Potentiodynamic Polarization Tests Research Articles

A Surface and Corrosion Characterisation of Micro Arc Oxidation Treated Friction Stir Welded ZM21 and ZE41 Magnesium Alloy: A Comparison Study

Abstract Magnesium alloys have gained attention as promising materials in industrial applications, for their high specific strength and low density. Magnesium alloys have desirable mechanical properties, but their poor corrosion resistance prevents their safe implementation. Alloys such as ZM21 and ZE41, possess unique properties that provide improved machinability and increased red-hot strength, respectively, while remaining prone to corrosion. To improve corrosion resistance, surface treatments and coating processes are employed. Comparing the corrosion characteristics of ZM21 and ZE41 is vital for aerospace and automotive applications, directly affecting component durability, reliability, and performance against corrosion. Magnesium alloys are frequently joined through friction stir welding (FSW), hence, similar importance is provided to studying the corrosion performance of welds, since FSW introduces microstructural changes that alter corrosion performance of welded joints. The paper discusses electrochemical corrosion mechanisms and analyzes the effect of Micro Arc Oxidation (MAO) coating on electrode potential, passivity, and electrical resistance of ZM21 and ZE41 plates welded through FSW. MAO treatments were performed on both base material and FSW joints. The corrosion performance of MAO-coated FSWed ZM21 and ZE41 alloys was compared through the Electrochemical Impedance Spectroscopy (EIS) and Potentio-Dynamic Polarisation (PDP) tests. The PDP test revealed that MAO treatment enhanced the corrosion resistance of both base and FSWed ZM21 and ZE41 magnesium alloys. There was an improvement in potential polarization (Rp) values from 565 Ω cm2 to 11245 Ω cm2 for ZM21 and from 1184.4 Ω cm2 to 11435.69 Ω cm2 for ZE41 alloys. While exhibiting improvements in corrosion resistance, MAO-treated ZE41 performed better than MAO-treated ZM21. PDP results were verified through confirmatory EIS results. Therefore, MAO treatments are effective methods to improve the corrosion performance of Mg alloys. Evaluation of MAO coating performance on various FSW Mg alloys and studying their corrosion performance is crucial for engineering material selection.

Influence of Deposition Temperature and WC Concentration on the Microstructure of Electroless Ni-P-WC Nanocomposite Coatings with Improved Hardness and Corrosion Resistance

This study aims to develop Ni-P coatings with high P content (≥11 wt.%) reinforced with WC nanoparticles on F22 steel substrates. The introduction of conductive WC in the plating solution dramatically increases reactivity of the plating solution, and consequently a tuning of deposition parameters, in terms of temperature and WC concentration, is required to obtain nanocomposite coatings with improved mechanical properties. The coatings’ porosity and incorporation and dispersion of the reinforcing phase as a function of temperature and WC concentration were analyzed by quantitative image analysis from Scanning Electron Microscopy (SEM) micrographs. Increasing the temperature and concentration of nanoparticles leads to a faster plating rate and a dramatic increase in both porosity and agglomeration of the reinforcing phase, with detrimental effects on the coatings’ microhardness. The best compromise between coating parameters was obtained by deposition at 70 °C and 6.5 g/L of WC, with a plating rate ≈ 12 μm/h, porosity lower than 1.5%, and a good combination between particle incorporation and agglomeration. In these conditions, a hardness increase by 34% is achieved in comparison to standard Ni-P. Coatings were then heat treated in air at 200 °C for 2 h, to induce growing stress relaxation, or 400 °C for 1 h, to study effects of crystallization and precipitation. X-Ray Diffraction (XRD) analysis demonstrated that WC introduction does not alter the microstructure of Ni-P coatings, but delays grain growth coarsening of precipitates. Hardness improvement by 6.5% and 45% is registered after treatment at 200 °C and 400 °C, respectively. An increase in elastic modulus, measured by instrumented indentation, was found in WC-reinforced coatings compared with Ni-P. Potentiodynamic polarization tests revealed that both introduction of WC nanoparticles and heat treatment also enhance corrosion resistance.

