Passive Film Resistance Research Articles

Multi-scale investigation of stainless-steel passivation in seawater concrete pore solution

Stainless-steel bars can be effectively used in seawater sea sand concrete due to their excellent resistance to chloride ions, contributing to resource conservation and sustainable development. However, the underlying impact mechanism of chloride ion on the passivation of stainless steel in seawater sea sand concrete has not been thoroughly studied. In this work, a multi-scale study was carried out to reveal the role of chloride ion on the passivation of stainless-steel bar in concrete. At the macro level, the presence of chloride ions reduced the corrosion resistance of the stainless-steel passive film, but did not cause corrosion. On the micro level, chloride ion interfered with the phase transformation of the passive film, increased Cr oxides and decreased the loose Fe3 + oxides. From the atomic view of point, the incorporation of chloride into the passive film was mainly due to the higher adsorption energy of Fe2O3 and Cr2O3 with chloride ion, increasing the reactivity of passive film. The presence of Mo in the outer layer of passive film presented a much lower adsorption energy of chloride compared with Fe2O3 and Cr2O3, impeding the ingress of chloride ion in the inner layer. Density functional theory (DFT) calculation complimented the knowledge of interaction of chloride ion with the passive film.

A study integrating in-process thermal signatures, microstructure, and corrosion behaviour of AISI 316L coatings on low carbon steel substrate deposited by laser-directed energy deposition (L-DED)

Surface coating through Laser Directed Energy Deposition (L-DED) of AISI 316L on low-carbon steel was carried out by varying laser fluence. The resulting melt pool characteristics, obtained through IR pyrometer, played a significant role in evolution of the microstructure. A higher heat input resulted in an equiaxed grain structure with finer grain sizes and improved deposition quality. The quantitative phase analysis revealed the presence of a dominant austenite phase and a secondary ferrite phase, along with traces of molybdenum carbide. Corrosion analysis reveals improved resistance at a higher laser fluence, attributed to increased content of corrosion-resistant alloying elements (Mo, Cr) and predominance of the austenite phase. Electrochemical Impedance Spectroscopy (EIS) confirms a higher corrosion resistance at a higher laser fluence, supported by a significantly higher polarization resistance and presence of a duplex-structured passive film. Results indicate that moderate laser fluence levels, ranging from 5 to 7.5 kJ/cm2, accompanied by medium to high thermal signatures and moderate cooling rates, yield coatings with refined microstructures, enhanced mechanical strength, and corrosion resistance. For superior corrosion resistance, a laser fluence of 10 kJ/cm2 is recommended, although careful consideration of its potential impact on mechanical properties is advised.

Assessing Nonlinear Polarization in Electrochemical Cells Using AC Impedance Spectroscopy

Electrochemical energy storage and conversion devices are used to power a range of electrical loads including portable electronics, electric vehicles, and utility grids. The energy efficiency of these systems decreases with increasing current load due to energy losses (in the form of heat) associated with different processes. Electrochemical impedance spectroscopy (EIS) is a nondestructive technique commonly used to assess rate-limiting steps in electrochemical devices. Most EIS measurements for energy storage devices are only performed around open-circuit and do not probe system behavior under non-zero biases where these devices operate. Despite its widespread use, this approach does not provide information about the relative overpotentials associated with coupled nonlinear processes (e.g., diffusion limited redox reactions) commonly encountered in these systems. Furthermore, ambiguous terms such as equivalent series resistance and interfacial resistance can lead to confusion and data misinterpretation. For example, Ohm’s law cannot be applied to calculate nonlinear overpotentials using a resistance that was measured from a locally linear response.To determine overpotentials in nonlinear systems using EIS, one must integrate the individual resistive elements of the equivalent circuit as a function of steady state current. Recent experimental work has used this method to decouple ohmic, kinetic, and transport overpotentials in redox flow batteries. In these prior studies, impedance elements were derived, but analytical expressions for the corresponding overpotentials were not presented.While integrated resistance measurements are a powerful experimental tool, a more rigorous mathematical framework describing the approach is needed. The present work bridges this gap by: (i) deriving a general impedance expression for coupled charge transfer and diffusion processes and (ii) integrating the individual resistive elements as a function of steady-state current to obtain global polarization relationships. Analytical expressions for diffusion overpotentials are obtained for special cases, and numerical methods are applied when closed-form expressions do not exist. The work considers three model electrode geometries (planar, cylindrical, and spherical) and two diffusion boundary types (reflective and transmission). Finally, this treatment is extended to macroscopically homogenous porous electrodes which are relevant for describing practical devices.This presentation will highlight how measuring impedance at different steady-state biases provides critical insights on the rate-limiting processes in energy storage devices. While this work focuses on a simple Faradaic charge transfer process, the method can be used to evaluate other nonlinear phenomena in electrochemical power supplies. For example, the resistance of passive films (e.g., solid electrolyte interphase layer) in Li-ion batteries is typically only probed near open-circuit. Similarly, literature on solid-state batteries commonly uses ambiguous terms such as interfacial resistance to describe rate-limiting processes. For these more complex systems, integrating the resistive elements can provide insights on how these phenomena influence device efficiency. Overall, combining these experimental observations with physical models derived using the approach illustrated herein represents a powerful tool to guide component/system design and improve device performance. Acknowledgements This research was conducted at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE). This work is sponsored by the U.S. Department of Energy in the Office of Electricity through the Energy Storage Research Program and the Office of Energy Efficiency and Renewable Energy (EERE) in the Vehicle Technologies Office (VTO) through the Advanced Battery Materials Research (BMR) Program.

