Properties Of Passive Films Research Articles

Surface Chemistry and Semiconducting Properties of Passive Film and Corrosion Resistance of Annealed Surgical Stainless Steel

ASTM F-139 surgical stainless steel was subjected to annealing treatments at 700 °C for different times. The effect of annealing on the chemical composition of the passive film was evaluated by x-ray photoelectron spectroscopy. The correlation of the surface chemistry with the corrosion behavior and semiconducting properties of the passive film was also investigated. Potentiodynamic polarization tests were conducted in phosphate-buffered solution at 37°C. The semiconducting character of the passive film was assessed by the Mott–Schottky approach. The microstructure of the annealed samples was characterized by optical microscopy. The grain size increased after annealing, but the differences between each annealing condition were not significant and could not be associated with the corrosion behavior of the annealed samples. The corrosion resistance was improved depending on the heat treatment condition due to compositional changes of the passive film upon annealing. The best corrosion properties were observed after annealing for 8 h which was ascribed to Cr2O3, MoO3 and FeO enrichment in the passive film.

Synergistic effect of erosion and hydrogen on properties of passive film on 2205 duplex stainless steel

Stainless steels have shown great potential in the application of offshore oil and gas industry. However, the internal surface of stainless steel pipeline may simultaneously suffer erosion from the fluid media inside the pipeline and the damage of hydrogen that is generated from the external activities such as cathodic protection. The synergistic effect of erosion and hydrogen on the properties of passive film on 2205 duplex stainless steel was studied for the first time in a loop system coupled with a hydrogen-charging cell. The components, protective performance and semiconductive structure as well as properties of the passive film under different conditions were investigated using in-situ electrochemical techniques, surface characterization and computational fluid dynamics simulation. The results show that the combination of erosion and hydrogen could greatly thin the passive film, furthermore, the Fe3+/Fe2+ ratio and O2−/OH- ratio in the passive film also decrease dramatically under such a condition. Therefore, the hydration degree of the passive film greatly increases, resulting in an increase in active sites and a decrease in the stability of the passive film. Erosion could destroy the passive film through the impact of sand particles and accelerate the mass transfer process of electrochemical reaction. While hydrogen can not only enhance the charge transfer process, but also make the passive film highly defective. Under the combination of erosion and hydrogen condition, erosion could enhance the hydrogen damage and simultaneously hydrogen could also enhance erosion. Therefore, the synergistic effect of erosion and hydrogen could dramatically change the passive film component, decrease the protective performance, and increase the susceptibility of pitting corrosion of 2205 stainless steel in Cl--containing environment.

Study on corrosion behavior of the selective laser melted NiTi alloy with superior tensile property and shape memory effect

Corrosion has been treated as one of the biggest risks on implantation failure of selective laser melting (SLM) fabricated NiTi implants. This study performed corrosion tests in simulated body fluid at 37 ℃ on SLM-fabricated NiTi alloy. The mechanical property, electrochemical performance, microstructure, surface roughness, surface potential difference, electronic property and composition of passive film formed on the surface of SLM-fabricated NiTi alloy were detailed characterized. It has been revealed that the corrosion resistance performance was dependent on the building direction of the sample. The detail corrosion resistance mechanism was discussed in the paper.

Passive Film Properties of Bimodal Grain Size AA7075 Aluminium Alloy Prepared by Spark Plasma Sintering.