Comprehensive analysis of mechanical properties, wear, and corrosion behavior of AA7075-T6 alloy subjected to cryogenic treatment for aviation and defense applications

It is important that the parts to be used in the aviation and defense industry have high wear, fatigue and corrosion resistance. AA7075-T6 alloys are increasingly used in every field due to their advantageous physical and mechanical properties. However, some of the materials of this alloy types exhibit excellent fatigue strength and ductility, but their surface hardness and surface roughness after processing may be poor. For this reason, the wear resistance of AA7075-T6 aluminum alloy expected to be improved in order to increase their corrosion resistance properties. In this work, cryogenic treatment was applied to AA7075-T6 alloy and the mechanical characteristics, wear and corrosion behaviors of these samples were examined. As a result of the experiments, it was determined that cryogenic treatment improved the wear behavior of AA7075-T6 alloy. The untreated sample was found to have the highest wear rate, whereas the sample with deep cryogenic treatment (DCT) had the lowest wear rate. The hardness of the DCT process increased by 5.79 %, according to macro hardness measurements, making the AA7075-T6 alloy harder from 80.16 HRB to 84.8. The SEM images revealed that, the shallow cryogenic and deep cryogenic operations had substantial effects on the microstructure by modifying the size and distribution of precipitates in the AA7075-T6 alloy. In addition, tensile and hardness tests were carried out to assess the mechanical characteristics of the samples. Accordingly, the maximum tensile strength and hardness values were obtained in the deep cryogenically treated sample. The tensile strength of the DCT sample was approximately 544.18 MPa, a considerable 11.5 % increase above the untreated sample's 488.07 MPa strength. In potentiodynamic polarization testing, the DCT treated sample was determined to have the maximum corrosion resistance. Among the materials tested, the DCT sample showed the strongest corrosion resistance, with a corrosion potential of −0.689 V and a corrosion rate of 0.021 mm/year. Wear rate analysis revealed that DCT samples experienced the least material loss, demonstrating improved abrasion resistance. Enhanced hardness and the formation of stable oxide tribo-layers contributed to these superior wear characteristic.

Fabrication and Characterization of Hydroxyapatite Coatings on Anodized Magnesium Alloys by Electrochemical and Chemical Methods Intended for Biodegradable Implants

The fabrication of hydroxyapatite (HAP)/MgO composite coatings on Mg alloy is crucial for enhancing the corrosion resistance and biocompatibility of biomedical implants. In this study, we aimed to investigate the effects of two different surface modification methods, i.e., electrochemical (electrodeposition, ED) and chemical (solution treatment, ST), on the phase structure, degradation properties, and biocompatibility of the composite coatings in comparison to the anodized coating. The surface morphologies and crystalline structures of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Subsequently, the degradation rate of the coatings in simulated body fluid were comprehensively evaluated by using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and scanning electrochemical microscopy (SECM) tests. Additionally, in-vitro cell proliferation assays were employed to quantitatively assess the biocompatibilities of the coatings. The results showed that both ED and ST methods were effective in depositing HAP on anodized Mg alloy, resulting in different surface morphologies with hydroxyapatite layer thicknesses of 2.71 μm and 3.56 μm, respectively. In this way, the HAP-deposited coatings exhibited improved corrosion resistances and biocompatibilities compared with those of the anodized coating. Specifically, the ST-deposited composite film displayed superior degradability and biocompatibility which was attributed to its filiform surface morphology and thicker HAP layer. Overall, the present study demonstrates the potential of HAP/MgO composite coatings for biomedical applications, with implications for the development of advanced implant materials with improved performance and biocompatibility.

Effect of sputtering power and substrate bias on microstructure, mechanical properties and corrosion behavior of CoCrFeMnNi high entropy alloy thin films deposited by magnetron sputtering method

