Microelectrochemical corrosion study of super martensitic welds in chloride-containing media

Pitting corrosion was studied in welded joints of supermartensitic stainless steels. The electrochemical behavior of three different weldment zones (weld metal (WM), parent metal (PM) and heat affected zone (HAZ)) was characterized independently using an electrochemical minicell through potentiodynamic and potentiostatic techniques. The minicell design selected for this work has the additional advantage of showing promise for service application. Macro-electrochemical characterization was also used to provide a basis for comparison and check the effectiveness of minicell techniques in characterizing the corrosion resistance of welded super martensitic stainless steels. Minicell experiments exhibit a great capacity to discriminate between the different welding zones. The electrochemical response can be correlated with the microstructure of the different zones. Thermal cycles resulting from the welding procedure do not have an important effect on the amount of retained austenite or on the values of the pitting potential E_P in the HAZ.     

氮、铌添加对304奥氏体不锈钢电化学腐蚀行为的影响

采用极化曲线和电化学动电位再活化技术（EPR）研究了不同含量氮（N）、铌（Nb）元素的添加对304奥氏体不锈钢的耐点蚀和耐晶间腐蚀性能的影响。结果表明：N元素的添加可以显著提高材料的耐点蚀性能,但对于晶间腐蚀性能的影响却有不同的机制。少量的N会降低材料的耐晶间腐蚀性能,但含量增加到0.2%时,却可以提高耐晶间腐蚀性能;Nb元素的添加会明显增加材料的耐晶间腐蚀性能,但会降低其耐点蚀性能。基于以上结果,确定了N和Nb添加的最佳含量,并给出上述微量元素改变材料耐腐蚀性能的作用机制。     

非晶合金Zr55Al10Cu30Ni5在3.5%NaCl溶液中的电化学行为

利用电化学极化曲线方法和电化学阻抗（EIS）技术研究了非晶合金Zr55Al10Cu30Ni5在3.5%NaCl溶液中的电化学行为。极化曲线测试结果表明，非晶合金Zr55Al10Cu30Ni5在3.5%NaCl溶液中具有很好的耐蚀性能，阳极过程表现出钝化特征，当极化电位很高时，非晶合金出现了点腐蚀。电化学交流阻抗测试表明，在阴极极化，开路电位和钝化电位下，非晶合金的Nyquist图由单容抗构成，具有很高的电荷转移电阻，表现出优良的耐蚀性，在点蚀电位附近和点蚀电位区EIS分别有两个时间常数和三个时间常数，非晶合金在3.5%NaCl溶液中浸泡12h后，耐蚀性能有所下降。     

Intergranular corrosion of welded joints of austenitic stainless steels studied by using an electrochemical minicell

An intergranular corrosion study of welded joints of austenitic stainless steels (AISI 304 and 316L) has been addressed. A specific small-scale electrochemical cell (minicell) has been used. Four different weldment zones have been studied. The electrochemical methods applied were the electrochemical potentiokinetic reactivation test and electrochemical potentiokinetic reactivation double loop test. These techniques showed that the HAZ was the most critical zone to intergranular corrosion for both materials. The weld metal was susceptible to interdendritic corrosion and the fusion line showed a mixture of intergranular and interdendritic corrosion. The effect of pre- and post-welding heat treatments for AISI 316L was analyzed. The HAZ was again the most critical zone in every heat treatment condition. The results were correlated to the microstructural features of the materials.     

The effect of temperature on corrosion behavior of AA5083 in brackish water and seawater

Al‐alloy, AA5083, as a lightweight structural material with favorable mechanical properties and, compared with other lightweight materials, good corrosion resistance has an increased usage in the marine environment. It is well known that all Al‐alloys, including AA5083, in the presence of chloride ions are more prone to corrosion. Determination of corrosion behavior of AA5083 in seawater and brackish water has been investigated and compared at 18, 25, and at 30°C. To obtain more accurate and realistic results, fresh seawater and brackish water were sampled as an electrolyte in Sibenik region. The investigation was carried out using the following electrochemical methods: open circuit potential measurement, electrochemical impedance spectroscopy, linear polarization resistance, potentiodynamic polarization, and cyclic polarization. After potentiodynamic polarization measurement, each alloy was examined using a metallographic microscope to clarify corrosion morphology. Obtained results have shown that an increase in temperature leads to an increase in corrosion activity of AA5083 in both electrolytes, while microscopic examination reveals that the dominant type of corrosion is pitting.     

