Duplex Oxide Layer Research Articles

General corrosion behavior and mechanism of ferritic/martensitic steel with and without TaWVCr coating in static oxygen-saturated lead bismuth eutectic at 550 °C

Here in present work, the ferritic/martensitic (F/M) steel HT9 and refractory TaWVCr high entropy alloy coated HT9 were tested in a static oxygen-saturated lead bismuth eutectic (LBE) at 550 °C through corrosion tests and slow strain rate tension tests to investigate the corrosion behavior and mechanism. The fracture pattern of HT9 and TaWVCr/HT9 both show the ductile fracture. Comprehensive microstructural characterizations from atomic-scale examinations to micro-scale fracture analyses were performed to illustrate the underlying mechanisms of the liquid LBE corrosion. It was revealed that the corrosion of HT9 is related to the surface oxide scale cracking, which propagates into the matrix but terminated in the Cr2O3 enriched zone at the crack tip. On the contrary, the stress concentration caused by local degradation of the TaWVCr coating accelerates the oxidation and dissolution of the coating in LBE, leading to the formation of a duplex oxide layer underneath the coating, which allows cracks initiate in the magnetite layer and annihilate in the chromite layer. The micrometer-scale penetrative oxide layer was found within the matrix, due to the inward diffusion of O through the diffusion channels such as dislocation channels of the matrix and the dissolution channels of the coating and this can accelerate the oxidation corrosion of the matrix.

Corrosion behavior of magnetron sputtering Fe31Cr20Al17Ti16Nb16 high entropy coating in liquid lead-bismuth eutectic with different oxygen concentration at 500 °C

The major concern of the structure integrity of lead cooled reactor is the corrosion behavior of fuel cladding and other core internal materials. Magnetron sputtering technology is adopted as an surface coating method to improve the corrosion resistance of nuclear fuel cladding exposed to liquid lead-bismuth eutectic (LBE). Fe31Cr20Al17Ti16Nb16 high entropy alloy (HEA) coatings were prepared on tubular ferritic/martensitic (F/M) steel which is the candidate fuel cladding material, and the corrosion behaviors of Fe31Cr20Al17Ti16Nb16 coatings in LBE are investigated in this work. F/M steel specimens with Fe31Cr20Al17Ti16Nb16 coatings were exposed to 500 °C stagnant liquid LBE with oxygen concentration of Co ≈ 1 × 10−4 wt% and Co ≈ 1 × 10−7 wt% for 1000 h respectively. The primary findings suggest that the oxygen content of LBE mainly affects the morphology of duplex oxide layers generated during corrosion process, which resulting from the different inward diffusion flux of oxygen. In oxygen-saturated (Co ≈ 1 × 10−4 wt%) LBE, the overall oxide layer exhibits bulging and incompact morphology and infiltration of Pb is probed at inner Cr2O3 oxide layer, larger-sized cavities (the observed maximum dimension reaches 233.5 nm) distribute close to the outer Fe3O4/FeCr2O4 layer; In oxygen-depleted (Co ≈ 1 × 10−7 wt%) LBE, duplex oxide layer presents relatively dense and uniform state, tiny cavities (observed maximum dimension is 38.3 nm) dispersing at the internal of oxide areas. Corrosion rates of the Fe31Cr20Al17Ti16Nb16 coatings under two oxygen situations are 2 orders of magnitude lower than uncoated F/M steel under same exposure condition, the oxide layers with better uniformity and density produced in Co ≈ 1 × 10−7 wt% LBE indicating the better application advantage of Fe31Cr20Al17Ti16Nb16 coatings in oxygen-depleted LBE.

