The influence of sulphate-reducing bacteria biofilm on the corrosion of stainless steel AISI 316

This work investigates microbially-influenced corrosion (MIC) of stainless steel AISI 316 by two sulphate-reducing bacteria, Desulfovibrio desulfuricans and a local marine isolate. The biofilm and pit morphology that developed with time were analyzed using atomic force microscopy (AFM). Electrochemical impedance spectroscopy (EIS) results were interpreted with an equivalent circuit to model the physicoelectric characteristics of the electrode/biofilm/solution interface. D. desulfuricans formed one biofilm layer on the metal surface, while the marine isolate formed two layers: a biofilm layer and a ferrous sulfide deposit layer. AFM images corroborated results from the EIS modeling which showed biofilm attachment and subsequent detachment over time.     

Chromium–palladium films on 316L stainless steel by pulse electrodeposition and their corrosion resistance in hot sulfuric acid solutions

Chromium–palladium alloy films with good adhesive strength and higher micro-hardness have been deposited on 316L stainless steel by pulse electroplating. The films are composed mainly of chromium and palladium crystallites in the metallic state, with grain sizes less than 100 nm. On the film surface Cr(OH)₃ and Cr₂O₃ are present. The co-deposited Cr and Pd in the films show a synergetic effect on passivation. In boiling 20 wt.% H₂SO₄ solution, boiling acetic–formic acid mixture, and simulated PEM fuel cells environment, the Cr–Pd-plated 316L steel shows excellent corrosion resistance.     

Electrodeposition of polypyrrole on 316L stainless steel for corrosion prevention

The electrosynthesis of polypyrrole films onto 316L stainless steel from near neutral and alkaline solutions containing molybdate and nitrate is reported. The corrosion behavior of the coated electrodes was investigated in NaCl solutions by electrochemical techniques and scanning electron microscopy. The polymer formed potentiostatically in a solution of pH 12 is the most efficient in terms of adhesion and corrosion protection. The coating significantly reduces the pitting corrosion of the substrate. The results are interpreted in terms of the nature of dopants, the good electroactivity of the polymer formed in alkaline solution and the passivating properties of the oxide layer.     

Corrosion characteristics of polyaniline-coated 316L stainless steel in sulphuric acid containing fluoride

The corrosion resistance of conducting polyaniline (PANi) coatings deposited on 316L stainless steel (316L SS) at various cycle numbers of cyclic voltammetry (2-, 3- and 4-cycles) by electro-polymerization in sulphuric acid solution containing fluoride was investigated by electrochemical techniques. The corrosion resistance of the 316L SS substrate was considerably improved by the PANi coating. The increase of the cycle number of cyclic voltammetry increased the thickness and enhanced the performance of the PANi coating due to low porosity.     

Study on corrosion resistance of palladium films on 316L stainless steel by electroplating and electroless plating

Palladium films with good adhesive strength were deposited on 316L stainless steel by electroless plating and electroplating. Scanning electronic microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, weight loss tests and electrochemical methods were used to study the properties of the films. The electroless plated palladium film mainly consisted of palladium, phosphorus and nitrogen, and the electroplated palladium film was almost pure palladium. XPS analysis indicated that palladium was present in the films as metal state. The palladium plated stainless steel samples prepared by both methods showed excellent corrosion resistance in strong reductive corrosion mediums. In boiling 20% dilute sulfuric acid solution, the corrosion rates of the palladium plated 316L stainless steel samples were four orders of magnitude lower than that of the original 316L stainless steel samples. In the solution with 0.01 M NaCl, the palladium plated samples also showed better corrosion resistance. In comparison, the electroplated samples showed slightly better corrosion resistance than electroless plated samples, which may be attributed to less impurities and thereby higher corrosion potential for the former.     

