相对流速对316L钢焊缝在液态铅铋合金中腐蚀行为的影响

在核工业领域,316L不锈钢因其优异的性能常被作为核用钢种,液态铅铋合金常作为加速器次临界驱动系统(ADS)的冷却剂,高速流动的液态铅铋合金(LBE)会对316L不锈钢焊缝造成氧化腐蚀,同时氧化腐蚀后的产物也会对液态LBE造成污染,所以研究316L不锈钢焊缝在液态铅铋合金中的腐蚀行为具有重要意义. 文中对比研究了使用母材作为焊丝进行TIG焊的316L不锈钢焊缝在550 ℃动态(相对流速为1.70,2.31,2.98 m/s)液态LBE中的耐腐蚀性能,试验时间为1 500 h. 结果表明,三组试样都生成了双氧化层,外氧化层主要为Fe₃O₄,内氧化层主要为FeCr₂O₄,内氧化层相对于外氧化层较致密;随着流速的提高,元素的传质过程变快,氧化腐蚀加剧,内氧化层增厚.     

Liquid metal corrosion of T91 and A316L materials in Pb-Bi eutectic at temperatures 400-600 °C

The corrosion resistance of T91 and A316L materials was tested in stagnant liquid lead-bismuth eutectic (LBE). The materials were exposed for 175, 500, 1250, 2300 and 3000 h at temperatures from 425 to 600 °C under 5%H₂ + Ar cover gas atmosphere. Severe corrosion occurred at temperatures above 500 °C where three corrosion modes were distinguished: stable oxide film mode, transition mode, and final dissolution mode featuring Cr and Ni leaching and material loss. The principle corrosion mechanisms were uniform penetration and dissolution of the penetrated volumes. At these temperatures (>500 °C) T91 had a better corrosion resistance (corrosion rate ∼ ?137 μm/year) compared to A316L (?250 μm/year). The transition corrosion mode continued 2-3 times longer for T91 material due to residual oxides found even after 3000 h of exposure. At low temperatures (<450 °C) both materials showed good corrosion resistance but A316L performed better than T91 with corrosion rates 2-5 times lower.     

The corrosion of Fe3Al alloy in liquid zinc

A systematic study of the isothermal corrosion testing and microscopic examination of Fe₃Al alloy in liquid zinc containing small amounts of aluminum (less than 0.2 wt.%) at 450 °C was carried out in this work. The results showed the corrosion of Fe₃Al alloy in molten zinc was controlled by the dissolution mechanism. The alloy exhibited a regular corrosion layer, constituted of small metallic particles (diameter: 2-5 μm) separated by channels filled with liquid zinc, which represented a porosity of about 29%. The XRD result of the corrosion layer formed at the interface confirmed the presence of Zn and FeZn_6.67. The corrosion rate of Fe₃Al alloy in molten zinc was calculated to be approximately 1.5 × 10⁻⁷ g cm⁻² s⁻¹. Three steps could occur in the whole process: the superficial dissolution of metallic Cr in the corrosion layer, the new phase formation of FeZn_6.67 and the diffusion of the dissolved species in the channels of the corrosion layer.     

Effect of underpotential deposition of lead on polarization behavior of nickel in acidic perchlorate solutions at room temperature

The effect of Pb²⁺ on polarization behavior of nickel has been investigated in 0.1 M NaClO₄ + 10⁻² M HClO₄ + x M PbO solutions (x = 0, 10⁻⁵, 10⁻⁴, 10⁻³) at room temperature. The cyclic voltammogram has suggested that Pb²⁺ degrades the stability of the passive film on Ni. The corrosion potential of Ni shifted to the more noble direction and the anodic current peak of Ni dissolution decreased with increasing Pb²⁺ concentration in solution, indicating that Pb²⁺ suppresses significantly the anodic dissolution. The underpotential deposition (UPD) of lead on Ni in the potential range more noble than −0.215 V (SHE) corresponding to the equilibrium potential of the Pb²⁺ (10⁻³ M)/Pb electrode was confirmed by XPS and GDOES analyses. The anodic Tafel slope, b⁺, of Ni dissolution changed from b⁺ = 40 mV decade⁻¹ in the absence of Pb²⁺ to b⁺ = 17 mV decade⁻¹ in the presence of 10⁻⁴ or 10⁻³ M Pb²⁺, which was ascribed to the increase in active sites of Ni surface emerged as a result of electrodesorption of Pb adatoms. The roles of Pb adatoms in active dissolution and active/passive transition of Ni were discussed from the above results.     