The CoCrFeMnNi high entropy alloy thin films with crystalline (solid solution) structure or amorphous state were fabricated by magnetron sputtering process at different target powers and different substrate bias. Effects of the target power and substrate bias on the characteristics of the CoCrFeMnNi thin films such as microstructures, morphology and surface topography, as well as mechanical properties and corrosion behavior were studied. Phase prediction was calculated by using thermodynamic and kinetic criteria under various deposition conditions. The enthalpy, entropy, δ and Ω parameters, and electronegativity differences influenced the solid solution stability of thin films. These parameters led to the formation of solid solutions with crystalline or amorphous structures under specific limits, which corresponded to the practical XRD and TEM analysis results. Using a substrate bias in the deposition of CoCrFeMnNi thin film changed the amorphous structure to a crystalline (solid solution (BCC + FCC)) at higher target powers (200 and 300 W). On the other hand, the film structure was entirely amorphous at all sputtering target powers without the substrate bias. The mechanical properties, such as hardness, Young's modulus, film strength, and fracture toughness of CoCrFeMnNi thin film, can be enhanced by using the substrate bias and increasing the sputtering power. The potentiodynamic polarization test in 3.5 wt% NaCl aqueous solution indicated that the deposition of CoCrFeMnNi thin films at different sputtering powers and without substrate bias could increase the corrosion resistance of 304 stainless steel substrate. Using the substrate bias of −100 V in the fabrication of CoCrFeMnNi thin film decreased the corrosion current density and increased its polarization resistance.

Characterization of Electrochemical and Biocompatibility of Zinc Oxide Coating Electrodeposited on Commercial Pure Titanium Alloy

This study examines how the duration of electrodeposition affects the morphology and electrochemical characteristics of zinc oxide coatings applied to a pure titanium substrate. The morphology of the coating and the phases present within it are analyzed using a scanning electron microscope and the X‐ray diffraction technique. The coating's resistance to corrosion in a phosphate‐buffered saline solution is evaluated using two electrochemical methods: impedance spectroscopy and potentiodynamic polarization tests. The surface roughness of the coated samples is assessed using interferometry. The results demonstrate that an increase in electrodeposition time, ranging from 150 to 1200 s, leads to an enhanced texture intensity in the (0002) and (010) planes of the ZnO coating. Furthermore, the thickness of the ZnO crystals and surface roughness increases by factors of 3.25 and 2.79, respectively, as the deposition time is extended. This extended duration results in the formation of larger needle‐shaped and flower‐like ZnO crystals, leading to a significantly nonuniform structure. Correspondingly, the corrosion rate also increases as the electrodeposition time is extended from 150 to 1200 s, rising from 0.001951 to 9.117 μm year−1. The lowest corrosion rate (1.654 μm year−1) is achieved in coatings deposited for 300 s using a potential of 3 V.

Comprehensive Investigation of the Adsorption, Corrosion Inhibitory Properties, and Quantum Calculations for 2-(2,4,5-Trimethoxybenzylidene) Hydrazine Carbothioamide in Mitigating Corrosion of XC38 Carbon Steel under HCl Environment.

This study investigates the inhibitory effects of 2-(2,4,5-trimethoxy benzylidene) hydrazine carbothioamide (TMBHCA) on the corrosion of carbon steel in a 1 M HCl solution across various concentrations. The assessment employs a comprehensive approach, combining gravimetric analysis, potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS). Additionally, scanning electron microscopy (SEM) and quantum chemical calculations are employed to provide a thorough understanding of the corrosion inhibition mechanism. The influence of exposure time on mild steel corrosion is systematically examined. Results reveal a remarkable reduction in the corrosion rate of steel, with TMBHCA demonstrating its highest inhibition efficiency of 97.8% at 200 ppm. Potentiodynamic polarization studies characterize TMBHCA as a mixed-type inhibitor, while Nyquist plots illustrate increased charge transfer resistance and decreased double-layer capacitance with escalating TMBHCA concentrations. Consistency between weight loss measurements and electrochemical findings further validates the efficacy of TMBHCA as a corrosion inhibitor. SEM images substantiate and visually support the obtained results. An immersion test conducted at 25 °C over 28 days showcases a notable enhancement in TMBHCA efficiency (IE%) from 45.16% to 92.43% at 200 ppm as the immersion period progresses from 1 day to 28 days. This improvement is attributed to the augmented adsorption of inhibitor molecules on the steel surface over time. These comprehensive findings significantly contribute to our understanding of TMBHCA's corrosion inhibition behavior, emphasizing its potential as a highly efficient corrosion inhibitor for diverse industrial applications.