Electrochemical behavior of YAG laser-welded NiTi shape memory alloy

Electrochemical behaviors of laser-welded Ti-50.6%Ni（mole fraction） shape memory alloy and the base metal in 0.9% NaCl solution were investigated by electrochemical techniques as corrosion potential measurement, linear and potentiodynamic polarization. The results indicate that the laser-welded NiTi alloy is less susceptible to pitting and crevice corrosion than the base metal, which is demonstrated by the increase in polarization resistance（Rp） and pitting potential（φpit） and decrease in corrosion current density（Jcorr） and mean difference between φpit and φprot values. It is confirmed by scanning electron microscope micrographs that pits could be observed on the surface of base metal but not on the surface of laser-welded alloy after potentiodynamic tests. An improvement of corrosion resistance of laser-welded NiTi alloy could be attributed to almost complete dissolution of inclusions upon laser welding.     

The effect of recrystallization on corrosion and electrochemical behavior of 7150 Al alloy

By weight loss, potentiodynamic polarization, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS) techniques complemented by optical and scanning electron microscopy observations, the effect of recrystallization on the corrosion, and electrochemical behavior of 7150 Al alloy was studied. The results indicated that the high recrystallization fraction 7150‐1# was worse than the low recrystallization fraction 7150‐2# on corrosion resistance. The analysis of EIS indicated that 7150‐1# exhibited obvious pitting corrosion at 5 h immersion time, whereas 7150‐2# showed no obvious pitting corrosion even at 33 h. The corrosion route developed along the grain boundary of recrystallization grains, not along the grain boundary of unrecrystallization grains.     

Corrosion Behavior of Novel Al-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composites in Aerated 3.5% Chloride Solution

The corrosion behavior of novel Al-Al₂O₃ MMCs was evaluated in aerated 3.5% NaCl solution through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). These materials corrode almost spontaneously by pitting in aerated 3.5% NaCl solution. Observations indicate that intermetallic particles in these composites appear to play an important role in this pitting corrosion behavior. Addition of Al₂O₃ particles to the base alloys did not appear to increase their corrosion resistance significantly, although corrosion rate was affected by these reinforcement particles. In cyclic polarization experiments, the small difference between the pitting potentials and the repassivation potentials for these MMCs indicated their low resistance to pitting corrosion. EIS measurements indicate adsorption/diffusion phenomena at the interface of the composites. Electrically equivalent circuits are proposed to describe and substantiate the corrosion processes occurring in these materials.     

Effect of microcrystallization on pitting corrosion of pure aluminium

A microcrystalline aluminium film with grain size of about 400 nm was prepared by magnetron sputtering technique. Its corrosion behaviour was investigated in NaCl containing acidic solution by means of potentiodynamic polarization curves and electrochemical noise (EN). The polarization results indicated that the corrosion potential of the sample shifted towards more positive direction, while its corrosion current density decreased compared with that of pure coarse-grain Al. The EN analysis based on stochastic model demonstrated that there existed two kinds of effect of microcrystallization on the pitting behaviour of pure aluminium: (1) the rate of pit initiation is accelerated, (2) the pit growth process was impeded. This leads to the enhancement of pitting resistance for the microcrystallized aluminium.     

炼油厂冷却水系统硫酸盐还原菌对316L不锈钢点腐蚀的研究

用开路电位、动电位扫描、电化学阻抗技术和扫描电镜等方法,研究了316L不锈钢在硫酸盐还原菌(SRB)溶液中的腐蚀电化学行为,分析了炼油厂冷却水系统微生物腐蚀的特征及机制.结果表明,在含有SRB溶液中的自腐蚀电位(Ecorr)和点蚀电位(Epit)随浸泡时间的增加而负移,极化电阻(Rp)随浸泡时间的增加而减小;在含有SRB溶液中的腐蚀速率均大于在无菌溶液中;SRB的生长代谢活动影响了316L SS表面的腐蚀过程,使不锈钢表面的钝化膜层腐蚀破坏程度增加,加速了316L SS的腐蚀.     

