Electrochemical corrosion behavior of LDX 2101® duplex stainless steel in a fluoride-containing environment

The effect of fluoride on the electrochemical corrosion behavior of an LDX 2101® duplex stainless steel (DSS) was studied. Open-circuit potential (E_OC) and electrochemical impedance spectroscopy (EIS) measurements were carried out in artificial saliva and with the addition of fluoride (1 wt% NaF). The electrochemical corrosion behavior of the AISI 316L austenitic stainless steel (SS) was also evaluated for comparison. Both open-circuit potential and EIS results indicate that DSS and austenitic SS undergo spontaneous passivation due to spontaneously formed oxide film passivating the metallic surface, in the simulated aggressive environments. However, LDX 2101® exhibits superior corrosion resistance as compared with AISI 316L, and this improvement is ascribed to the formation of a passive film which shows a higher protective effect than the one formed on AISI 316L.     

Numerical simulations study of the localized corrosion resistance of AISI 316L stainless steel and pure titanium in a simulated body fluid environment

The resistance of both AISI 316L stainless steel (AISI 316L SS) and commercially pure titanium (cpTi) to localized corrosion in a simulated body fluid solution was investigated using numerical simulations. The resulting model, based on transport equations in dilute solutions, is designed to predict the susceptibility of these two biomaterials to crevice corrosion initiation. The results show that cpTi and AISI 316L SS alloy are very resistant to the initiation of crevice corrosion in 0.9% NaCl solution and AISI 316L SS alloy is more susceptible to corrosion initiation over the long term than cpTi.     

Effect of austenite instability on the hydrogen-enhanced crack growth of austenitic stainless steels

Fatigue crack growth tests were performed to assess the fatigue behavior of AISI 316L and 254 SMO stainless steels (SSs) in air and gaseous hydrogen. 254 SMO SS generally exhibited a greater resistance to fatigue crack growth than 316L. Sensitization treatment had only a marginal effect on the fatigue crack growth behavior of both alloys in air. Moreover, 316L SS exhibited significant hydrogen-enhanced crack growth but 254 SMO, even sensitized 254 SMO specimens, did not. A thin layer of strain-induced martensite was formed on the fatigue-fractured surface of the 316L SS, and its content increased when raising the stress ratio. The thin martensite layer was responsible for the hydrogen-enhanced fatigue crack growth of the 316L SS. By contrast, the extremely stable austenite was responsible for the low susceptibility of 254 SMO SS to hydrogen-accelerated crack growth. The trapping of hydrogen at the grain boundaries and the transformed martensite in the sensitized 316L specimens led to increased fatigue crack growth rates and intergranular fracture of the material.     

Investigation of corrosion behaviors at different solutions of boronized AISI 316L stainless steel

In this study, corrosion behaviors of boronized and non-boronized AISI 316L stainless steel (AISI 316L SS) were investigated with Tafel extrapolation and linear polarization methods in different solutions (1 mol dm^?3 HCl, 1 mol dm^?3 NaOH and 0.9% NaCl) and in different immersion times. AISI 316L SS were boronized by using pack boronizing method for 2 and 6 hours at 800 and 900°C within commercial Ekabor®-2 powder. Surface morphologies and phase analyses of boride layers on the surface of AISI 316L SS were characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis. SEM-EDS analyses show that boride layer on AISI 316L SS surface had a flat and smooth morphology. It was detected by XRD analyses that boride layer contained FeB, Fe₂B, CrB, Cr₂B, NiB and Ni₂B phases. Boride layer thickness increases with increased boronizing temperature and time. The corrosion experiments show that boride layer significantly increased the corrosion resistance of the AISI 316L SS in 1 mol dm^?3 HCl solution. While no positive effect of the boride layer was observed in the other solutions the corrosion resistance of the borid layer on AISI 316L SS was increased in all solution with the increase of the waiting periods.     

Corrosion behaviour of a dissimilar joint TIG weld between austenitic AISI 316L and ferritic AISI 444 stainless steels

The AISI 444 stainless steel (SS) has become an option to substitute the AISI 316L SS because of its low cost and satisfactory corrosion resistance. However, the use of AISI 444 alloy tubes in heat exchangers causes the welding of a dissimilar joint. The aim of this study was evaluate the corrosion resistance of the tube-to-tubesheet welded by a TIG process composed of AISI 316L and AISI 444. Preparation of samples was executed through replication of tube-to-tubesheet joints. In order to test the corrosion resistance of the welded joint, the following tests were applied: sensitisation, mass loss from room temperature up to 90 °C and electrochemical corrosion tests in 0.5 mol/L HCl and 0.5 mol/L H₂SO₄ electrolytes. The results have shown that the dissimilar joint suffers galvanic corrosion with increased degradation of the heat-affected zone of the AISI 444 tube. Nevertheless, the mechanisms of localised corrosion (pit and intergranular) were more active in the AISI 316L alloy. It is concluded that the dissimilar joint showed better corrosion resistance than the welded joint composed solely of AISI 316L at temperatures up to 70 °C, as the conditions observed in this work.     