Gamma-radiation-induced corrosion of carbon steel in neutral and mildly basic water at 150 °C

The effect of γ-radiation on the kinetics of carbon steel corrosion has been investigated by characterizing the oxide films formed on steel coupons at 150 °C and at two pH values. Results show that continuous irradiation enhances surface oxide formation with the type of oxide formed dependant on the solution pH. For experiments at 150 °C and a [OH⁻] equivalent to that for pH_{25 °C} = 10.6, the surface oxide on carbon steel after γ-irradiation was non-porous and uniform, and no localized corrosion was observed. This oxide, however, appears to be susceptible to brittle fracture during cooling. Raman spectroscopy of the surface film indicates that it is a mixture of the phases of Fe₃O₄ and γ-Fe₂O₃. In contrast, at 150 °C with [OH⁻] equivalent to neutral pH_{25 °C}, metal dissolution is significant and the surface oxide film is very porous. Raman spectra show that this oxide film is also composed of a mixture of Fe₃O₄ and γ-Fe₂O_3. The results from this work combined with previously reported electrochemical studies of the same system as a function of pH and temperature can be used to deconvolute the effects of radiation, pH and temperature on the nature of the corrosion process.     

Influence of temperature on the interaction mode of T91 and AISI 316L steels with Pb-Bi melt saturated by oxygen

Corrosion tests of T91 and AISI 316L steels in stagnant Pb-Bi eutectic saturated by oxygen at 500, 520, 540 and 560 °C were carried out. The corrosion mode as a function of temperature was revealed. The oxidation was the main interaction mechanism for both T91 and AISI 316L steels. At 560 °C temperature the interaction mode for AISI 316L was mixed: the oxidation as well as the dissolution of steel components accompanied by the penetration of liquid metal into the solid metal was observed simultaneously. The corrosion rate of AISI 316L steel was less than that of T91 due to higher content of chromium in the austenitic steel. However, the spinel layer containing Ni was more vulnerable to the liquid metal attack. The kinetic model describing nucleation, growth and degradation of double oxide layer on the surface of steels contacting with Pb-Bi melt saturated by oxygen was proposed.     

Depassivation-repassivation behavior of type-312L stainless steel in NaCl solution investigated by the micro-indentation

Repassivation behavior of type-312L stainless steel containing 6% of molybdenum was examined in NaCl solution using in situ micro-indentation technique, together with type-304 and 316L stainless steels. High stability of the passive film formed on the type-312L stainless steel was also examined by depth profiling analysis of passive films using glow discharge optical emission spectroscopy (GDOES). In 0.9 mol dm⁻³ NaCl solution at 296 K the type-304 and 316L stainless steels are passive only up to 0.3 V (SHE), above which pitting corrosion occurs. In contrast, no pitting corrosion occurs on type-312L stainless steel. Despite the significant difference of the pitting corrosion resistance, the repassivation kinetics of the three stainless steels, examined by micro-indentation at 0.3 V (SHE), is similar. The presence of molybdenum in the stainless steel does not influence the repassivation kinetics. The charge required to repassivate the ruptured type-312L stainless steel surface increases approximately linearly with the potential, even though the passivity-maintaining current increased markedly at potentials close to the transpassive region. Repassivation occurs without accompanying significant dissolution of steel, regardless of the stability of passive state. Depth profiling analyses of the passive films on the type-312L stainless steels formed at several potentials revealed that molybdenum species enrich in the outer layer of the passive film, below which chromium-enriched layer is present. The permeation of chloride ions may be impeded by the outer layer containing molybdate, enhancing the resistance against the localized corrosion of the type-312L stainless steel.     

Erosion-corrosion behavior of nano-particle-reinforced Ni matrix composite alloying layer by duplex surface treatment in aqueous slurry environment