In-vitro biocompatibility, antibacterial activity, and corrosion resistance of HA-TiO2/ZnO coating fabricated by plasma electrolytic oxidation on Ti6Al4V

The hydroxyapatite/Zinc Oxide (HA-TiO2/ZnO) coatings were grown on the Ti6Al4V substrate by plasma electrolyte oxidation from the CaP-based electrolyte containing 1, 3, and 6 g/L ZnO nanoparticles. XRD results confirmed the presence of ZnO, HA, and rutile phases in all coatings. According to SEM observations, coatings presented the porous morphology as a result of micro-arc discharges during the PEO process, whereas some of the pores in the composite coatings were filled by ZnO proportional to its content. After 7 days of immersion in SBF solution, accumulations of bone-like clusters were visible on the surface, demonstrating a promising bio-mineralization ability for all coatings, although the higher amount of 6 g/L ZnO had partially an inhibitory effect on the apatite nucleation. In-vitro studies demonstrated a time and concentration-dependent impact of ZnO on the viability of MG-63 osteoblast-like cells so that the concentration of 3 and 6 g/L caused the death of some cells after 7 days. The antibacterial tests also showcased that the presence of ZnO decreased the activity of gram-negative bacteria (E. coli) and gram-positive bacteria (S. aureus), while the higher concentration of ZnO particles led to more antibacterial activity of the coating. Finally, evaluating the corrosion behavior of PEO coatings through a potentiodynamic polarization test in Ringer's solution manifested a better protection against corrosion by increasing the ZnO content in the coating, mainly owing to the blocking of the pores by the ZnO particles, and as a result, the greater difficulty of electrolyte to reach the titanium substrate.

Emerging Mo-doped MgAl-LDH lamellar/carbon nanotubes as 3D sustainable nanohybrid for designing a durable smart anti-corrosion composite

This paper focused on the utilization of 3D hybrid nanocomposites composed of layered double hydroxides (L) containing sodium molybdate (SM), which are chemically bonded with functionalized multi-walled carbon nanotubes (FCN), as nanocarriers for smart corrosion prevention. The SM molecules were loaded into the L, and L/FCN nanocarriers by an anion exchange process, and then the 3 synthesized nanoparticles (i.e., L, SM-L, and SM-L/FCN) were characterized. Following the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) tests' outcomes, the maximum corrosion prevention efficiency (about 90.88 %) belongs to the SM-L/FCN nano reservoir containing saline extract. Additionally, for the epoxy phase, the EIS results (on the intact and scratched specimens) revealed a significant diminish in the chloride and water penetration into the epoxy coating during 63 days of immersion. EIS results indicated the enhancement of the charge transfer resistance (Rct) of the scratched coatings, from 17.42 kΩ.cm2 for the EP sample to 72.47 kΩ.cm2 for the SM-L/FCN/EP one in long immersion times, revealing the self-repairing behavior of the designed coating. The results of intact coating revealed that the Log (|Z|0.01 Hz) value reached 10.63 in long immersion time indicating a decreased occurrence of coating disbondment attributed to the electrolyte infiltration and corrosion of the underlying metal substratum. According to the pull-off and cathodic disbonding tests results, there was an enhancement in adhesion (51.5 % decrease in loss of adhesion strength, & a 52 % decline in diameter of cathodic disbondment), and a strong interaction between the interface of epoxy and substratum. According to the mechanical tests (Tensile and DMTA) results the incorporation of L and FCN nanoparticles into the SM-L/FCN sample enhanced the nanocomposite's mechanical properties. The tensile test showed an increase in ultimate tensile strength (σUTS) and elongation at break (Ɛb) of 130.61 % and 107.59 %, respectively, compared to the pure epoxy (EP) sample. Additionally, the dynamic mechanical thermal analysis (DMTA) test indicated a 144 % increase in crosslinking density for the SM L/FCN sample compared to the neat epoxy.

