Effect of nitrogen alloying on the semiconducting properties of passive films and metastable pitting susceptibility of 316L and 316LN stainless steels

The beneficial effect of nitrogen alloying on the corrosion resistance of stainless steels has been attributed to the increase of the local pH within the active sites and the enhanced repassivation of the metastable pits. In order to better understand the effect of nitrogen alloying, in situ capacitance measurements and potentiostatic polarization were conducted for 316L and 316LN stainless steels with different nitrogen contents in deaerated 0.1 M Na₂SO₄ and 0.1 M NaCl aqueous solutions. The Mott–Schottky plots obtained from the in situ capacitance measurements offered information on the donor concentration and the thickness of the space charge region within the passive film. The metastable pitting susceptibility was investigated by performing potentiostatic polarization tests. The results showed that nitrogen alloying decreased the donor densities and the number of metastable pits, while the absorption of chloride ions on the passive film had the opposite effect. Auger electron spectroscopy (AES) analysis demonstrated that nitrogen alloying enriched the chromium within the passive film. The relationship between the semiconducting properties of the passive film and the metastable pitting susceptibility was elucidated.     

Recent advances on environmental corrosion behavior and mechanism of high-entropy alloys

In the past decade,the sudden rise of high-entropy alloys (HEAs) has become a research hotspot in the domain of metal materials.HEAs break through the design concept of traditional single-principal element alloys,and the four core effects,especially the high entropy and cocktail effects,make HEAs exhibit much better corrosion resistance than traditional corrosion-resistant metal materials,e.g.,stain-less steels,copper-nickel alloys,and high-nickel alloys.Currently,the corrosion resistance of HEAs causes great concern in the field of corrosion research.This article reviews the corrosion behavior and mechanism of HEAs in various aqueous solutions,revealing the correlation among the composition,microstructure and corrosion resistance of HEAs,and elaborates the influence of heat treatment,anodizing treatment and preparation methods on the corrosion behavior of HEAs.This knowledge will benefit the on-demand design of corrosion-resistant HEAs,which is an important trend of future development.Finally,perspec-tives regarding the corrosion research of HEAs are outlined to guide future studies.     

Influence of Surface Treatment on the Corrosion Resistance of Stainless Steel in Simulated Human Body Environment

In the present research,the influence of chromium enrichment by surface treatment on corrosion resistance of type 316L stainless steel in body environment was investigated.For this study,weight loss test during 18 months,cyclic and liner polarization tests before and after surface treatment and metallography by electron and light microscopy were used to evaluate the effectiveness of the proposed method.In addition,X-ray photoelectron spectroscopy(XPS)method was used to determine the chromium concentration i...     

The novel strategy for enhancing mechanical properties and corrosion resistance via regulating multi-scale microstructure characteristics in Al-Si-Cu-Mg-Zr cast alloy

High strength and low corrosion resistance are always the contradiction in Al-Si-Cu-Mg cast alloy due to introducing high Cu and Mg levels.In this work,the new strategy was achieved for enhancing corrosion resistance and mechanical properties by regulating multi-scale microstructure characteristics in Al-9Si-4.2Cu-0.25Mg-Zr alloy.Electrochemical and corrosion morphology results indicate that the addition of Zr significantly enhances the corrosion resistance of the alloy.The grain refinement inhibits the charge transfer process between cathode phases and the matrix is the main reason at the Zr level of less than 0.15％.When the Zr level is up to 0.3％,the multi-scale synergistic effect of grain refinement and passive film enhancement significantly inhibits the corrosion process.Moreover,0.3％Zr addition increases the yield strength to 419 MPa,tensile strength to 490 MPa,and the acceptable fracture elongation to 3.8％.The strengthening of mechanical and corrosion properties originates from the nano-Al3Zr precipitates after T6 treatment.This study provides a novel micro-mechanism and design strategy for simultaneously improving corrosion resistance and enhancing the mechanical properties of Al-Si-Cu-Mg cast alloy.     

Dissolution and repair of passive film on Cu-bearing 304L stainless steels immersed in H2SO4 solution

The antibacterial Cu-bearing 304L stainless steel is a new kind of structural and functional integrated metal material. In this work, evolution behavior of passive film of different heat treated Cu-bearing 304L stainless steel immersed in 0.5?M H₂SO₄ solution was investigated by using electrochemical measurements, atomic force microscopy (AFM) observation and X-ray photoelectron spectroscopy (XPS) analysis. The results show that the solution and aging treated samples have the similar polarization behaviors. The passive film impedance experiences an initial decrease within 7?days followed by a subsequent increase, while the defect density of passive film presents the opposite trend. Meanwhile, the evolution of surface morphology and the estimated thickness of the passive film confirm that it experiences initial dissolution and follow-up repair. Furthermore, the Cr³⁺ content in passive film undergoes sequential reduction to increase, however the variation tendency of Cu²⁺ content is just opposite, indicating that the content variation of Cr and Cu in passive film reflects the competitive process of film dissolution and repair. In addition, compared with solution treated samples, aged samples have a bigger i_corr value and the rougher passive film. This indicates that the passive film of solution treated steel is more compact and stable.     