Investigation of intergranular corrosion of 316L stainless steel diffusion bonded joint by electrochemical potentiokinetic reactivation

Electrochemical potentiokinetic reactivation technique (EPR) was employed to assess degree of sensitization in 316L stainless steel diffusion bonded joint (DBJ). The result showed the degree of sensitization of DBJ was much smaller than that of base material (BM). No chromium carbides precipitated at grain boundaries in DBJ after 100 h treatment at 650 °C, while chromium carbides could be seen clearly in the BM after 8 h treatment, indicating that DBJ has better intergranular corrosion resistance than BM. Diffusion bonding technique will not increase intergranular corrosion susceptibility of 316L DBJ. Reactivation potential has the biggest effect on sensitization.     

An experimental study of crevice corrosion behaviour of 316L stainless steel in artificial seawater

The effects of applied torque on corrosion behaviour of 316L stainless steel with crevices were investigated using the cyclic potentiodynamic polarization method. Three kinds of crevices (316L-to-polytetrafluoroethylene, 316L-to-fluoroelastomeric and 316L-to-316L) were tested in artificial seawater at 50 °C. Corroded surface morphology was also investigated using scanning electron microscopy. Results indicate similar trends in crevice corrosion susceptibility with increasing applied torque. Among the three crevices, the 316L stainless steel specimen, coupled to the 316L stainless steel crevice former, is the most susceptible to crevice corrosion.     

电弧喷涂316L不锈钢涂层的结构与性能

采用电弧喷涂优化工艺制备316L不锈钢涂层,利用扫描电镜、能谱仪和X射线衍射仪等对涂层的组织及物相进行分析,同时对涂层的硬度、结合强度进行了测定。结果表明：涂层具有典型的层状形貌,涂层截面较为致密,局部区域出现粗大孔洞;涂层与基体之间主要为机械结合,结合强度较高;涂层硬度的最大值出现在涂层中部,靠近界面的基体组织发生加工硬化。     

The role of alkaline-earth additives on the molten carbonate corrosion of 316L stainless steel

The corrosion behavior of 316L stainless steel in eutectic Li/Na molten carbonate containing various amounts of Mg, Ca and Ba ions has been evaluated by electrochemical techniques in combination with oxygen solubility determinations. Open circuit potential and corrosion rates have been correlated to the oxygen solubility properties of the carbonate melt for an understanding of the kinetic aspects of the corrosion process. It has been found that minor additions of Mg and Ca ions (1.5% molar fraction) distinctly promote a higher carbonate oxygen solubility, whereas Ba has only a marginal effect on it. In general, the electrochemical investigations showed that at 1.5% molar fraction addition there exist a strong correlation between steel corrosion rate and oxygen solubility indicating that (i) corrosion process takes place under a diffusion-limited cathodic reduction of dissolved O₂ and (ii) corrosion rate is significantly increased with respect to the no-added Li/Na carbonate by the introduction of Mg and Ca ions that therefore serve as a sort of oxidizing agents. However, with larger Mg and Ca additions (up to 10% mol) the corrosion process was found to pass progressively under an anodic control despite decreasing oxygen solubility values. This effect is ascribed to the growth of an alkaline-earth doped lithium ferrite layer with enhanced barrier-like properties. In contrast, further additions of Ba cation in carbonate did not change the corrosion mechanism for its inability to react with the growing corrosion scale. Only minor reductions of corrosion rate are detected in agreement with the lower tendency of the melt containing high molar fractions of Ba to solubilize the oxygen gas.     

Effect of sulphide on the corrosion behaviour of AISI 316L stainless steel and its constituent elements in simulated Kraft digester conditions

The electrochemical behaviour of AISI 316L steel and its constituent metals in simulated Kraft digester white liquor at 170 °C has been studied by registering slow scan rate voltammograms and impedance spectra at the corrosion potential. Interpretation of the results in terms of two approaches - the Mixed-Conduction Model for passive films and a two-step dissolution reaction - allowed for the estimation of corrosion currents and polarisation resistances as depending on the material and electrolyte medium. Tentative conclusions on the effect of sulphur-containing species in the white liquor on the corrosion mechanism of the studied materials are drawn.     