Development of electrophoresed anti-corrosion coating for copper from functionalized multi layered graphene nano-sheets synthesized through anionic acidic electrochemical exfoliation

Following the discovery of graphene, a two-dimensional carbonaceous substance, numerous possibilities in materials science domain have evolved, one being its function as a corrosion inhibitor. This investigation undertakes the synthesis of functionalized multi-layered graphene nanosheets (FMLGNs) from pyrolytic graphite sheets through electrochemical exfoliation involving four distinct acid-based solutions (H2SO4, HCLO4, HNO3 and combination of the above three in 1:1:1 ratio). Post-exfoliation analysis of FMLGNs included X-ray diffraction (XRD) wherein 2θ values were reported at 26° confirming graphene's presence. Raman spectroscopy reiterated the same observation along with an increase in ID/IG ratio to ≈ 1 hinting at the presence of functional groups and defects. UV–visible spectroscopy indicating π-π* transitions, Fourier transform infrared spectroscopy (FTIR) showing CO stretching and X-ray photoelectron spectroscopy (XPS) with a C/O ratio = 3.12 gave an idea about the functionalization in FMLGNs. Average particle sizes of FMLGNs was in the range of 400–500 nm and zeta potential measurements showed stable dispersion behaviour (≈−40 mV). Utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), authors observed a layered (10–15 layers), overlapping shape of FMLGNs. Electrophoretic deposition (EPD) method was employed to coat FMLGNs onto copper substrates under various iterative conditions (number of layers and time of deposition) which produced depositions of ≈20–30 μm. SEM images displayed adequate coverage of graphene sheets on copper surfaces, backed by energy-dispersive x-ray spectroscopy (EDS). Crack propagation resistance (CPR) values of 34.03 N highlighted better adherence than other similar coatings. The coated copper samples were subjected to cyclic voltammetry (CV), potentio-dynamic polarization (PDP) and electrochemical impedance (EIS) tests in 3.5 wt% NaCl solution for analysing the inhibitory impacts of coatings. An inhibition efficiency of 85 % and charge transfer resistance of 5535 Ω.cm2 was observed, which highlighted better corrosion mitigation than reported literatures. The authors also identified that 1 layered coatings showed better reliability than two layered coatings.

A predictive model for corrosion of carbon steel exposed to organic acids: Theory and validation in formic, azelaic and citric acid

Organic acids can severely corrode metals, despite rarely reaching particularly low pH values. The mechanisms underlying the corrosion process in the presence of organic acids can be different and more complex with respect to the ones in the presence of strong acids. Since organic acids are commonly found in several industrial environments, they pose a serious threat that needs to be carefully addressed and investigated. Throughout the years, many research efforts have been put towards predictive modeling of corrosion. The Tafel-Piontelli model aims at becoming a universal and versatile model for acidic corrosion, able to adapt to different situations and predict corrosion rates of active metals exposed to all kinds of acidic environments. The model foundations are grounded in the principles of the corrosion process, regulated by the Tafel law. The efficacy of the model was tested on carbon steel samples immersed in solutions of weak acids with increasing proticity — formic, azelaic, and citric acid — at temperatures ranging from 20°C to 60°C and pH values from 3 to 4. The validation analysis was conducted using two primary tests: mass loss tests to assess corrosion rates and potentiodynamic polarization tests to determine the kinetic parameters of the cathodic and anodic reactions involved in the corrosion process. The results from the experiments are promising, confirming and extending the predictive capabilities of the model to the case of organic acids. These findings have broad implications for improving safety and durability in industrial applications where organic acids are prevalent, highlighting the model’s potential to significantly enhance preventive strategies and material selection.

A novel AlCo1.2Cr0.8FeNi2.1 eutectic high entropy alloy with excellent corrosion resistance

A novel AlCo1.2Cr0.8FeNi2.1 eutectic high entropy alloy (EHEA) was designed and prepared. The microstructure of the as-cast alloy was characterized that a fine lamellar structure composed of FCC (L12) phase and B2 phase. The mechanical of the EHEA was studies by the tensile tests, and the corrosion properties of the EHEA in 3.5 wt% NaCl solution at room temperature was investigated. The results shown that the alloy exhibits synergistic effect of strength- plasticity with a high tensile strength of 1048.42 MPa and an excellent elongation of 18.92%. Potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) indicated that the EHEA exhibits spontaneous passivation in 3.5 wt% NaCl solution, forming a protective passive film that exhibits p-type and n-type semiconductor properties, with the main components of Al2O3, CoO, Cr2O3, Fe(OH)3, and NiO. Furthermore, the corrosion mechanism of EHEA was discussed.

