicator for localized corrosion of steels.

Corrosion behavior of a duplex stainless steel under cyclic loading: a scanning Kelvin probe force microscopy (SKPFM) based microscopic study

Corrosion fatigue behavior of the duplex stainless steel AISI 2205 was studied by the scanning Kelvin probe force microscopy (SKPFM) in the ambient temperature and pressure condition (25 °C, one standard atmospheric pressure). Surface-polished AISI 2205 samples were subject to a cyclic tensile stress while immersed in a 0.5 M NaCl solution. At specified time intervals, surface Volta potential of the samples was measured using the SKPFM in an oxygen and water regulated environment. The steel samples demonstrated a map of potentials with high contrasts between ferritic and austenitic grain domains, which was then linked to the actual corrosion potential (w.r.t. a saturated calomel electrode—SCE) based on a rigorous calibration procedure. The corrosion fatigue behavior of AISI 2205 was studied by comparing the SKPFM-measured Volta potentials of the same sample under applied cyclic strain and under no applied cyclic strain. It was found that AISI 2205 became more prone to corrosion when the applied tensile strain exceeds one percent (1 %).