The present study concerns a duplex surface treatment of AISI 316L stainless steel to enhance the erosion-corrosion resistance. The duplex surface treatment consisted of Ni/nano-SiC and Ni/nano-SiO₂ predeposited by brush plating and a subsequent surface alloying with Ni-Cr-Mo-Cu by double glow process of the substrate. Results showed that under alloying temperature (1000 °C) condition, the amorphous nano-SiO₂ particles still kept the amorphous structure, whereas the nano-SiC particles had been completely decomposed and Ni, Cr reacted with SiC to form Cr_6.5Ni_2.5Si and Cr₂₃C₆. The electrochemical corrosion behaviors of composite alloying layers compared with the single alloying layer and 316L stainless steel were measured under a range of hydrodynamic conditions by recording the current response, open circuit potential, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS). Results showed that the increase of the impact velocity had significant influence on the current density of composite alloying layer with brush plating Ni/nano-SiC particles interlayer obtained under flowing condition at a potential of 200 mV, whereas there were only small fluctuations occurred at current response of composite alloying layer with brush plating Ni/nano-SiO₂ particles interlayer. The results of potentiodynamic polarization indicated that, with increasing impact velocity under slurry flow conditions, the corrosion potentials of test materials decreased and the corrosion current densities of test materials increased. The corrosion resistance of composite alloying layer with brush plating Ni/nano-SiO₂ particles interlayer was prominently superior to that of single alloying layer under slurry flow conditions; the corrosion resistance of composite alloying layer with brush plating Ni/nano-SiC particles interlayer was evidently lower than that of single alloying layer, but higher than that of 316L stainless steel under slurry flow conditions. The results of EIS indicated that, with respect to the R_tot obtained in sand-free flow, the impacts of sand particles dramatically decreased the R_tot values of composite alloying layer with brush plating Ni/nano-SiC particles interlayer, single alloying layer and 316L stainless steel, whereas the impact action slightly decreased that of composite alloying layer with brush plating Ni/nano-SiO₂ particles interlayer. The weight loss rate studies suggested that the highly dispersive nano-SiO₂ particles were helpful to improve the erosion-corrosion resistance of composite alloying layer, whereas the carbides and silicide phase were deleterious to that of composite alloying layer due to the fact that preferential removal of matrix around the precipitated phase takes place by the chemical attack of aggressive medium.     

Corrosion of uranium dioxide in hydrogen peroxide solutions

The corrosion behaviour of specimens cut from nuclear grade CANDU pellets has been studied electrochemically and under open-circuit corrosion conditions in hydrogen peroxide containing, slightly alkaline (pH=9.5) sodium perchlorate solution with and without added carbonate. The compositions of the electrode surfaces were determined using X-ray photoelectron spectroscopy (XPS). Three distinct ranges of behaviour are observed as a function of H₂O₂ concentration. For H₂O₂ concentrations lower than 10⁻⁴ mol/L, the UO₂ corrosion potential is directly proportional to H₂O₂ concentrations. For H₂O₂ concentrations between 10⁻⁴ and 10⁻² mol/L, the UO₂ surface appears to be redox buffered by the H₂O₂ decomposition. For H₂O₂ concentrations higher than 10⁻² mol/L, the formation of U(VI) corrosion product deposits may block H₂O₂ decomposition. Under these conditions UO₂ corrosion is driven by reaction with H₂O₂. When carbonate is present, the formation of U(VI) deposits is avoided and H₂O₂ decomposition continues to occur at high [H₂O₂]. When the pH is decreased, UO₂ dissolution is accelerated and for pH?5 uranyl peroxide deposits may form on the electrode surface. The importance of H₂O₂ decomposition at low pH (i.e. ?6) is not fully understood.     

Determination of electrochemical parameters and corrosion rate for carbon steel in un-buffered sodium chloride solutions using a superposition model

Corrosion of carbon steel in un-buffered NaCl solutions was studied applying linear potential sweep technique to a rotating disk electrode. Current-potential curves were obtained from linear potential sweep at a rate of 1 mV s⁻¹ in solution with concentrations in the range 0.02-1 M NaCl and rotation rates in the range 170-370 rad s⁻¹, at 22 °C. Potential sweeps, which were conducted in the potential range −700 to −100 mV/SHE, were started from the cathodic limit in order to approach the measurement of corrosion under rust-free conditions. Polarization curves were analyzed with a superimposition model developed ad hoc and implemented in a computer program, which enabled determining the corrosion rate and kinetics parameters of the underlying anodic and cathodic sub-processes. The anodic sub-process, dissolution of iron, was well described in terms of a pure charge transfer controlled reaction, while the cathodic sub-process, oxygen reduction on iron, was well described in terms of mixed mass transfer and charge transfer control. Increase of electrode rotation rate increases the limiting current of oxygen reduction, which results in an enhanced corrosion rate of carbon steel. Increase of NaCl concentration has a dual effect: the limiting current of oxygen reduction decreases as a result of the influence of NaCl concentration on solution viscosity and the anodic dissolution of iron increases due to the influence of NaCl on pitting formation. However, this last mechanism predominates and a net increase in carbon steel corrosion rate is observed in this case.     