Electrochemical corrosion behavior of a novel antibacterial stainless steel

A novel antibacterial stainless steel (ASS) with martenstic microstructure has been recently developed, by controlled copper ion implantation, as a new functional material having broad-spectrum antibacterial properties. The electrochemical corrosion behavior of the ASS in 0.05 mol/L NaCl was assessed using linear polarization and electrochemical impedance spectroscopy (EIS) and compared with that of a conventional stainless steel (SS) without copper ion implantation. The ASS exhibited higher corrosion susceptibility in the chloride medium; with a more negative (active) corrosion potential, higher anodic current density and lower charge transfer and polarization resistance. This has been attributed to the occurrence of copper-catalyzed interfacial reactions. A functional tool, 3-D presentation of EIS data, has been employed in analyzing the electrochemical corrosion processes as well as probing complex interfacial phenomena.     

Hydrogen-assisted fatigue crack growth of AISI 316L stainless steel weld

The fatigue crack growth behaviors of AISI 316L stainless steel (SS) welds in air and gaseous hydrogen were evaluated, and further compared with the base plate. In air, the fatigue crack growth rate (FCGR) of the weld after heat-treatment at 1050 ^oC/1 h was similar to that of the base metal. Furthermore, all specimens became susceptible to hydrogen-accelerated crack growth. Mainly quasi-cleavage fracture related with the strain-induced martensite accounted for the accelerated crack growth in hydrogen. A smaller amount of martensite in the weld was responsible for the decreased susceptibility to hydrogen-enhanced fatigue crack growth relative to the base metal.     

Corrosion behaviour of HVOF sprayed SUS316L stainless steel in seawater

SUS316L stainless steel was coated onto the SUS316L plate by the high velocity oxy-fuel (HVOF) spray technique. Its corrosion behaviour in seawater was investigated by the electrochemical method and the microscopy. The coating had corrosion resistance inferior to the bulk plate. The corrosion of the HVOF sprayed SUS316L coating was related to both its porosity and its oxygen content. Depending on them, the corrosion took place at the small pore and the boundary between the spray particles on the surface.     

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.     

Electrochemical polishing as a 316L stainless steel surface treatment method: Towards the improvement of biocompatibility

A 316L stainless steel (316L-SS) surface was electrochemically polished (EP) in an electrolyte of a new chemical composition at different cell voltages, with the aim of improving its corrosion resistance and biocompatibility. X-ray photoelectron spectroscopy results revealed that the EP-formed oxide films were characterized by a significantly higher atomic Cr/Fe ratio and film thickness, in comparison to the naturally-grown passive oxide film formed on the untreated (control) 316L-SS surface. As a result of the increase in the oxide film thickness and relative Cr enrichment, the EP-treated 316L-SS surfaces offered a notable improvement in general corrosion resistance and pitting potential. In addition, the attachment of endothelial cells (ECs) and smooth muscle cells (SMCs) to the 316L-SS surfaces revealed a positive effect of electropolishing on the preferential attachment of ECs, thus indicating that the EP surfaces could be endothelialized faster than the control (unmodified) 316L-SS surface. Furthermore, the EP surfaces showed a much lower degree of thrombogenicity in experiments with the platelet-rich plasma. Therefore, the use of the electrochemical polishing technique in treating a 316L-SS surface, under the conditions presented in this paper, indicates a significant improvement in the surface’s performance as an implant material.     