Use of SECM to compare corrosion resistance of DIN W. Nr. 1·4460 high N and AISI 316L austenitic stainless steels in physiological solutions

Abstract

The pitting corrosion resistance of DIN W. Nr. 1·4460 stainless steel (SS) with high amounts of nitrogen (0·87%) was evaluated to be used for medical implants. The SS pitting corrosion resistance was tested in a minimum essential medium at 37°C by electrochemical impedance spectroscopy and potentiodynamic polarisation curves and in a 0·1 mol L^?1 NaCl solution at 25°C, by scanning electrochemical microscopy. This last technique measures the concentration of chemical species released by corrosion processes. The potential of an ultramicroelectrode was set to amperometrically detect the Fe²⁺ ions released at the anodic areas and also the depletion of oxygen due to the cathodic reactions in the vicinity of the cathodic areas. The AISI 316L stainless steel was also tested for comparison reasons. The results showed that the DIN W. Nr. 1·4460 with 0·87% nitrogen presents higher pitting corrosion resistance than the AISI 316L SS, being a potential candidate for biomaterial applications.     

Corrosion behavior and fibrinogen adsorptive interaction of SS316L surfaces covered with ethylene glycol plasma polymer-coated Ti nanoparticles

A novel plasma treatment involving the deposition of ethylene glycol plasma polymer-coated titanium nanoparticles on a 316L stainless steel surface is presented. The surface properties of SS316L modified with these coated nanoparticles were compared to untreated SS316L. The deposition of ethylene glycol plasma polymer-coated nanoparticles confers properties to the surface making it more biocompatible, which is beneficial in applications of SS316L as a blood-contacting implant (e.g. vascular stents, heart valves). These properties include increased hydrophilicity and general corrosion resistance of the surface, and reduced substrate-dependent denaturation of adsorbed protein fibrinogen.     

Corrosion of aluminium,stainless steels and AISI 680 nickel alloy in nitrogen‐based fuels

Nitrogen‐based compounds can potentially be used as alternative non‐carbon or low‐carbon fuels. Nevertheless, the corrosion of construction materials at high temperatures and pressures in the presence of such fuel has not been reported yet. This work is focused on the corrosion of AISI Al 6061, 1005 carbon steel (CS), 304, 316L, 310 austenitic stainless steels (SS) and 680 nickel alloy in highly concentrated water solution of ammonium nitrate and urea (ANU). The corrosion at 50 °C and ambient pressure and at 350 °C and 20 bar was investigated to simulate storage and working conditions. Sodium chloride was added to the fuel (0–5 wt%) to simulate industrial fertilizers and accelerated corrosion environment. Heavy corrosion of CS was observed in ANU solution at 50 °C, while Al 6061, 304 and 316L SS showed high resistance both to uniform and pitting corrosion in ANU containing 1% of sodium chloride. Addition of 5% sodium chloride caused pitting of Al 6061 but had no influence on the corrosion of SS. Tests in ANU at 350 °C and 20 bar showed pitting on SS 304 and 316L and 680 nickel alloy. The highest corrosion resistance was found for SS 310 due to formation of stable oxide film on its surface.     

Influence of molybdenum on passivation of polarised stainless steels in a chloride environment

Polarised specimens of AISI 304L and 316L stainless steels (SS) were studied using X-ray photoelectron spectroscopy in conjunction with Ar⁺-ion sputtering. A 5% NaCl test solution was used at room temperature. The polarised passive films formed consist mainly of chromium oxide and hydroxide and a small proportion of iron oxides. The composition of the films depend strongly on the potential. Chloride and molybdenum ions appear when the AISI 316L SS alloy is polarised at a potential close to pitting potential.     

Effects of Rare Earth Metal addition on the cavitation erosion-corrosion resistance of super duplex stainless steels

Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0.4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance.     

Effect of ferric ions in AISI 316L stainless steel pickling using an environmentally‐friendly H2SO4‐HF‐H2O2 mixture

A mixture of hydrogen peroxide, sulphuric and hydrofluoric acids has been used as pickling solution at pH 2.0 for AISI 316L austenitic stainless steel (SS). The stability of the H₂SO₄‐HF‐H₂O₂ mixture is assessed varying the ferric ions content from 0 to 40 g/L, the temperature from 25 to 60°C, and with and without stirring of the pickling solution. The AISI 316L SS pickling rate at 50°C was 2.6 and 0.2 mg/dm² day (mdd) in the absence and presence of 40 g/L ferric ions, respectively. p‐toluene sulphonic acid (PTSA) has been used as stabiliser of hydrogen peroxide.     

