•Al xCoCrFeNi high entropy alloys present superior corrosion-preventive ability.•Increased Al-content in Al xCoCrFeNi alloys degrades localized corrosion resistance.•Pitting behavior is influenced by ...passive film properties and migration of Cl− ions.•Mean field theory can predict the distribution of current fluctuations.
The present work investigates the influence of Al-content and potential-scan-rate on stable/metastable pitting of Al xCoCrFeNi high-entropy alloys in a 3.5wt.% NaCl solution. The increased Al content causes the volume fraction of the Cr-depleted phase to increase, resulting in thicker/dispersive passive films that degrade the localized corrosion resistance. The varied stable/metastable pitting behavior under different potential scan rates indicates that pit generation is influenced by the properties of passive films and the interactions between chloride ions and the active sites. Furthermore, a mean-field theory is employed to predict the scan-rate dependent, power-law distribution of current fluctuations.
•Pitting corrosion of SLM 316L SS in different aggressive solutions was studied.•A model was built to explain the pitting mechanism induced by gas-pore.•Metastable pitting at covered gas-pores is ...more likely to transition into stable.
In this study, the pitting behaviors of wrought and SLM 316L SSs (stainless steels) are comparatively investigated under the conditions of different aggressiveness. The experimental results show that SLM 316L SS exhibits higher sensitivity to pitting corrosion in extremely aggressive solutions, while the wrought sample is more vulnerable to pitting in conditions with low aggressiveness. Gas pores are the pitting-sensitive sites in SLM 316L SS, and metastable pits initiated at covered gas pores are easier to evolve to stable growth compared to open pores due to the greater diffusion resistance.
•1250 °C heat treatments enhance the corrosion resistance of AlxCoCrFeNi HEAs.•Homogenization is revealed by the decreased work function variations among phases.•Thermodynamic calculations could ...predict the phase transformation of HEAs.
The present work investigates the homogenization effect of 1250 °C heat treatment on the AlxCoCrFeNi high-entropy alloys (HEAs). The multi-phase microstructures with chemical segregations are inevitable with the increased Al content in the alloys, which cause work function variations and localized corrosion. After heat treatment, the homogenization effect revealed by the microstructure simplification and chemical-segregation reduction leads to the decreased work function variations and the improved corrosion resistance. Thermodynamic calculations that are reliable to predict the phase transformations of the AlxCoCrFeNi HEAs, indicates a further enhancement in corrosion resistance through annealing could be guided for many other HEAs systems.
This work addresses the dissolution corrosion behaviour of 316L austenitic stainless steels. For this purpose, solution-annealed and cold-deformed 316L steels were simultaneously exposed to ...oxygen-poor (<10−8 mass%) static liquid lead-bismuth eutectic (LBE) for 253–3282 h at 500 °C. Corrosion was consistently more severe for the cold-drawn steels than the solution-annealed steel, indicating the importance of the steel thermomechanical state. The thickness of the dissolution-affected zone was non-uniform, and sites of locally-enhanced dissolution were occasionally observed. The progress of LBE dissolution attack was promoted by the interplay of certain steel microstructural features (grain boundaries, deformation twin laths, precipitates) with the dissolution corrosion process. The identified dissolution mechanisms were selective leaching leading to steel ferritization, and non-selective leaching; the latter was mainly observed in the solution-annealed steel. The maximum corrosion rate decreased with exposure time and was found to be inversely proportional to the depth of dissolution attack.
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•Dissolution corrosion was more severe in cold-deformed than solution-annealed 316L steels.•LBE penetration occurred along preferential paths in the steel microstructure.•The maximum dissolution rate was inversely proportionate to the depth of dissolution.
The metastable pitting corrosion behavior of laser powder bed fusion (LPBF) produced Ti-6Al-4V is still unclear. Therefore, this work investigated the metastable pitting corrosion of LPBF-produced ...Ti-6Al-4V in Hank’s solution by electrochemical methods. The LPBF-produced sample (dominant by α′ phase in the microstructure) shows a higher frequency of pit nucleation than the annealed counterpart (composed by α + β dual phase). The passive films formed on the LPBF-produced sample exhibit a higher flux of oxygen vacancies, resulting in the absorption of more aggressive ions (e.g., Cl-) thereby producing more cation vacancies. The condensation of excessive cation vacancies contributes to the pit nucleation.
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•Laser powder bed fusion (LPBF) produced Ti–6Al–4 V alloy was used as the sample.•Corrosion behavior of the LPBF-produced sample was investigated in Hank’s solution.•The LPBF-produced Ti-6Al-4 V shows frequent metastable pitting corrosion.•The flux of oxygen vacancy is large in the passive film of LPBF-produced Ti-6Al-4 V.•Redundant vacancies assemble and condense into a void at metal/film interface.