The bimodal-grain-size 7075 aluminium alloys containing varied ratios of large and small 7075 aluminium powders were prepared by spark plasma sintering (SPS). The large powder was 100 ± 15 μm in diameter and the small one was 10 ± 5 μm in diameter. The 7075 aluminium alloys was completely densified under the 500 °C sintering temperature and 60 MPa pressure. The large powders constituted coarse grain zone, and the small powders constituted fine grain zone in sintered 7075 aluminium alloys. The microstructural and microchemical difference between the large and small powders was remained in coarse and fine grain zones in bulk alloys after SPS sintering, which allowed for us to investigate the effects of microstructure and microchemistry on passive properties of oxide film formed on sintered alloys. The average diameter of intermetallic phases was 201.3 nm in coarse grain zone, while its vale was 79.8 nm in fine grain zone. The alloying element content in intermetallic phases in coarse grain zone was 33% to 48% higher than that on fine grain zone. The alloying element depletion zone surrounding intermetallic phases in coarse grain zone showed a bigger width and a more severe element depletion. The coarse grain zone in alloys showed a bigger electrochemical heterogeneity as compared to fine grain zone. The passive film formed on coarse grain zone had a thicker thickness and a point defect density of 2.4 × 1024 m−3, and the film on fine grain zone had a thinner thickness and a point defect density of 4.0 × 1023 m−3. The film resistance was 3.25 × 105 Ωcm2 on coarse grain zone, while it was 6.46 × 105 Ωcm2 on fine grain zone. The passive potential range of sintered alloys increased from 457 mV to 678 mV, while the corrosion current density decreased from 8.59 × 10−7 A/cm2 to 6.78 × 10−7 A/cm2 as fine grain zone increasing from 0% to 100%, which implied that the corrosion resistance of alloys increased with the increasing content of fine grains. The passive film on coarse grain zone exhibited bigger corrosion cavities after pitting initiation compared to that on fine grain zone. The passive film formed on fine grain zone showed a better corrosion resistance. The protectiveness of passive film was mainly determined by defect density rather than the thickness in this work.

Corrosion behaviour of 2205 DSS in the artificial industrial-marine environment

ABSTRACT The corrosion behavior of 2205 duplex stainless steel (2205 DSS) was investigated by atomization tests, which was performed in an S-bearing thin electrolyte layer used as the artificial industrial-marine environment. Electrochemical methods and X-ray photoelectron spectroscopy (XPS), were conducted to reveal the protection properties and the composition evolution of the passive film. The results indicated that the corrosion time would weak the protectiveness of passive film, which was attributed to the accumulation of defects and metal sulfides in the passive film. The decrease of composition percentage of Cr2O3 made more negative effects on the protection properties of passive film than the increase of Cr(OH)3 and CrO3, whose formation was related to the adequate supply of oxygen and water molecules. The metal sulfides such as NiS and MoS2 formed during atomization tests reduced the content of alloy oxides in the passive film, and provided locations for the growth of defects.

Semiconducting properties of passive films and corrosion layers on weathering steel

Anodic films were grown on Weathering Steel by potentiostatic polarization in slightly alkaline solution. The photoelectrochemical results reveal that they are n-type iron oxide with Eg = 2.0 eV. Rust layer grown by atmospheric corrosion are n-type semiconductors with a band gap higher than that estimated for the anodic film attributed to the formation of γ-lepidocrocite. The electrochemical impedance spectra allow to evidence that rust layers have a higher conductivity with respect to anodic films due to the presence of highly doped iron oxide layers. The use of Mott-Schottky theory to model the dependence of oxide capacitance as function of potential is critically discussed.

Comparison of the corrosion and passivity behavior between CrMnFeCoNi and CrFeCoNi coatings prepared by argon arc cladding

The corrosion behavior and passive film properties of CrMnFeCoNi and CrFeCoNi coatings in 0.5 mol/L H2SO4 solution were investigated by potentiodynamic and potentiostatic measurements, electrochemical impedance spectroscopy and Mott-Schottky tests. The chemical compositions of passive film were characterized by X-ray photoelectron spectroscopy (XPS). Results indicated that CrFeCoNi coating possessed lower passive current density, higher polarization resistance, lower donor and acceptor density compared with CrMnFeCoNi coating, which determined CrFeCoNi coating has higher corrosion resistance than CrMnFeCoNi coating. The excellent resistance to corrosion could be attributed to the structure and chemical compositions of passive film

Electrochemical Properties of Passive Film Formed on Supermartensitic Stainless Steel in a Chloride Medium

The electrochemical behavior and the electronic properties of passive films formed on a super martensitic stainless steel (SMSS) used in oil and gas industries were investigated in aqueous 0.6 M and 2.1 M NaCl solutions with additions of sodium acetate and acetic acid (pH 4.5). Open-circuit potential transients, electrochemical impedance spectroscopy, cyclic voltammetry, and x-ray photoelectron spectroscopy were measured to characterize the passive film formed on SMSS. The electrochemical behavior of the steel in an aqueous solution of 0.6 M NaCl presented the highest pitting potential and the highest polarization resistance in relation to the NaCl/NaAc solution. The passive film of SMSS in an aqueous solution of NaCl presented a thickness of 18.40 nm, three times the thickness of the oxide film in NaCl/NaAc, and consisted of FeO, Cr2O3, MoO2, and spinels such as FeCr2O4 species that are a p-type semiconductor, but may also contain a small fraction of the Fe2O3 and MoO3 oxides. Additionally, it was shown that the passive layer after immersion in a saline solution also contains hydroxides such as FeOOH and Cr(OH)3.

