Composition Of Passive Film Research Articles

Passivation and Potential Fluctuation of Mg-Alloy AZ31B in Alkaline Environments

The pH effect on the passivation and corrosion behavior of Mg alloy AZ31B was investigated in chloride-free NaOH solutions in the range of 10 to 14. The electrochemical behavior of α-Mg matrix, secondary (β-phase) Mg17Al12, and constituent intermetallic particles (AlxMny) were compared in these solutions using various techniques such as open circuit potential (OCP) monitoring, potentiodynamic and potentiostatic polarization, scanning vibration electrode technique (SVET), microcapillary cell technique as well as electrochemical atomic force microscope (EC-AFM) technique. Optical microscope (both in-situ and ex-situ) was utilized to characterize corrosion morphology of AZ 31B alloy in different pH NaOH solutions and yield information on the cathodic and anodic behavior of different phases and particles. Microscopic examination of the passive film formation and composition on different phases/particles was carried out via field emission scanning electron microscope (FE-SEM) equipped with energy dispersive spectroscopy (EDS). Gallium focused ion beam (FIB) was used to examine the cross section of different phases after exposure. The results indicate that significant potential fluctuations (from -1.6 VSCE to -0.4 VSCE) occurred to AZ31B in high pH (≥ 13) NaOH solutions with the presence of oxygen. Removal of oxygen by argon sparging diminished the fluctuation range (from -1.6 VSCE to -1.3 VSCE). Oxide nodules and associated cracks were found at the interface between α-matrix and β-phase. Thick oxide film was found to form on the α-matrix and the thickness decreased as the distance increased from the α/β interface (~1500 nm) into the α-matrix (~700 nm). In contrast, oxide film thickness of <100 nm was determined on β-phase. AlxMny particles were found to preferentially dissolve in high pH NaOH solutions and crevice was identified at the interface between Mn oxide layer and α-matrix. In relatively low pH (≤ 11) NaOH solution, OCP remained constant at -1.4 VSCE during long term exposure with the presence of oxygen. No significant potential fluctuation was observed. SEM/FIB examination indicated that corrosion occurred on the α-matrix in these NaOH only environment. In comparison, β-phase remained intact with thin passive film. Mg(OH)2 dome formed on AlxMny particles suggesting cathodic nature of the intermetallic particles. This was also corroborated by the in-situ microscopic examination of the gas formation on the AlxMny particles. OCP and polarization experiments suggest that hydrogen evolution reaction is the dominant cathodic reaction at these pH levels and the bubbles were found to initiate and grow preferentially on the AlxMny particles. At pH 12, thin oxide film (<100 nm) formed across the entire sample surface without any preferential corrosion and/or passivation on different phases/particles. The OCP remained constant at -1.3 VSCE during long term exposure. This was approximately 0.1 V higher than the value observed in pH 11 solution and no significant potential rise and drop was observed. Both potentiodynamic and potentiostatic polarization indicated that anodic current density decreased with increasing pH from 10 to 12 but increased with increasing pH from 12 to 14. Lowest passivation current density was identified at pH 12, which agrees with SEM/FIB and optical microscopic examinations. It is hypothesized that below pH 12, microgalvanic effect exists between α-matrix (anode) and AlxMny particles (cathode), which leads to the preferential dissolution of α-matrix. This was verified by SVET technique and AlxMny particles were found to be the cathode compared to α-matrix. At pH 13 and above, better passive film formation on β-phase may lead to the significant increase in OCP where the dominant cathodic reaction switched to oxygen reduction reaction, which in turn caused significant oxidation of α-matrix by microgalvanic coupling. AlxMny particles were anodic compared to the α-matrix and preferential dissolution of Al is suggested by SEM/EDS.

Passive behaviour of alloy corrosion-resistant steel Cr10Mo1 in simulating concrete pore solutions with different pH

The passive behaviour of new alloy corrosion-resistant steel Cr10Mo1 and plain carbon steel (as a comparison) in simulating concrete pore solutions of different pH (ranging from 13.5 to 9.0) under open circuit potential conditions, was evaluated by various electrochemical techniques: potentiodynamic polarization, capacitance measurements and electrochemical impedance spectroscopy. The chemical composition and structure of passive films were investigated by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). The electrochemical responses of passive films show that Cr10Mo1 steel has an increasing passivity with pH decreasing while carbon steel dose conversely, revealing carbonation does no negative effect on passivation of the corrosion-resistant steel. SIMS reveals that the passive film on the corrosion-resistant steel presents a bilayer structure: an outer layer mainly consisting of Fe oxides and hydroxides, and an inner layer enriched in Cr species, while only a Fe-concentrated layer for carbon steel. According to the XPS analysis results, as the pH decreases, more stable and protective Cr oxides are enriched in the film on Cr10Mo1 steel while Fe oxides gradually decompose. Higher content of Cr oxides in the film layer provides Cr10Mo1 corrosion-resistant steel more excellent passivity at lower pH.

