Composition Of Passive Film Research Articles

Passive behavior of TNB intermetallic and Inconel 625 in electrochemical machining

The TNB alloy, a novel lightweight material, shows great potential for application in crucial aero-engine parts. This paper reveals the passive behavior of TNB alloy in electrochemical machining (ECM), Inconel 625 alloy was used for comparison. The polarization curve shows that TNB and Inconel 625 alloys have obvious passivation phenomenon at the passivation potential. Research reveals that the passive film structure of TNB alloy comprises a compact layer (about 7 nm) and a loose layer (about 13 nm), with significantly higher corrosion resistance in the compact layer compared to the loose layer. In contrast, the passive film structure of Inconel 625 alloy is a single layer with a thickness of approximately 11 nm. It was also found that the passive film composition for TNB alloy is TiO2, Al2O3, and Nb2O5. The composition of passive film for Inconel 625 alloy is NiO, Ni(OH)2, Cr2O3, MoO3, Nb2O5, FeO, and Fe2O3, and the content of Ni and Cr is high. TNB alloys exhibit uneven and loose lamellar morphology at low current densities, but can reach Ra 0.15 μm at greater than 15 A/cm2. There are always some disordered carbides rich in Nb and Mo on the surface of Inconel 625 alloy. Quantitative models were developed for both alloys to describe their electrochemical dissolution behavior.

Corrosion resistance enhancement for 6Mo austenitic stainless steel through B alloying coupled with a simple pre-aging method

The effect of boron (B) addition coupled with 500 ℃ pre-aging on the corrosion resistance of S31254 was systematically investigated. The results suggested that the diffusion of Mo to grain boundaries (GBs) played a crucial role in enhancing intergranular corrosion resistance. Additionally, the addition of B further promoted the uniform distribution of Mo during the pre-aging process by suppressing Mo segregation at GB. Ultimate, the B microalloying coupled with the pre-aging strategy optimized the composition of passive film through promoting the formation of Mo-rich passivation film, which significantly enhanced the corrosion resistance of Mo-containing stainless steel.

Effect of Cr on the microstructure and corrosion behavior of nickel-based alloys in hydrochloric acid

Nickel-base alloy is a type of metal material with excellent properties and is widely used in many fields. However, in the harsh environment of the acid solution, corrosion causes the reduction of the service life of the alloys, thereby limiting the alloys' use and development. In this paper, the effect of Chromium (Cr) content on the microstructure and corrosion behavior of nickel-based alloys in hydrochloric acid (HCl) was studied by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), electron backscatter diffraction (EBSD) and electrochemical workstation. Meanwhile, X-ray photoelectron spectroscopy (XPS) was used to investigate the composition and properties of the surface passive films. For the Cr20 and Cr30 alloys with a single face-centered cubic (FCC) structure, the Cr2O3 content in the passive films increased with the Cr content, effectively improving the corrosion resistance. As the Cr content continued to increase, the second phases having a body-centered cubic (BCC) lattice were precipitated both in the Cr40 and Cr50 samples, inducing microgalvanic corrosion, thus deteriorating the corrosion resistance. XPS results showed that, in the Cr30 alloy, the relative content of Cr2O3 and the bound water were the highest, indicating that its passive film had the best corrosion resistance. For the passive film, the pitting resistance was related to Cr content, appropriate Cr content improved the corrosion resistance.

Mechanical characteristics and electrochemical corrosion of NiCoCr alloys

Previous studies have shown that NiCoCr medium entropy alloys (MEAs) have perfect strength-ductility balance and significant escape fracture toughness. This work aimed to determine the effects of annealing temperature and alloy composition on the mechanical characteristics and corrosion behaviors of the NiCoCr MEAs. The results showed that the grains generated in the NiCoCr MEAs became more petite with the cooling rate increasing. The Vickers hardness (HV) of annealed NiCoCr MEAs increased with increasing annealing temperature. For NiCoCr alloys with different alloy compositions, the potentiodynamic polarization results showed that the NiCoCrFeMn alloy has the highest polarisation resistance, lowest current density, and lowest corrosion rate. However, the composition of Fe2O3-based passivation film makes it highly reactive and easily cleaved by Cl−. The NiCoCr and NiCoCrFe MEAs with high Ni content had a denser and slowly dissolved NiO passivation layer and better corrosion resistance. Moreover, the hardness of corroded NiCoCr MEAs decreased by 7.7%.

