Effect of p H on the Electrochemical Behaviour and Passive FilmComposition of 316L Stainless Steel

The effect of pH on the electrochemical behaviour and passive film composition of 316 L stainless steel in alkaline solutions was studied using electrochemical measurements and a surface analysis method. The critical pH of 12.5 was found for the conversion from pitting corrosion to the oxygen evolution reaction(OER). OER was kinetically faster than pitting corrosion when both reactions could occur, and OER could postpone pitting corrosion. This resulted in pitting being initiated during the reversing scan in the cyclic polarization at the critical pH. According to the X-ray photoelectron spectroscopy analysis, the content of Cr and Mo decreased with pH, while Fe content increased. This induced the degradation of the passive film, which resulted in the higher passive current densities under more alkaline conditions. The selective dissolution of Mo at high p H was found, which demonstrated that the addition of Mo in austenitic stainless steels might not be beneficial to the corrosion resistance of 316L in strong alkaline solutions.     

Corrosion Behaviour of a Non-equiatomic CoCrFeNiMo High-Entropy Alloy in H2S-Containing and H2S-Free Environments

The corrosion behaviour of a non-equiatomic CoCrFeNiMo high-entropy alloy (HEA) in H₂S-containing and H₂S-free environments was studied by electrochemical tests, surface characterization, and solution analysis. The results showed that the HEA exhibited primary and secondary passivation in the H₂S-free environment, and the transition was owing to the enhanced dissolution of Fe species. Compared with the primary passive film, the Cr/Fe ratio in the secondary passive film increased at the expense of the selective dissolution of Fe. Therefore, the corrosion resistance of HEA decreased with the applied potential. Cr was the most stable element in the film of HEA, regardless of H₂S. The presence of H₂S accelerated the dissolution of all the cationic elements in the HEA. H₂S promoted the formation of thicker but less protective surface film and induced the loss of passivity.     

Effect of surface oxide properties on corrosion resistance of 316L stainless steel for biomedical applications

Surface passivation is a promising technique for improving the corrosion resistance both in vitro and in vivo as well as the biocompatibility of 316L stainless steel. In this work, we studied the effect of different passivative processes on the in vitro corrosion resistance of 316L stainless steel wire. Characterization techniques such as anodic polarization test, scanning electron microscopy, auger electron spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy were employed to co-relate the corrosion behavior to various surface characteristics and surface treatments. Results showed that all of these surface treatments did not improve the corrosion resistance of the alloy satisfactorily except amorphous oxidation. This improvement is attributed to the removal of plastically deformed native air-formed oxide layer and the replacement of a newly grown, more uniform and compact one which is composed of nano-scale oxide particles with higher oxygen and chromium concentrations. The properties of surface oxide layer, rather than its thickness, seem to be the predominant factor to explain the improvement of in vitro corrosion resistance.     

Corrosion Behavior of 316L Stainless Steels Exposed to Salt Lake Atmosphere of Western China for 8 years

The evolution of corrosion behavior of 316 L stainless steels exposed to salt lake atmosphere for 8 years was investigated.The results showed that the stainless steel in salt lake atmosphere had a greater corrosion rate during the initial exposure time and relatively lower corrosion rate during the subsequent exposure time.Dust depositions accumulated on the downward surface caused severe local corrosion of stainless steel.As exposure time prolonged,the relative amount of Cr_(oxide) and Fe_(oxide)in the corrosion products gradually increased,which may directly affect the corrosion rate of stainless steels.Moreover,the maximum pit depth followed a power function with respect to exposure time.     

Relationship of Corrosion Behavior Between Single-Phase Equiatomic CoCrNi,CoCrNiFe,CoCrNiFeMn Alloys and Their Constituents in NaCl Solution

The composition is a significant issue for corrosion resistance of metallic materials.To reveal the correlation of corro-sion behavior between multiprinciple alloys and their constituents,a series of single-phase equiatomic alloys of CoCrNi,CoCrNiFe and CoCrNiFeMn was fabricated.The electrochemical and scanning electron microscope results demonstrated that corrosion resistance of the equiatomic alloys in 0.1 M NaCl solution is located in the range but not the average value of their constituents.X-ray photoelectron spectroscopy analysis indicated that the protective performance of passive film is mainly determined by the constituent with the highest corrosion resistance and the breakdown of passive film is mainly dominated by the elements with the highest corrosion rate.Our findings can guide the materials design of multiprinciple alloys with expected corrosion performance.     

Investigation on carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water

The carbon dioxide corrosion behaviour of HP13Cr110 stainless steel in simulated stratum water is studied by potentiodynamic curve and electrochemical impedance spectroscopy (EIS); the micro-structure and composition of the corrosion scale formed at high-temperature and high-pressure are analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that 13Cr stainless steel is in passive state in the stratum water, the passive current density increases and the passive potential region decreases with increasing temperature. The corrosion scale formed at high-temperature and high-pressure is mainly composed of iron/chromium oxides and a little amount of FeCO₃.     