Study on the corrosion behavior of laser surface remelted and laser cladding of ferritic/martensitic steels after exposure to lead-bismuth eutectic at 700 °C

This study explores two vital structural materials, T91 (Fe-9Cr) and SIMP (Fe-11Cr) steels, in the context of lead-cooled fast reactors and accelerator-driven sub-critical systems (ADS). Lead-bismuth eutectic (LBE) functions as a key coolant and spallation target material due to its impressive thermal conductivity, neutron yield, and chemical properties. Unfortunately, materials in contact with LBE are prone to severe corrosion at elevated temperatures (T>500 °C), compromising their integrity. To bolster corrosion resistance, we utilized laser remelting and laser cladding to apply FeCrAl/TiN coatings on the steel surfaces. Our study scrutinizes the corrosion behavior of steel in LBE saturated with oxygen at 700 °C and investigates the underlying causes. Following 240 h of exposure to corrosion, T91 and SIMP steels subjected to laser remelting displayed substantial oxide scale formation. Lead-bismuth atoms infiltrated the outer oxide layer (Fe3O4), diminishing adhesion between the inner and outer oxide layers, leading to the detachment of the outer oxide layer. The inner oxide layers, composed of Fe-Cr spinel, were approximately 123 μm thick for T91 steel and 77 μm for SIMP steel, underscoring SIMP steel's superior corrosion resistance. For T91 steel treated with laser cladding FeCrAl/TiN coating, a characteristic duplex oxide layer with a total thickness of around 83 μm was formed, with noticeable deposition of Pb-Bi atoms at the interface between the outer and inner oxide layers. Conversely, only a protective alumina layer safeguarded SIMP steel from LBE corrosion. This outcome emphasizes the efficacy of laser cladding FeCrAl/TiN coating in providing superior protection for SIMP steel over T91 steel. Our research significantly contributes to the development of anti-corrosion coatings for high-temperature LBE environments.

Effect of laser shock peening and surface mechanical attrition treatment on the oxidation resistance of a 20Cr-25Ni-Nb stainless steel

In this study, the effects of laser shock peening (LSP) and surface mechanical attrition treatment (SMAT) were comparatively investigated on the oxidation behaviors of 20Cr-25Ni-Nb stainless steel in a high-temperature (650 °C) CO2 environment up to 1000 h. The results show that the oxidation resistance of stainless steel can be improved by LSP but deteriorated by SMAT. LSP promoted the formation of a thin and uniform Cr-rich oxide layer on the 20Cr-25Ni-Nb stainless steel instead of a thick duplex oxide layer with Fe-rich outer layer and Cr-rich inner layer which appeared on the untreated sample. For the SMAT-treated sample, besides the oxide scale, a thick internal oxidation zone (IOZ) and oxides spallation were also observed. The formation of a Cr-rich oxide layer was facilitated by the enhancement of the Cr diffusion within the LSP-induced hardened layer. The unsatisfying oxidation performance of the SMAT-treated sample is due to the surface micro-cracks and significant grain refinement which synergistically contributed to the visible carburization and oxidation in a high-temperature CO2 environment.

Corrosion performance of alloy 800H and alloy 625 for potential use as molten salts solar receiver materials in concentrating solar power tower plants

Two high corrosion resistant super-alloys, alloy 800H and alloy 625, were evaluated for corrosion compatibility with molten nitrate salts at 565 °C under air atmosphere since these super-alloys are possible candidates for the manufacturing of molten salts solar receivers in the CSP tower technology. Both alloys are tested in two different molten nitrate salts grades to identify how the impurities of the final mixture affect to corrosion damage. Accordingly, a technical grade molten nitrate salt (Solar_Salt_T) and refined molten nitrate salt (Solar_Salt_R) are selected as test media. In addition to corrosion rates calculation, techniques such as XRD, EDS, optical and scanning electron microscopy are used to identify the corrosion morphology and oxides layers chemistry. Alloy 800H and alloy 625 show uniform corrosion after testing without detecting localized phenomena such as pitting, stress corrosion cracking, crevice, or intergranular corrosion. While alloy 800H develops a duplex oxide layer consisting of iron oxides in its external part, and chromium oxide in its innermost layer, alloy 625 generates a compact and highly adherent oxide layer consisting mainly of nickel oxide. Corrosion rates decrease with time, being higher for alloys exposed to Solar_Salt_T mixtures. Moreover, alloy 625 shows lower corrosion rates than alloy 800H in all conditions tested in this study.

