Breakdown Of Passive Layer Research Articles

Exploring the mechanism of stress-induced passive layer degradation in additively manufactured Ni-Fe-Cr-based alloy 718

This study explores the formation and degradation mechanisms of the passive layer on laser powder bed fusion (L-PBF) processed Ni-Fe-Cr-based alloy 718 using high-resolution submicron analysis and microcapillary electrochemical techniques. The findings provide new insights into passive layer breakdown under tensile loading, revealing the influence of microstructural characteristics, dislocation distribution, and mechanical stresses. Tensile loading caused oxide layer cracking near cell boundaries with higher dislocation density. Detachment of the oxide layer from the matrix created voids, allowing aggressive ions to penetrate, promoting crevice corrosion. Cell boundaries remained mostly intact, as metallic particles within the surface oxide layer.

Corrosion Behaviour of Aluminium Matrix Composite Reinforced with Boron Carbide in 3.5% NaCl

The corrosion behavior of Aluminium matrix composite reinforced with micro-size boron carbide was investigated in a 3.5% NaCl solution. The sample was prepared using the stir casting technique with compositions of 2, 4, 6, 8 and 10 wt% of B4C particles. Potentiodynamic polarisation methods were used to derive the electrochemical parameters while hardness analysis methods were used to derive the mechanical properties. A field emission scanning electron microscope (SEM) was employed to investigate the particle boron carbide distribution on the matrix and surface morphology of the metal surface before and after the corrosion test. The X-ray diffraction (XRD) analysis was used to investigate the received powders and matrix samples for phase recognition and the presence of reinforcement particles (B4C) in the composite samples. The findings demonstrated that in a 3.5% NaCl solution, the aluminium matrix composite corrosion rate was inferior to that of the base alloy. At the same time, the corrosion rates of the composite increased with the increase in the composition of B4C in matrix aluminium. Passive layer breakdown due to agglomeration of boron carbide particles caused the increased corrosion rate. Hardness analysis has shown that the value of hardness was improved with the increase in the composition of B4C in the aluminium matrix.

INCIDENCE OF HEAT TREATMENT ON THE CORROSIVE BEHAVIOR OF AISI 316L AUSTENITIC STAINLESS STEEL

Heat treatments of AISI 316L samples were conducted at 900°C with slow cooling in air to induce varied precipitation of chromium-rich carbide particles at grain boundaries, resulting in a microstructure susceptible to intergranular corrosion. The corrosion behavior of the material in this state was investigated in a salt spray chamber containing 5% NaCl. The temperature inside the chamber was set at 35°C, while the saturated air temperature was recorded at 47°C. Samples were periodically extracted for observation and analysis using a stereoscopic magnifying glass, optical microscope, and scanning electron microscope. The results revealed the detrimental effect of chloride ions on the corrosion behavior of these stainless steels. Metallographic examination of corroded specimens after the salt spray test confirmed that the passive layer's breakdown was responsible for the intergranular corrosion occurring along preferential paths of chromium carbides.

Effect of triethanolamine and sodium hexametaphosphate on formation, growth and breakdown of passive layer in concrete pore solution

In present study, 0.1 (M) triethanolamine (C6H15NO3: TEA) and 0.01 (M) sodium hexametaphosphate [(NaPO3)6: SHMP] have been dissolved in deionized water to synthesize the TS inhibitor solution. Different amounts such as 0.01, 0.10 and 0.25% of TS inhibitor have been taken to study the corrosion performance of steel rebar in 0.6 (M) NaCl contaminated concrete pore (CPNC) solution. The corrosion mechanism and kinetics of the steel rebars in presence of inhibitor have been studied by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) with exposure periods while the morphology and nature of passive film formed on rebar surface have been examined by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS), after 192 h of immersion. The steel rebar immersed in without inhibitor solution (CPNC) has exhibited lowest film resistance (Rf) and charge transfer resistance (Rct) with pits formation in passive film. Alternatively, the steel rebars exposed to inhibitor added CPNC solutions show higher in Rf, Rct values, lowest corrosion current density (icorr), nobler OCP and cluster like morphology of the passive films. It is attributed to the adsorption of TEA molecules on the rebar surface by donating lone pair of electrons from N atom while PO43− ions (from SHMP) transform the Fe(OH)2 into FePO4. The corrosion inhibition efficiency of the inhibitor containing samples are increased with exposure periods and the maximum is found to be 97.57% by 0.10% TS after 192 h of exposure.