Multi-objective optimization of heat treatment criteria on the corrosion and wear behaviour of ZA27/SiC/TiB2 hybrid metal matrix composite

The current study presents a methodology for examining the effect of solutionizing and aging parameters on the wear and corrosion behaviour of ZA27/SiC/TiB2, a Hybrid Metal Matrix Composite(HMMC). ZA27 alloy is widely used in applications where high bearing resistance and wear resistance properties are desired. However, its usability is limited to temperatures less than 1000 C as its properties exhibit a declining trend. The addition of SiC and TiB2 were found to contribute in circumventing this lacuna. Furthermore, no studies were reported on the process of augmenting the corrosion and wear resistance of this hybrid composite. This research gap is specifically addressed in this work. The chosen Hybrid Composite consisting of 15% of reinforcing elements(SiC + TiB2) proportioned equally among them along with 85% of ZA27 alloy matrix is produced by Mechanical Stir casting method. The experimental work has been broadly divided into two major spectrums. The first part consisting of analysing the change in properties being studied before and after heat treatment. Besides, this part of the work also involved the study of the variation in artificial aging temperature on the properties under consideration. The Potentiodynamic Polarisation tests showed that the solution heat treatment produces a significant decline in corrosion rate. Further, aging at a temperature of 1800 C has also evidently improved the properties of corrosion and wear resistance. However, results also depicted that over aging would deteriorate these properties. The final and subsequent part was completely devoted to identifying the best and optimised heat treatment parameters viz., solutionising time, aging temperature and time. Further, Taguchi L9 orthogonal array is taken to design the experiments in the second phase. Regression Equations were developed from the observations of this set of experiments. These equations were later subjected to Multi-Objective Genetic Algorithm (MOGA) which produces a pareto set of optimal solutions. The Pareto frontier was then analysed using Multi criteria decision making approaches viz., VIKOR, LINMAP and TOPSIS to arrive at the most optimal solution. This approach has culminated in an optimal solution of corrosion and Wear rates of 2.27mpy, 2.75 ˟ 10-3 mm3/m and coefficient of friction as 0.271 at the input variables of solutionizing time −5 h, aging temperature-1890 C and aging time-2 h.

The role of Zinc Molybdate in the anticorrosion and antibacterial characteristics of sustainable polyurethane coating derived from epoxidized soybean oil

Vegetable oils are important renewable sources that have been used as alternative feedstocks to petroleum for the synthesis of polyols. Polyols are compounds that contain multiple hydroxyl groups in a molecule and are a major component of polyurethanes. One of the oldest problems that many industries face today is corrosion. Polyurethane coatings reduce the rate of corrosion reactions but are not completely impermeable to corrosive agents. Nanoparticles, due to their high surface area and small particle size, can improve the performance of polyurethane coatings and block the penetration of corrosive agents. This research aims to prepare polyurethane coatings using soybean oil-based polyol and investigate the corrosion resistance performance of polyurethane coatings by adding Zinc Molybdate (ZnMoO4) nanoparticles. To achieve this goal, a polyol based on soybean oil was synthesized through the ring-opening reaction of Epoxidized soybean oil. Then, polyurethane coatings with 0.5, 1, 1.5, and 2 wt% of ZnMoO4 nanoparticles were prepared. Characterization of the polyurethane coatings was performed using FTIR, HNMR, and FESEM. The mechanical properties were also examined. Finally, the corrosion resistance activity of these nanocomposites was evaluated using electrochemical impedance spectroscopy and potentiodynamic polarization tests. The results showed that adding 0.5%w/w of ZnMoO4 nanoparticles can improve the performance of polyurethane coatings against corrosion, as the nanoparticles were uniformly dispersed on the surface of the coating and blocked the penetration of corrosive agents. Therefore, 0.5 wt% ZnMoO4 nanoparticles can be considered as the optimal amount in this experiment. Moreover, the modified coating with ZnMoO4 nanoparticles can effectively act against both gram (+) and gram (-) bacteria.