Stability of passive film and pitting susceptibility of 316 L stainless steel in the aggressive oilfield environment containing Cl−-CO2-O2

In this paper, the effects of chloride ions, oxygen, and carbon dioxide on the corrosion resistance of passive films formed on 316 L stainless steel were investigated in the aggressive oilfield environment using electrochemical testing and microscopic characterization techniques. The results showed that Cl− accelerated the anodic dissolution of the metal and compromised the structure and densification of the passive film, thus reducing its corrosion resistance. An increase in the partial pressure of carbon dioxide initially promotes pitting, but subsequently inhibited further corrosion development. The presence of oxygen enhanced the cathodic reaction and passive film formation, effectively preventing the invasion of aggressive chloride ions, thus inhibiting further corrosion. These findings provide a significant scientific basis for material selection and protection of oil extraction equipment in oilfield environments.

Tribocorrosion behaviour of additively manufactured β-type Ti–Nb alloy for implant applications

β-type Ti–Nb alloys are promising materials for load-bearing implant applications with improved mechanical biofunctionality and biocompatibility. In this work, the electrochemical and tribo-electrochemical behaviour of laser powder bed fusion (LPBF) produced β-type Ti–42Nb alloy processed via Gaussian and top hat laser was investigated and compared with commercial grade β-type Ti–45Nb and α+β-type Ti–6Al–4V ELI. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization experiments were performed in phosphate-buffered saline (PBS) for corrosion behaviour. Tribocorrosion behaviour was studied under open circuit potential (OCP) conditions in PBS by using a reciprocating pin-on-disk tribometer. The passivation nature of the LPBF alloys is more decisive than the microstructural particularities for electrochemical behaviour. The overall corrosion response is similar due to the protective nature of the passive films formed on Ti alloys. Ti–6Al–4V ELI exhibits the best corrosion performance among all tested alloys with lower corrosion and passivation current density values. However, LPBF-produced alloys exhibit less reactive surfaces with better passive film properties compared to Ti–45Nb. In addition, EIS results revealed that passive film resistance values are higher for LPBF-produced alloys than conventionally produced Ti–45Nb. LPBF-produced alloys exhibit better tribo-electrochemical behaviour compared to Ti–45Nb. The differences in volume loss are mainly attributed to the microhardness of the alloys and the volume loss is dominated by mechanical wear. The alloys produced with LPBF show promising corrosion and tribocorrosion performance to be a potential candidate for load-bearing implant applications.