Corrosion properties of laser cladded CrCoNi medium entropy alloy coating

CrCoNi medium entropy alloy is an intriguing new material showing excellent mechanical properties but little is known about its corrosion properties. In this study, CrCoNi coating is fabricated by laser cladding, and its corrosion resistance and passive film properties in 3.5 wt% NaCl solution and 0.5 M H2SO4 solution have been investigated and compared with SS304. Optical microscope (OM) and Scanning electron microscope (SEM) shows that CrCoNi coating is near-fully dense without evident defects. In 3.5 wt% NaCl solution, CrCoNi coating is more easily corroded than SS304 while its passive film stability is better. The passive film formed on CrCoNi coating is a n-type semiconductor which consists of a single Cr oxide layer and the X-ray photoelectron spectroscopy (XPS) results reveal the presence of Cl− ion. In 0.5 M H2SO4 solution, CrCoNi coating exhibits better corrosion resistance than SS304. Electrochemical impedance spectroscopy (EIS) measurements reveal a slight pitting behavior during immersion and XPS results reveal that the Cr oxide and its hydroxides are the primary constituents of the passive film. Energy dispersive spectrometer (EDS) mapping shows Cr plays an important role in preventing pitting corrosion in both test solutions.

Investigation of the passive behavior of a Ni–Cr binary alloy using successive electrochemical impedance measurements

The passive behavior of a Ni–20Cr binary alloy was studied using an original methodology, based on successive electrochemical impedance spectroscopy (SEIS), over a wide potential range. The proposed method was first validated by comparing the resulting potentiostatic polarization curves with more conventional potentiodynamic polarization curves and determining the effect of the dwell time (30, 120, and 600 s) and potential step size (25 and 50 mV). Using the optimized parameters from this preliminary work, the passive behavior of the Ni–Cr alloy was then studied in solutions of varying pH: 10 g/L Na2SO4 with H2SO4 (pH = 2), 0.01 M Na2SO4 (pH = 5.8), and 0.05 M H3BO3 + 0.075 M Na2B4O7 10H2O (pH = 9.2). The obtained impedance diagrams were interpreted using enhanced graphical representation and fitted using the power-law model to determine the resistivity distribution throughout the passive film during polarizations. The results demonstrated that SEIS provides complementary information to conventional potentiodynamic curves. The evolution of the passive film properties was monitored in situ within the potential range corresponding to stable passivity. With the help of this original method, complementary to the evolution of the current density (measured at each potential step), the thickness, chemical composition, and reactivity changes were also highlighted.

Enhanced passivation of galvanized steel bars in nano-silica modified cement mortars

This work investigated the electrochemical behavior of galvanized steel bars in nano-silica modified cement mortars. The internal environmental factors of the mortar were firstly characterized. Then the passivation process of the galvanized steel bars was monitored. The results showed that the presence of nano-silica influenced the passivation process of galvanized steel bars and improved the protective properties of passive film. The morphology of passive film was changed, and the thickness was increased by the addition of nano-silica. The CHZ layer performed as a bonding agent between the galvanized steel and mortar matrix. The addition of nano-silica promoted the formation of gaps at the rebar/mortar interface, and there was no evidence for the presence of a lime-rich layer at the interface.

Effect of cold rolling on microstructure, corrosion and electrochemical response of the lean duplex stainless steel LDX 2101® by a correlative EBSD–SKPFM investigation

