Cyclic Potentiodynamic Polarization Research Articles

Comparison of test methods for crevice corrosion propagation and repassivation potential of stainless steel AISI 316

The crevice corrosion propagation modes and repassivation potential of stainless steel AISI 316 in chloride solution were compared using cyclic potentiodynamic polarization (CPP), potentiodynamic-galvanostatic-potentiodynamic (PD-GS-PD) and Tsujikawa– Hisamatsu electrochemical (THE) methods. The PD-GS-PD method was found to be the most conservative electrochemical technique which delivered the lowest repassivation potential value in a relatively short time. The crevice corrosion propagation modes in these three electrochemical methods were also compared with crevice corrosion propagation mode in galvanically coupled small area stainless steel AISI 316 anode with large area titanium cathode. The crevice corrosion propagation mode achieved in galvanically coupled AISI 316 anode at open circuit potential simulated the crevice corrosion propagation mode in real systems. The crevice corrosion propagation modes achieved in PD-GS-PD and THE methods mimicked the crevice corrosion propagation in real systems.

Pitting corrosion performance of plasma oxidized Cp-Ti and effects of fabrication methods

In this study, the electrochemical corrosion properties of commercial pure titanium (Cp-Ti) samples produced by additive manufacturing and forging were compared by plasma oxidizing. Plasma oxidizing processes were carried out at temperatures of 650 °C and 750 °C for 1 h and 4 h. Electrochemical corrosion experiments were carried out in Simulated Body Fluid (SBF) using open circuit potential, cyclic potentiodynamic polarization and electrochemical impedance spectroscopy methods. It was found that the coating thickness of F 750 °C-4 h and S 750 °C-4 h samples was the highest. The corrosion resistance of the samples produced by additive manufacturing is lower than that produced by forging due to the Lack of fusion (LOF) effect. The barrier layer developed by the plasma oxidizing process significantly improved the corrosion performance of additive manufacturing by reducing the LOF effect. The minimum corrosion rate was obtained at S 750°-4 h. While the total material loss due to corrosion was the lowest on this surface, the last corroded surface was F 750°-4 h. The maximum resistance was observed on the plasma oxidized surfaces for the group produced by forging.

Cr-Co Oxide Coatings Resistant to Corrosion, Electrodeposited on 304 SS Using an Ethylene Glycol-Water Solvent

The electrochemical co-deposition of Cr-Co oxide coatings at room temperature on 304 stainless steel (SS) was studied using an electrolyte composed of a mixture of ethylene glycol (EG), hydrated metal chloride salts (MCln∙YH2O), and water as a secondary hydrogen donor (HBD). Metallic Cu and Ni undercoats were applied to improve the adhesion of a posterior Cr-Co metallic and oxide layer. The electroactive events that took place during both electrodeposition processes were studied using cyclic voltammetry (CV) and chronoamperometry. The microstructure and composition of the surface layers were studied using scanning electron microscopy (SEM/EDS), X-ray diffraction (XRD) and cross-sectional elemental mapping via transmission electron microscopy (TEM). The surface of steel with the Cr-Co:EG-H2O coating showed greater resistance to pitting corrosion (123.93 mV) compared to untreated stainless steel (62.3 mV). This sample showed a large hystere-sis area, which is associated with high resistance to pitting corrosion by the occurrence of a re-passivation of the sample at a Erep value of 24.31 mV. After the cyclic potentiodynamic polariza-tion (CPP) test, the lowest specific mass loss (0.001 mg/cm2) was achieved for the AISI 304 SS sample coated using EG-water solvents (Cr-Co:EG-H2O), while the untreated AISI 304 SS reached a higher specific mass loss (0.01 mg/cm2). The Electrochemical Impedance Spectroscopy (EIS) tests showed that the uniform corrosion resistance varied significantly from the untreated AISI 304 SS (35 kΩ) to the coated sample (57 kΩ), which is attributed to the protection provided by the chromium and cobalt oxides coating. The best corrosion resistance achieved was correlated with a superhydrophobic character (with a contact angle of 158.41°) of the Cr-Co coatings. This was in turn a consequence of a needle-like morphology characteristic of these oxides.