LOCALISED CORROSION OF STAINLESS STEELS 316L AND 2205 IN SYNTHETIC BENTONITE PORE WATER AND BENTONITE SLURRY

One concept for Czech canister construction for deep geological repository considers stainless steel as an inner case material. Corrosion resistance to localised (pitting/crevice) corrosion and stress corrosion cracking of austenitic stainless steel 316L and duplex steel 2205 was studied. The environment was synthetic bentonite pore water (SBPOW) of domestic bentonite BaM, or a slurry of bentonite in SBPOW. Tests were carried out between 40 °C and 90 °C under anaerobic conditions of a nitrogen atmosphere. The following methods were used for evaluation: potentiostatic tests at oxidation-reduction potential of the environment, long-term exposure tests in SBPOW and slurry, slow strain rate tensile test (SSRT), exposure test of U-bends, and optical microscopy. Results showed no susceptibility of either material to stress corrosion cracking. No localised corrosion was observed up to 70 °C. There was no localised attack observed in SBPOW at 90 °C, but there was localised corrosion detected in the bentonite slurry. Forced breakdown of the passive layer during SSRT, and artificial crevices (O-rings), showed no effect on localised corrosion propagation. The detrimental effect was probably a result of the adsorption ability of the bentonite particles, which allowed breakdown of passive layer and disabled repassivation of metastable pits.

Crevice and pitting corrosion of low temperature plasma nitrided UNS S32750 super duplex stainless steel

The UNS S32750 super duplex stainless steel (SDSS) was low temperature plasma nitrided at 350 °C and 400 °C for 4 h. Pitting and crevice corrosion resistance was evaluated using electrochemical techniques in a NaCl neutral solution. Nitriding treatments resulted in increased in hardness, general corrosion resistance and in the passive layer breakdown potential. Regarding crevice corrosion tests, the nitrided surfaces showed lower current densities during the potentiostatic polarization and lower corrosion depths when compared to the untreated surface. The nitrogen played a fundamental role in the passivation behavior and in the susceptibility to repassivation of localized corrosion.

Influence of Chloride Ions on Electrochemical Corrosion Behavior of Dual-Phase Steel over Conventional Rebar in Pore Solution

Reinforced steel bars (rebar) are extensively used in construction, and the main challenge is in minimizing corrosion due to oxide or passive layer breakdown. In contrast, dual-phase (DP) steel has good corrosion resistance. This study investigated the effect of Cl− ions on the electrochemical corrosion behavior of DP rebar and conventional rebar. Corrosion behavior studies and electrochemical measurements were conducted on DP rebar and conventional rebar in simulated concrete pore solution with different concentrations of Cl− ions. Microstructure analysis, surface morphology analysis, and corroded surface characterization were performed using optical microscopy, field emission scanning electron microscopy, and Raman spectroscopy, respectively. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements revealed that DP rebar has good passivity, leading to better corrosion resistance and greater strength compared to ordinary rebar. In addition, DP rebar showed better passivity behavior compared to conventional rebar in alkaline solution. Therefore, the presence of a dual phase (ferrite and martensite) in reinforced concrete structured steel induces good corrosion resistance.

LOCALISED CORROSION OF STAINLESS STEELS 316L AND 2205 IN SYNTHETIC BENTONITE PORE WATER AND BENTONITE SLURRY

<p class="AMSmaintext">One concept for Czech canister construction for deep geological repository considers stainless steel as an inner case material. Corrosion resistance to localised (pitting/crevice) corrosion and stress corrosion cracking of austenitic stainless steel 316L and duplex steel 2205 was studied. The environment was synthetic bentonite pore water (SBPOW) of domestic bentonite BaM, or a slurry of bentonite in SBPOW. Tests were carried out between 40 °C and 90 °C under anaerobic conditions of a nitrogen atmosphere. The following methods were used for evaluation: potentiostatic tests at oxidation-reduction potential of the environment, long-term exposure tests in SBPOW and slurry, slow strain rate tensile test (SSRT), exposure test of U-bends, and optical microscopy. Results showed no susceptibility of either material to stress corrosion cracking. No localised corrosion was observed up to 70 °C. There was no localised attack observed in SBPOW at 90 °C, but there was localised corrosion detected in the bentonite slurry. Forced breakdown of the passive layer during SSRT, and artificial crevices (O-rings), showed no effect on localised corrosion propagation. The detrimental effect was probably a result of the adsorption ability of the bentonite particles, which allowed breakdown of passive layer and disabled repassivation of metastable pits.</p>