Feasibility of using 2304 duplex stainless steel in seawater-mixed concrete pore solutions: A preliminary passivation consideration

Due to the growing shortage of fresh water resources worldwide, it is necessary to explore the feasibility of using seawater to produce concrete. However, the passivation and pitting corrosion resistance of reinforcing steel will inevitably be impaired by the chlorides contained in seawater. Therefore, it is particularly important to develop a corrosion-resistant steel that could be employed in seawater-mixed concrete. One option being considered is using duplex stainless steel (DSS). To evaluate the feasibility of application in seawater-mixed concrete, the passive films of 2304 DSS were both generated by cyclic voltammetry and naturally formed in alkaline solutions with and without admixed chlorides, which was further compared with those of the conventional low-carbon steel (HRB400E steel). Unlike 2304 DSS, HRB400E steel failed to be passivated with admixed chlorides. Furthermore, the passive film of 2304 DSS was investigated by EIS, AFM and XPS measurements. Although the passivation ability was slightly reduced by admixed chlorides, and the morphology and composition of passive film were also modified, the high pitting corrosion resistance of 2304 DSS guaranteed its application in seawater-mixed concrete.

Corrosion characteristic of vitallium 2000 CoCrMo casting alloy in fluoride containing artificial saliva

In order to reveal the effect of fluoride ions (F−) on the passive film corrosion resistance and composition of CoCrMo dental prosthesis. The passivity of casting Vitallium 2000 CoCrMo series alloy was systematically studied by adopting electrochemical and surface techniques. The results show that F− have a certain effect on the passive film corrosion resistance of casting CoCrMo in oral environment, and the increase of F− concentration weakens the passive film corrosion resistance. With the increase of F− concentration, the open circuit potential moves negatively, the corrosion current density increases, the polarization resistance decreases, and the defect density in the passive film increases. With the extension of immersion time, the corrosion resistance of alloy will be enhanced and shows: AS > AS + 0.5 wt% NaF > AS + 1 wt% NaF. The addition of F− can decrease Co, Cr and Mo peaks sharply and promote the dissolution of the passive film. The result of present study could regulate and guide the application dose of oral fluorine-containing products.

Detecting structure and composition of passive film on Mo-containing stainless steel formed in alkaline environment by aberration-corrected TEM

In this paper, the structural and compositional evolution of the passive films formed on the Mo-containing stainless steels induced by chloride ions in 0.1 mol L−1 NaOH solution has been studied by means of aberration-corrected transmission electron microscopy and X-ray photoelectron spectroscopy. Mo is enriched at the outer layer of the passive film, which is attributed to the induction of Cl-. Moreover, MoO42- is formed due to the alkaline solution, which impedes the film formation process and inhibits the thickening of the film. Consequently, the positive effect of Mo in the passive film on the corrosion resistance is strongly suppressed.

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.

Exploring the Interplay between Tribocorrosion and Surface Chemistry of the ASTM F139 Surgical Stainless Steel in Phosphate-Buffered Saline Solution.