Effect of overlap rate on the microstructure and properties of Cr-rich stainless steel coatings prepared by extreme high-speed laser cladding

In this work, Cr-rich stainless steel coatings at different overlap rates were prepared by extreme high-speed laser cladding (EHLA) technology, and microstructures, elemental distributions, phase compositions, electrochemical corrosion behaviors, and frictional wear properties were analyzed. The results indicated that increasing the overlap rate enhanced the coating's surface quality and microstructural density. The grain sizes of the coatings at overlap rates of 60 %, 70 %, and 80 % were 2.63 μm, 2.08 μm, and 1.14 μm, respectively. The coatings were predominantly composed of martensite and residual austenite, and residual austenite was extensively distributed within the coatings with a high overlap rate. Electrochemical corrosion results revealed that the coating with an 80 % overlap rate exhibited the best corrosion resistance, with a transfer resistance (Rt) of 981.05 kΩ·cm2 and a passive film resistance (Rc) of 227.31 kΩ·cm2, surpassing other coatings. Under the load of 5 N, the coating's wear rate at 80 % overlap rate was 3.91 × 10−6 mm3/N·m, demonstrating excellent wear resistance. The dense microstructure and refined grain structure assisted the coating in forming a stable passive film during the corrosion stage. The enhancement in coating hardness promoted the rapid development of the oxide film, thereby strengthening the coating's wear resistance properties.

Comparative Study on Passive Film Formation Mechanism of Cast and PBF-LB/M-TC4 in Simulated Physiological Solution.

Personalized laser powder bed fusion (PBF-LB/M) Ti-6Al-4V (TC4) has a broader application prospect than that of traditional casting. In this paper, the composition and corrosion resistance of the passive film formation mechanism of TC4 prepared by optimization of PBF-LB/M techniques and traditional casting were systematically studied in 0.9 wt.% NaCl at 37 °C by electrochemical technique and surface analysis. The rates of the passive film formation process, corrosion resistance and composition of TC4 show different characteristics for the different preparation processes. Although the rate of passive film formation of cast-TC4 was higher at the initial immersion, the open circuit potential was more positive, and the film thickness was larger after stabilization, those facts show no positive correlation with corrosion resistance. On the contrary, with no obvious defects on the optimized PBF-LB/M-TC4, the passive film resistance is 2.5 times more, the defect concentration is reduced by 30%, and the TiO2 content is higher than that of the cast-TC4, making the martensitic-based PBF-LB/M-TC4 exhibit excellent corrosion resistance. This also provides good technical support for the further clinical application of PBF-LB/M-TC4.

Corrosion resistance of additively manufactured aluminium alloys for marine applications

Additive manufacturing opens new possibilities for designing light-weight structures using aluminium alloys. The microstructure of two Al alloys and their corrosion resistance in NaCl and natural seawater environments were investigated. The newly designed Al-Mn-Cr-Zr based alloy showed a higher corrosion resistance than reference AlSi10Mg alloy in both environments in as printed and heat-treated conditions. The corrosion initiated in the Al matrix along the precipitates in the alloys where the Volta potential difference was found the highest. The coarser microstructure and precipitate composition of the new Al-alloy led to the formation of a resistant passive film which extended the passivity region of the Al-Mn-Cr-Zr alloy compared to the AlSi10Mg alloy. The effect of heat treatment could be seen in the microstructure as more precipitates were found in between the melt pool boundaries, which affected the corrosion initiation and slightly the pitting resistance. Overall, this study shows that a newly designed Al-alloy for additive manufacturing has a suitable corrosion resistance for applications in marine environments.

DFT study on Mo-stabilized passive films: Hydroxylation effects on chromium and iron oxide surfaces

Hydrous Cr2O3 and Fe2O3 surfaces without and with substitutional molybdenum were simulated by DFT modelling to investigate at the atomic scale the role of Mo in improving the corrosion resistance of passive films on stainless steels. The surface structures most energetically favoured were determined in the conditions of interest. For surfaces with a high degree of hydroxylation, the preferential location of substitutional Mo is just under the hydroxyl groups, in agreement with the experimental observations. The substitution by Mo is exothermic and Mo preferentially substitutes in Fe- than in Cr-rich zone of the inner barrier layer of passive films.

