Cyclic Potentiodynamic Polarization Research Articles

The effect of slow strain rate tension and cyclic loading on biodegradable Zn–2%Fe–0.8%Mn alloy in a simulated physiological environment

Zinc-based alloys have gained increased interest as biodegradable structural materials for medical applications due to their adequate biocompatibility, crucial roles in many physiological functions and attractive antibacterial properties. However, the major drawbacks of zinc alloys relate to their inadequate mechanical properties and tendency to provoke fibrous encapsulation due to relatively high standard potential. Based on the promising effect of Mn on properties of Zn-based alloys, the present study aimed at evaluating the suitability of Zn–2%Fe–0.8%Mn alloy as a potential biodegradable implant under in-vitro conditions. This evaluation focused on the passivation characteristics as determined by cyclic potentiodynamic polarization analysis, immersion test, stress corrosion behavior by slow strain rate testing (SSRT), corrosion fatigue and direct cell viability in terms of cell adherence and proliferation after 24 and 48 h post incubation. The results showed that the addition of 0.8%Mn to the base Zn–2%Fe alloy improves the specific strength and direct cell viability characteristics while decreasing the effectiveness of natural passivation processes. The main overall effect of adding 0.8%Mn to Zn–2%Fe alloy were (i) reduced stress corrosion resistance in terms of time to failure at a low strain rate (2.5 × 10−7 s−1) from 285 h to 205 h (ii) reduced corrosion fatigue endurance from 4,997,285 cycles to only 377,552 cycles to failure at the lowest load of 30 MPa.

Portland cementitious coating with autogenerated oxide film and its anticorrosion behavior on magnesium alloy

A simple one-step anticorrosion Portland cement (PC)-based coating with an autogenerated oxide film on the surface of Mg alloy was successfully prepared in this study. The anticorrosion of coated Mg alloys was assessed by several electrochemical methods including open circuit potential, electrochemical impedance spectroscopy, and cyclic potentiodynamic polarization. The morphology and composition of PC-based coatings were characterized via scanning electron microscopy and X-ray diffraction. The composition of the autogenerated oxide film was analyzed via X-ray photoelectron spectroscopy. Results show that the PC-based coatings can significantly enhance the corrosion resistance of AZ41 Mg alloy due to the synergetic effect of PC-based coating and autogenerated oxide film. Particularly, the quality of oxide film plays a dominant role in determining anticorrosion of Mg alloy. Furthermore, the addition of metakaolin and dolomite enhances the resistance of PC-based coating and meanwhile, MoO42– ions from PC-based coating can adsorb in the oxide film, improving the quality of the oxide film.

Microstructure and Pitting Corrosion Characteristics of Tig Welded Joints of Super 304HCu Austenitic Stainless Steel

Abstract Super 304HCu is an advanced ultra-super critical (A-USC) boiler grade austenitic stainless steel with the distinct addition of 3 wt.-% of Copper. A-USC power plants intended to operate in chloride rich environments (sea shore, feed water residues, etc.) are susceptible to chloride assisted corrosion failures. In this study, the pitting corrosion behaviour of the Super 304HCu parent material and tungsten inert gas weld joints was studied using a potentiodynamic cyclic polarization test in 3.5 % NaCl solution at three different pH levels (pH = 3, pH = 7, and pH = 11). The Epit values of the parent material is found to be much nobler than that of the weld joints. The micrographs of the pitted weld joints and the oxalic acid etched structure of Super 304HCu joints are presented. From the micrographs it is revealed that the heat affected zone is the most susceptible region to pitting corrosion.

Lignin-Derivative Ionic Liquids as Corrosion Inhibitors.