Corrosion of type 316L stainless steel in molten LiCl–KCl salt

Pyrochemical reprocessing in molten chloride salt medium has been considered as one of the best options for the reprocessing of spent metallic fuels. The AISI 316L stainless steel (SS) is envisaged as a candidate material for the fabrication of components for various unit operations like salt preparation vessel, electro‐refiner and cathode processor, on which ceramic coatings with metallic bond coat will be applied by the thermal plasma spraying. The unit operation like electro‐refining is carried out in the molten lithium chloride–potassium chloride (LiCl–KCl) eutectic salt at 773 K in argon atmosphere. The corrosion behaviour of the container vessel in molten chloride salts is therefore important, hence corrosion tests were carried out in a molten salt test assembly under argon gas atmosphere. The present paper discusses the corrosion behaviour of 316L SS in the molten LiCl–KCl eutectic salt at 873 K. The 316L SS samples were immersed in the molten LiCl–KCl eutectic for 25, 100 and 250 h, while 316L SS with yttria stabilized zirconia coating was exposed for 1000 h. The exposed samples were examined by optical and scanning electron microscope for corrosion attack. The X‐ray mappings of the cross‐section of the degraded layer onto the 316L SS indicated that the mechanism of corrosion corresponds to the selective diffusion of Cr to the surface with the formation of voids below, and the formation of chromium compounds at the surface. The results of the present study indicated that the yttria stabilized zirconia coating onto the 316L SS exhibits a better corrosion resistance in molten chloride salt than with uncoated 316L SS.     

Characterization, Corrosion Resistance, and Cell Response of High-Velocity Flame-Sprayed HA and HA/TiO2 Coatings on 316L SS

The main aim of this study is to evaluate corrosion and biocompatibility behavior of thermal spray hydroxyapatite (HA) and hydroxyapatite/titania bond (HA/TiO₂)-coated 316L stainless steel (316L SS). In HA/TiO₂ coatings, TiO₂ was used as a bond coat between HA top coat and 316L SS substrate. The coatings were characterized by x-ray diffraction and scanning electron microscopy/energy dispersive spectroscopy, and corrosion resistance determined for the uncoated substrate and the two coatings. The biological behavior was investigated by the cell culture studies using osteosarcoma cell line KHOS-NP (R-970-5). The corrosion resistance of the steel was found to increase after the deposition of the HA and HA/TiO₂ bond coatings. Both HA, as well as, HA/TiO₂ coatings exhibit excellent bond strength of 49 and 47?MPa, respectively. The cell culture studies showed that HA-coated 316L SS specimens appeared more biocompatible than the uncoated and HA/TiO₂-coated 316L SS specimens.     

Repassivation rates of surgical implant alloys by rotating‐disk scratching measurements

As the dissolution of metals ions in living tissues is an issue of primary importance in the field of surgical implant alloys, a rotating disk scratch technique has been used to examine this aspect by studying the potentiostatic repassivation behavior of pure titanium of commercial grade 11 and AISI 316L Stainless Steel (SS) samples in aqueous chloride solutions. By evaluating the effects of applied potential, pH and surface treatment on the current decay transients in the millisecond regime the higher tendency to passivate of titanium with respect to the stainless steel has been clearly demonstrated. An analysis conducted to estimate the efficiency of the oxide formation process has led to the conclusion that the majority of the measured transient current goes to the anodic dissolution process on both the materials investigated. Moreover, a repetitive process of film formation/breakdown on the AISI 316L surface related to pitting corrosion has been observed to strongly increase the ion release in the vicinity of the characteristic pitting potentials.     

A comparison of hydrogen embrittlement susceptibility of two austenitic stainless steel welds

Slow displacement rate tensile tests were carried out to assess the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of AISI 316L and 254 SMO stainless steel (SS) plates and welds. 254 SMO generally exhibited a better resistance to hydrogen embrittlement than 316L. The strain-induced transformation of austenite to martensite in the 316L SS was responsible for the high hydrogen embrittlement susceptibility of the alloy and weld. Sensitized 254 SMO (i.e., heat-treated at 1000 °C/40 min) base plate and weld comprised of dense precipitates along grain boundaries. Interfacial separation along solidified boundaries was observed with the tensile fracture of 254 SMO weld, especially the sensitized one. Dense grain boundary precipitates not only reduced the ductility but also raised the susceptibility to sulfide stress corrosion cracking of the sensitized 254 SMO plate and weld.     