Surgical ASTM F139 stainless steel is used for temporary fixtures in the biomedical field. Tribocorrosion is a major concern in this application. The aim of the present work was to study the interplay between tribocorrosion behavior and the surface chemistry of the ASTM F139 stainless steel in phosphate-buffered saline solution (PBS). Sliding wear tests were conducted against alumina balls at different electrochemical potentials: open circuit potential (OCP), cathodic potential (-100 mV versus the OCP), and anodic potentials (+200 mVAg/AgCl and +700 mVAg/AgCl). The normal load was 20 N. The wear volume was estimated based on micrographs obtained from the wear tracks using confocal laser scanning microscopy. Moreover, the wear tracks were also examined by scanning electron microscopy (SEM). The surface chemistry of the ASTM F139 specimens was analyzed by X-ray photoelectron spectroscopy (XPS). The wear volume was dependent on the electrochemical potential, being maximized at +700 mVAg/AgCl. Delamination areas and grooves were observed in the wear tracks. Detailed assessment of the surface chemistry inside the wear tracks allowed identification of the main chemical species and their relative quantities, thus enabling correlation of the passive film composition with the observed tribocorrosion behavior.

Effect of phase composition on the corrosion behavior of Ti-xMo alloy films

The corrosion behavior of Ti-xMo alloy films was investigated by preparing a series of Ti-xMo (x = 0, 4, 11, 20 wt%) alloy films using non-equilibrium magnetron sputtering ion plating technology. XRD and TEM results show that these films have obvious phase composition, which are single α phase, α + β phase and single β phase, respectively. The composition of passivation film of alloy thin films is analyzed by XPS analysis method. The passivation film can be divided into inner passivation film and outer passivation film. The corrosion behavior of Ti-xMo alloy films in a 3.5 wt% NaCl solution was investigated through the electrochemical impedance spectroscopy (EIS). The findings suggest that the corrosion resistance of Ti-xMo alloy films is not only influenced by the Mo content but also governed by the composition of phases. Due to the absence of α/β interfaces in its structure and higher Mo content, the Ti-20Mo alloy film with a single β phase exhibits superior corrosion resistance compared to Pure-Ti film with a single α phase and Ti-4Mo and Ti-11Mo alloy films with an α + β phase.

The influence of microstructural evolutions on electrochemical corrosion and passive behavior in precipitation-strengthened high-entropy alloys

Effects of microstructural evolutions on electrochemical corrosion properties and passive film characteristics of precipitation-strengthened (Ni2Co2FeCr)92Al4Nb4 high-entropy alloys (HEAs) were investigated in a saline environment. Compared with single-phase FCC alloys, the appearance of nano-sized L12 particles increases the metastable pitting activities and slightly reduces the pitting potential, while the lamellar D019 phase further deteriorates the localized corrosion resistance. The chemical composition and oxide state of passive films are closely related to the different precipitation scenarios. The corrosion morphologies of the single-phase and L12-strengthened alloys are dominated by pitting, whereas the intergranular corrosion (IGC) and intragranular dealloying-like corrosion occur in the D019-strengthened alloy.

Formation and long-time exposure aging of oxides on Ni-Cr and Ni-Cr-X (X = Mo, W) alloys in acidic chloride solutions: Ramifications towards corrosion resistance

The passivation of Ni-22Cr, Ni-22Cr-6Mo, and Ni-22Cr-6Mo-3W (wt%) was characterized from 100 s to 10 days in 0.1 M NaCl in pH 4 at various potentials in the passive range. The influence of aqueous solution exposure time in NaCl (exposure aging), passivation potential, as well as Ni-Cr-X alloy composition (Mo or W) on passive film growth, composition, oxidation state, molecular identity, and inner versus outer film layering were investigated. Initial passive film formation was dominated by Ni(II). Cr(III) oxides and hydroxides tended to enrich upon formation and exposure aging. Corundum and rock salt are speculated to undergo a solid-state phase transformation to form NiCr2O4 at long times under certain conditions. The concept of the time-potential-transformation diagrams to describe the evolution of passive film phases and protectiveness is introduced. Factors limiting Cr(III) enrichment were discussed. Aliovalent Mo and W ions were detected in passive films, particularly after aging. The roles of Cr enrichment, Ni depletion, and Mo and/or W aliovalent cations after oxide aging towards protectiveness to passive and localized corrosion in chloride (Cl-) solutions were discussed.

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.