Electrochemical Behavior in Simulated Physiological Solution of Ti-Nb-Zr-Calcium Pyrophosphate Composite with Enhanced Bioactivity by Spark Plasma Sintering

The potential biomedical application near β-type Ti-35Nb-7Zr alloy with different CPP ceramic additions were evaluated in vitro using electrochemical method and osteoblasts co-cultured. A small amount addition of calcium pyrophosphate (CPP) ceramic induced the formation of oxide film on the surface of the composites that can withstand passive layer breakdown and the onset of localized forms of corrosion. But localized breakdown of the oxide layer occurred on composites as the CPP exceeded 20 wt%. Ti-35Nb-7Zr-10CPP exhibits a wide passive range in the polarization curve and gets a higher potential for inducing growth of bone-like apatite and proliferation of osteoblasts on its surface compared to that of the Ti-35Nb-7Zr, CP Ti and Ti6Al4V (TC4) alloys. The favorable cell viability and growth inside the pores of the composites arise from the rough micro-porous surface and the release of bioactive metal-ceramic phase ions into the physiological environment.

Effect of Heat Treatment on Corrosion Behavior of Al-4Ti/MgO-SiC Composite

This work focuses on the effect of annealing, normalizing and tempering on corrosion behavior of Al-4Ti/1 wt% MgO-2 wt% SiC composite fabricated by stir casting method. The XRD analysis and optical examination indicate that the heat treatments lead to breaking up the main phase (Al3Ti) in Al-4Ti alloy and form many oxides that cover the composite surface. Linear and cyclic polarizations have been investigated in seawater at room temperature by Potentiostat. The corrosion data showed that the corrosion potential became more negative for heat treated composites compared with untreated once. Corrosion current density decreased after heat treatments. The normalized composite has lowest corrosion rate due to expose the specimen to atmosphere for quenching which leads to form SiO2 in addition to MgO and Al2O3. The breakdown of passive layer in composite decreased by heat treatments which assessed by cyclic polarization test.

Anodic dissolution behavior of zirconium in Bun4NBr-containing isopropanol solution

Anodic dissolution behavior of zirconium in Bun4NBr-contaning isopropanol solution was investigated using cyclic voltammetry, linear sweep voltammetry and chronoamperometry, complemented with a scanning electron microscope (SEM). The voltammograms did not exhibit active dissolution until the breakdown of passive layer induced by aggressive bromide anions. SEM images confirmed the existence of pits on zirconium surface. The depth and breadth of pits were intensified with increasing potential. The pitting potential shifted negatively as either temperature or Bun4NBr concentration was increased, while it increased with increasing scan rate. The corrosion current density increased with increasing temperature. The apparent activation energy of anodic dissolution of zirconium was 21.88 kJ/mol. The chronoamperometry revealed that increasing Bun4NBr concentration shortened the incubation time for passivity breakdown and accelerated the pit nucleation and growth. The experimental results were helpful to obtain the optimum conditions for electrosynthesis of zirconium isopropoxide.

Passivation Dynamics in the Anisotropic Deposition and Stripping of Bulk Magnesium Electrodes During Electrochemical Cycling.