Improved Test Methods and Models for Localized Corrosion Assessment of Stainless Steels in Aqueous Chloride Media with Low Dissolved Oxygen

Experimental foundation has been established for improving corrosion models for stainless steels exposed to neutral aqueous chloride media with low levels of dissolved oxygen (DO). Accurate repassivation potentials were measured for UNS S31603 and UNS S32205 alloys in chloride electrolytes at room and elevated temperatures using Tsujikawa-Hisamatsu electrochemical (THE) and cyclic potentiodynamic polarization (CPP) methods. It was observed that the repassivation potential values measured using the CPP method were lower than the ones obtained from THE method for the same environmental conditions. Cyclic polarization scans in aqueous chloride media were conducted at different reverse scan rates resulting in varied repassivation potentials. Medium-term corrosion potentials were measured in chloride media with controlled dissolved oxygen levels ranging from 20 ppb to 400 ppb. These results were used as inputs for improving model prediction for repassivation and corrosion potentials. In an extension of previous modeling studies, an improved mechanistic repassivation model was developed based on a new generalized theory that explicitly accounts for the adsorption of water rather than treating it as an ever-present background. With a flexible definition of the repassivation current density, the new repassivation model reproduces the experimental repassivation potentials obtained using THE and CPP methods. The dependence of corrosion potential on DO has been modeled using a mixed-potential model. It has been demonstrated that the effect of agitation (caused by the bubbling of oxygen) needs to be accounted for to describe the corrosion potential, especially at low DO, where mass transport is important. The combined model correctly predicts the occurrence of localized corrosion when tested against exposure data from the literature.

Effect of Vaporized Hydrogen Peroxide and Nitrogen Dioxide Sterilization on Nitinol.

Background: Nitinol is used as the structural framework in numerous types of medical devices (e.g., guidewires, transcatheters, stents). The desire to understand the material compatibility of nitinol with vaporized hydrogen peroxide (VH2O2) and nitrogen dioxide (NO2) sterilization is increasing in healthcare technology. As a result of increased regulatory pressure and capacity limitations related to ethylene oxide (EO) sterilization, the industry is seeking alternative, sustainable sterilization options. Objective: This study sought to characterize the corrosion resistance of nitinol metal alloy wire when exposed to varying levels of VH2O2 and NO2 sterilization. Methods: Scanning electron microscopy (SEM) imaging and energy-dispersive X-ray spectroscopy (EDS) scans were performed to understand the effects of VH2O2 and NO2 sterilization treatments on the surface morphology and chemical composition of nitinol. Results: From the SEM-EDS results, no notable difference was observed when comparing VH2O2 and NO2 test samples with nonsterile control samples. In addition, cyclic potentiodynamic polarization measurements were performed per ASTM F2129-19a to determine corrosion susceptibility. No considerable changes were detected in the electrochemical potential after VH2O2 and NO2 sterilization treatments, when compared with the nonsterile control samples. Conclusion: SEM-EDS and corrosion test results indicated no considerable changes in the surface properties or electrochemical potential of the sterilized samples compared with the nonsterilized control samples. Therefore, nitinol metal showed promising results for compatibility with VH2O2 and NO2 sterilization.

Effect of Sulfide and Chloride Ions on Pitting Corrosion of Type 316 Austenitic Stainless Steel in Groundwater Conditions Using Response Surface Methodology.

This study investigates the corrosion resistance of Type 316 stainless steel as a candidate material for radioactive waste disposal canisters. The viability of stainless steel is examined under groundwater conditions with variations in pH, bisulfide ions (HS-), and chloride ions (Cl-) concentrations. Utilizing response surface methodology, correlations between corrosion factors and two crucial response variables, passive film breakdown potential and protection potential, are established. Cyclic potentiodynamic polarization tests and advanced analytical techniques provide detailed insights into the material's behavior. This research goes beyond, deriving an equation through response surface methodology that elucidates the relationship between the factors and breakdown potential. HS- weakens the passive film and reduces the pitting corrosion resistance of the stainless steel. However, this study highlights the inhibitory effect of HS- on pitting corrosion when Cl- concentrations are below 0.001 M and at equivalent concentrations of HS-. Under these conditions, immediate re-passivation occurs from the destroyed passive film to metal sulfides such as FeS2, MoS2, and MoS3. As a result, no hysteresis loop occurs in the cyclic polarization curve in these conditions. This research contributes to the understanding of Type 316 stainless-steel corrosion behavior, offering implications for the disposal of radioactive waste in geological repositories.