Interfacial morphology and corrosion resistance of Fe–B cast steel containing chromium and nickel in liquid zinc

The interfacial morphology and corrosion resistance of low carbon Fe–B cast steels in zinc bath at 520 °C were investigated. The results show Fe–B cast steel containing high Cr and Ni exhibits the best corrosion resistance to liquid zinc. The corrosion layers are composed of Γ-Fe₃Zn₁₀, δ-FeZn₁₀, ξ-FeZn₁₃ and η-Zn. The corrosion behaviour of Fe–B cast steels includes the following processes: the preferential leach and dissolution of Cr and Ni, the formation of Fe–Zn compounds controlled by zinc atom diffusion, and the spalling of borides without the supporting role of α-(Fe, Cr) matrix corroded by liquid zinc.     

The stress corrosion cracking behavior of austenitic stainless steels in boiling magnesium chloride solutions

The change in the mechanism of stress corrosion cracking with test temperature for Type 304, 310 and 316 austenitic stainless steels was investigated in boiling saturated magnesium chloride solutions using a constant load method. Three parameters (time to failure; t_f, steady-state elongation rate; l_ss and transition time at which a linear increase in elongation starts to deviate; t_ss) obtained from the corrosion elongation curve showed clearly three regions; stress-dominated, stress corrosion cracking-dominated and corrosion-dominated regions. In the stress corrosion cracking-dominated region the fracture mode of type 304 and 316 steels was transgranular at higher temperatures of 416 and 428 K, respectively, but was intergranular at a lower temperature of 408 K. Type 310 steel showed no intergranular fracture but only transgranular fracture. The relationship between log l_ss and log t_f for three steels became good straight lines irrespective of applied stress. The slope depended upon fracture mode; −2 for transgranular mode and −1 for intergranular mode. On the basis of the results obtained, it was estimated that intergranular cracking was resulted from hydrogen embrittlement due to strain-induced formation of martensite along the grain boundaries, while transgranular cracking took place by propagating cracks nucleated at slip steps by dissolution.     

Corrosion Behavior of AISI 316L Stainless Steel and ODS FeAl Aluminide in Eutectic Li2CO3–K2CO3 Molten Carbonates under Flowing CO2–O2 Gas Mixtures

A kinetics study on AISI 316L stainless steel and ODS(Oxide-Dispersion-Strenghtened) FeAl iron aluminide was conducted concerningits corrosion behavior in moltenLi₂CO₃-K₂CO₃ eutectic at 650°C in flowingCO₂-O₂ gas mixtures. The corrosion resistance of FeAl ODS wasdemonstrated to be significantly superior to that of austenitic AISI 316Lsteel under all gas conditions tested in this work. At low CO₂partial pressure (PCO₂=0.3 atm) the corrosion rate of bothalloys decreased with time due to the formation of a protective oxidelayer. In dry CO₂ gas, corrosion of AISI steel proceeded at anear-linear rate, indicative of a surface-controlled reaction. FeAl corrodedinitially following parabolic behavior, but, on further reaction, exhibitedsome weight loss. A similar behavior was also observed in a67CO₂-33O₂ gas mixture. Corrosion of FeAl in highCO₂ gas has been postulated to initiate by acidic fluxing ofyttria particles. The attack then develops as pitting and leads to furtherreaction by general corrosion as a consequence of the formation ofactive-passive electrochemical cells between the interior of pits and theexternal surface. The weight loss of AISI 316L in67CO₂-33O₂ gas can be ascribed to the high oxidizing power ofthe gas causing a continuous dissolution of theCr₂O₃ layer into a soluble chromate.     

The electroplated palladium-copper alloy film on 316L stainless steel and its corrosion resistance in mixture of acetic and formic acids

Palladium-copper alloy films (Cu 2.93-5.66 at.%) were deposited on 316L stainless steel by electroplating. The films showed good adhesive strength and increased surface micro-hardness. In boiling mixture of 90% acetic acid + 10% formic acid + 400 ppm Br⁻ under stirring (625 r/min), the Pd-Cu films showed better corrosion resistance than Pd film. The Pd-5.66%Cu films showed the lowest corrosion rate almost three orders of magnitude lower than that of 316L matrix. The increased corrosion resistance of Pd-Cu films was attributed to the improved passivity, better barrier effect, increased surface hardness and the effect of Cu to resist pitting.     