Although rechargeable magnesium (Mg) batteries show promise for use as a next generation technology for high-density energy storage, little is known about the Mg anode solid electrolyte interphase and its implications for the performance and durability of a Mg-based battery. We explore in this report passivation effects engendered during the electrochemical cycling of a bulk Mg anode, characterizing their influences during metal deposition and dissolution in a simple, nonaqueous, Grignard electrolyte solution (ethylmagnesium bromide, EtMgBr, in tetrahydrofuran). Scanning electron microscopy images of Mg foil working electrodes after electrochemical polarization to dissolution potentials show the formation of corrosion pits. The pit densities so evidenced are markedly potential-dependent. When the Mg working electrode is cycled both potentiostatically and galvanostatically in EtMgBr these pits, formed due to passive layer breakdown, act as the foci for subsequent electrochemical activity. Detailed microscopy, diffraction, and spectroscopic data show that further passivation and corrosion results in the anisotropic stripping of the Mg {0001} plane, leaving thin oxide-comprising passivated side wall structures that demark the {0001} fiber texture of the etched Mg grains. Upon long-term cycling, oxide side walls formed due to the pronounced crystallographic anisotropy of the anodic stripping processes, leading to complex overlay anisotropic, columnar structures, exceeding 50 μm in height. The passive responses mediating the growth of these structures appear to be an intrinsic feature of the electrochemical growth and dissolution of Mg using this electrolyte.

Corrosion resistance evaluation of Al‐based alloys by means of dynamic electrochemical impedance spectroscopy

Purpose – The purpose of this paper is to present the investigation of aluminum alloy by means of dynamic electrochemical impedance spectroscopy (DEIS), which is simultaneous method of AC impedance and DC polarization measurements.Design/methodology/approach – A method of DEIS has been applied. Changes in equivalent circuit (EC) parameters versus potential for both investigated aluminium alloys are evaluated.Findings – On the basis of obtained results, it is unambiguously demonstrated that the addition of 4.5 percent magnesium degraded the anticorrosive properties of the test alloys. It is difficult to define unequivocally the range of passive state and a moment of passive layer breakdown on the basis of current/voltage dependencies. However, application of the DEIS method and analysis of the evolution of particular elements of an electrical EC allowed identification of the instant of corrosion process initiation.Practical implications – The presented method is only suitable for laboratory evaluation of m...

Corrosion, passivation and breakdown of passivity of neodymium

The anodic polarisation behaviour of neodymium was investigated in various solutions (pH 1–12). While in sulphuric acid solution high dissolution rates were observed, spontaneous passivity occurred in phosphoric acid solutions, oxalic acid solutions and sodium hydroxide solutions. However, the stability of these protecting layers strongly depends on the kind and concentration of anions present, especially in acidic environments. A mechanism of the passive layer breakdown is proposed. During pitting corrosion erosive degradation of the electrode was observed. In all solutions, abnormal hydrogen evolution was observed when neodymium was in the active state during anodic polarisation.

Modeling the effects of nuclear environments on crevice corrosion of pure nickel by coupling of phase and polarization behavior

As from long-term operating experience the high purity primary water cycle of light water nuclear reactors may exhibit excursions from the recommended water chemistry leading to potentially favorite conditions for stress corrosion cracking (SCC) which may be initiated and its propagation controlled by local pitting and crevice corrosion. Deterministic modeling of local corrosion including incubation times for crevice corrosion should therefore provide a basis for lifetime predictions of components, which have been subjected to sporadic intermediate water chemistry fluctuations. Based on previous work for room temperature (RT), the chloride-induced crevice corrosion at 288 °C of pure nickel as an important base element in respective high alloyed nuclear materials is modeled by coupling anodic polarization with the precipitation of nickel oxide and nickel chloride calculated from the water–hydrogen–nickel chloride heterogeneous phase equilibrium diagram. The surface corrosion potentials are fixed by bulk levels of hydrogen and oxygen contents as well as pH simulating hydrogen treatment of irradiation subjected cooling water for the reduction of corrosion potentials and mitigation of SCC at operating temperature 288 °C in Boiling Water Reactors (BWRs). Assuming chemical equilibrium conditions during the selected time steps in a relevant component crevice the calculated change of the crevice solution composition is quantitatively shown to initiate crevice corrosion by the breakdown of the passive nickel oxide layer followed by the formation of non-passive nickel chloride and the subsequent acidification of the crevice solution. The effects of corrosion potentials, bulk levels of pH and chlorides, are investigated. As a result, the reduction of corrosion potentials and increase in bulk pH provide significant increases in the passive layer breakdown times and acidification times inside the crevice. Depending on bulk pH and corrosion potentials the reduction of bulk chlorides down to recommended levels in BWRs retards crevice corrosion significantly. For a standard 100,000 h time for crevice acidification to locally less than pH = 0 the respective chloride–pH domain is evaluated. Such diagrams may be related to respective effects on stress corrosion cracking and its mitigation by hydrogen water chemistry (HWC).