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.     

Enhanced corrosion resistance of interstitially hardened stainless steel: Implications of a critical passive layer thickness for breakdown

Immense interstitial hardening of 316L austenitic stainless steel via low-temperature paraequilibrium carburization also leads to greatly improved corrosion resistance. Both the hardening and the improved corrosion resistance owe their origin to a “colossal” supersaturation of interstitial carbon. The corrosion resistance of stainless steel involves a Cr₂O₃-rich passive film, and the composition and thickness of the passive film developed during anodic polarization at various potentials were determined for both carburized and non-treated steels using grazing incidence X-ray photoelectron spectroscopy. Passive oxide film breakdown is a necessary step in pitting corrosion, and appears to occur in these steels at a critical film thickness of ≈3 nm. We suggest that this breakdown is of chemomechanical origin. Long wavelength thickness perturbations occur during film growth to reduce the strain energy density in the passive film arising from intrinsic and electric field-induced stresses. At the critical thickness, the localized thinning is sufficient to lead to dielectric breakdown and nucleation of pitting corrosion. The improved corrosion resistance for the carburized material results from thinner passive films at a given potential and hence a delay in the detrimental effect of the thickness perturbations.     

The semiconducting properties of passive films formed on AISI 316 L and AISI 321 stainless steels: A test of the point defect model (PDM)

The semiconductor properties of passive films formed on AISI 316L in 1 M H₂SO₄ in three temperatures and AISI 321 in 0.5 M H₂SO₄ were studied by employing Mott–Schottky analysis in conjunction with the point defect model (PDM). Based on the Mott–Schottky analysis in conjunction with PDM, it was shown that the calculated donor density decreases exponentially with increasing passive film formation potential. Also, the results indicated that donor densities increased with temperature. By assuming that the donors are oxygen ion vacancies and/or cation interstitials, the diffusion coefficients of the donors for two stainless steels are calculated.     

XPS analysis of manganese in stainless steel passive films on 1.4432 and the lean duplex 1.4162

Passive films were compared on two stainless steels: the recent lean duplex EN 1.4162 and EN 1.4432 (316L). For alloys with significant amount of manganese and nickel, the Mn 2p_3/2 peak will overlap with the Ni-LMM. To resolve this overlap, Ni 2p_3/2 to Ni-LMM intensity ratios were recorded on 1.4432, compensated for overlayer thickness, and then used to fix the Ni-LMM intensities in the Mn 2p spectra on the duplex material. Manganese was found in oxidation states II and V/VI; its film content was not dependent on the bulk composition.     

Corrosion and passivation of low-temperature nitrided AISI 304L and 316L stainless steels in acidified sodium sulphate solution

304L and 316L steels were nitrided at 425 °C for 30 h and examined at various depths in 0.1 M Na₂SO₄ acidified to pH 3.0. In the near-surface region with about 7-14 wt% N, at potentials of active state anodic currents were much higher than those for untreated steels, whereas in deeper regions with <7 wt% N the currents were only slightly increased in comparison with untreated steels or they were even lower in passive and transpassive states. Surface films were composed of oxygen-containing species on top and of Cr-N species in deeper layers. It is suggested that strong corrosion of near-surface regions is associated with nitride precipitates. Beneficial effect of low nitrogen concentrations can be due to initially accelerated corrosion which leads to larger amounts of passivating species and to the accumulation of corrosion resistant chromium nitrides.     

Effects of alloy and solution chemistry on the fracture of passive films on austenitic stainless steel

The Taguchi analysis method was used to simultaneously study the effects of alloy chemistry, pH, and halide ion concentrations on the fracture of electrochemically grown passive films using a nanoindentation technique. Three austenitic stainless steels, 304L, 316L, and 904L were potentiostatically polarized in hydrochloric acid solutions. The fracture load was dominated primarily by alloy chemistry. Passive films mechanically weaken as the atomic iron concentration increases in the film. Prolonged anodic ageing time increases the fracture load of passive films.     

Effects of nitrogen on the passivity of Fe-20Cr alloy

Influences of nitrogen on the passivity of Fe-20Cr-(0, 1.1)N alloys were examined by in situ electrochemical techniques. Nitrogen was incorporated in the form of (Fe, Cr)-nitrides in the passive film, and Cr was enriched in the film of the alloy with nitrogen. Photocurrent analysis demonstrated that the structure of passive film formed on Fe-20Cr-1.1N alloy is Cr-substituted γ-Fe₂O₃ with (Fe, Cr)-nitrides. Mott-Schottky analysis revealed that the film formed on Fe-20Cr-1.1N contained higher Cr⁶⁺ and lower Cr³⁺ vacancy concentrations compared with that on Fe-20Cr alloy. All of these results were associated with the enhanced protectiveness of the film on Fe-20Cr-1.1N.     