Corrosion Behavior of New Dental Co-Cr-Nb-Mo-Zr Alloy

This paper presents a complete and complex characterization of the new Co-Cr-Nb-Mo-Zr alloy in comparison with the commercial CoCrMo (Heraenium CE) alloy. The alloy microstructure was showed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS); the composition and thickness of the native passive film were identified by X-ray photoelectron spectroscopy (XPS). Also, the surface roughness was revealed by atomic force microscopy (AFM) and the contact angle evinced the alloys hydrophilic properties. The amounts of ions released in artificial Carter-Brugirard saliva were evaluated by the inductively coupled plasma-mass spectroscopy (ICP-MS) technique. The corrosion rate was obtained by the linear polarization method. The cast new Co-Cr-Nb-Mo-Zr alloy is characterized by a multicomponent, fine dendritic structure with typical interdendritic distances of few microns. EDS spectra detected the alloying elements, Co, Cr, Nb, Mo, Mn, Si, etc. EDS elemental analysis quantified that Mo, Nb, Si and C are enriched in the interdendritic regions. XPS survey spectrum for the new Co-Cr-Nb-Mo-Zr alloy surface showed a complex feature that included the peaks for Co 2p, Cr 2p, Nb 3d, Mo 3d, Zr 3d, o 1s; this film is composed from chromium, niobium, molybdenum, zirconium, manganese, silicon oxides and is thicker (6.5 nm – 8.0 nm), more compact and enhanced with oxides as compared with that of commercial Co-Cr-Mo alloy. The topography and roughness parameters (AFM data) are similar for the two studied alloys and very proper for the cell adhesion. An increase in the contact angle value for the new Co-Cr-Nb-Mo-Zr alloy has been observed as compared to the commercial Heraenium CE alloy. The increase from 75.920 to 86.790 values indicates that the both alloys have hydrophilic character but the stronger one is for the commercial alloy. The quantity of ions (determined by ICP-MS method) released in artificial saliva for the both alloys is relatively small, but for the new alloy, the amount is significant lower. The quantified amounts in ppb (parts-per-billion, 10−9) sustain increased stability for the new alloy. The evolution of open circuit potentials in time for the both alloys depicts a trend to steady state sooner after immersion in the both cases; it is a specific aspect for passivity due to the protective oxides formed on the surface of the both alloys. The open circuit potentials tend to more electropositive values, indicating an increase of passive film thickness. The Tafel results showed that the new alloy is included in conventional stability scale „Perfect Stable” while the commercial alloy in “Very Stable” in the corrosion resistance group (corrosion classification). With the increase of immersion time, the penetration index, corrosion rate decreased. Also, the polarization resistance, Rp values for the new alloy increased in time as result of the passive film thickening; for the commercial alloy, polarization resistance decreased in time, denoting some dissolution and repassivation processes. Rp have higher values from about 8 times to 175 times than those of Heraenium CE alloy; correlating with the lower values of the corrosion current densities, it results a better corrosion resistance, a more resistant passive film for the new alloy due to its passive film that contains beside chromium oxide, niobium (Nb2O5, 49.8%) and zirconium oxides (ZrO2, 54.9%), as was showed by XPS analysis. In conclusion, the new Co-Cr-Nb-Mo-Zr alloy displayed an increased corrosion resistance as compared with the commercial Heraenium CE alloy.

Effect of 4-point bending and normal load on the tribocorrosion-fatigue (multi-degradation) of stainless steels

In many engineering environments tribocorrosion is combined with fatigue (multi-degradation). In the present work, the effect of static/cyclic bending and normal load on multi-degradation of austenitic and super duplex stainless steels has been studied. Investigating surface and subsurface characteristics by SEM/FIB, tribologically refined layers (TRL), crack matrices and pits were observed and their role on wear mechanisms was elucidated. Passive film thickness and composition was examined with XPS. Observations showed surface tensions increase the passive film thickness which can control pit and crack matrix formation thus wear loss mechanisms. Static and cyclic bending resulted in thicker oxide layer, enhanced pit formation and wear debris detachment while in the absence of 4-point bending larger subsurface cracks and TRL were observed.

