| 1. |
- Sand, Tommy, 1982, et al.
(författare)
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Effective Reduction of Chromium-oxy-hydroxide Evaporation from Ni-Base Alloy 690
- 2019
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 92:3-4, s. 259-279
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Tidskriftsartikel (refereegranskat)abstract
- The corrosion of the Ni-base alloy 690 (60Ni, 30Cr and 10Fe) in humidified air was studied at 500–800 °C, and the rate of CrO2(OH)2 volatilization was measured quantitatively as a function of exposure time using a denuder technique. Different gas velocities were employed in exposures with a maximum duration of 200 h. Corrosion morphology was investigated by SEM/EDX using BIB-milled cross sections. The rate of chromium volatilization increased with increasing temperature and gas velocity. The rate of volatilization decreased with exposure time. Two oxide scale morphologies were observed, depending on temperature and gas velocity. In the 500–700 °C range, the scale consisted of chromia-rich corundum-type oxide, while exposures with high gas velocities at 800 °C produced an entirely different type of scale that included a Ni-rich and Cr-poor cap layer. The latter scale morphology is suggested to result from extensive chromium depletion of the alloy substrate which triggers a new mode of oxidation involving formation of NiCr spinel oxide. Continued volatilization of CrO2(OH)2 causes the NiCr spinel to decompose into a Ni-rich oxide that forms a cap layer on the scale surface. This cap layer is very efficient in decreasing the rate of chromium volatilization, allowing the chromium levels in the substrate to recuperate. We show that volatilization of chromium (VI) from the alloy can be mitigated by an oxidation pre-treatment that allows the Ni-rich cap layer to form.
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| 2. |
- Sand, Tommy, 1982, et al.
(författare)
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Exploring the Effect of Silicon on the High Temperature Corrosion of Lean FeCrAl Alloys in Humid Air
- 2021
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 95:3-4, s. 221-238
-
Tidskriftsartikel (refereegranskat)abstract
- A new approach to reduce the chromium and aluminium concentrations in FeCrAl alloys without significantly impairing corrosion resistance is to alloy with 1-2 wt.% silicon. This paper investigates the "silicon effect" on oxidation by comparing the oxidation behavior and scale microstructure of two FeCrAl alloys, one alloyed with silicon and the other not, in dry and wet air at 600 degrees C and 800 degrees C. Both alloys formed thin protective oxide scales and the Cr-evaporation rates were small. In wet air at 800 degrees C the Si-alloyed FeCrAl formed an oxide scale containing mullite and tridymite together with alpha- and gamma-alumina. It is suggested that the reported improvement of the corrosion resistance of Al- and Cr-lean FeCrAl's by silicon alloying is caused by the appearance of Si-rich phases in the scale.
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| 3. |
- Babic, Vedad, 1990, et al.
(författare)
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Fates of Hydrogen During Alumina Growth Below Yttria Nodules in FeCrAl(RE) at Low Partial Pressures of Water
- 2017
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Ingår i: Electrocatalysis. - : Springer Science and Business Media LLC. - 1868-5994 .- 1868-2529. ; 8:6, s. 565-576
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Tidskriftsartikel (refereegranskat)abstract
- Oxidation of FeCrAl(Re), when exposed to similar to 35 ppm of water as sole supply of oxygen in predominantly nitrogen atmosphere, has two characteristic signatures. One is the internal nitridation owing to chromia nodules acting windows toward nitrogen permeation locally short-circuiting the protective alpha-Al2O3 scale. The second remarkable feature is the growth of thick, apparently defect-rich alumina scale under yttria-rich nodules. Hence, one part of the present study comprises exploratory DFT calculations to discriminate between the impacts of chromia and yttria viz. nitrogen permeation. The second part concerns boundary conditions for apparent rapid growth of alumina under yttria nodules. Yttria-associated surface energy stabilization of defect-rich alumina in presence of water was argued to involve hydrolysis-driven hydroxylation of said interface. Subsequent inward growth of the alumina scale was associated with outward diffusion of oxygen vacancies to be accommodated by the remaining proton producing a hydride ion upon surfacing at yttria-decorated alumina interfaces. The latter comprises the cathode process in a quasi-Wagnerian context. Two fates were discussed for this surface ion. One has H--H+ recombination to form H-2 at the interface in conjunction with OH- accommodation upon hydration, while the second allows hydrogen to be incorporated at V-O sites in hydroxylated grain boundaries of the growing alumina scale. The latter was taken to explain the experimentally observed rapid oxide growth under yttria-rich nodules. Space charge due to proton reduction was proposed to cause transient inward cationic drag.
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| 4. |
- Babic, Vedad, 1990, et al.