Effect of non-metallic carbon content on the microstructure and corrosion behavior of AlCoCrFeNi high-entropy alloys

The addition of carbon has been reported to improve the corrosion resistance of various alloys. However, few studies have investigated the effect of non-metallic elements on the corrosion behaviour of AlCoCrFeNi high-entropy alloys (HEAs), which are among the most extensively developed alloys and potential alternatives to structural materials. Therefore, herein the microstructure and corrosion behaviour of AlCoCrFeNiCx (x = 0, 0.1, 0.2, 0.3, and 0.4 in molar ratio) HEAs were studied in a 3.5 wt% NaCl solution. The results show that adding carbon increased the carbide (Cr23C6) content and reduced the mean grain size. Further, increasing the carbon content improved the stability of the passive film and corrosion resistance of the AlCoCrFeNiCx HEAs. The corrosion resistance of AlCoCrFeNiC0.4 HEAs is optimal, and the passive current density is 2.57 μA/cm2, which is 0.16 times that of AlCoCrFeNi HEAs without carbon. The corrosion mechanisms of the AlCoCrFeNi HEAs with various carbon contents were also elucidated. The results of this study provide excellent theoretical guidance and experimental basis for the development and application of corrosion-resistant metallic materials.

Corrosion Resistance, Composition, and Stratification of Passive Films: Ni-22Cr and Ni-22Cr-6Mo Alloys Passivated and Exposure Aged in Acidic Chloride Solutions

Ni-Cr based super-alloys have exceptional corrosion resistance, which is further improved with Mo alloying. The correlation between passive layer performance and composition was studied to gain a deeper mechanistic understanding of the role of Mo by comparing the behavior of Ni-22Cr to Ni-22Cr-6Mo (wt%) alloys. The passive layers were formed using galvanostatic holds to create fast and slow growth conditions using high and low current densities. A potentiostatic hold was added to initiate exposure aging. The passive film was characterized using electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), atomic emission spectro-electrochemistry (AESEC), and X-ray photoelectron spectroscopy (XPS). Combined electrochemical and XPS characterization offered insight in cation concentrations and stratification, bonding states (oxide, hydroxide), and their modulation as a function of electrochemical conditions and performance. Most importantly: (i) Mo addition enhanced Cr(III) bound in oxide, (ii) fast growth conditions resulted in less corrosion resistant films, and (iii) exposure aging increased Cr-enrichment and reduced stratification of Mo-cations. The correlation between passive film performance and Cr, Ni, and Mo oxidation states, bonding, oxide-hydroxide contributions, and stratification is discussed. Generally accepted correlations, such as Cr-cation concentration and performance of the passive layer, have to be reexamined in order to account for the complex chemical make-up of the passive layer.

Effect of h-BN on corrosion behavior of nickel-copper alloy coatings prepared by high-speed laser cladding

Nickel-copper alloy is widely used because of its strong corrosion resistance in marine environment. There are great potentials to prepare NiCu alloy coatings on the surface of structural steel to replace cast NiCu alloys due to its high cost. High-speed laser cladding has characteristics of fast melting rate, low surface roughness, fine microstructure and low dilution ratio. However, nickel alloy coatings has the problem of solidification cracks. In this study, a series of composite coatings were prepared by using NiCu powders with different h-BN contents, then the effect of h-BN on structure and anti-corrosion of coatings was analyzed. The study shows that the structure of the NiCu composite alloy coatings was equiaxed crystals, columnar crystals and planar crystals from top to bottom portion. After adding h-BN, the coating had a lower oxygen vacancy mobility rate, resulted in the optimal corrosion resistance of passive film.

Mechanical Integrity and In vitro Degradation Behavior of Mg–Zn–Ca Biodegradable Alloy Prepared by Different Casting Technologies