1-Benzyl-4-Phenyl-1H-1,2,3-Triazole as a Green Corrosion Inhibitor for Carbon Steel Reinforcing Bars in Concrete Elements

Reinforced concrete (RC) plays a crucial role in the construction of structures around the world. But these structures are frequently subjected to corrosive conditions, which can degrade their structural performance, shorten their service life, resulting in failure with catastrophic consequences. The concrete high pH stabilizes the formation of an oxide passive layer on the rebar. Nevertheless, this protective film can be compromised if the chloride ion concentration threshold is reached at the steel rebar surface, which can occur as the structure ages while exposed to chloride containing environments. Considering growing environmental concerns about the effectiveness of existing corrosion control methods, this study investigates the potential of 1-Benzyl-4-Phenyl-1H-1,2,3-Triazole (BPT), an organic compound, as a green corrosion inhibitor for rebar corrosion. BPT was found to inhibit corrosion of mild steel in acidic environments and has been synthesized in an eco-friendly and sustainable method.The objective of this work is to evaluate the corrosion inhibition of BPT to protect steel reinforcement in simulated marine environments. BPT was evaluated in synthetic pore solution (SPS, 8.33 g/L NaOH + 23.3 g/L KOH + 2.0 g/L Ca(OH)2, pH: 13.6) in the presence of chlorides to determine its optimal concentration. Exposure took place following a modified version of ASTM G180. In addition different electrochemical techniques were used including linear polarization resistance, electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization. Then, mortar specimens containing BPT were tested under accelerated exposure by simulated seawater spray (modified ISO 11474) and the electrochemical response characterized using electrochemical techniques. Also, the physical-mechanical properties were evaluated. The BPT was found to provide different mechanisms to inhibit rebar corrosion including, adsorption on the material (EIS results) and reduced mortar permeability (resistivity and capillary absorption tests). Furthermore, BPT (at the optimal concentration) did not affect the mechanical properties of the mortar.This work highlights the efficacy of an eco-friendly corrosion control technology to extend the service life of critical reinforced concrete structures for a sustainable future.

(Corrosion Division Rusty Award for Mid-Career Excellence) Enhancing the Corrosion Resistance of Additively Manufactured Metallic Materials: The Role of Feedstock Modification

The properties of metallic materials produced through additive manufacturing (AM), including their corrosion behavior, depend on various parameters such as the type of AM technique, processing parameters, built environment, and the feedstock used [1]. These factors collectively influence the occurrence of processing defects and the microstructure of the alloy, which can be controlled through feedstock modifications. To illustrate the impact of feedstock modification on both microstructure and corrosion, two examples will be presented. These examples will compare the corrosion behavior of additively manufactured 316L stainless steel (SS) produced using three different types of feedstocks: the as-received feedstock, feedstock modified with CrN, and feedstock modified with carbon nanotubes. The feedstock modification was carried out by ball milling of commercial 316L SS powder with the selected additive [2-4]. Test coupons were produced by laser powder bed fusion of the commercial feedstock and modified feedstock. Corrosion resistance was evaluated using cyclic potentiodynamic polarization tests in NaCl solution. The pitting and repassivation potentials of the 316L SS produced by modified feedstock were significantly higher compared to those of 316L SS produced using as-received feedstock [2-4]. The mechanistic aspects of the feedstock modifications and their influence on corrosion behavior will be discussed in detail.1. V.B. Vukkum, R.K. Gupta, Review on Corrosion Performance of Laser Powder-Bed Fusion Printed 316L Stainless Steel: Processing Parameters, Manufacturing Defects, Post-Processing, Feedstock, and Microstructure, Materials & Design, 221, 110874 (2022)2. A. Nieto, V. B. Vukkum, P. Jalagam, K. Nema, J. Budan, R.K. Gupta, T.Y. Ansell, 3D Printed Carbon Nanotube Reinforced Stainless Steel via Selective Laser Melting, MRS Communications 12, 578, 20223. V.B. Vukkum, J. Christudasjustus, A.A. Darwish, S.M. Storck, R.K. Gupta, Enhanced corrosion resistance of additively manufactured stainless steel by modification of feedstock, npj Materials Degradation 6, 1 (2022)4. V.B. Vukkum, F. Ozdemir, S. Storck, R.K. Gupta, Corrosion performance of feedstock modified - Additively manufactured stainless steel. Corrosion Science, 209, 110724 (2022).