Atmospheric Plasma Surface Modification on Stainless Steel Bipolar Plate in PEMFC

In this research,stainless steel bipolar plates for proton exchange membrane fuel cell(PEMFC)have been treated by an atmospheric plasma surface modification technology.The chemical composition and thickness of the oxide film formed by plasma are conducted to verify by Auger electron spectroscopy(AES).Pitting resistance,potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS)are measured to evaluate the corrosion mechanism and electrochemical properties.The results show that the treated plates have a much thicker oxide film which leads to higher pitting potential,improved corrosion rate,less and smaller pitting holes than those without treatment.The stable chemical and electrochemical properties of the treated stainless steel bipolar plate indicate the stabilization of cell performance and longer service life.     

电弧喷涂Al-Zn-Si-RE合金涂层在3.5%NaCl溶液中的电化学腐蚀行为(英文)

采用电弧喷涂方法在低碳钢表面获得高铝含量的Al-Zn-Si-RE涂层。通过测量Al-Zn-Si-RE涂层在3.5%NaCl溶液中的动电位极化曲线,腐蚀电位-时间曲线和电化学阻抗谱,系统地研究涂层的电化学腐蚀行为。通过将测量电化学阻抗谱拟合成等效电路图,研究涂层在3.5%NaCl溶液中浸泡不同时间的阻抗行为。结果表明:Al-Zn-Si-RE涂层与Zn-15Al涂层具有相似的极化行为,阳极极化曲线均无钝化特征,仅呈现出活性溶解,但其腐蚀性能优于Zn-15Al涂层。Al-Zn-Si-RE涂层可以给钢基体提供有效的牺牲阳极保护作用,且牺牲阳极保护作用在涂层腐蚀过程中占主导地位。此外,腐蚀电位-时间曲线和电化学阻抗谱结果表明:在浸泡过程中存在点蚀-溶解-再沉积、活化溶解、阴极保护、腐蚀产物引起的物理屏蔽和涂层失效五个腐蚀阶段。     

Corrosion Behavior of Mild Carbon Steel in Ethanolic Solutions

Electrochemical evaluation of ASTM A36 steel was performed in ethanolic solutions containing small concentrations of water ranging from 0 to 10 vol.%. Electrochemical techniques such as open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization were utilized to analyze corrosion parameters. A fixed concentration of chloride, as per the ASTM specification for fuel grade ethanol, was added to increase the conductivity of the solutions. The effects of water and oxygen on the corrosion behavior of steel in these solutions have been discussed. Pitting corrosion of the steel specimens in these solutions was evaluated using scanning electron microscopy (SEM) and pitting analysis. This investigation was performed to establish a baseline for the microbiologically influenced corrosion (MIC) of steel in ethanolic solutions.     

不锈钢在含有溴离子的醋酸溶液中的腐蚀

采用浸泡试验及电化学试验,对304、254 SMO和HastelloyC－276三种材料在醋酸和含有Br^-离子的醋酸溶液中的腐蚀行为进行了测试。用SEM和XPS分析点蚀形貌。结果发现材料表面所形成的钝化膜中含有Cr2O3和MoO2,对材料起保护作用。     

铣削加工参数对304奥氏体不锈钢耐蚀性的影响

利用电化学动电位极化法测试了不同铣削加工参数下304奥氏体不锈钢的腐蚀行为。结果表明:铣削加工后材料的耐蚀性高于原始材料的。耐点蚀能力随着铣削加工进给率和切削速率的上升而下降,不同加工参数之间材料的点蚀电位差高达138mV,表明铣削加工参数对于奥氏体不锈钢的耐蚀性有着强烈的影响。     

The Estimation of Localized Corrosion Behavior of Ni-Based Dental Alloys Using Electrochemical Techniques

The aim of this study is to investigate the electrochemical behavior of the five non-precious Ni-based dental casting alloys in acidified artificial saliva. For comparison, nickel was also investigated. In order to study the localized corrosion resistance, the cyclic potentiodynamic polarization (CCP) and electrochemical impedance spectroscopy were performed. Scanning electron microscopy (SEM) observations were made after the CCP tests. The Ni-Cr alloys with chromium (14-18%) contents were susceptible to localized corrosion. The Ni-Cr-Mo alloy with contents of chromium (??13%) and molybdenum (9%) presents a dangerous breakdown, but have a zero corrosion potential so that the difference between them is around 650?mV. The Ni-Cr-Mo alloys with higher chromium (22-25%) and molybdenum (9-11%) contents had a much larger passive range in the polarization curve and were immune to pitting corrosion. Pitting resistance equivalent (PRE) of about ??54 could provide the Ni-based alloy with a good pitting corrosion resistance.     