Electrochemical Behavior and Compositions of Passive Films of Amorphous Ni-P Coating in Acidic Environment

Electrochemical Behavior and Compositions of Passive Films of Amorphous Ni-P Coating in Acidic Environment

Characterization of passive film formed on 304 SS in simulated alkaline water chemistries containing sulfur at 300°C

Passivity degradation of 304 stainless steel (SS) in simulated alkaline water chemistries at 300°C was investigated using polarization curve, scanning electron microscope, time-of-flight secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). Experimental results indicated that 304, SS was selfpassive in the test solution and the thickness of passive film was about 500 nm. Hydroxide was enriched in the outer layer whereas oxide was enriched in the inner layer. Sulfur in thiosulfate could be reduced into lower valence of sulfur and enter the passive film so that the composition of passive film was modified by sulfur. Fe and Cr were enriched in the passive film whereas Ni was depleted in the passive film.

Electrochemical comparison and biological performance of a new CoCrNbMoZr alloy with commercial CoCrMo alloy

A new CoCrNbMoZr alloy, with Nb and Zr content is characterized from the point of view of surface features, corrosion resistance and biological performance in order to be proposed as dental restorative material. Its properties are discussed in comparison with commercial Heraenium CE alloy based on Co, Cr and Mo as well. The microstructure of both alloys was revealed by scanning electron microscopy (SEM). The composition and thickness of the alloy native passive films were identified by X-ray photoelectron spectroscopy (XPS). The surface characteristics were analyzed by atomic force microscopy (AFM) and contact angle techniques. The quantity of ions released from alloys in artificial saliva was evaluated with inductively coupled plasma-mass spectroscopy (ICP-MS) measurements. The electrochemical stability was studied in artificial Carter–Brugirard saliva, performing open circuit potentials, polarization resistances and corrosion currents and rates. The biological performance of the new alloy was tested in vitro in terms of human adipose stem cells (hASCs) morphology, viability and proliferation status. The new alloy is very resistant to the attack of the aggressive ions from the artificial saliva. The surface properties, the roughness and wettabiliy sustain the cell behavior. The comparison of the new alloy behavior with that of existing commercial CoCrMo alloy showed the superior properties of the new metallic biomaterial.

Chemical composition and electronic structure of anodic passive films on low-C 13CrNiMo stainless steel

Mott–Schottky analysis and electrochemical and X-ray photoelectron spectroscopy (XPS) measurements were performed on passive films formed on low-C 13CrNiMo stainless steel with different applied heat treatments. Heat treatments render particular microstructural features of the alloy with a significant impact on the ability of the passive films to afford adequate protection against localized corrosion. A lower level of retained austenite in the substrate renders thinner passive films. Phosphates coexist with oxidized Fe(III) compounds as the prevailing species in the anodic layers. Mo was only detected in the oxide film formed on the sample with a higher retained austenite content. Passive layers behave as n-type semiconductors with two types of donors, namely, shallow-level and deep-level states. The observed flat band potential V FB≅ -0.425 ± 0.005 V vs. standard calomel electrode (SCE) is independent of the thermal treatment of the alloy but under potential bias conditions at the corrosion potential the occurrence of the cathodic reaction on the oxide surface is hindered on the sample with higher retained austenite in its microstructure as compared to the sample with lower retained austenite content.

Electrochemical behavior and compositions of passive films formed on the constituent phases of duplex stainless steel without coupling

Abstract The electrochemical behavior and compositions of passive films formed on the constituent phases (α-phase, γ-phase) of 2205 duplex stainless steel (DSS) without coupling in neutral 3.5% NaCl solution were investigated, utilizing single-phase samples prepared by selective dissolution. The results demonstrate that, compared to γ-phase, Fe species in passive film of α-phase are more stable due to the higher content of Mo within α-phase. The superior stability of Cr (III) species in the passive layer of γ-phase may result from the higher content of Ni in γ-phase, which leads to the higher content of Cr, Cr/Fe ratio, and better passivity of passive layer. The beneficial effect of coupling of two phases on the passive behavior of 2205 DSS is also found.

Surface analysis, microstructural, mechanical and electrochemical properties of new Ti-15Ta-5Zr alloy

This paper describes the synthesis of a novel Ti-15Ta-5Zr alloy with an α + s stable, homogeneous, biphasic microstructure (by optical microscopy, X-ray diffraction and scanning electron microscopy) and the determination of its mechanical properties, hardness and a Young’s modulus of 42.2 GPa. The alloy passive film composition and thickness were analyzed by X-ray photoelectron spectroscopy; a thick, compact native passive film containing the protective oxides of all constituent elements (TiO2, Ta2O5, ZrO2) was identified. The electrochemical parameters confirmed a nobler behaviour and a more capacitive, resistant passive film on the alloy surface compared to Ti and other existing implant alloys; these facts are due to the alloying elements that, by their oxides stabilize and reinforce the alloy passive film. This passive film thickened in time, which increased its protective capacity. The new alloy had no susceptibility to galvanic or local corrosion. Ti-15Ta-5Zr alloy is recommended as an advanced orthopaedic implant material.