Synergistic Effect of Mo,W, Mn and Cr on the Passivation Behavior of a Fe-Based Amorphous Alloy Coating

In this work, the electrochemical behaviors of SAM2 X5 Fe-based amorphous alloy coating and hard chromium coating were comparatively studied in 3.5 wt% Na Cl solution. In comparison with the hard chromium coating, the SAM2 X5 coating exhibited a wider and stable passive region with lower passive current density in the potentiodynamic polarization and showed a considerably lower current density at different anodic potentials in the potentiostatic polarization. In order to understand the passivation mechanism of the Fe-based amorphous coating, the components of the passive films formed at various polarization potentials were examined by X-ray photoelectron spectroscopy. The synergistic effect of Mo, W, Mn and Cr in the passive films was systemically analyzed. It has been revealed that Mo and W facilitate the formation of compact and stable Cr_2O_3 passive film at lower potentials, and the substantial enrichment of Mn in the passive film enhances the passivation ability at relatively higher potentials. The deep understanding of the passivation characteristics in multicomponent alloy systems could provide a guide for the design of corrosion-resistant amorphous alloy coatings for engineering applications.     

Laser Raman microscopic studies of passive films formed on type 316LN stainless steels during pitting in chloride solution

The surface films formed on type 316LN stainless steels (SS) with different nitrogen contents, during potentiodynamic polarization in acidified 1 M NaCl solution, were characterized by Laser Raman Spectroscopy (LRS). LRS confirmed the presence of oxides and oxychlorides of iron and chromium, hydrated chlorides and nitrates in the film. Raman mapping showed increasing nitrate content in the film with increasing nitrogen content. The film on the uncorroded material showed the presence of chromium and molybdenum oxides. The improvement in pitting corrosion resistance of type 316LN SS with increasing nitrogen content was attributed to increased amount of nitrates in the passive film.     

A surface study of the oxidation of type 304L stainless steel at 600 K in air

The oxidation of type 304L stainless steel at 600 K in air was studied using a number of surface-analytical techniques, including Auger electron spectroscopy (AES), scanning electron microscopy with energy-dispersive analysis of X-rays (SEM-EDAX), secondary ion mass spectrometry (SIMS), and X-ray photoelectron spectroscopy (XPS). Spectral analysis showed that a duplex oxide was formed, the outer layer of which formed rapidly and was essentially iron (III) oxide. Beneath this was a mixed iron-chromium oxide. SIMS sputter-profile curves showed region of relatively low iron concentration in the oxide film at the metal-oxide interface. This resulted from the rapid diffusion of iron within the oxide film. The oxide grain boundaries were examined using SEMEDAX. Higher chromium and silicon levels were detected in these regions compared with the corresponding grain centers. AES indicated the presence of silicon as SiO₂.     

Generation of hydroxyl radicals by sonochemistry: Effects on the electrochemical behaviour of a 316L stainless steel

In this study, water radiolysis occurring in nuclear power plants was simulated by sonochemistry. Generated hydroxyl radicals can recombine in others species such as H₂O₂ and H₂. It is shown that solution conductivity is an important parameter on the evolution of open circuit potential due to the thickness variation of the diffusion layer which may contain sonolysed species (OH, H₂, H₂O₂) in different concentrations. Dissolved gases have also an impact on the 316L electrochemical behaviour. Increase of gas solubility leads to cavitation activity enhancement and further hydroxyl radical production. The latter leads to increased current density values under irradiation.     

Fatigue strength of 316L-type stainless steel in simulated body fluids

The fatigue strength of commercial SUS316L stainless steel was studied in PBS(−) (phosphate buffer solution) with different dissolved oxygen contents and CPBS (a 0.9 mass% NaCl-containing citric phosphate buffer solution) with different pH levels, i.e., 5.0, 6.0, and 7.5. The results obtained are as follows. (1) The fatigue behaviour in PBS(−) was hardly affected by the dissolved oxygen content. (2) The fatigue strength in a high-cycle region was much lower in CPBS of pH 7.5 than in PBS(−) of pH 7.5. (3) The fatigue strength in CPBS decreased with decreasing pH from 7.5 to 5.0.     

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.     

316L不锈钢、690合金在氢氧化钠溶液中的电化学性能

采用动电位极化、电化学阻抗和电容测量等方法研究了316L、690合金在NaOH溶液中的电化学行为及生成钝化膜的半导体性质.在NaOH溶液中,316L不锈钢存在明显的钝化区间;316L不锈钢、690合金在NaOH溶液中电化学阻抗谱的阻抗模值相近.动电位电化学阻抗谱(DEIS)表明,随扫描电位正移,钝化膜的阻抗在测试溶液中...