Accelerated corrosion of MoO3-deposited copper

The accelerated oxidation kinetics of MoO₃-deposited copper were studied in the temperature range of 480–700 °C in air. The accelerated oxidation followed the parabolic-rate law, indicating that the process was diffusion-controlled. Oxygen diffusion along liquid channels in the oxide scale was inferred to be the rate-limiting step in the overall mechanism. The rate constant increased from 9.2 × 10⁻⁶ to 3.8 × 10⁻⁵ kg² m⁻⁴ s⁻¹ with increasing the deposit mass from 0.3 to 0.9 kg m⁻² at 700 °C.     

Effects of solution pH and Cl on electrochemical behaviour of an Aermet100 ultra-high strength steel in acidic environments

In this work, the effects of solution pH and Cl⁻ on the electrochemical behaviour of an Aermet100 ultra-high strength steel in 0.5 M (Na₂SO₄ + H₂SO₄) solution were studied by polarization curve and electrochemical impedance spectroscopy (EIS) measurements, combined with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) characterization. The results show that, when solution pH is below 4, the steel is in the active dissolution state, and corrosion current decreases with the increase of pH. There exists a critical pH value, above which the steel is passivated. Moreover, the oxides and hydroxides of Fe, Co, Ni and Cr are the primary components of the passive film. With addition of Cl⁻, pits are initiated on the steel electrode.     

AC corrosion - Part 1: Effects on overpotentials of anodic and cathodic processes

AC-induced corrosion is a controversial subject and many aspects of it need to be clarified, first and foremost, the mechanism and relationship between AC density and corrosion rate. This paper (Part 1) presents and discusses the effects of AC interference on kinetics parameters; the effects on corrosion rate and corrosion mechanism will be discussed in Part 2. Polarisation curves were obtained in different solutions (soil-simulating solution, 35 g L⁻¹ NaCl, 1 M FeSO₄, 1 M CuSO₄ and 1 M ZnSO₄) on different metallic materials (carbon steel, galvanised steel, zinc and copper) in the presence of AC interference (30-1000 A/m²).     

Corrosion characteristics of electroless Ni–P coating in sulfur‐bearing solution

The corrosion behaviors of electroless Ni–P coatings deposited on carbon steel in sulfur‐bearing solutions were investigated by weight gain test and scanning electron microscopy. The results indicate that the corrosion rate of electroless Ni–P coating was directly related to the sulfur content, immersion time, and test temperature. The corrosion rate increased with the prolonged immersion time. Increasing the temperature can markedly increase the corrosion rate of electroless Ni–P coating. The electroless Ni–P coating had a better corrosion resistance than 316L stainless steel against Cl^? corrosion in sulfur‐bearing solution.     

On the sulphidation mechanism of niobium and some of Nb-alloys at high temperatures

The kinetics and mechanism of niobium sulphidation have been studied as a function of temperature (700-1000 °C) and sulphur pressure (10⁻⁴-10⁴ Pa) in pure sulphur vapour and H₂-H₂S gas mixtures, using microthermogravimetric technique. It has been found that in both different sulphidizing atmospheres the sulphidation process follows parabolic kinetics, being thus diffusion controlled. Marker experiments have shown that the slowest step of the overall reaction rate is the outward diffusion of cations. No influence of small amounts of impurities on the sulphidation rate has been observed in this study. Excellent agreement between calculated and experimentally determined parabolic rate constants has been obtained under the assumption, that the correct formula of the sulphide scale on niobium is Nb_2±yS₃ and not Nb_1+xS₂, as suggested by Gesmundo.It has been found that the rate of niobium sulphidation in H₂-H₂S gas mixtures is much higher than in pure sulphur vapour, strongly suggesting that the dissolution of hydrogen in the growing scale influences the defect structure in this sulphide.     

Investigation of AISI 1040 steel corrosion in H2S solution containing chloride ions by digital image processing coupled with electrochemical techniques

This paper presents a study of AISI 1040 steel corrosion in aqueous electrolyte of acetic acid buffer containing 3.1 and 31 × 10⁻³ mol dm⁻³ of Na₂S in both the presence and absence of 3.5 wt.% NaCl. This investigation of steel corrosion was carried out using potential polarization, and open-circuit and in situ optical microscopy. The morphological analysis and classification of types of surface corrosion damage by digital image processing reveals grain boundary corrosion and shows a non-uniform sulfide film growth, which occurs preferentially over pearlitic grains through successive formation and dissolution of the film.