Surface decontamination of protective duplex oxide layers on stainless steel waste using deep eutectic solvents

The decontamination capabilities of deep eutectic solvents (DESs) formed from choline chloride (ChCl) and p-toluenesulfonic acid monohydrate (PtsA), ChCl:PtsA, under different conditions (hydrated, heated, and agitated) were tested with simulant oxidized stainless steel 304 specimens. Although the leaching rates were satisfactory under all conditions, hydrated and stirred ChCl:PtsA at 60 °C showed the fastest leaching rate of 0.1647 mg/min. Oxidized specimens with an average mass gain of 1.2 ± 1 mg were leached, and their masses were reduced by 558 ± 22 mg after 26 h. These results were understood by improved physical properties of ChCl:PtsA upon hydration. Metal oxide solubility of CoO and NiO increased with water, and those of Cr2O3 and Fe3O4 decreased with hydration. Importantly, the use of choline chloride-based DESs in decontamination applications may significantly reduce the cost of decontamination because these DESs can be mass-produced and their components are both easily obtainable and economical. Also, DESs are biodegradable and eco-friendly. The different speciation of Co and Ni, which bond with Cl-, compared with Fe and Cr, which bond with H2O, illustrated the potential for a metal recovery for secondary liquid waste reduction.

Unravelling the Fe Effect on the Corrosion of Chromium Coatings: Chemical Composition and Semiconducting Properties

A model trivalent chromium-based electroplating bath doped with different concentrations of Fe was used to obtain different metallic coatings. The impact of the Fe was investigated on both the Cr layer and its native passive film by a detailed characterisation using X-ray Photoelectron Spectroscopy (XPS), Angle Resolved XPS and Auger Electron Spectroscopy. Moreover, the semiconducting properties of their oxide layers were explored by Mott-Schottky and the corrosion performance of the coating by linear polarisation resistance and kinetics of the oxide formation. Results revealed not only a homogeneous Fe distribution in the Cr layer but also the presence of an iron-chromium duplex oxide layer for concentrations ≥ 100 mg l−1 Fe in the bath. The Mott-Schottky analysis showed a p-n junction for such coatings due to the presence of an iron oxide layer on top of a chromium oxide one, which increased the total amount of point defects (charge carrier density) and drastically affected to their corrosion resistance (the polarisation resistance decreased by one order of magnitude and their oxide layer showed slower kinetics and a higher passivation current). In contrast, coatings with a single chromium oxide layer showed a p-type semiconducting behaviour as well as the best corrosion performance.

Oxidation and carburization behaviour of two type 316H stainless steel casts in simulated AGR gas environment at 550 and 600 °C

• Duplex oxide and carburized layers form on steels exposed to AGR reactor coolant • Cracking in the oxide layer increases the oxidation and carburization rates • Carbon locates in the austenite lattice and predominately M 23 C 6 carbides • Diffusion of substitutional solutes is the rate-limiting mechanism of carburization • Small precipitates lead to a reduced carburization rate at 550ºC The time-dependent oxidation and carburization behaviour of two type 316H austenitic stainless steels with varying Mn content and differing average austenite grain size of 142 µm in ‘Low Mn’ (0.98 wt.% Mn) and 81 µm in ‘High Mn’ (1.52 wt.% Mn), were assessed at 550 °C and 600 °C in the presence of simulated reactor primary gas coolant containing 500 vppm H 2 O, 100 vppm H 2 , 300 vppm CH 4 and 1 vol.% CO, balanced with CO 2 . Rupture and spallation of the initial protective chromia layer occurs in the ‘High Mn’ steel after 2000 h at 550 °C, and leads to the formation of a magnetite/spinel oxide layer that reaches 75% surface coverage only after 8000 h. In contrast, ‘Low Mn’ steel reaches ~ 85% coverage after only 1000 h at the same temperature. The development of an inner carburized layer occurs gradually in both steels once the duplex oxide layer is forming. The differences in steel behaviour are reduced at 600 °C, where both oxidation and carburization are significantly accelerated. Only 0.02 wt.% carbon remains in solid solution in the austenite lattice in the carburized layer, the excess carbon atoms precipitating out in the form of Cr-rich M 23 C 6 particles, present both inter- and intragranularly. The experimental values of the activation energy for carburization suggest that diffusion of substitutional solutes as the rate-limiting mechanism of the process. Previously observed carburization depths of ≥ 200 µm in ex-service austenitic stainless steels, may be achieved by pre-conditioning 316H steel in simulated reactor gas coolant for ≥ 6000 h at 600 °C.