Corrosion Electrochemistry at Micro/Nano-Scale

A fundamental understanding of corrosion mechanisms is the key to developing suitable corrosion protection approaches for metallic structures and new corrosion resistant alloys for emerging technologies. However, corrosion testing methods such as mass loss and conventional electrochemical testing average over large areas and thus often mask the underlying mechanisms, due to either low sensitivity, low resolution, and/or a lack of element-resolved information. Recent advances in electron microscopy have led to development of liquid-cell transmission electron microscopy (LC-TEM) that allows in-situ monitoring of morphological and even compositional evolution in materials at high spatial resolution during interactions of surfaces with aqueous environments. However, electrochemical testing in such restricted volume with a very thin (~ 500 nm) electrolyte layer places stringent demands not only for a reference electrode, but also for a comprehensive understanding of the factors affecting electrochemical kinetics at the nano-scale1.In order to solve the need for a micro-reference electrode, we recently proposed the concept of metallic Luggin-Haber probe2. The metallic Luggin-Haber probe is a metal wire that serves as a bridge between the test solution and the reference electrode that was in a physically-distinct container. In standard-scale electrochemical cells, it was found that the metal bridge (MB) provides a means of making potential measurements that are identical to those made using a direct reference electrode or using a salt bridge.The MB is shown to be compatible with a wide range of electrochemical techniques including cyclic potentiodynamic polarization and electrochemical impedance spectroscopy. The present work explores the compatibility of the MB for electrochemistry in LC-TEM using Pt as working electrode. The work includes the effect of radiolysis of electrolyte, electrolyte flow rate, pH and potential scan rate on electrochemical kinetics when using LC-TEM, in a detailed comparison with results obtained using a standard-scale electrochemical cell. Present work is a discrete effort towards developing advanced methodologies for electrochemical measurement in situations involving restricted electrolyte volume including thin electrolyte layers, droplets, localized corrosion sites, batteries and fuel cells. References A. Kosari, H. Zandbergen, F. Tichelaar, P. Visser, H. Terryn, and A. Mol, Corrosion, 76, 4–17 (2020).S. Choudhary, K. Marusak, T. Eldred, and R. G. Kelly, J. Electrochem. Soc., 169, 111505 (2022).

The effect of Fe-anion interactions on corrosion of ferrous surfaces by phosphonium ionic liquids

Experiments and simulations were used to investigate interactions between ferrous surfaces and trihexyltetradecylphosphonium benzoate or salicylate. Differences between the ionic liquids were observed in open circuit potential, potentiodynamic polarization, cyclic potentiodynamic polarization, electrochemical impedance spectroscopy, and long-duration corrosion tests. While both ionic liquids were far less corrosive than water, salicylate exhibited slower charge transfer and lower surface protection potential than benzoate. These observations were analyzed using simulations of chemical reactions between ions and an ideal Fe(100) surface. Simulation results showed that salicylate and benzoate differed in their bonding configurations and orientations, suggesting distinct adsorption mechanisms for these similar ionic liquids.

Coconut coir dust extract as a novel green corrosion inhibitor for carbon steel in the chloride-contaminated concrete pore solution

The potential of coconut coir dust to inhibit corrosion, especially the pitting of rebars in concrete was tapped by electrochemical techniques. Electrochemical impedance spectroscopy and linear polarization results show that both deionized water and ethanol extracts of coconut coir dust can slow down corrosion development by forming a protective film even after long-term exposure to chloride and the latter performs better and is more stable. Cyclic potentiodynamic polarization results further show that ethanol extract at a concentration of 0.1 g/L can significantly delay the initiation of pitting. This inhibitor has exhibited the highest inhibition efficiency, which can be sustained at over 90 % even after six months of immersion in solutions with high chloride concentration, but increasing the concentration of the inhibitor does not result in any additional improvement in its efficiency. Critical chloride concentration for corrosion initiation prediction and corrosion resistance evaluation was also discussed.