Sintering atmosphere and temperature effects on hydroxyapatite coated type 316L stainless steel

Electrophoretically deposited hydroxyapatite (HAP) coatings on type 316L SS was developed at the optimum coating parameters of 60 V and 3 min. Sintering of the coating enhances the metal-ceramic bond strength, but HAP structure is sensitive to temperature as it decomposes to other calcium phosphate phases. Sintering of HAP coatings in air at 900 °C for 1 h indicate the formation of a composite surface containing oxides of the alloy and decomposition products of HAP, mainly tricalcium phosphate. Open circuit potential-time measurements, potentiodynamic cyclic polarisation and electrochemical impedance experiments performed in Ringer’s solution indicate that the corrosion performance of HAP coatings were severely affected by the sintering atmosphere and temperature. Higher capacitance and low polarisation resistance values obtained from electrochemical impedance spectroscopic studies further indicate that the coatings are more prone to dissolution on comparison with the pristine type 316L SS. The sintering of the coatings in vacuum at 600, 800 and 900 °C for 1 h did not alter the phase purity of the coatings, and shifted the electrochemical parameters towards noble direction. Sintering of the coatings in vacuum lead to the formation of an adherent, stoichiometric HAP coating with enhanced corrosion resistance.     

Oxidation of 316 stainless steel in supercritical water

The oxide scales of 316 stainless steel (316 SS) have been examined after exposure to supercritical water (SCW) with 2.0% H₂O₂ for up to 250 h. The exposed samples were analyzed using weight measurement, scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). It was found that mass gain of all samples increased with increasing temperature and exposure time. Higher temperature SCW resulted in rougher surfaces and thicker oxide scales. Duplex layer oxide structures with Ni-enrichment at the oxide/metal interface developed on all samples exposed to SCW, which were identified as Fe₂O₃/Fe₃O₄ + spinel/Cr₂O₃/Ni-enrichment/316 SS from the outer to inner layer. The possible oxidation mechanisms are also discussed.     

High corrosion resistance of austenitic stainless steel alloyed with nitrogen in an acid solution

Passivity of austenitic stainless steel containing nitrogen (ASS N25) was investigated in comparison with AISI 316L in deareated acid solution, pH 0.4. A peculiar nature of the passivation peak in a potentiodynamic curve and the kinetic parameters of formation and growth of the oxide film have been discussed. The electronic-semiconducting properties of the passive films have been correlated with their corrosion resistance. Alloying austenitic stainless steel with nitrogen increases its microstructure homogeneity and decreases the concentration of charge carriers, which beneficially affects the protecting and electronic properties of the passive oxide film.     

Effect of marine Pseudoalteromonas sp. on the microstructure and corrosion behaviour of 2205 duplex stainless steel

The effects of isolated marine Pseudoalteromonas sp. on the microstructure and corrosion behaviour of 2205 duplex stainless steel were investigated using electrochemical and surface analysis methods. Electrochemical studies demonstrated a negative shift in corrosion potential and an increase in corrosion current density in the presence of bacteria. EDS results showed a high concentration of chloride ions in the biofilm structure and a decrease in Cr content beneath the biofilm layer and near cracks. These results could lead to localised corrosion on metal surfaces. FESEM images illustrated the process of bacterial attachment on the metal surfaces at different exposure times.     

Microstructural evolution and localized corrosion resistance of an aged superduplex stainless steel

The present investigation was undertaken to analyze the effects of isothermal ageing treatments, carried out between 700 and 900 °C for a variety of times up to two weeks and followed by water quenching, on the microstructure and on the localized corrosion resistance of a superduplex stainless steel, SAF 2507.The quantitative metallography coupled with X-ray diffraction techniques was adopted to follow the microstructural evolution, together with SEM microscopy.Electrochemical potentiodynamic tests, as cyclic polarization curves recorded in sodium chloride solutions, together with weight loss measurements were employed to evaluate the susceptibility of the aged specimens to pitting corrosion.The influence of the transformation of ferrite into secondary austenite and sigma phase and of other microstructural variations, as chromium nitrides precipitation, on the stability of the passive film is shown. The susceptibility of the aged alloy to pitting corrosion phenomena, is related to sigma phase precipitation in association to the secondary austenite formation, which lead to a noticeable Cr depletion at grain boundaries.