EIS investigation of passive film formation on mild steel in oxalic acid solution

The properties of oxide films on mild steel formed anodically in aqueous solution containing oxalic acid were investigated by means of electrochemical impedance spectroscopy (EIS). The morphology of the passive layers at different stages of film formation was investigated using scanning electron microscopy (SEM). Passivation of mild steel in oxalic acid solution is a multi-stage process that occurs before passive layer breakdown. The influence of potential on the electrochemical behavior of the passive layer was also investigated. Depending on the passive layer potential, the EIS spectra obtained exhibited a one- or two-time constant system. This suggests the formation of either a one layer or two layer oxide film on the mild steel surface, depending on the passivation potential.

Monitoring of Conductivity Changes in Passive Layers by Scanning Electrochemical Microscopy in Feedback Mode: Localization of Pitting Precursor Sites on Surfaces of Multimetallic Phase Materials

Scanning electrochemical microscopy (SECM) in feedback mode was applied to monitor changes in the electronic conductivity of a passive layer existing on a nanocrystalline Nd-Fe-B-type permanent magnet of the following composition, Nd13.5Fe79.5Si1B6 (where subscripts denote at. %). This model magnet being a complex multimetallic-phase material (fabricated according to the hydrogenation-disproportionation-desorption-recombination route) contained intrinsic iron inclusions, as evident from SEM and EDX mapping. SECM measurements performed in feedback mode using ferrocenecarboxylic acid as a mediator (in phosphate buffer at pH 7) in the presence and absence of chloride anions permitted evaluation of the local surface (passive layer) conductivity changes during pitting corrosion caused by Cl- anions. The spots of high conductivity (electronic or redox) act as precursor sites for initiation of pits. It can be rationalized that iron inclusions are responsible for the high susceptibility of Nd-Fe-B magnets to pitting corrosion. The approach is fairly general and allows localization of pitting precursor sites under different corrosion environments that include a wide range of concentrations of anions causing the passive layer breakdown.

A SECM assisted EQCM study of iron pitting

The local breakdown of the iron passive layer and the resulting pitting corrosion of iron were studied for massive material and for a thin film on an electrochemical quartz crystal microbalance (EQCM). The initiation and the propagation of a single pit on iron were controlled through the local production of chloride anion thanks to the silver chloride reduction at the tip of the scanning electrochemical microscope (SECM). Experiments were performed in borate buffer and in KOH solution, in order to investigate the influence of the solution pH. The influence of the iron potential and of the amount of chloride anion necessary for the breakdown of the passive layer were also investigated. The frequency response of the quartz was correlated to the pit evolution with respect to time. After the breakdown of the passive layer, the frequency changes were then directly linked to the generation of Fe(II) during the pit growth.

The effects of the cementite phase of iron-carbon alloys on their electrochemical behavior in an oxalic acid medium

Anodic dissolution and passivation of iron-carbon alloys containing a pearlitic constituent are investigated. The role of the cementite phase in the passivation, as well as the possibility of the passive layer breakdown at the boundary between the ferritic and cementite phases, is shown.

Development of a Coupled SECM-EQCM Technique for the Study of Pitting Corrosion on Iron

The local breakdown of the iron passive layer and the resulting pitting corrosion were studied with a coupled scanning electrochemical microscopy/electrochemical quartz microbalance technique (SECM/EQCM). The initiation and the propagation of a single pit on iron deposited on the quartz gold electrode were controlled through the local production of chloride anion thanks to the silver chloride reduction at the tip of the scanning electrochemical microscope. The frequency response of the quartz was correlated to the pit evolution with respect to time. After the breakdown of the passive layer, the frequency changes were then directly linked to the generation of Fe(II) during the pit growth. It was also shown that in 0.1 M NaOH solution, the local amount of necessary to initiate the pit was about 0.15 M. In addition to the presence of the oxidized passive layer and corrosion products like -FeOOH, and Green Rust, Raman analysis evidenced the formation of inside the pit. Moreover, the influence of the pit size was also studied by varying the amount of chloride ions generated close to the iron substrate.