Effects of phosphate on the chloride-induced corrosion behavior of reinforcing steel in mortars

The influence of phosphate as a corrosion inhibitor on the corrosion behavior of as-received and pre-rusted reinforcing steels in mortar specimens was investigated after 360 days exposure in 3.5% NaCl solution. This involved the use of electrochemical techniques for studying the steel surface reactions and microscopic observations of the steel–mortar interface. The electrochemical methods, including electrochemical impedance spectroscopy (EIS) and measurements of corrosion potential (E_corr) and linear polarization resistance (LPR), were employed to evaluate the corrosion tendency and general corrosion rate of steel. In addition, the pitting corrosion resistance of steel was also determined by cyclic polarization (CP) measurements. The results indicate that different from nitrite, which is generally accepted as an anodic inhibitor, phosphate may be a cathodic inhibitor according to its reduced corrosion rate and more negative E_corr at the same dosage as nitrite in mortar specimens. The study also reveals that the inhibiting efficiency of phosphate against general corrosion of both as-received and pre-rusted specimens is lower than 10%, which is inferior to nitrite in some respects. However, as indicated by cyclic polarization measurements, the presence of phosphate provides slightly higher pitting corrosion resistance in comparison to nitrite. Furthermore, it suggests that the corrosion inhibition mechanism of phosphate in mortars mainly depends on a dual effect occurring at the steel–mortar interface. Furthermore, it is confirmed that phosphate has little effect on the long-term mechanical properties of mortars.     

Enhancement of corrosion resistance of a biomedical grade 316LVM stainless steel by potentiodynamic cyclic polarization

The paper discusses the results on the use of a simple cyclic linear potentiodynamic polarization technique as a method of improving corrosion properties of passive oxide films formed on a biomedical-grade 316LVM stainless steel surface in phosphate buffer. The results demonstrate that the modification of 316LVM surface by cyclic potentiodynamic polarization between the potential of hydrogen and oxygen evolution results in the formation of a passive film that offers significantly increased corrosion resistance (both pitting and general) when compared to the naturally grown passive film. The effect of number of cycles and anodic potential limit on the resulting corrosion properties is discussed. The capacitance analysis demonstrates that the major difference between the electrochemically formed and naturally grown passive film is in the type of semiconductivity in the potential region where pitting on the unmodified surface occurs. The XPS analysis shows that this is due to the presence of Cr(VI)-species in the electrochemically formed passive film, which contribute to the increased density of metal vacancies, and thus to the increased pitting corrosion resistance of the passive film.     

Effect of Cl- on the Properties of the Passive Films Formed on 316L Stainless Steel in Acidic Solution

The corrosion behavior of 316L stainless steel （31 6L SS） has been investigated in solutions containing various concentrations of chloride ions by using potentiodynamic polarization, capacitance measurement and Mott- Schottky relationship analysis （M-S）. The result indicates that passive currents change slightly with the addition of chloride ions. The pitting potential （Epit） decreases linearly with Iog[CI-]. Correspondingly, the point defect diffusion coefficient （Do） of the passive film increases linearly with increasing Iog[CI-]. The results also indicate that the pitting corrosion of 316L SS follows the adsorption mechanism in NaCI solution.     

混凝土设计参数对氯盐环境下钢筋锈蚀的影响研究

研究了混凝土设计参数包括水胶比、胶凝材料组成、保护层厚度和混凝土氯离子含量等对氯盐环境下混凝土中钢筋锈蚀的影响。通过模拟氯盐环境下混凝土中钢筋所处的锈蚀环境,并以一定的方法加速混凝土中钢筋的锈蚀,采用电化学测试手段(钢筋腐蚀电位和钢筋腐蚀电流密度)来评价各设计参数对钢筋锈蚀的影响。结果表明,水胶比越小、保护层厚度越大、混凝土氯离子含量越小、使用矿物掺合料能有效延缓钢筋开始锈蚀时间,并在不同程度上减小钢筋的锈蚀速率。试件在试验一段时间后被破损,将钢筋周围砂浆制样并进行SEM扫描电镜元素分析试验,进一步验证电化学测试方法的准确性及钢筋的锈蚀程度。     

Interactive Effects of Fly Ash and CNI on Corrosion of Reinforced High-Performance Concrete

The interactive effects of fly ash and CNI in corrosion of reinforced concrete were investigated. A 3⁴ full factorial design was developed considering water to cement ratio, fly ash percent, CNI and cracked condition as factors. The response factors were the weight loss calculated from Linear Polarization Resistance measurements and the pit depth of the steel bars embedded in concrete. Small-scale concrete slabs containing steel reinforcement with a cover depth of 20 mm were cast for this purpose. The slabs were subjected to a simulated marine environment with two cycles of wetting and drying per day during one year; after the exposure, the slabs were broken, the bars were cleaned and the pith depth measured by using SEM. Under the studied conditions, it was found that CNI alone does not provide corrosion protection of the steel reinforcement even for uncracked silica fume concrete in a 0.45 w/c ratio; however, the combination of CNI and fly ash can be useful to overcome this problem. The results indicate that low w/c ratio concrete in its crack state creates conditions suitable for the development of pitting corrosion.     