In this paper we introduce a peridynamic model for the evolution of damage from pitting corrosion capable of capturing subsurface damage. We model the anodic reaction in corrosion processes (in which ...electroplating is negligible) as an effective peridynamic diffusion process in the electrolyte/solid system coupled with a phase-change mechanism that allows for autonomous evolution of the moving interface. In order to simulate creation of subsurface damage, we introduce a corrosion damage model based on a stochastic relationship that connects the concentration in the metal to the damage of peridynamic mechanical-bonds that are superposed onto diffusion-bonds. We study convergence of this formulation for diffusion-dominated stage. The model leads to formation of a subsurface damage layer, seen in experiments. We validate results against experiments on pit growth rate and polarization data for pitting corrosion. We extend the 1D model to the 2D and 3D, and introduce a new damage-dependent corrosion model to account for broken mechanical bonds that enhance the corrosion rate. This coupled model can predict the pit shape and damage profile in materials with microstructural heterogeneities, such as defects, interfaces, inclusions, and grain boundaries.
Quantitative monitoring of steel corrosion plays a crucial role in evaluating structural safety and predicting structural performance. The electromechanical impedance (EMI) technique has already ...emerged for uniform corrosion monitoring. This study explores its potential for pitting corrosion monitoring. Specifically, two EMI-based sensor designs were proposed, namely the cylinder and the tube structures. Finite element models were developed to analyze the influence of the pit’s location, morphology parameters, as well as the random distribution of multiple pits, on the conductance peak frequency of sensors. The computer numerical controlled processes were employed to create random pits on sensors. Experimental results revealed that different distributions of pits correspond to distinct conductance peak frequencies, even with the same mass loss. Additionally, the tubular sensor exhibited reduced sensitivity to pits distribution compared to the cylindrical sensor. This is beneficial for accurately predicting mass loss induced by random pitting. This paper enhances the capability of EMI-based sensors for quantitatively monitoring pitting corrosion by focusing on structural design aspects.
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•The quantitative corrosion monitoring capability of EMI-based sensors under pitting corrosion was investigated.•The finite element models of the sensors with random pitting corrosion were established and validated by experiment.•The prediction accuracy of the sensor for mass loss was improved by optimizing its structure.
•Intrinsic kinetics of pit/crack initiation induced by inclusions is provided.•Chemical dissolution of complex oxide inclusions induces pits.•Dissolution of CaS generates circular protected region ...around Ds type inclusions.•Si-enriched inclusions remain intact but can induce micro-cracks.
In-situ 2D and 3D microscopic technologies are used to analyze the influence of inclusions on pitting and stress corrosion cracking initiation of X70 steel in near-neutral pH solution. The chemical dissolution of complex oxide inclusions or part of them induces corrosion pits. Circular protected region forms around Ds inclusions due to dissolution of CaS. The Si-enriched inclusions remain intact, but interstice forms at the inclusion/matrix interface due to the dissolution of the matrix. Both complex oxide inclusions and Si-enriched inclusions can induce initiation of SCC micro-cracks, but most of the micro-cracks are generated inside the ferrite grains.
•Compressive residual stress reduced by 90% of the as-built value following 1100 °C for 5 min.•Pitting potential decreased by around 180 mV on stress-relieving specimens.•Repassivation potential ...increased with decreasing compressive stress for all specimens.•Donor density in the passive film increased with decreasing compressive stress.
Selective Laser Melting (SLM) and various subsequent stress-relieving treatments were used to obtain 316 L specimens with compressive residual stresses, varying from 15 to 250 MPa. This enabled a study on the effect of residual stress on corrosion of 316 L using electrochemical methods, which is relevant for durability of additively manufactured materials. Overall, compressive stresses in SLM 316 L result in a measurable increase in the pitting potential, accompanied by a decrease in the passive film currents and donor densities. It is proposed that compressive stresses lower the film growth and repassivation kinetics but slightly enhances the pitting resistance of SLM 316 L.
•Pitting behavior of X80 steel in aerated NaCl solutions is studied systematically.•Unique large pit morphology is observed in neutral/acidic NaCl solutions.•In low pH solutions, pit will propagate ...in the horizontal direction, leading to the shallow shape of pitting morphology; in high pH solutions, the pit sizes are much smaller.•Film growth, which is dependent on the pH and chloride concentration, has great influence on the cathodic reaction by affecting oxygen diffusion process.
The pitting corrosion mechanism of high strength pipeline steel in aerated NaCl solutions with different pH and chloride content was investigated, using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The pitting behavior in alkaline solutions was found to be significantly different from that in neutral and acidic solutions. Electrochemical results and SEM images indicate that the product film formed on the steel surface results in different corrosion behavior in an alkaline solution. SEM images show that pH and chloride concentration in the bulk solution have a great influence on the pitting morphology. Unique large pit morphology due to corrosion in neutral/acidic solutions with 0.05mol/L NaCl was observed. The relationship between solution pH and the effect of chloride concentration is also discussed.
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