Corrosion is a significant problem that negatively affects a wide range of structures and buildings, resulting in their premature failure, which causes safety hazards and significant economic loss. For this reason, various approaches have been developed to prevent or minimize the effects of corrosion, including corrosion inhibitors. Recently, biobased inhibitors have gained a certain interest thanks to their unique properties, eco-friendliness, and availability. Among all the green precursors, lignin is of particular interest, being a natural polymer that can be obtained from different sources including agricultural residues. Corrosion inhibitors based on ionic liquids (ILs) also present interesting advantages, such as low volatility and high tunability. If combined, it may be possible to obtain new lignin-based ILs that present interesting corrosion inhibitor properties. In this work, the inhibition properties of new biobased lignin ILs and the influence of anions and cations on the corrosion of mild steel in an aqueous solution of 0.01 M NaCl were investigated by Potentiostatic Electrochemical Impedance Spectroscopy (PEIS) and Cyclic Potentiodynamic Polarization (CPP). Moreover, the surface was characterized using SEM, EDS, and optical profilometry. The IL choline syringate showed promising performance, reducing the corrosion current after 24 h immersion in 0.01 M sodium chloride, from 1.66 µA/cm2 for the control to 0.066 µA/cm2 with 10 mM of the IL present. In addition to its performance as a corrosion inhibitor, both components of this IL also meet or exceed the current additional desired properties of such compounds, being readily available, and well tolerated in organisms and the environment.

Passive film and surface characterization of Alx(CoCrFeNi)100-x (x = 0, 5, 10, 15, 20) high entropy alloys

The current research on the corrosion resistance of high entropy alloys (HEAs), mainly focuses on the influence of element composition and percentage difference. Considering the almost consistent passivation range with different corrosion resistance contributed by element addition, it inevitably exists obvious differences the passive film properties. The effect of passive film on corrosion behavior of HEA is worthy to be investigated in detail. Considering the microstructure transformation detected by electron probe X-ray microanalysis (EPMA) and surface feedback effect measured by approach curve of scanning electrochemical microscopy (SECM), the passivity of Alx(CoCrFeNi)100-x (x = 0–20) HEAs in 0.5 M H2SO4 solution has been investigated by cyclic potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott-Schottky analysis and X-ray photoelectron spectroscopy (XPS). The results demonstrate that the passive film is thick and dense at low Al content (5%), which shows excellent corrosion resistance. However, with the increase of Al content, the corrosion resistance of passive film deteriorates gradually. XPS are adopted to detect film composition to explain the reason of film property change. The results suggest that there are more oxidized states of Al and less oxidized states of Cr in the passive film of HEAs with Al addition. The dominate semiconductor characteristics of Alx(CoCrFeNi)100-x with Al addition change from p-type to n-type. All results indicate that the addition of Al has a significantly influence on the composition and properties of passive film on the Alx(CoCrFeNi)100-x alloys surface.

Effect of MBF-20 Interlayer on the Microstructure and Corrosion Behaviour of Inconel 625 Super Alloy after Diffusion Brazing.

The joining zone includes three main parts, which comprise an isothermal solidification zone (ISZ), the athermal solidification zone (ASZ), and a diffusion affected zone (DAZ). Field emission scanning electron microscopy (FESEM) was used here to observe the microstructure equipped with ultra-thin window energy dispersive X-ray spectrometer (EDS) system. Additionally, electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization tests were conducted to evaluate the effect of the DB process on the corrosion resistance of the Inconel 625 superalloy. In the bonding time period, some Mo- and Cr-rich boride precipitations and Ni-rich γ-solid solution phases with hardened alloy elements, such as Mo and Cr, formed in DAZ and ASZ, respectively, because of the inter-diffusion of melting point depressants (MPD). Moreover, during cooling cycles, Ni-Cr-B, Ni-Mo-B, Ni-Si-B, and Ni-Si phase compounds were formed in the ASZ area at 1110-850 °C. The DAZ area developed by borides compound with cubic, needle, and grain boundary morphologies. The corrosion tests indicated that the DB process led to a reduction in the passive region and increased the sensitivity to pitting corrosion.