Accelerated corrosion tests of Al-B4C neutron absorber used in spent nuclear fuel pool

Accelerated corrosion tests of Al-B 4 C neutron absorber, equivalent to 37 months in a spent nuclear fuel pool, were conducted on three different period-installed surveillance coupons (33, 52, and 92 months) to further investigate the underlying mechanisms of premature surface corrosion and 10 B depletion which we had recently reported in another study. Microstructure characterization, electrochemical analysis, and neutron attenuation tests were conducted after the corrosion tests, and two types of galvanic corrosion, Al matrix/stainless steel and Al matrix/B 4 C particles, were discovered. The duplex oxide layer comprised of amorphous oxide and Al(OH) 3 films and pit corrosion were also observed on the surface with reduced densities (< 1%). The neutron attenuation tests on the absorbers and ICP-MS measurement of the coolant showed no considerable change in 10 B areal density.

Oxidation in wire arc additive manufacturing of aluminium alloys

Abstract Wire Arc Additive Manufacturing is a near-net-shape machining technology that enables low-cost production of large and customised metal parts. In the present work, oxidation effects in Wire Arc Additive Manufacturing of the aluminium alloy AW4043/AlSi5(wt%) were investigated. Two main oxidation effects, the surface oxidation on aluminium parts and the oxidation anomalies in aluminium parts were observed and analysed. The surface oxidation on aluminium parts changed its colour during Wire Arc Additive Manufacturing from transparent to white. In the present work, it was shown by high-speed imaging that this change in the surface oxidation took place in the process zone, which was covered by inert gas. Since the white surface oxidation formed in an inert gas atmosphere, it was found that the arc interacts with the existing amorphous oxide layer of the previously deposited layer and turns it into a white duplex (crystalline and amorphous) oxide layer. In addition to the analysis of the white surface oxidation, oxidation anomalies, which occur at low shielding from the environment, were investigated. It was shown by physical experiments and Computational Fluid Dynamics simulations, that these oxidation anomalies occur at inadequate gas flow rates, too big nozzle-to-work distances, process modes with too high heat input, or too high wire feed rates. Finally, a monitoring method based on light emission spectroscopy was used to detect oxidation anomalies as they create peaks in the spectral emission when they occur.

High-Temperature Corrosion Behaviors of Structural Materials for Lead-Alloy-Cooled Fast Reactor Application

The corrosion of nuclear-grade steels in lead–bismuth eutectic (LBE) complicates the realization of high coolant temperatures. Corrosion tests of T91, HT9, and SS316L were performed in static cells at 600 °C for 2000 h at an oxygen level of 10−6 wt.%. The obtained corrosion surfaces of post-processed samples were characterized by several microscopy methods. Up to 1000 h, all the alloys exhibited an evolution of duplex oxide layers, which were spalled until 2000 h due to their increased thickness and decreased integrity. Following the spallation, a thin internal Cr-rich oxide layer was formed above the Cr-depleted zone for T91 and HT9. SS316L was penetrated by LBE down to 300 μm in severe cases. A comparison on the corrosion depths of the materials with regard to the parabolic oxidation law with abundant literature data suggests that it may lose its validity once the duplex layer is destroyed as it allows LBE to penetrate the metal substrate.

Corrosion Behavior of Ti-Si-B-C Nanocomposite Hard Coating with Different Si Contents on 4130 Steel

Microstructural, mechanical and electrochemical properties of a Ti-Si-B-C nanocomposite coating with different Si percentages on 4130 steel were investigated. All the films with different SI contents in the range of 10 to 12 µm thickness showed amorphous structures by X-ray diffraction. The hardness decreased with the increase of Si content in Ti-Si-B-C film. The particle size, pores, roughness and phases were responsible for the decrease of hardness with the increase of Si content. Electrochemical behavior is studied using open-circuit potential, impedance spectroscopy (EIS) and anodic polarization methods in 3.5 wt pct NaCl solution. The corrosion current density (icorr) was much lower, 0.45 to 2.34 µA/cm2, with varying Si content compared with uncoated steel (9.37 µA/cm2), and passivation behavior was observed during the polarization study. The EIS fit model suggested the presence of a duplex oxide layer on the Ti-Si-B-C nanocomposite coatings. The Ti-Si-B-C coatings with lower Si (24 pct) content showed the best corrosion resistance compared with higher Si content (36 to 52 pct). Overall, the present study suggests that the hard Ti-Si-B-C nanocomposite coating significantly improved the corrosion resistance of 4130 steel.