High performance aluminized Monel coatings with prolonged corrosion resistance in saline environment

This study compares the corrosion resistance of as-sprayed and aluminized Monel 400 coatings annealed at 900 °C, and deposited on sand-blasted stainless steel. The coatings were immersed in 3.5 wt % NaCl solutions and analyzed using electrochemical impedance spectroscopy and cyclic Potentiodynamic polarization techniques for up to 100 days. Microstructural analysis showed decreased porosity as well as oxide and aluminide layer formation in annealed Monel 400 coatings. Formation of aluminides enhances the Vicker's hardness up to 4 times as compared to as-sprayed coatings. The results showed that the annealed coatings, particularly the aluminide coatings, exhibited higher corrosion resistance than the as-sprayed coatings. Additionally, the corrosion rate decreased exponentially, and the polarization resistance increased significantly as the immersion time increased. This study provides insights into cost-effective Ni-based coatings for corrosion resistance applications.

Electrodeposition of neodymium from betaine-ethylene glycol deep eutectic solvent using neodymium oxide as a precursor

The electrodeposition of neodymium was investigated in betaine-ethylene glycol (Bet-EG) deep eutectic solvent (DES) containing neodymium oxide (Nd2O3) at different temperatures ranging from 353 K to 373 K. The electrochemical behavior of Nd2O3 dissolved in Bet-EG DES was researched by cyclic voltammetry, potentiodynamic polarization and chronoamperometry methods. Cyclic voltammograms (CVs) manifest that Nd(III) reduction in Bet-EG is an irreversible process with diffusion-controlled, and the reduction overpotential of Nd(III) decreases with the increase of the temperature. The temperature has an impact on the diffusion coefficient of Nd(III) species, obeying the Arrhenius equation. The activation energy is estimated to be 36.78 kJ mol−1. The cathodic polarization analysis shows that the rise of temperature promotes the reduction of Nd(III). The UV–Vis and ESI-MS analyses show that [Nd2(bet)8(H2O)4]6+ complex anions are formed as Nd2O3 is dissolved in Bet-EG DES. Electrodeposited neodymium with various morphologies were characterized and analyzed by EDX, XPS, XRD and SEM. It is found that the electrodeposition temperature has a great effect on the morphology of Nd electrodeposits. Depending on the deposition temperature, metallic Nd with submicron particles or porous structures were obtained.

Tensile Effect on Sensitization and Corrosion Resistance of Stainless Steels

The purpose of this research is to investigate cold work effect on corrosion behavior of stainless steels of type AISI 304, AISI 316L and AISI 2101. The specimen were processed through cold work simulated by the tensile test at various percentages elongation and then tempered at 600°C for different time intervals. Two electrochemical techniques and hardness test were utilized in this investigation. The first technique was the double loop electrochemical potentiokinetic reactivation (DL-EPR) that yields the values of degrees of sensitization (DOS). The second one was the cyclic potentiodynamic polarization (CPP) to study the ability of the metals to build or repair the damaged films under localized corrosion. The DOS values from the DL-EPR tests of the samples under the same heating conditions suggested that specimens drawn at higher percentage elongation tend to have more chromium depleted areas. Also, the test specimens with more exposure time to heat were more prone to chromium deficiencies. As for the ability of the metal to create or repair damaged film after corrosion has occurred, it was found that AISI 316L had hihger corrosion resistance than AISI 304. However, AISI 2101 stainless steel had highest corrosion resistance. In this study, it was also found that AISI 2101 did not exhibit pitting corrosion, but the crevice corrosion. This could be due the fact that AISI 2101 which is a duplex stainless steel has high corrosion resistance and could trigger the crevice corrosion take place before the pitting initiation.

Interphase corrosion inhibition mechanism of sodium borate on carbon steel rebars in simulated concrete pore solution