Corrosion and wear behaviors of boronized AISI 316L stainless steel

In this study, the effects of a boronizing treatment on the corrosion and wear behaviors of AISI 316L austenitic stainless steel (AISI 316L) were examined. The corrosion behavior of the boronized samples was studied via electrochemical methods in a simulation body fluid (SBF) and the wear behavior was examined using the ball-on-disk wear method. It was observed that the boride layer that formed on the AISI 316L surface had a flat and smooth morphology. Furthermore, X-ray diffraction analyses show that the boride layer contained FeB, Fe₂B, CrB, Cr₂B, NiB, and Ni₂B phases. Boride layer thickness increased with an increasing boronizing temperature and time. The boronizing treatment also increased the surface hardness of the AISI 316L. Although there was no positive effect of the coating on the corrosion resistance in the SBF medium. Furthermore, a decrease in the friction coefficient was recorded for the boronized AISI 316L. As the boronizing temperature increased, the wear rate decreased in both dry and wet mediums. As a result, the boronizing treatment contributed positively to the wear resistance by increasing the surface hardness and by decreasing the friction coefficient of the AISI 316L.     

医用 316L 不锈钢表面多巴胺 / BSA 复合膜缓蚀性能研究

目的研究医用316L不锈钢表面组装多巴胺/牛血清白蛋白分子(BSA)复合膜的缓蚀性能。方法采用浸泡法在医用316L不锈钢表面制备以多巴胺自组装膜为桥接层的多巴胺/BSA复合双层自组装膜,通过动电位扫描、交流阻抗测试,SEM,EDX等手段分析BSA组装液质量浓度对复合双层自组装膜吸附行为及耐蚀性能的影响。结果在合适的自组装条件下可获得具有缓蚀效果的复合双层膜。BSA质量浓度过高和过低均对缓蚀性能有不利影响,当BSA质量浓度为40 g/L时,复合双层膜对生理盐水环境中316L不锈钢取得最佳缓蚀效率,缓蚀效率由单层多巴胺的62.4%增加至83.9%。结论多巴胺成功嫁接BSA分子,使其吸附在不锈钢表面,和单层BSA吸附相比,其吸附量大大提高,表明对于316L不锈钢人体植入材料,可以利用多巴胺桥接BSA获得兼具生物活性和耐腐蚀性的改性表面。     

Electrochemical corrosion of Ti6Al4V,Ti and AISI 316L SS after immersed in concentrated simulated body fluid

The biomimetic method is used to obtain hydroxyapatite (HAP) coatings on Ti6Al4V, Ti and AISI 316L SS substrates. These substrates with different pretreatment surface operations (HNO₃, anodic polarization, base-acid) were immersed in concentrated simulated body fluids (SBF) for different days at physiologic conditions of 37°C, initial pH of 7.4. Then the corrosion behaviours of substrates after immersion in concentrated SBF were examined by electrochemical methods in Ringer’s and 0.9 wt% NaCl solutions at a temperature of 37°C. Ions concentrations and pH analyses were carried out after incubation in concentrated SBF. After immersion in SBF for different days, the surface morphology remains almost unchanged and no apatite formation is observed. Corrosion currents of substrates increased after immersion. Ions concentrations and pH values were shown variability according to soaking time and pretreatment surface operations.     

Corrosion behaviors of hydroxyapatite coated by electrodeposition method of Ti6Al4V, Ti and AISI 316L SS substrates

Electrodeposition method was used to obtain hydroxyapatite (HAP) coatings on Ti6Al4V, Ti and AISI 316L SS substrates. Electrodeposition solution is prepared as Ca(NO₃)₂ · 4H₂O and (NH₄)H₂PO₄. Additionally, three different pretreatment surface operations (PTSO) (HNO₃, anodic polarization, baseacid) were applied to the substrates. Surface morphology of HAP coated substrates were characterized by SEM, EDS, XRD. HAP coatings were successfully deposited on Ti6Al4V, AISI 316L SS and Ti substrates Corrosion behavior of uncoated and HAP coated substrates were examined in the Ringer and 0.9% NaCl solutions. The XRD, SEM-EDS results supported that HAP formation on the substrates. i _cor values for all three HAP coated substrates are higher than uncoated substrates This showed that, electrochemical deposition HAP coating could not prevent the corrosion. The lowest corrosion rates were founded HNO₃ PTSO substrates.     

316不锈钢在通氢稀盐酸中的腐蚀行为

采用电化学测量技术研究了316不锈钢在通高纯氢气的稀盐酸中的腐蚀行为，极化曲线和电化学阻抗谱测定结果表明，316不锈钢在腐蚀电位下处于活化区，其表面能形成多孔的腐蚀产物膜，氢渗入不锈钢试样表面将导致腐蚀阻力减小，且试样表面层的含氢量随腐蚀的进行而增加，SO4^2-对316不锈钢在测试介质中的腐蚀有抑制作用。