Impact of the voids on the cracking behavior of the duplex oxide scale on the 18%Cr austenite alloy surface

This work investigated the oxide cracking behavior of 18%Cr austenitic steels. The role of voids at the duplex oxide layer interface has been discussed. Simulation results demonstrate that the stress concentration facilitates the crack nucleation at the void top. Interestingly, the interface of the duplex oxide layer exhibits better cracking resistance. Experiment results confirm that the voids facilitate cracking when the temperature drop is beyond 119 °C during oxidizing at 650 °C for TP347H alloy. By comparing, more than 290 °C of temperature drop is needed for the cracking on TP347HFG alloy, which is because the void diameter is small.

Corrosion behaviors of four stainless steels with similar chromium content in supercritical carbon dioxide environment at 650 °C

The corrosion behavior of four stainless steels (SSs) with similar chromium content was investigated in supercritical carbon dioxide environment. Overall, weight gain was the smallest for 630 SS which formed thin and continuous Cr-rich oxide layer. Due to large Mn3O4 nodules, weight gain was larger for 430 SS. For 347H and 316LN SSs, thick duplex oxide layers were formed following the extensive oxide spallation, resulting in much greater weight gains than 430 and 630 SSs. The oxide spallation was explained by the formation of Nb-rich layer or amorphous matters at the matrix/oxide interface as well as the matrix structure.

Kinetics of oxide scale growth on a (Ti, Mo)5Si3 based oxidation resistant Mo-Ti-Si alloy at 900-1300∘C

Abstract High-temperature oxidation behaviour of Mo-40Ti-30Si (at.%) alloy was investigated in the temperature regime of 900-1300∘C in air. Isothermal weight change data recorded up to 100 h of exposure revealed parabolic weight gain kinetics at all the tested temperatures. The protective oxide scale composed with SiO2 (silica) and TiO2 (titania) forming a duplex oxide microstructure consisting of TiO2 particles embedded in the continuous SiO2 matrix. The oxide scale showed parabolic growth kinetics, and the activation energies for the scale growth were found to be 72.2 kJ/mol in 900-1200∘C and 324.9 kJ/mol in 1200-1300∘C. The kinetics of the protective scale growth on the alloy surface was mainly controlled by the growth of the silica film and the inward diffusion of oxygen through the duplex oxide layer.

Oxidation behavior and lifetime prediction of three commercial alloys used in power plants at 550 °C in CO2 environment

The oxidation behaviors of CrMoV, F91, and 310S alloys in CO2 at 550 °C for up to 1000 h were studied by weight change measurements, scanning electron microscopy, X-ray diffraction, Raman microscopy, optical microscopy, and glow discharge optical emission spectroscopy. 310S showed the best oxidation resistance followed by F91 and then CrMoV. Both CrMoV and F91 formed a duplex oxide layer, consisted of Fe2O3, Fe3O4, and Fe–Cr spinel, while 310S formed NiFe2O4 spinel and Cr2O3. Carburization was only observed in F91 and 310S alloys. The rates of metal loss were evaluated for long-term applications in power plants.