AbstractThis study elucidates the effect of cold rolling on the microstructure, corrosion and electrochemical response of the lean duplex stainless steel LDX 2101®. With thickness reductions of 0%, 20% and 40%, three different specimens are investigated in terms of microstructure (electron backscattered diffraction [EBSD] and energy‐dispersive X‐ray spectroscopy [EDS]), corrosion properties (ASTM G150, ASTM G61 and field testing), passive film properties (X‐ray photoelectron spectroscopy) and electrochemical response (scanning Kelvin probe force microscopy [SKPFM]). It is shown that deformation of LDX 2101 leads to changes in the microstructure such as mechanical twinning and martensite formation. The combination of EBSD, EDS and SKPFM maps shows that the work function is clearly dependent on composition, deformation and local misorientation, but not on the crystallographic orientation of the grains in the microstructure. Zones with low work function are seen to have the highest pitting susceptibility, which includes deformed ferritic, martensitic phase and areas with a high concentration of dislocations such as grain boundaries and mechanical twins. The overall conclusion is that cold deformation up to a 40% thickness reduction has a significant influence on the microstructure, but a small impact on the corrosion resistance of LDX 2101.

Application of Electrochemical Atomic Force Microscopy (EC-AFM) in the Corrosion Study of Metallic Materials.

Electrochemical atomic force microscopy (EC-AFM), a branch of a scanning probe microscopy (SPM), can image substrate topography with high resolution. Since its inception, it was extended to a wide range of research areas through continuous improvement. The presence of an electrolytic cell and a potentiostat makes it possible to observe the topographical changes of the sample surface in real time. EC-AFM is used in in situ corrosion research because the samples are not required to be electrically conductive. It is widely used in passive film properties, surface dissolution, early-stage corrosion initiation, inhibitor efficiency, and many other branches of corrosion science. This review provides the research progress of EC-AFM and summarizes the extensive applications and investigations using EC-AFM in corrosion science.

Study on the Microstructure and Alternating Current Corrosion Behavior of SAF2507 Super-Duplex Stainless Steel in 3.5%NaCl Solution

The effect of solution annealing temperature on microstructure and the corresponding AC (alternating current) corrosion behavior was investigated by electrochemical impedance spectroscopy, polarization curve, Mott–Schottky curve and immersion test. With or without AC application, the 2507 SDSS (super-duplex stainless steel) samples annealed at various temperatures exhibit a difference in corrosion resistance. Among them, the corrosion resistance first increases and then decreases as the annealing temperature increases, that is, the 2507 SDSS annealed at 1060 °C has the optimum corrosion resistance, followed by the specimen annealed at 1000 °C, and finally the specimen at 1120 °C. The variation trends of Rct, Rf and ip can verify the above law. The σ phase and an excessive amount of α phase within the microstructure can decrease the corrosion resistance. Additionally, the stability and protective property of passive film formed on the electrode surface is associated with the microstructure of 2507 SDSS. An imposed AC can decrease the passivity of 2507 SDSS and damage the film formed on the sample surface. Furthermore, the corrosion rate and pitting sensitivity of the SDSS increase with the increasing AC current density.

Role of Molybdenum on the Electronic Properties of Passive Films on Stainless Steels

Potentiostatic polarization of different stainless steel grades with a mirror surface finishing was performed in order to investigate the role of Mo on stainless steels corrosion behaviour. In the attempt to gain more insight into transpassive dissolution mechanism, passive films were grown in neutral aqueous solution (pH ∼ 7) at different polarizing potentials ranging from passive to transpassive conditions. According to the photoelectrochemical characterization, Cr dissolution occurs even at low polarizing potentials in the case of AISI 304L, while higher band gap values were obtained for passive films grown on austenitic 316L and duplex SSs. Capacitance measurements suggest that the flat band potential values estimated for passive films grown on austenitic 316L and duplex SS are more noble if compared to that of AISI 304L at all polarizing potentials. This is rationalized by considering that passive films on 316L and duplex are doped with Mo during film growth, changing their electronics properties (band gap and flat band potential) with a consequent shift to more positive value of the potential for chromate formation and dissolution.

Influence of Systematically Changed Martensite Content on the Passive Film Properties of Austenitic Stainless Steel in Neutral Electrolyte

Influence of Systematically Changed Martensite Content on the Passive Film Properties of Austenitic Stainless Steel in Neutral Electrolyte

Role of noble metal fission products on the microstrutural evolution and corrosion behaviour of ferritic steel-Zr based metal waste form alloys in the simulated repository environment