(författare)
-
On Water Induced Sensitization of Ni (Fe,Cr) alloys towards Stress Corrosion Cracking in LWR Piping from 1st Principles Modelling
- 2021
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In Swedish Light Water Reactors (LWR), stress corrosion cracking of reactor components and welds occurs from time to time. As the nuclear power plants are ageing, it is essential to study and further understand the mechanism for environmentally induced sensitization. Natural cracking is a phenomenon that is difcult to predict and very hard to study since it occurs suddenly and often unexpectedly. In order to study the crack initiation and growth, the crack is traditionally experimentally provoked and it is not known to what degree these experimental cracks correspond to those that occur naturally. The environment in an LWR contributes to material ageing through chemical reactions with the environment. An in-depth examination has shown that the microstructures of oxide flms changes along the crack path and the oxide flm in the crack tip is signifcantly diferent from what one detects at the crack opening. In this study, 1st principles modelling is used to articulate an environment induced sensitization mechanism for stress corrosion cracking of Ni(Fe,Cr) alloys in LWR conditions.
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| 5. |
- Babic, Vedad, 1990, et al.
(författare)
-
Reactive Element Effects in High-Temperature Alloys Disentangled
- 2020
-
Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 93:1-2, s. 229-245
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Tidskriftsartikel (refereegranskat)abstract
- Reactive elements—REs—are decisive for the longevity of high-temperature alloys. This work joins several previous efforts to disentangle various RE effects in order to explain apparently contradicting experimental observations in alumina forming alloys. At 800–1000 °C, “messy” aluminum oxy-hydroxy-hydride transients initially formed due to oxidation by H2O which in turn undergo secondary oxidation by O2. The formation of the transient oxide becomes supported by dispersed RE oxide particles acting as water equivalents. At higher temperatures, electron conductivity in impurity states owing to oxygen vacancies in grain boundaries (GBs) becomes increasingly relevant. These channels are subsequently closed by REs pinning the said vacancies. The universality of the emerging understanding is supported by a comparative first-principles study by means of density functional theory addressing RE(III): Sc2O3, Y2O3, and La2O3, and RE(IV): TiO2, ZrO2, and HfO2, that upon reaction with water, co-decorate a generic GB model by hydroxide and RE ions. At 100% RE coverage, the GB model becomes relevant at both temperature regimes. Based on reaction enthalpy ΔHr considerations, “messy” aluminum oxy-hydroxy-hydride transients are accessed in both classes. Larger variations in ΔHr are found for RE(III)-decorated alumina GBs as compared to RE(IV). For RE(III), correlation with GB width is found, increasing with increased ionic radius. Similarly, upon varying RE(IV), minor changes in stability correlate with minor structural variations. GB decorations by Ce(III) and Ce(IV) further consolidate the emerging understanding. The findings are used to discuss experimental observations that include impact of co-doping by RE(III) and RE(IV).
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| 6. |
- Babic, Vedad, 1990, et al.
(författare)
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Transition metal attenuated mechanism for protective alumina formation from first principles
- 2018
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Ingår i: RSC Advances. - 2046-2069. ; 8:72, s. 41255-41269
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Tidskriftsartikel (refereegranskat)abstract
- A mechanistic perspective on the growth of protective oxides on high temperature alloys at elevated temperatures is provided. Early, defect rich transient alumina is understood to form by outwards diffusion of oxygen vacancies and electrons. The impact of transition metal (TM) ions (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) on the oxygen vacancy diffusion and electron transport in α-alumina was studied by employing density functional theory. Activation energies for electron transfer EA(ET) between oxygen vacancies in pure as well as TM doped α-alumina were subject to analysis, and similarly so for the TM and charge dependent activation energy for oxygen vacancy diffusion EA(VO). EAQ(ET) were found to be ∼0.5 eV while 2 eV < EAQ(VO) < 5 eV was obtained. The higher and lower EAQ(VO) values correspond to uncharged and doubly charged VO sites, respectively. Redox processes among VO sites, addressed by a bipolaron approach, were understood to enhance VO mobility and thus to facilitate oxide growth. TM adatoms induced asymmetry in the potential energy surface for oxygen vacancy diffusion was subject to analysis. Competition for electrons between all-Al3+surrounded oxygen vacancies and vacancies adjacent to the late 3d adatoms comes out in favor of the latter. A novel take on the 3rd element effect in FeCrAl emerges from analysis of the ternary TM-TM*-Al system.
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| 7. |
- Cantatore, Valentina, 1986, et al.