Electrochemical study of aluminum–cubic boron nitride composites synthesized via spark plasma sintering for engineering applications

Herein, aluminum−cubic boron nitride (Al−BN) composites with different reinforcement sizes (20, 40, and 60 µm) were developed via spark plasma sintering while maintaining a constant weight percentage (10 wt%; reinforcement). The powder materials were sintered at a temperature of 550 °C and constant uniaxial pressure of 50 MPa with a heating rate of 100 °C/min. Field-emission scanning electron microscopy analysis of the developed composites revealed a uniform dispersion in the Al matrix. X-ray diffraction analysis indicated the presence of aluminum and cubic boron nitride major and minor phases, respectively. Evidence of chemical reactions and the presence of an interfacial phase were not observed at 550 °C in the Al−cBN composite. The mechanical and electrochemical properties of the composites were investigated as a function of the cBN particle size. The results demonstrated that the composite with a cBN particle size of 20 µm (i.e., more particles in the Al matrix than other compositions) strengthens the matrix owing to the better stress drive in the matrix and exhibits the highest average hardness (1.78 GPa), elastic modulus (76.1 GPa), and percentage of densification (98.1%) compared to the other tested composites. The corrosion behavior and resistance against pitting corrosion of pure Al and cBN-based composites were investigated in a 3.5 wt% NaCl solution using electrochemical techniques, such as open circuit potential, electrochemical impedance spectroscopy, and cyclic potentiodynamic polarization analyses. Electrochemical studies revealed that among the analyzed samples, the composite with 20 µm cBN particles exhibits an excellent polarization resistance, in addition to the lowest corrosion rate (∼5 mills per year) and a very high resistance to pit formation in a corrosive environment.

Microstructure and corrosion of CrFeMnV multi-principal element alloy

A multi-principal element alloy consisting of equiatomic concentrations of Cr, Fe, Mn, and V was produced by arc melting. The combination of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy indicated that the CrFeMnV MPEA was comprised of a BCC matrix with a dispersion of a secondary phase. Cyclic potentiodynamic polarization tests in 0.6 M NaCl revealed high corrosion resistance – superior to that of stainless steel 304L, as evident from high breakdown and repassivation potentials. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry provided insight into the formed multi-layer surface film after constant immersion and potentiostatic conditioning.

Corrosion behaviors of super austenitic stainless steel weldment by GTAW welding for ships desulfurization system

This study aims to clarify how filler-typed metals which were ERNiCrMo-3 and ERNiCrMo-4 affect corrosion resistance characteristics in the weldment of super austenitic stainless steel joints under the simulated desulfurization environment for ships. The desulfurization environment includes high temperature, chlorides, and acidic conditions, which, inevitably, can cause severe corrosion to great extent. For exact clarification, the variations of microstructure and the composition distribution in the weldment before and after welding was examined by using scanning electron microscope and energy dispersive X-ray spectroscopy. Then, the corrosion resistance characteristics were comparatively evaluated through the cyclic potentiodynamic polarization test together with potential measurement under the desulfurization simulated environments. In addition, the correlation between passive film and corrosion resistance characteristics was investigated after identifying the formed features of the passive film through the X-ray photoelectron spectroscopy analysis. Through these studies, it made certain, ERNiCrMo-4 filler metal with high Mo content is advantageous for the formation of MoO3 oxide on the surface, which belongs to form a stable passive film and maintains the corrosion resistance characteristics under the simulated desulfurization environment.

ELECTROCHEMICAL REDUCTION OF CADMIUM IONS FROM ETHYLENE GLYCOL ELECTROLYTE

The work is devoted to the study of the process of cathodic reduction of Cd ions from anhydrous ethylene glycol electrolyte. The mechanism of the process of cadmium reduction was studied by taking linear and cyclic potentiodynamic polarization curves. The influence of cadmium chloride concentration, potential sweep rate and temperature on the process of electrochemical deposition of cadmium ions was studied. With an increase in the concentration of cadmium in the electrolyte, the rate of its release at the cathode increases. Precipitates of good quality are obtained at current densities of 25 mA/sm2. It has been established that the cadmium deposition potential almost does not change with increasing potential sweep rate. The dependence of cadmium electrodeposition from ethylene glycol electrolyte on temperature was studied, which made it possible to establish the optimal deposition temperature, which was 363–373 K, and to conclude that the deposition process is controlled by electrochemical polarization. The diffusion coefficient of cadmium ions to the cathode surface has been calculated

Effect of Heat Treatment on Crevice Corrosion Behavior of 304 Stainless Steel Clad Plate in Seawater Environment.