In the present work, the noble metal fission products (NMFPs) alloyed ferritic steel-Zr based metal waste form (MWF) alloys and its influence on microstructure and corrosion behavior in simulated ground water environment was investigated for pyrochemical nuclear spent fuel reprocessing applications. Ingots of 9Cr1Mo steel-12Zr-NMFPs MWF alloy with different NMFP (Ru, Rh and Pd) concentrations (1–4 wt%) were fabricated via vacuum arc melting. Microstructural examination revealed the eutectic layer microstructure consisting of α-Fe and Fe–Zr phases with the preferential distribution of NMFP along with Fe–Zr phases. XRD analysis confirmed that the noble metal does not show any discrete noble metal phases but as intermetallics phases. Electrochemical corrosion studies of the MWF alloys in the simulated Rajasthan Ground Water (RGW) and Kalpakkam Ground Water (KGW) media showed improved corrosion resistance with increase in noble metal content of the alloy due to cathodic modification. Higher noble metal-containing MWF alloys exhibited more protective passive film properties is attributed to the enhancement of Ru, Rh and Pd noble metals in the alloy which influences on the formation of more stable Fe3+ state than unstable Fe2+ state and vice versa with less noble metal-containing MWF alloy confirmed by XPS. Thus, the current investigation addressed the immobilization of noble metals fission product in the alloy microstructure and their beneficial impact on corrosion performance of ferritic steel-Zr based MWF alloy which are of primary concern in the high-level radioactive waste disposal in a geological repository.

The passivity of selective laser melted 316L stainless steel

The passive film properties of as-received selective laser-melted 316L stainless steel (SLMed 316L SS) without obvious pores were studied and compared with those of wrought and solution-annealed (SA) SLMed 316L SSs. Among the samples, the as-received SLMed 316L SS had the lowest passive current density, which was attributed to two factors: the super high sub-grain boundary density increased the number of nucleation sites for passive film formation, and the micro-galvanic effect between the sub-grain boundary and the inner sub-grains also accelerated the rapid formation of a thick protective layer. The poor passivation and re-passivation abilities of the SA SLMed 316L SS were ascribed to the extensively precipitated nanosized oxide and sulfide particles, especially those at the grain boundary.

Box-behnken design to enhance the corrosion resistance of plasma sprayed Fe-based amorphous coating

Fe48Cr15Mo14C15B6Y2 (at. %) amorphous coatings under various spraying parameters were deposited on Q235 steel by atmospheric plasma spraying. Passive film thickness was estimated by power-law formula proposed by Hirschorn to investigate the corrosion properties of passive film on the coating surface. Box-behnken design (BBD) in combination with response surface methodology (RSM) was utilized to gain the thickest passive film (about 1.60 nm) in 3.5 wt% NaCl solution. XPS results indicated that passive film formed on the optimal coating comprised of Fe, Cr and Mo oxide species and certain amount of bounded water. Mott-Schottky curve further confirmed an enhanced corrosion resistance of the optimal coating due to a low carrier density under the magnitude of 1018 cm−3. The surface morphology after 20 days immersion suggested that no corrosion products were observed on the optimal coating surface and the passive film retained its stability to protect the metal substrate effectively.

Influence of chloride and sulphate anions on the electronic and electrochemical properties of passive films formed on steel reinforcing bars

Reinforced concrete structures are suffering from the application of de-icing salts, particularly due to premature reinforcement corrosion. To understand and, thereby, identify solutions to this problem, a study has been conducted of the chloride- and sulphate-induced instability of the semiconductor passive films formed on carbon and 2304 stainless steel alloys in a simulated concrete pore solution environment. Steels’ vulnerability to corrosion when depassivation occurs, typically in the presence of chloride and/or low pH, makes it essential to understand the nature of their passive films in the effort to mitigate the effect of corrosion. The influence of major alloying elements in five different reinforcing bars and testing on different surface roughness was investigated in the first part of the study. In this second part, linear polarization resistance and potentiodynamic cyclic polarization techniques and Mott-Schottky (M-S) analysis were used to investigate the influence of varying ionic concentrations and, thus, pH of simulated concrete pore solutions on passive films formed on duplex 2304 stainless steel and carbon steel reinforcing bars. It was found that chloride ions increased the defect densities of passive films, most significantly in the lower pH solution, while sulphates decreased the densities. This is attributed to the formation of stable solid sulphides of Fe and Ni (as FeS, FeS2, NiS, Ni3S2) in the outer Fe-rich layer of the passive films as predicted by ThermoCalc© calculations.