Influence of ultrafine surface grain size on the passive film chemistry and critical pitting temperature (CPT) in AISI 316L austenitic stainless steel

ABSTRACT Severe shot peening (SSP) was applied to induce a profound surface deformation characterised by the formation of ultrafine-grained structures with an average grain size of 99 ± 5 nm on AISI 316L. The impact of these ultrafine-grains on the critical pitting temperature (CPT) was investigated in 3.5 wt.% NaCl solution. Additionally, this study comprehensively explored pit chemistry using electrochemical techniques and mechanistic analyses. Moreover, a comparative investigation of the chemical composition of passive films, developed on severe shot peened (SSPed) samples, was undertaken in contrast to their solution-annealed (SAed) counterparts, employing X-ray photoelectron spectroscopy (XPS). Potentiostatic measurements showed that the mean CPT value was 8.8 ± 0.3 °C for the SAed samples, whereas the SSPed counterparts demonstrated a notably higher CPT, averaging at 13.6 ± 0.5 °C. Insights from pencil electrode measurements revealed shallower pit depths and lower critical current density requirements for passivation in the SSPed sample. Furthermore, the passive films formed on the SSPed samples showed a higher concentration of Cr and Mo. These observations were comprehensively elucidated through effective diffusion equations, leading to a discussion regarding the improved resistance to pitting corrosion exhibited by the SSPed samples, thus shedding light on the pivotal role of surface grain refinement in corrosion behaviour improvements.

Inhibition efficiency and mechanism of nitrilo-tris(methylenephosphonato)zinc on mild steel corrosion in neutral fluoride-containing aqueous media

Abstract Corrosion-electrochemical behaviour of steel E 235 in borate buffer solution (pH = 7.4) containing F− ions with and with no added ZnNTP as an inhibitor, where NTP = N(CH2PO3)3, was studied by the potentiodynamic polarization and depth-profiling XPS analysis of specimens polarized at different potentials applied. Depending on the potential applied, F− ion was shown to influence differently on the formation, composition and structure of passive film. At E < 0.1–0.2 V/SSCE, F− ion promotes the passivation via forming sparingly soluble FeF2, and the resulting film is comprised of mainly iron(II) oxides and hydroxides, as well as sparingly soluble FeF2 and FeZnNTP. At E > 0.1–0.2 V/SSCE, F− ion works for the destruction of the passive film by forming soluble compounds with Fe3+ ions, which leads to its thinning. ZnNTP inhibitor forms FeZnNTP heterometallic complex with iron ions, which is the most stable constituent of the passive film. When F− ion concentration does not exceed 1.4 mmol/L, ZnNTP inhibitor is optimal to be added in amount of 0.5–1.0 g/L, whereas concentrations of 5.6 mmol/L F− ion and higher require 5 g/L ZnNTP or even more to be added.

Effect of nitrogen content on corrosion behavior of high-nitrogen austenitic stainless steel

A series of electrochemical tests combined with the techniques of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray photoelectron spectroscopy (XPS) were used to study the effect of nitrogen content on the composition, structure and protectiveness of passive films, which were formed on the surfaces of high-nitrogen austenitic stainless steels (HNSS) in 0.5 mol/L NaCl solution. The results showed that the HNSS with higher nitrogen content had a larger proportion of low-angle grain boundaries, and it also had a lower corrosion current density in 0.5 mol/L NaCl solution and thus a lower corrosion rate. The existence of a larger proportion of stable oxides (e.g., Cr2O3) in the passive films facilitates the passivation/repassivation process and contributes to the high corrosion resistance of HNSS.

Study of the passivation and repassivation behavior of pure titanium in 3.5 wt% NaCl solution and 6 M HNO3 solution

We reveal differences in composition and structure of passive films and repassivation rate of titanium in 3.5 wt% NaCl and in 6 M HNO3. Titanium in 6 M HNO3 shows worse corrosion resistance than in 3.5 wt% NaCl due to higher defect concentration and lower TiO2 content despite the thicker passive film, which is the result of accelerated cathodic process and promoted dissolution/formation dynamic equilibrium of passive film in 6 M HNO3. Repassivation rate in 3.5 wt% NaCl is higher although film growth rate is lower, as the film exhibits good barrier effect when it is thin. Our results provide insights needed to guide application of titanium in SNFR plants.