Electrochemical Characterization of Passive Films on Ni-Based Alloys in Acidic and Neutral Solutions

The present work reports the structure, chemical composition and electronic properties of passive films formed on Alloy 600 and Alloy 690 in borate buffer and sulfuric acid solutions. Photoelectrochemical response from passive films varied depending on the alloy substrates and the solutions. XPS analysis revealed that the passive films formed on Alloy 600 and Alloy 690 consisted of an outer hydroxide layer and an inner oxide layer in the borate buffer solution as well as the sulfuric acid solution. The chemical composition of the layers was relatively different depending on the solutions, that is, more Fe was incorporated into the passive films formed in the borate buffer solution. [doi:10.2320/matertrans.M2014384]

Influence of the microstructure on the corrosion behaviour of low-carbon martensitic stainless steel after tempering treatment

The microstructure of grade X4CrNiMo16.5.1 stainless steel was studied at different scales. The chemical composition of the native passive film formed on the different phases was then determined at the microscale. The degree of homogeneity of the native passive film is discussed. Subsequently, the susceptibility to pitting corrosion of X4CrNiMo16.5.1 was quantified using the electrochemical microcell technique. The nature of precursor sites and the morphology of pits were investigated by combining scanning electron microscopy with Electron BackScatter Diffraction and potentiostatic pulse tests. The role of the microstructure and the cold-worked layer generated by polishing in pitting is discussed.

Composition and formation analysis of an ultra-thin antitarnish passive film on electroless Ni-P coating

An ultra-thin passive film on electroless nickel phosphorus coating (ENPC) was obtained by treated in a passivation bath. The antitarnish and corrosion properties of the film were studied by acid exposure and potentiodynamic polarization. XPS was utilized to analyze the chemical composition and formation process of the film. The acid exposure test indicated the antitarnish property of the coating was obviously improved by passivation treatment. The potentiodynamic polarization test showed that the corrosion current for the passivated Ni-P coating was lower than that of untreated coating. By XPS measurement, the thickness of film was evaluated as a few nanometers and the film was made up of Cr, C, O and N. The N and C elements in the film suggested the nitryl aromatic compound should take part in the formation of film. The XPS spectra fitting results indicated that Cr was in the form of Cr2O3 and Cr(OH)3, while O was originated to Cr2O3, Cr(OH)3 and–NO2 in aromatic compound. And the XPS results were used to justify the formation mechanism of the passive film.

Adsorption of BSA on Passivated CoCrMo PVD Alloy: An EQCM and XPS Investigation

Adsorption of Bovine Serum Albumin (BSA) on an anodically passivated CoCrMo biomedical alloy has been studied using the Electrochemical Quartz Crystal Microbalance (EQCM) in phosphate buffer solution at 37°C. CoCrMo layers were deposited on the quartz crystals by physical vapor deposition. EQCM measurements were performed under potentiostatic conditions and combined with X-ray Photoelectron Spectroscopy (XPS) analysis. Adsorption of BSA onto the CoCrMo alloy surface was found to favor passive dissolution without modification of the chemical composition and thickness of the oxide passive film. In addition, passive film growth and adsorption kinetics of the protein follow a logarithmic trend. Both EQCM and XPS techniques demonstrated that protein coverage depends on the applied potential.

Observation of passive films on Fe–20Cr–xNi (x = 0, 10, 20 wt.%) alloys using TEM and Cs-corrected STEM–EELS

The structure and composition of passive film formed on Fe–20Cr–xNi (x=0, 10, 20wt.%) alloys in deaerated pH 8.5 borate buffer solution was examined by transmission electron microscope and Cs-corrected scanning transmission electron microscope-electron energy loss spectroscopy. Thickness of the passive film on each alloy was measured to be 2.5–2.7nm and the passive film was enriched with Cr. The passive film formed on the alloys exhibited an amorphous structure, as confirmed by the lack of diffraction contrast and by the fast Fourier transform images taken within a region of the passive film on each alloy.