Mg–Zn–Ca alloys have been widely used as biodegradable orthopedic and cardiovascular scaffolds because of their non-cytotoxicity, remarkable biodegradability, good biocompatibility and excellent mechanical properties similar to human bone. However, degradation causes poor corrosion resistance and mechanical properties. In this study, Mg-6%Zn-0.6%Ca alloys were produced using three distinct methodologies: casting, casting via the ultrasonic vibration process (USV), and casting via the mechanical vibration process (MV). Surface characterization, mechanical characteristics and corrosion resistance of the as-cast (untreated) and treated species were studied. The morphology and microstructure showed that the grain size of the as-cast, MV and USV specimens all had average grain sizes of about 191, 93 and 82 µm, respectively. The ultrasonic vibration treated specimen has the greatest degree of grain refinement. Mechanical tests showed that microstructure refinement promotes the mechanical characteristics of Mg alloy, such as compression, ultimate tensile strength as well as elongation. It was observed that the USV-treated sample has exceptional mechanical properties (Compressive strength 360.64 MPa, ultimate tensile strength (UTS) 178.41 MPa and Elongation 3.45%). Corrosion tests revealed that the USV-treated specimen exhibited uniform corrosion and low corrosion rate due to uniform compact fine grains with higher oxide concentration of about 42.82 wt%. The results of electrochemical analyses revealed that the average corrosion rate obtained from Potentiodynamic polarization curves of the as-cast, MV and USV specimens was about 5.3144, 4.5311 and 4.1087 mm/year, respectively and the passive film resistance (Rf) that was obtained from the electrochemical impedance spectroscopy (EIS) model of the USV, MV-treated samples and as-cast sample was 457 Ω, 430 Ω and 204 Ω, respectively. The results of immersion tests revealed that the USV-treated sample lost less weight and exhibits a relatively low degradation rate than the as-cast and MV-treated samples. After two weeks the weight of the as-cast, MV and USV samples decreased by about 18.6%, 18.5%, 16.8%., and the degradation rates were 7.304, 7.097 and 6.78 mm/y, respectively, and then gradually declining over the course of the immersion period.

Development of Novel Coating on Metallic Bipolar Plates for Proton Exchange Membrane Water Electrolyzer Application

Considering the demand for a more environmentally friendly system, renewable and sustainable energy sources, such as wind and solar power are regarded as a promising substitute for fossil fuels in the generation of electricity. Since these energy sources exhibit intermittency and unpredictability, there is a need to develop a highly efficient and rapidly responsive energy conversion system for the purpose of storing this energy as a chemical fuel. Due to their ability to manage the variability of intermittent energy sources, proton exchange membrane electrolyzer cells (PEMECs) are garnering considerable interest. However, their broad commercial adoption is hindered by their relatively modest performance and elevated costs. PEM electrolysis is a promising technology for generating substantial quantities of hydrogen from surplus electricity generated by renewable sources. Nonetheless, the expense of the electrolyzer stack arises primarily from the metallic bipolar plates, because it possesses heavy weight and expensive precious metal coatings. Significant efforts have been performed on the development of titanium-based bipolar plates, but it has high base material and fabrication cost. In recent years, there has been a substantial focus on stainless steel bipolar plates for PEM electrolyzer application. Stainless steel can serve as an alternative, but it requires a coating to enhance its anti-corrosion properties. Electroplated chromium coatings exhibit favorable mechanical characteristics and find extensive application in precision mechanical components such as molds and surgical instruments. Their outstanding wear resistance, high hardness, impressive corrosion resistance, and glossy finish make them appropriate for many other applications, including both decorative and functional coatings. As a result, chromium electroplating has emerged as one of the most extensively employed techniques within the electroplating sector. The dense pack chromium layer is prepared on a 316L stainless steel substrate to enhance the anti-corrosion property and electronic conductivity.Herein, the role of gold striking underlayer, and thick chromium coating is studied for preparing the anti-corrosive stainless steel bipolar plates. First, a gold striking film as an underlayer on the stainless-steel substrate is electroplated to passivate the chromium-based oxides. Further, a thick and dense chromium layer is deposited on the gold underlayer by electroplating. The electroplating bath is operated using platinized titanium felt as an anode and 316L stainless steel as a working electrode without the separation of anodic and cathodic compartments. The electroplating solution is consisting of Cr (VI) oxide and H2SO4 (pH = 2). The nanocrystalline chromium coating with a thickness of approximately 2 µm is bright and uniform. Furthermore, gold as a protective layer of thickness approximately 1 µm is coated by electroplating on the chromium surface. The Cr and Au/Cr coatings are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron microscopy (XPS) analysis. Subsequently, the protective layer-coated substrates were analyzed in a simulated PEM electrolyzer environment, and these coatings facilitated promising protective properties on the stainless-steel substrate. The corrosion testing was carried out in 0.5 M H2SO4 + 2 ppm HF solution at 70 0C purged with oxygen. The stable passive film and high corrosion resistance were obtained by gold striking underlayer and chromizing the 316L stainless steel substrate. As a result, the potentiodynamic polarization analysis showed the corrosion current density of 0.84 µA/cm2 for the Au/Cr-Au underlayer sample in a simulated operating environment. In contrast, the absence of the gold striking underlayer between Cr and stainless steel causes the pitting corrosion. The Au/Cr coating is tested in an acidic corrosion media for a long duration of 24 hours and it showed lower degradation as compared to without gold striking underlayer and without Cr film. The findings presented in this study illustrate the feasibility of employing stainless steel as the foundational material for the bipolar plate of a PEM electrolyzer.