PH-responsive anti-corrosion activity of gallic acid-intercalated MgAl LDH in acidic, neutral, and alkaline environments

Undoubtedly, designing pH-responsive particles is one of the most fascinating aims for corrosion experts. Local pH variations can occur through the corrosion process (chemical and electrochemical reactions), accelerating the corrosion rate. However, by designing this class of modern inhibitors, a significant part of the effects of pH variation during corrosion disappears. Herein, a novel layer double hydroxide-based (LDH) nanocomposite, which is filled by gallic acid (GA) molecules, was designed. To prove the composite inhibition proficiency, EIS tests were conducted in acid, neutral and alkaline atmospheres and then surface morphology of the protected and unprotected samples are visualized by FE-SEM images. Simultaneously, the EDS-Mapping technique was applied to predict the elemental composition of the generated inhibitive layer. The results of the EIS test indicated an increase in corrosion resistance after using nanoparticles in all three acidic, neutral and alkaline environments. In addition, the potentiodynamic polarization test confirmed the mixed-protection mechanism in these three media. Furthermore, FE-SEM approach demonstrated the formation of a protective film on metal surfaces, and the EDS-Mapping evaluation confirmed these results in line with the element recognition.

Ex-situ Characterization of Nb-Ti Alloy/Pt Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Fuel Cells

Metallic bipolar plates are crucial for the development of compact and lightweight proton exchange membrane fuel cell stacks; however, most of them encounter durability and conductivity challenges in the fuel cell environment. In this study, Nb-Ti alloy/Pt coatings are deposited on SS316L plates to enhance corrosion resistance, surface wettability, electrical and thermal conductivity, with reduced interfacial contact resistance. Corrosion resistance is assessed by exposing test samples to a 1M H2SO4 acidic environment at 25 °C and 80 °C, respectively, via potentiostatic and potentiodynamic polarization tests. It is found that Nb-Ti alloy/Pt coatings exhibit exceptional stability, with corrosion potential increased by 2.5 (at 25 °C) and 0.5 (at 80 °C) times and corrosion current density reduced by orders of magnitude; and their anti-corrosion performance far exceeds the technical targets set by the US Department of Energy, with a protective efficiency of 99.98 % at both temperatures tested. The coated samples have reduced water affinity, indicated by significantly larger contact angle values compared to the uncoated samples in both pre-and post-corrosion tests. The incorporation of Nb-Ti alloy/Pt coatings on SS316L increases the in-plane electrical conductivity by 42.6 % and thermal conductivity by 3.5 %; surpassing the US Department of Energy's technical targets in these categories as well. At a compaction force of 140 N/cm2, the interfacial contact resistance for the coated samples is about 2.5 times lower than the Department of Energy's requirements. These results indicate the viability of Nb-Ti alloy/Pt coated SS316L bipolar plates for fuel cell applications.

Developing a novel expression for chloride ion concentration threshold in reinforced concrete: Integration of electrochemical analysis and time-dependent modeling

Chloride ion concentration threshold is a crucial parameter for evaluating the durability of reinforced concrete. This study aimed to develop a novel expression method for this threshold by analyzing the open-circuit potential of steel in simulated mortar pore solution across three pH values. Concurrently, the correlation between pitting potential and chloride ion concentration was examined through potentiodynamic polarization testing. Additionally, Mott-Schottky analysis facilitated the investigation of the passivation film structure on the steel under both passivation and depassivation conditions. By integrating the analysis of the open-circuit potential and pitting potential models in the simulated solution, a time-dependent relationship curve between the chloride ion threshold and time was established. The findings reveal that the steel’s passivation film comprises a dual-layer structure, with its corrosion resistance enhancing as the pH value of the simulated mortar pore solution increases. Furthermore, within the simulated mortar pore solution, the chloride ion concentration threshold exhibited a decreasing trend over time, suggesting a minimum threshold value exists. This research provides a significant foundation for forecasting the corrosion state of steel in steel-reinforced engineering projects.