With the application of stainless steel clad plate (SSCP)-enlarging in the marine engineering field, awareness of the consequences of heat treatment on ameliorating microstructure and mechanical properties in stainless steel (SS)/carbon steel (CS) joints is being raised. However, carbide diffusion from a CS substrate to SS cladding may damage the corrosion resistance during inappropriate heating. In this paper, the corrosion behavior of a hot rolling-produced stainless steel clad plate (SSCP) after quenching and tempering (Q-T) treatment, especially crevice corrosion, was studied by electrochemical and morphological methods, such as cyclic potentiodynamic polarization (CPP), confocal laser scanning microscope (CLSM) and scanning electron microscopy (SEM). Q-T treatment led to more significance in carbon atoms diffusion and carbide precipitation, which made the passive film of the SS cladding surface on the SSCP unstable. Subsequently, a device for measuring the crevice corrosion performance of SS cladding was designed; the Q-T-treated cladding showed lower re-passivation potential (-585 mV) during CPP when compared to as-rolled (-522 mV), with the maximum corrosion depth ranging from 70.1 μm to 150.2 μm. In addition, the processing of crevice corrosion on SS cladding could be divided into three parts, including the initiation, propagation and development stages, which were driven by the interactions between corrosive media and carbides. The generation and growth mechanism of corrosive pits in crevices were revealed.

Comparative Research on Corrosion Resistant Non-Skid Al and Al-3%Ti Coating Fabricated by Twin Wire arc Spraying

To ensure the lifetime of marine constructions and the safety of workers and pedestrians, corrosion protective non-skid coating is an effective solution. However, the conventional polymer-based coating has some limitations. In this study, newly-suggested Al and Al-3%Ti coatings were deposited on high strength low alloyed steel substrate using twin wire arc spraying (TWAS). The static and dynamic friction coefficients of the Al-based coatings under dry and wet conditions were measured using portable friction testers. To evaluate the corrosion behavior under sea water conditions, a cyclic potentiodynamic polarization test (CPDP) and salt solution immersion test (SSIT) were performed with a 3.5% NaCl solution. To confirm the coating degradation, mechanical properties (Vickers hardness and adhesion strength) were compared before and after SSIT. The results showed that the TWAS Al-based coatings were well fabricated on HSLA steel and had the general microstructure of a thermal spray. The coatings provided excellent corrosion protection for the steel substrate and greatly increased the friction coefficient of the surface. The Vickers hardness slightly increased and adhesion strength decreased after SSIT. The microstructure observation revealed that the TWAS coatings had a bimodal structure induced by non-uniform droplet generation at the TWAS tips. After SSIT, some oxides formed on the surface and porous regions of the coatings. This indicated that the TWAS coating successfully provided corrosion protection and non-skid properties.

Electrochemical Investigations on the Corrosion Behavior of 904L Stainless Steel in LiBr Solutions

The pitting corrosion susceptibility of 904L stainless steel in aerated LiBr solutions was investigated. The influence of various experimental variables, including electrolyte concentrations, pH, scan rate, temperatures, and constant potential has been studied using electrochemical measurements, such as cyclic potentiodynamic polarization, potentiostatic techniques, and electrochemical impedance spectroscopy (EIS). The surface morphology of 904L stainless steel was examined by scanning electron microscope (SEM). The rate of uniform corrosion and susceptibility toward pitting corrosion increases with an increase in LiBr concentrations and temperature. Increasing the pH of the solution decreases the rate of both uniform and pitting corrosion. An increase in the scan rate enhances the uniform corrosion, but suppresses the pitting corrosion. EIS diagrams displayed a depressed semicircles with the center under the real axis. Bode plots support the result that the uniform corrosion resistance of the alloy in LiBr solutions decreases with increasing Br− anion concentration. The observations suggest that this one time constant may actually be the overlap of two-time constants.