Designing FeCr0.7NiCu0.5Ti0.5 high-entropy alloy doped with rare earth yttrium: Effects on microstructure and passive film

After constant potential passivation (CPP), the effect of rare earth yttrium (Y) on the corrosion resistance of the passive film on the surface of FeCr0.7NiCu0.5Ti0.5 alloy in H2SO4 was investigated. The results manifested that when Y content exceeded 0.04, the microstructure of Ni3Ti transformed into Cu5Y phase, and gradually expanded with the addition of Y. XPS etching analysis of passive film composition with changing etching depth and cyclic polarization analysis of passive film pitting corrosion sensitivity are two methods used to assess the corrosion resistance of alloy. Compared with FeCr0.7NiCu0.5Ti0.5 alloy and FeCr0.7NiCu0.5Ti0.5Y0.06 alloy, the passivation current density after CPP reduced from 5.682 × 10−3 to 4.630 × 10−4 A/cm2. With the addition of Y, the protection and density of the passive film was enhanced, resulting in an improvement in the corrosion resistance of the alloy. The pitting corrosion behavior was related to the changes in inclusion content and morphology caused by Y, and rare earth was advantageous to boost the passivation capability of FeCr0.7NiCu0.5Ti0.5 series alloy.

Understanding the intrinsic effect of fly ash on passivity and chloride-induced corrosion of carbon steel and stainless steel in cement extract solutions

Compared with the ordinary Portland cement extract solution (OPC solution), the passivation capability and chloride-induced corrosion behavior of carbon steel (Q235) and 316 stainless steel (316ss) in fly ash modified cement extract solution (FA solution) were intensively investigated in this study. The composition and electrochemical properties of steel passive films were studied using XPS technique and a series of electrochemical measurements including M − S, EIS and CPP. Moreover, FT-IR, AFM and SEM/EDS were employed to analyze the corrosion products and morphology on the steel surface. After 10 d of passivation, the film resistance of Q235 in OPC solution was 1.42 times that in FA solution, but an opposite result was observed for 316ss, which is consistent with the subsequent chloride-induced corrosion behavior. Steel passive films of different thicknesses and protective characteristics for Q235 and 316ss formed in alkaline solutions were confirmed to be the dominating reason for the distinct passivity and corrosion resistance to chloride attack. Accordingly, the intrinsic impact mechanisms of fly ash on passivation capability and chloride-induced corrosion of Q235 and 316ss in extract solutions were proposed.

How does the pore solution chemistry influence the passivation of reinforced alkali‐ and salt‐activated slag materials?

AbstractService life predictions of reinforced concrete structures are underpinned by the passivation film chemistry, structure, and thickness. In this work, we present how the formation of passive films at the steel–concrete interface of reinforced alkali‐ and salt‐activated slag materials can be affected by the pore solution chemistry, namely, pH, Eh, and chemical composition. Thermodynamic simulations are used to illustrate the time‐dependent changes to the pore solution chemistry, where estimated electrical conductivities of the pore solution are used as a single‐value parameter to understand the solution complexity and capacity for charge transfer. A set of passivation reactions are proposed to understand the effects of OH− and HS− (reduced sulfur species) competition on the passivation pathways. These passivation reactions become more complex considering that a reducing pore solution might not establish until 3 days into the curing process—a crucial factor explaining the significant differences in the phase composition of passive films of activated slag materials (FeOOH, FeS). This study sheds light on recent progress in understanding these initial passivation reactions, emphasizing the essential role of material design and, therefore, the pore solution chemistry of these cements, along with significant insights for vital research and development concerning the corrosion durability of activated slag materials.