Sodium borate (Na2B4O7) corrosion inhibition mechanism was studied on carbon steel rebars in 0.6 mol/L Cl– simulated concrete pore solution (SCPS) at different temperatures and concentrations. Electrochemical testing including cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and Mott–Schottky plots were utilized to understand the influence of inhibitor concentration and temperature on the thermodynamics of the adsorption and activation processes. It was found Na2B4O7 imparts corrosion protection due to the formation of a 3D Fe–B–O stable interphase passive film, achieving an inhibition efficiency up to 86%. This can be attributed to the film having a lower donor current density and less vacancies, according to the Mott–Schottky tests. The formed interphase passive film was more stable and compact with less point defects compared to the blank due to Na2B4O7 adsorption, this phenomenon was substantiated using the atomic packing factor, film thickness, and Mott–Schottky plots. It was revealed, using adsorption isotherms, that Na2B4O7 interacted with the surface via physiochemical adsorption, creating a thinner/compact passive film composed of a rhombohedral calcite-type structure. SEM, XRD, and XPS were used to illustrate that Na2B4O7 aides in the formation of a stable double-layered net structure Fe2O3/FeBO3 passive oxide film. Finally, an interphase corrosion inhibition mechanism of Na2B4O7 was proposed.

The concentration effect of HF on pitting corrosion behavior of 904 L SS in a phosphoric environment

The electrochemical behavior of 904 L austenitic stainless steel is investigated in an industrial phosphoric acid, with a focus on the synergetic effect of HF and chloride and the concentration effect of HF. For this purpose, electrochemical measurements such as cyclic potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) have been used. Cyclic potentiodynamic polarization demonstrated that chlorides affect mainly the activation domain density and the presence of HF alongside chloride enhances this effect. Also, HF affects especially the passive and trans-passive domains by enhancing the appearance of the hysteresis which is a sign of the appearance of local corrosion. Whereas, the presence of HF alongside Cl− makes the passive film more destabilized, asserting the synergetic effect of these two species on weakening the protective layers. Furthermore, EIS revealed that HF promotes the dissolution of the outer layer, aggressively affecting the inner layer resistance, and resulting in a loss of protective properties. These findings are confirmed by Raman and UV–Vis spectroscopy. Scanning electron microscopy (SEM) analyses assert that in the presence of HF, a new type of large-shape pitting corrosion appeared on the surface.

Influence of carbon nanotubes on microstructure and corrosion performance of additively manufactured 316L stainless steel

Laser powder bed fusion (LPBF) was performed on feedstock-modified 316L stainless steel powder with 1 and 2 vol% carbon nanotubes (CNT). The corrosion resistance was evaluated following cyclic potentiodynamic polarization tests conducted in 0.6 M NaCl at room temperature, 35 and 50 °C, and immersion tests in 6 % FeCl3. The CNT addition has increased the pitting potential and decreased number of pits formed during immersion in FeCl3 solution, which could be attributed to Mn-Si-O nano inclusions refinement and segregation of chromium around the inclusions. The observed corrosion behavior was correlated with the altered microstructure due to CNT addition.

Corrosion resistance and microstructure analysis of additively manufactured 22% chromium duplex stainless steel by laser metal deposition with wire

Microstructure characteristics and pitting corrosion of a duplex stainless steel (DSS) manufactured by laser metal deposition with wire (LMDw) were studied. The layer-by-layer LMDw process resulted in a mixed microstructure of predominantly ferrite with 2% austenite and chromium-rich nitrides, and reheated regions with ∼33% austenite. The high cooling rate of LMDw restricted the distribution of Cr, Mo, and Ni, in ferrite and austenite, while N diffuses from ferrite to austenite. Subsequent heat treatment at 1100 °C for 1 h resulted in homogenized microstructure, dissolution of nitrides, and balanced ferrite/austenite ratio. It also led to the redistribution of Cr and Mo to ferrite, and Ni and N to austenite. At room temperature, cyclic potentiodynamic polarization measurements in 1.0 M NaCl solution showed no significant differences in corrosion resistance between the as-deposited and heat-treated samples, despite the differences in terms of ferrite to austenite ratio and elemental distribution. Critical pitting temperature (CPT) was the lowest (60 °C) for the predominantly ferritic microstructure with finely dispersed chromium-rich nitrides; while reheated area with ∼33% austenite in as-deposited condition achieved higher critical temperature comparable to what was obtained after heat treatment (73 and 68 °C, respectively). At temperatures above the CPT, selective dissolution of the ferrite after deposition was observed due to depletion of N, while after heat treatment, austenite preferentially dissolved due to Cr and Mo concentrating in ferrite. In summary, results demonstrate how microstructural differences in terms of ferrite-to-austenite ratio, distribution of corrosion-resistant elements, and presence of nitrides affect corrosion resistance of LMDw DSS.

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.