Investigation of the electrochemical behavior of a newly designed TiMg dental implant

This study is aimed to evaluate the galvanic corrosion of a newly designed TiMg dental implant. The TiMg composite was tested in two forms: (1) cylinders (TiMg cyl) and (2) dental implants (TiMg DI). Surface roughness was measured using a confocal microscope. The electrochemical behavior was determined in a Hank’s balanced salt solution (HBSS) by the open-circuit potential (OCP), potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) measurements. Surfaces after corrosion were examined by a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). OCP of TiMg cyl and TiMg DI increased in the noble direction, indicating the formation and growth of a base film on their surfaces. After 2-h immersion, TiMg cyl had higher values of iCorr and RCorr compared with those of TiMg DI. After 24-h immersion, a prominent reduction in the values of iCorr and RCorr was observed, and ECorr shifted positively. The Nyquist plots of TiMg cyl and TiMg DI show capacitive loops that tended to close after 2-h exposure. As the time extended, TiMg DI showed higher corrosion resistance compared with that of TiMg cyl, and the linear diffusion response arose from the formation and dissolution of chemically non-stable by-products caused by the hydrogen evolution. In such a case, the involved reaction was controlled by charge transfer and diffusion processes. The formation of a film composed of stable CAp species that attached directly to the surface and chemically non-stable by-products that included (Mg3(PO4)2) and Mg(OH)2 was demonstrated. To conclude, the obtained results revealed that TiMg DI of a complicated threaded design had a more stable passive film and higher corrosion resistance in HBSS compared with those of TiMg cyl of a cylindrical design. These findings have the utmost importance for the fabrication of dental implants.Graphical abstract

Study on corrosion resistance of passive film promoted by natural rosin-based passive sealant

An eco-friendly Rosin-based passive sealant is prepared, which can seal the micropores and repair the passive film in one-step. Sealing performance of sealants and the growth kinetics of the passive film were analyzed by 3D-XRT tomography, Electrochemistry and XPS. The results showed that the permeation depth of sealant reached more than 150 μm, and the natural rosin effectively prolonged the loss time of sealant. The phosphate conversion layer at the passive film/sealant interface changes the semiconductor properties of the passive film. After immersion for 360 h in 3.5 wt% NaCl solution, the amount of Fe2O3 and Cr2O3 in the passive film increased by 34 % and 20 %, respectively, and the film thickness increased by 257.9 %. Rosin-based passive sealant can directly inhibit the diffusion rate of defects in passive film. This study provides a new theoretical support for the application of rosin sealant.

Influence of a D-enantiomeric peptide on the anticorrosion ability of titanium with different surface roughness against Streptococcus mutans biofilms

ObjectiveTo investigate the effectiveness of a d-enantiomeric antibiofilm peptide (DJK-5) on the anticorrosion ability of titanium (Ti) with different surface roughness against Streptococcus mutans biofilms. MethodsCommercially pure Ti disks with machined (MA, smooth) or sandblasted + acid-etched (SLA, rough) surfaces were prepared and characterized. All disks were divided into three groups: a positive control (PC) group with S. mutans, a DJK-5-treated group, and a negative control (NC) group without S. mutans. Biofilm formation and corrosion on Ti surfaces were determined by confocal laser scanning microscopy and scanning electron microscopy after 2 and 6 days, and the electrochemical properties were evaluated. ResultsTen μg/mL of DJK-5 killed 83.3 % and 87.4 % of biofilms on SLA and MA Ti surfaces, respectively after 2 days, and 72.9 % and 77.7 % after 6 days, with more bacteria surviving on SLA surfaces with higher roughness (p < 0.05). DJK-5 treatment induced less surface defects with tiny pit corrosion than PC. DJK-5 treatment when compared to PC, led to electrochemical properties more reflecting NC surfaces, including significantly less negative corrosion potential, lower corrosion current, and higher passive film resistance (p < 0.05). SLA surfaces exhibited higher current density and lower resistance than MA surfaces (p < 0.05). ConclusionDJK-5 effectively enhanced the corrosion resistance of Ti with different surface roughness while killing S. mutans biofilms, and smooth surfaces were more susceptible to peptide treatment. Clinical significanceThe antibiofilm peptide is promising for promoting the anticorrosion ability of Ti against biofilms, thereby preventing biofilm-related infections.