Experimental interrogations on morphologies and mechanical delineation of silicon nitride fortified Mg-Al-Zn alloy composites

The smart material used in aerospace and automotive industries has to withstand high load with minimum structural weight. Nowadays, in search of new lightweight materials for the industrial application, magnesium is rapidly replacing aluminium-based alloys. In this research, magnesium (AZ31) matrix composite reinforced with ceramic silicon nitride (Si3N4) particle is fabricated by vacuum stir casting. The proportion of strengthening particle was assorted to a maximum of 10 % in steps of 2 % variation in weight. Microstructural analysis carried out through optical microscope exposes the occurrence and near-uniform spread of Si3N4. The mechanical properties for various weight proportions are studied; microhardness and strength are enhanced at the expense of ductility reduction with rising Si3N4 content in the magnesium metal matrix. The porous nature and composites density rises with higher weight % of Si3N4 particles in the magnesium matrix. The corrosion characteristic was studied by salt spray and cyclic potentiodynamic polarization test, which demonstrates that increasing the reinforcement limits the corrosion by forming phases of Mg2Si intermetallics with galvanic corrosion mechanism. The inferences present that the fabricated composite are ideal for many industrial plans where less structural weight material is required.

Corrosion of Titanium Alloys Anodized Using Electrochemical Techniques

The anodization of titanium has been an excellent option for protecting titanium and its alloys from corrosive environments such as acids and chloride systems, by generating a homogenous oxide layer. The objective of the current investigation was to evaluate the electrochemical corrosion behavior of alloys Ti-6Al-2Sn-4Zr-2Mo and Ti-6Al-4V anodized in 1M H2SO4 and H3PO4 solutions at a current density of 2.5 × 10–3 A/cm2. The anodization’s electrochemical characterization was achieved in NaCl and H2SO4 at 3.5% wt. electrolytes. Scanning electron microscopy (SEM) was employed to determine the anodized thickness and morphology. Cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS), based on ASTM G61-86 and G106-15 Standards, were the electrochemical techniques mainly employed. The anodized samples presented a change in Ecorr values and a higher passivation zone. The EIS plot showed a higher resistance for samples anodized in H3PO4 and Ti-6Al-2Sn-4Zr-2Mo.

Corrosion mechanism of advanced high strength dual-phase steels by electrochemical noise analysis in chloride solutions

The corrosion behavior of ferrite-martensite and ferrite-bainite dual-phase steels in NaCl, CaCl2, and MgCl2 solutions was studied by cyclic potentiodynamic polarization (CPP) and electrochemical noise (EN) techniques. The results showed a trend for mixed corrosion due to no passivation by a protective oxide layer. For the ferrite-martensite dual-phase steels, the ferrite phase was preferentially corroded compared with the martensite phase in test solutions. Bainite-microstructure in ferrite-bainite dual-phase steels was preferentially corroded compared with ferrite-phase in CaCl2 and MgCl2 solutions. The corrosion behavior in test solutions in dual-phase steels could be divided into three steps: dissolution in anodic-phase/microstructure, non-uniform corrosion, and localized corrosion. The results indicated that factors such as galvanic coupling between ferrite/martensite, ferrite/bainite, metallic-matrix/inclusion-phases, metallic-matrix/secondary phases, and self-corrosion of each phase and microstructure contributed to the non-uniform and localized corrosion in dual-phase steels.