Combat molten aluminum corrosion of AISI H13 steel by low-temperature liquid nitrocarburizing

Possibility of improving the resistance of AISI H13 steel to molten aluminum corrosion by liquid nitrocarburizing (LNC) was explored. The effects of the LNC parameters in terms of temperatures (703/723/743 K) and soaking time (4/8/12 h) on phase transformation, microstructure, and resistance to molten aluminum were fully studied. The surface phase compositions and the cross-sectional phase distribution of the LNC treated specimens were studied by implementable X-ray diffraction analysis. Microstructure, element distribution, microhardness, and the kinetics of the nitrocarburized case formation were fully researched. Immersion test of corrosion resistance to molten aluminum was carried out at 1023 K for 30min. It is observed that an oxide layer can be produced on the top of the nitrocarburized case during LNC treatment, which cannot be regularly produced by other nitriding methods. The nitrocarburized case consists of a compound layer, a diffusion layer, and a transition layer. The growth of the nitrocarburized case is proportional to the squared treatment time and follows the Arrhenius law for the treatment temperature. The activation energy is estimated to be 195.4 kJ mol−1. While the nitrocarburized case provided limited resistance to molten aluminum, the oxide layer formed on the top of the nitrocarburized case conferred significantly improved molten aluminum corrosion resistance, especially a duplex oxide layer produced at 743 K.

Electrochemical behaviour of copper in alkaline glycine solutions

The fundamental electrochemical properties of the copper-glycine system were investigated in this study to understand the factors that affect the dissolution of metallic copper. Potentiodynamic polarisation measurements were carried out over the pH range 9.0 to 11.5, at temperatures of 22 °C and 60 °C and glycine concentrations 0.1 M and 0.3 M. A window for maximum corrosion current was determined to be between pH 10.0 and 10.5 with a maximum at 60 °C and 0.3 M glycine. Passivation was only observed at pH values >10.5, and then only at potentials above 0.4 V (vs SHE) for quiescent solutions. This passivation potential increased with the rotation speed of the copper electrode. The passive layer broke down after a short rest at the open circuit potential, which allowed reactivation of the surface and high initial currents to briefly flow until the layer re-formed. Potential-step and capacitance measurements are consistent with the formation of a duplex oxide layer of Cu2O and CuO that thickens with increasing potential. The copper glycinate complex itself also acts as an oxidising agent, the effectiveness is increased with its concentration and the concentration of free glycine. Free glycine is oxidised irreversibly above 1.2 V (vs SHE).

Study of continuous corrosion on astm a335 p91 steel in an environment of co2-o2-n2-h2o derived from the theoretical combustion products of a mixture of refining gases at high temperatures

The current energy production processes go hand in hand with corrosive phenomena; which is the case of combustion process in a refinery, where the presence of compounds such as CO2 and H2O, result in alloys catastrophic carburization and oxidation respectively. In this research work was evaluated the corrosive effect that can be generated in a real combustion environment, for which, it was necessary to select a model mixture of refinery gases and to simulate its theoretical combustions products. The main results showed the formation of a semi-protective duplex oxide layer; whose inner layer was composed mainly of chromium, while the outer layer was much richer in iron. On the other hand, the carburizing effect of CO2 was suppressed by the high oxygen potential in the combustion environment; leading to the conclusion that in real conditions, at 750 oC and after 200 h of testing, steels such as ferritic alloy ASTM A335 P91, could not present appreciable damages during their operation in refinery boilers and furnaces.

High Temperature Oxidation Behavior of Fe-Cr Steel in Air at 1000-1200 K

Normal 0 false false false EN-US JA X-NONE MicrosoftInternetExplorer4 The high temperature oxidation behavior of Fe-Cr steel was studied in air at elevated temperatures of 1000, 1100 and 1200 K for up to 72 ks. The mass change of all samples was recorded in order to evaluate their oxidation kinetic. The structure of oxide scales was investigated by mean of X-ray diffraction and SEM-EDX. According to oxidation kinetic curve, the mass gain of oxidized sample increases with increasing oxidation time and temperature. At 1000 and 1100 K, the Fe-Cr steel exhibits an excellent oxidation resistance. As oxidation temperature increase to 1200 K, however, the accelerated oxidation occurred. This is considered due to breakaway oxidation. The Fe-Cr steel forms a duplex oxide layer consisting of Fe-rich oxides in the outer layer and Fe-Cr oxides in the inner layer. The obtained results suggest that the oxidation temperature strongly affects the oxidation resistance of Fe-Cr steel and the structure of formed oxide layer on the steel surface. The influence of oxidation temperature on the oxidation resistance and scale structure is discussed in this paper. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"MS Mincho"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}