腐蚀介质中不同深处混凝土/钢筋界面电极电位分布的测量方法

由于混凝土的隔离和高绝缘性,常规的电化学技术、微探针扫描技术均难于获得在腐蚀介质的浸泡下混凝土/钢筋界面电极电位分布;更难测得不同深处混凝土/钢筋界面电位分布。本文提出用阵列电极法:将不同深处混凝土/钢筋界面的钢筋分为不同深处的点电极。结合电子技术和微机控制技术,获得不同深处混凝土/钢筋界面电位分布图的立体信息。结果表明:不同深处混凝土/钢筋界面腐蚀优先发生在混凝土覆盖较浅的部位。     

Relationship between concrete resistivity and corrosion rate – A literature review

The process of reinforcement corrosion in concrete is partially controlled by the transport of ions through the concrete microstructure. Ions are charged and the ability of a material to withstand transfer of charge is dependent upon the electrical resistivity. Thus, a connection could be expected between the corrosion process of steel embedded in concrete and the electrical resistivity of concrete. This paper reviews research concerning the relationship between corrosion rate and concrete resistivity. Overall, there exists an inverse proportional correlation between the parameters. However, the dependency varies between studies and one single relationship cannot be established between corrosion rate and resistivity. To address the variation, the article reviews and evaluates the influence of factors including the experimental setup, the concrete mix design and the cause of corrosion.     

模拟混凝土孔隙液中钢筋腐蚀行为的恒电量法监测

利用恒电量法监测了钢筋在不同ｐＨ 值的模拟混凝土孔隙液中的极化电阻、钝化膜电阻Ｒｐ、Ｒｆ 值,并与电位法监测值进行了比较,结果表明,恒电量法更加准确和更具定量性,适用于钢筋的腐蚀监测。     

The influence of corrosion on bond properties between concrete and reinforcement in concrete structures

The rebar corrosion in reinforced concrete is one of the most extensive pathologies affecting the performance of concrete structures. Chloride-induced rebar corrosion damage results mainly from the use of de-icing salts in cold climates and/or exposure to marine environments. Carbonation damage is a further important degradation mechanism. The internal consequences of corrosion are the modification of the steel behavior and degradation of the steel–concrete bond. This work is devoted to the influence of the controlled corrosion on the adherence between steel and concrete. A new geometry of specimen has been designed to: (i) avoid the lateral confining stresses that appear during the classical pullout tests and (ii) permit to impose a known confinement for the study of its influence on the behavior of the interface. Five specimens with different levels of corrosion have been tested in this contribution. Reinforcing bars embedded in concrete were submitted to accelerated corrosion using an external current source. The magnitude of corrosion was measured using both Faraday’s law and the weight loss method. The level of corrosion varied from 0% to 0.76%. The geometry of the specimens allowed us to take series of digital pictures during the tests, which were analyzed using a digital image correlation, the procedure named CORRELI^LMT. The results of pullout tests proposed in this contribution indicate that: (i) levels of corrosion that are less than 0.4% of weight loss improves the bond stress and (ii) levels of corrosion resulting in more than 0.4% of weight loss lead to a reduction of the bond stress value.     

Lattice modelling of corrosion induced cracking and bond in reinforced concrete

A lattice approach is used to describe the mechanical interaction of a corroding reinforcement bar, the surrounding concrete and the interface between steel reinforcement and concrete. The cross-section of the ribbed reinforcement bar is taken to be circular, assuming that the interaction of the ribs and the surrounding concrete can be captured by a cap-plasticity interface model. The expansive corrosion process is represented by an Eigenstrain in the lattice elements forming the interface between concrete and reinforcement. Several pull-out tests with varying degree of corrosion are analysed. The numerical results are compared with experiments reported in the literature. The influence of the properties of concrete are studied. The proposed lattice approach offers insight into corrosion induced cracking and its influence on bond strength.     

Pitting corrosion of 2Cr13 stainless steel in deep-sea environment

Pitting corrosion of 2Cr13 stainless steel was investigated by deep-sea exposure test at various depths of 500 m,800 m and 1200 m in the South China Sea for 4 months.With the aid of electrochemical measurements in simulated deep-sea environments and grey relational analysis,the influence of deepsea environments on passive film and the mechanism of pitting corrosion were discussed.The results indicated that with the increase of sea depth,pitting depth of 2Cr13 stainless steel increased,which can be attributed to the change of chemical composition and the degradation of pitting resistance of passive film.Film growth was greatly retarded in the condition of low seawater temperature and low dissolved oxygen content of deep sea,resulting in an unstable and vulnerable film.Pitting depth was most influenced by hydrostatic pressure,which can increase the adsorption and penetration of Cl-ion,and promote the proliferation of point defects in passive film,leading to rapid deconstruction of protective oxides of the film.Pitting sensitivity of 2Cr13 stainless steel increased eventually with the combination of accelerated dissolution and suppressed self-healing of passive film in deep sea.