An investigation of the corrosion behavior of zinc-coated stainless steel orthodontic wires: the effect of physical vapor deposition method

BackgroundReleasing of metal ions might implicate in allergic reaction as a negative subsequent of the corrosion of Stainless Steel (SS304) orthodontic wires. The aim of this study was to evaluate the corrosion resistance of zinc-coated (Zn-coated) SS orthodontic wires.MethodsZinc coating was applied on SS wires by PVD method. Electrochemical impedance spectroscopy (EIS), Potentiodynamic polarization tests and Tafel analysis methods were used to predict the corrosion behavior of Zn-coated and uncoated SS wires in both neutral and acidic environments.ResultsThe values of Ecorr ,icorr and Rct ,which were the electrochemical corrosion characteristics, reported better corrosion behavior of Zn-coated SS wires against uncoated ones in both artificial saliva and fluoride-containing environments. Experimental results of the Tafel plot analyses were consistent with that of electrochemical impedance spectroscopy analyses for both biological solutions.ConclusionApplying Zn coating on bare SS orthodontic wire by PVD method might increase the corrosion resistance of the underlying stainless-steel substrate.

Effect of alloy 625 buffer layer on corrosion resistance of nickel base hardfacing

Nickel base hardfacing alloys serve to mitigate corrosion losses at elevated temperatures. Efficacy of Nickel base hardfacing alloys can be compromised when applied onto Fe base substrates due to iron dilution in hardfacing. The degree of Fe dilution can be reduced by using advanced deposition methods and optimized deposition parameters. Gas Tungsten Arc Welding (GTAW) method is commonly employed for its cost-effectiveness and versatility, but it tends to induce higher Fe dilution due to increased heat input. This study aims to reduce the degree of Fe dilution and enhance corrosion resistance by introducing a nickel base buffer layer (alloy 625) between the nickel base hardfacing alloy and AISI 316L stainless steel substrate. For comparative purposes, Ni base hardfacing alloy was deposited on the substrate without any buffer layer. Hardfacing depositions were prepared using manual GTAW process. Process parameters namely, deposition current, voltage, travelling speed, pre-heating temperature, and cooling method were kept constant. Samples underwent aging at 1123 K for 4 h, followed by microstructural examination via optical and scanning electron microscopes. Iron (Fe) dilution quantification was performed using energy dispersive spectroscopy (EDS). The EDS analysis showed that the use of buffer layer between the hardfaced deposit and the substrate decreased the degree of Fe dilution in the hardfaced deposit. X-Ray diffraction (XRD) analysis was performed to identify various phases formed in the hardfaced deposit. Potentiodynamic polarization test was performed to assess the corrosion resistance of hardfaced deposit in 3.5 wt% NaCl solution. Results show significant improvement in corrosion resistance of hardfacings deposited sample with buffer layer as compared to those without buffer layer. Aging treatment further enhanced corrosion resistance. The corrosion resistance data is correlated with the microstructure and phases formed in various samples.

The effect of NaCl concentration on impact-sliding fretting corrosion behavior of Inconel 690TT heat transfer tubes

Purpose The purpose of this paper is to investigate the effect of NaCl solution with different concentrations on impact-sliding fretting corrosion behavior of Inconel 690TT steam generator heat transfer tubes. Design/methodology/approach The optical 3D profiler was used to measure the wear profile and calculated the wear volume. Corrosion behavior was studied using open circuit potential monitoring and potentiodynamic polarization testing. The morphologies and elemental distributions of wear scars were analyzed using scanning electron microscopy and energy-dispersive spectroscopy. The synergism of wear and corrosion was analyzed according to the ASTM G119 standard. Findings The corrosion tendency reflected by OCP and the corrosion current calculated by Tafel both increased with the increase of NaCl concentration. The total volume loss of the material increased with concentration, and it was known from the synergism that the volume loss caused by corrosion-enhanced wear accounted for the largest proportion, while the wear-enhanced corrosion also made a greater contribution to volume loss than tangential fretting corrosion. Through the analysis of the material morphologies and synergism of wear and corrosion, the damage mechanism was elucidated. Originality/value The research findings can provide reference for impact-sliding fretting corrosion behavior of Inconel 690TT heat transfer tubes in NaCl solution with different concentrations.