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.

Crevice Corrosion of High-Grade Stainless Steels in Seawater: A Comparison Between Temperate and Tropical Locations

The corrosion risk for stainless steel components is not the same in all seawaters, with more failures generally reported in tropical seas. In this study, the influence of biofilm on electrochemical behavior and corrosion resistance of passive films of high-grade alloys was studied in different seawaters, including temperate seawater (France-Brest, North Atlantic Ocean), tropical seawater (Malaysia-Kelatan, Meridional China Sea), and intermediate conditions in terms of temperature (Brazil-Arraial do Cabo, South Atlantic Ocean). The stabilized open-circuit potentials and the polarization behavior of high-grade stainless steels were measured as a function of temperature in all of the tested field marine stations, providing quantified data and direct comparison of the biofilm-enhanced corrosion risks. Significant differences were measured in tropical and in temperate seawaters in heated conditions. Above 37°C, the biofilm activity was much more pronounced in tropical seawater compared to Atlantic Ocean sites, leading to much higher localized corrosion risk. Crevice corrosion of eight high-grades passive alloys was also studied with the use of crevice formers specifically developed for tube geometries. Duplex UNS S32205, superduplex UNS S32750, hyperduplex UNS S33207 and S32707, and 6Mo stainless steels UNS S31266 have been evaluated together with Ni-based alloys UNS N06845 and N06625. In the more severe conditions, the high-grade alloys UNS S32707 and the 6%Mo UNS S31266, both with pitting resistant equivalent number (PREN) around 50, showed better performance than commonly used superduplex UNS S32750 and UNS S39274 (PREN 40). The corrosion results are discussed regarding the monitored biofilm-induced depolarization measured in the different test conditions.

Effect of minor gallium addition on corrosion, passivity, and antibacterial behaviour of novel β-type Ti–Nb alloys

Metastable Ti–Nb alloys are promising bone-implant materials due to improved mechanical biofunctionality and biocompatibility. To overcome increasing bacterial infection risk, alloying with antibacterial elements is a promising strategy. This study investigates the effect of minor gallium (Ga) additions (4, 8 wt% Ga) to as-cast and solution-treated β-type Ti–45Nb-based alloy (96(Ti–45Nb)-4Ga, 92(Ti–45Nb)-8Ga (wt.%)) on corrosion and passive film properties, as well as cytocompatibility and antibacterial activity. The electrochemical properties were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analyses in phosphate-buffered saline (PBS). X-ray photoelectron spectroscopy (XPS) was performed to analyze the chemical composition of passive films. Early adhesion and viability of macrophages and Staphylococcus aureus were assessed by nucleocounting and colony-forming unit counting, respectively. The results showed that high corrosion resistance and passive film properties of Ti–45Nb are retained and even slightly improved with Ga. EIS results revealed that Ga addition improves the passive film resistance. XPS measurements of 92(Ti–45Nb)-8Ga show that the passive film contains Ti-, Nb- and Ga-based oxides, implying the formation of mixed (Ti–Nb-Ga) oxides. In addition, marginal Ga ion release rate was detected under free corrosion conditions. Therefore, it can be assumed that Ga species may contribute to passive film formation on Ga-containing alloys. The 92(Ti–45Nb)-8Ga elicited an antibacterial effect against S. aureus compared to cp-Ti at 4 h. Moreover, Ga-containing alloys showed good cytocompatibility with THP-1 macrophages at 24 h. In conclusion, it was demonstrated that Ga additions to Ti–45Nb are beneficial to corrosion resistance and showed promising initial host and bacterial interactions.