Developing Improved Corrosion-Resistant AA5083—BN/WC Composites for Tribological Applications

In this study, corrosion-resistant AA5083-BN/WC composites were developed for tribological applications through adequate control of the reinforcement content (WC and BN) in the matrix (AA5083 alloy). The effects of 6% and 12% tungsten carbide (WC) as well as 6% and 12% boron nitride (BN) additions on the corrosion behavior of AA5083 aluminum composite in 3.5% NaCl solution were carried out. Electrochemical techniques such as cyclic potentiodynamic polarization (CPP), changes in the chronoamperometric current with time (CCT), and electrochemical impedance spectroscopy (EIS) were utilized. The polarization results showed that the addition of 6% WC to the AA5083 alloy matrix improved its resistance to corrosion (RP). Rp exhibited an additional increase by adding 12% WC to the matrix. The values of RP were observed to increase for the AA5083 composite when adding 6% BN, and the highest RP values were recorded for the composite that contains 12% BN. The results obtained by the CPP method were confirmed by CCT and EIS measurements, where the presence of WC and BN protected the developed AA5083- BN/WC composites against corrosion. The corrosion resistance revealed an additional improvement with an increase in WC and BN content from 6% to 12%. The results also confirm that pitting corrosion decreased in the presence of WC and BN in the fabricated composites.

Cyclic Potentiodynamic Polarization on Titanium Alloys Anodizing in Alkaline Solutions

Titanium alloys are used in different industries such as biomedical, aerospace, aeronautic, chemical, and naval. Those industries have high requirements with few damage tolerances. The aim of this work was to study the corrosion behavior of titanium alloys anodizing and non-anodizing in alkaline (KOH and NaOH) solutions, exposed in 3.5%wt. NaCl and 3.5% wt. H2SO4 solutions at room temperature using cyclic potentiodynamic polarization (CPP) according to standards to obtain electrochemical parameters as the passivation range (PR), corrosion type, passive layer persistence, corrosion potential (Ecorr), and corrosion rate. The alloy Ti Beta-C anodized presented better corrosion resistance than Ti-6Al-4V in both media. The smallest corrosion rate is presented in Beta-C samples (4.72 E-8 A/cm2) and the highest corrosion rate is CP2 (1.61 E-5 A/cm2)

Influence of the Martensite Phase of the Cu-9Al-3Ag Alloy and Its Corrosion Behavior in NaCl-Containing Media

The present investigation shows the influence of the microstructure resulting from the heat treatment termed betatization of an aluminum bronze containing Cu-9Al-3Ag alloy, in as-cast and heat-treated samples immersed in 0.5M NaCl-containing media with all experiments conducted at 25 ºC. The said treatment corresponds to heat saturation conditions in the phase region where the beta phase predominates in the microstructure. The corrosion behavior was recorded through using cyclic voltammetry and potentiodynamic polarization techniques, supplemented by OCP recordings. The results obtained through the polarization curves showed that at more positive potentials the current density decreases considerably, which is attributed to the formation of corrosion products on the surface of the working electrode.

Citric Acid as an Alternative to Sulfuric Acid for Hard Anodizing in Aluminum Alloys Used in the Aeronautical Industry

In the aircraft industry, Al-Cu alloys are widely used as a structural material in the manufacture of commercial aircraft due to their high mechanical properties and low density. Al-Cu alloy have low resistance to corrosion in aggressive substances; as a result, these alloys are surface treated to increase their resistance to corrosion. Anodizing was done hard in aluminum alloy AA 2024 in a solution composed of citric and sulfuric acid for 60 minutes with constant agitation using current densities of 3 and 4.5 A/dm2. Afterwards, a sealing procedure was performed for 60 minutes in water at 95 °C. Scanning electron microscopy (SEM) was used to characterize the microstructure and Vickers microhardness (HV) as a mechanical test of the material. The electrochemical evaluation was carried out using cyclic potentiodynamic polarization curves (CPP). The results indicate that the corrosion resistance in citric acid solutions with a current density of 4.5 A/dm2 was the best, with corrosion current densities of 2 x 10-8 and 2 x 10-9 A/cm2.