The corrosion resistance and passive film compositions of 12% Cr and 15% Cr oxide dispersion strengthened steels in nitric acid media

The passive film compositions and corrosion resistance of 12% Cr and 15% Cr oxide dispersion strengthened (ODS) steels in 3M HNO3 to 9M HNO3 was evaluated. The potentiodynamic polarization plots exhibited a shift in corrosion potential, and higher passive current density with increasing HNO3 concentrations. In 12% Cr ODS steel, high corrosion rate was observed in all HNO3 concentrations. However, low corrosion rate observed in 15% Cr ODS steel was attributed to Al2O3 enrichment. The TEM analysis indicated a complex Y2Hf2O7 formation in 15% Cr ODS steel, and this may have a role in suppressing intergranular corrosion attack.

Microstructure, mechanical properties, and corrosion resistance of Ti-20Zr alloy in undoped and NaF doped artificial saliva

The corrosion behavior of a new, advanced Ti-20Zr alloy with α+β microstructure (determined by optical microscopy, XRD, and SEM) and very good mechanical properties (obtained from the stress-strain curve) is studied in this paper. The composition of the alloy native passive film was determined from a XPS analysis and the long-term corrosion resistance in undoped and doped states with 0.05M NaF artificial Carter-Brugirard saliva of different pH values, simulating the severe functional conditions of a dental implant, was analyzed by electrochemical methods. This alloy possesses an advantageous balance between good mechanical resistance and plasticity and Young’s modulus and exhibits more favorable electrochemical parameters and corrosion resistance than CP Ti due to its more resistant passive layer containing Ti2O3, TiO2, and ZrO2 protective oxides. After 1000 h of immersion in saliva, the protective properties of the alloy were enhanced due to the deposited surface layer that incorporated protective phosphates (shown by SEM and XPS).

Duplex stainless steel passive film electrical properties studied by in situ current sensing atomic force microscopy

The duplex stainless steel passive film electrical properties before and after passivation were investigated by current sensing atomic force microscopy and X-ray photoelectron spectroscopy (XPS). The current maps and band gap energies extracted from I–V curves show that the conductivity of passive film covering austenite and ferrite is different and decreases with increasing film formation potential due to the changes in the passive film thickness and composition, confirmed by XPS analysis. I–V curves reveal that the passive films exhibit p-type or n-type semiconducting properties depending on the film formation potential, attributed to different film chemical composition, supported by XPS results.

Corrosion Resistance of 9 - 15% Cr ODS Steels and its Comparison with Austenitic Stainless Steel

An oxide dispersion strengthened steels are one of the most promising high temperatures, and high performance advanced structural material being developed for future fast reactors and high-temperature Generation IV reactors. In the present work, the corrosion resistance and its correlation with the passive film compositions of 11% Cr F/M and 9-15% Cr (with Zr or Hf) ODS steels is examined and compared with AISI type 304L stainless steel in boiling 60 - 62% (~13 M) HNO3. The corrosion rate measured in 62% HNO3 for 240 h of 11% Cr F/M, 9% Cr and 15% Cr (Zr) ODS steels show high corrosion rate. On the other hand, low corrosion rate was observed in 304L stainless steel (0. 21 to 23 mm y-1). However, severe intergranular corrosion attack was revealed in type 304L SS after 240 h exposure, but none in ODS steels. Such an intergranular corrosion attack seen in type 304L stainless steel is undesirable. On the contrary, low corrosion rate (0.04 0.15 mm y-1) of 15% Cr (Hf) ODS steel in 3 M, 6 M and 9 M HNO3, comparable to that of type 304L stainless steel was observed. The improved corrosion resistance of 15% Cr (Hf) ODS steel was attributed to enrich (20 at. %) and protective Al2O3 layer formation in addition to Cr2O3 in the passive film.

The surface characterization and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr ODS steels for nuclear fuel reprocessing application

In spent fuel nuclear reprocessing plant, nitric acid is the main medium used in PUREX method. The passive film compositions and corrosion resistance of 11 % Cr ferritic/martensitic and 9–15 % Cr oxide dispersion strengthened steels in different nitric acid concentrations were studied. The open circuit potential is shifted toward more noble potential as the concentrations increased from 1 M HNO3 to 9 M HNO3 in all the investigated alloy steels. The results of the potentiodynamic polarization plots also exhibited a shift in corrosion potential as the concentrations increased from 1 M to 9 M HNO3. This shift is undesirable because of risk of overshooting the potential beyond passive region and may result into transpassive corrosion. The X-ray photoelectron spectroscopy results of the passive film analysis are composed mostly of Fe2O3, Cr2O3, and Y2O3, and the depth profile of Fe and Cr concentrations vary depending upon the nitric acid concentration. The surface morphology after the corrosion test does not show intergranular corrosion attack at the nitric acid concentrations studied. It is desirable that materials for use in nitric acid service are resistant to such corrosion induced degradation.