The comparison of the corrosion resistance of advanced ferromagnetic stainless steels by Mott–Schottky approach

Ferromagnetic stainless steels (SSs) have been investigated as potential candidates for dental prosthesis applications in replacement of magnetic attachments made of noble and expensive alloys. In order to be used as biomaterials, their corrosion resistance has to be appropriate. The corrosion resistance of passive materials is related to the characteristics of the passive film formed and their properties might be investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and Mott–Schottky approach. The corrosion resistance and the capacitance of the passive films formed on PM2000, DIN 1.4575, and 17‐4 PH advanced SSs during 2 days of immersion in a phosphate buffered saline solution (PBS), at 25 °C and pH 7.0 were studied by electrochemical techniques. A commercial alloy Dyna EFM was also analyzed for comparison reasons. The results showed that films on tested materials behave as both n‐type and p‐type semiconductors and the PM2000 presented the highest corrosion resistance among all of them.     

Pitting and Intergranular Corrosion Resistance of AISI Type 301LN Stainless Steels

The pitting and intergranular corrosion (IGC) resistance of AISI type 301LN stainless steels were evaluated using ASTM methods, anodic polarization, and electrochemical impedance techniques. The IGC results indicated that the microstructure of the samples after sensitization heat treatment at 675 °C for 1 h shows step or dual structure for both imported and indigenous materials indicating insignificant Cr₂₃C₆ precipitation. The results of immersion tests in boiling 6% copper sulfate + 16% sulfuric acid + copper solution for 24 h followed by the bend test (ASTM A262 Practice-E method) indicated no crack formation in any of the tested specimens. Pitting corrosion resistance carried out in 6% FeCl₃ solution at different temperatures of 22 ± 2 and 50 ± 2 °C (ASTM G 48) up to the period of 72 h revealed pitting corrosion attack in all the investigated alloys. The potentiodynamic anodic polarization results in 0.5 M NaCl revealed variation in passive current density and pitting potential depending on the alloy chemistry and metallurgical condition. The passive film properties studied by electrochemical impedance spectroscopy (EIS) correlated well with the polarization results. The x-ray diffraction (XRD) results revealed the presence of austenite (γ) and martensite (α′) phases depending on the material condition. The suitability of three indigenously developed AISI type 301LN stainless steels were compared with imported type 301LN stainless steel and the results are highlighted in this article.     

The effect of annealing on the corrosion behaviour of 444 stainless steel for drinking water applications

In this study, the corrosion behaviour of annealed and not annealed AISI 444 ferritic stainless steel in tap water with and without addition of selected concentrations of chloride ions was investigated. Cyclic potentiodynamic macro (large area) and micro (small area) polarization measurements (CPP), salt spray test, SEM and EDS analysis were employed to evaluate the pitting and crevice corrosion susceptibility of annealed and not annealed AISI 444. The results obtained indicate that annealing does not improve the resistance to pitting and crevice corrosion. Moreover, micro CPP indicates local susceptibility to pitting on both annealed and not annealed materials; such susceptibility was not evident from macropolarization tests.     

Effect of Ti3SiC2 content on the corrosion behavior of Al/Ti3SiC2 composite coatings

The purpose of this study was to investigate the electrochemical corrosion properties of flame-sprayed Al and Al/(5, 10, 15)% Ti₃SiC₂ coatings in a 3.5% NaCl solution. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used for analyzing the microstructural characteristics of the coatings. For examining the corrosion behavior of the coatings, a potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) were used. After the potentiodynamic polarization test, the SEM micrograph of coatings indicated that Ti₃SiC₂ particles played a significant role in pitting corrosion. The results of potentiodynamic polarization tests revealed that Al/Ti₃SiC₂ coating is nobler than that of the pure aluminum coating. On the contrary, the addition of Ti₃SiC₂ particles reduced the process of thickening the passive layer. The results of the EIS tests demonstrated that the presence of Ti₃SiC₂ particles significantly enhances the corrosion resistance of the coatings.