(författare)
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Insights into the zinc effect on radio-cobalt deposition on stainless steel piping surfaces under BWR conditions from experiment guided 1st principles modelling
- 2020
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 540
-
Tidskriftsartikel (refereegranskat)abstract
- The beneficial effect of zinc to mitigate radio-cobalt uptake on stainless steel piping surfaces under BWR conditions is revisited by means of 1st principles modelling. A viable generic hydroxylated grain boundary interface (HGBI) model for magnetite, i.e., an inverse spinel, is formulated and interrogated in order to unravel how Zn may cause exclusion of Co by competing for the same sites. While Co2+ as well as Ni2+ reside preferentially in the octahedral lattice sites of the inverse spinel lattice, Zn2+ prefers to reside at the HGBI. The difference is consolidated for M(II), M being Cr, Mn, Fe, Co, Ni, Cu, or Zn. Similar affinities as well as mobilities of Co2+ and Zn2+ in the HGBI are taken to explain how, upon Fe2+ dissolution, Zn2+ may compete with Co2+ for the Fe2+ sites in the inner layer of the duplex oxide film. Impacts of Zn2+ and Ni2+ on Co2+ uptake in the outer oxide layer is also addressed. Zn2+ guided precipitation is found to be less effective than the Ni2+ guided process. Reported beneficial effects on radio-cobalt uptake upon sealing off the stainless steel acting Ni2+ source by coating with magnetite as well as hematite are discussed.
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| 8. |
- Geers, Christine, 1982, et al.
(författare)
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Impact of Grain Boundary Density on Oxide Scaling Revisited
- 2019
-
Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 91:1-2, s. 55-75
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Tidskriftsartikel (refereegranskat)abstract
- A straightforward conceptual tool for discriminating between different oxide scaling processes deviating from the parabolic standard model is formulated. Grain boundary diffusion-controlled oxide scaling is generalized to include lateral grains coarsening. Building on traditional Wagner theory, attenuation of rates of inwards growing oxides owing to the gradual loss of grain boundary density is revisited. Two viable cases are identified. One has the rate of grain boundary density loss to be independent of the rate of oxide growth, while the second case takes the two instantaneous rates to be equal. Simple parabolic–logarithmic and superparabolic–cubic expressions are arrived at for the two cases, respectively. Usefulness is demonstrated by applying the models to published experimental data from 1990 to date. Upon arrival at the superparabolic–cubic behaviour, a generic mathematical form analogous to a ‘spring force’ attenuating the scale growth was identified. ‘Parabolic’, ‘cubic’ and ‘logarithmic’ scaling emerges as limiting cases.
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| 9. |
- Geers, Christine, 1982, et al.
(författare)
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Properties of Alumina/Chromia Scales in N2-Containing Low Oxygen Activity Environment Investigated by Experiment and Theory
- 2017
-
Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 87:3-4, s. 321-332
-
Tidskriftsartikel (refereegranskat)abstract
- The FeCrAl alloy Kanthal APMT™ was exposed to N2–5%H2 at 900 °C. Trace oxygen in the gases supplied an oxygen activity which was sufficient to render alumina and chromia thermodynamically stable. The exposures revealed that the oxide scale was penetrated by nitrogen exclusively at chromia domains. Microscopic analyses of the oxide scale did not reveal micro-cracks that could serve as points-of-entry for nitrogen. Instead it is suggested that nitrogen is transported through a dense chromia layer. Density functional theory was employed to investigate decisive nitrogen surface chemistry and transport properties in chromia and alumina. The study was used to validate that the complex redox chemistry of Cr3+ as opposed to Al3+ is a sufficient discriminating factor between alumina and chromia, facilitating N2 dissociation and mobility of N in chromia.
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| 10. |
- Geers, Christine, 1982, et al.
(författare)
-
Surface Reaction and Transport in Oxides Formed on FeCrAl Alloys in High Temperature Nitridation Environments
- 2017
-
Ingår i: TMS 2017 146TH ANNUAL MEETING & EXHIBITION SUPPLEMENTAL PROCEEDINGS. - Cham : Springer International Publishing. - 2367-1181. - 9783319514932 ; , s. 387-392
-
Konferensbidrag (refereegranskat)abstract
- An extended experimental study on corrosion of commercial FeCrAl alloys in predominantly N-2 atmosphere at high temperatures raises fundamental questions concerning nitrogen permeation through oxide scale components, each commonly perceived to constitute a robust barrier. State-of-the-art microscopy combined with DFT calculations is employed to unravel the underlying mechanisms for how chromia nodules support nitrogen dissociation and subsequently act windows for internal nitridation. A similar analysis addressed the role of yttria nodules shown to exhibit apparent expulsion of nitrogen, while favoring rapid alumina growth underneath the nodules. In this case, as for the slowly growing bare alpha alumina scale, the origin for the protection towards nitrogen permeation was identified as the inability to satisfy the necessary conditions for N-2 dissociation.
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| 11. |
- Jahns, Katrin, et al.
(författare)
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Formation of corrosion pockets in FeNiCrAl at high temperatures investigated by 3D FIB-SEM tomography
- 2020
-
Ingår i: Materials and Corrosion - Werkstoffe und Korrosion. - : Wiley. - 1521-4176 .- 0947-5117. ; 71:11, s. 1774-1782
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Tidskriftsartikel (refereegranskat)abstract
- A recently published study of high temperature nitridation of iron chromium aluminum alloys (FeCrAl) at 900 degrees C in N-2-H(2)has redundantly shown the formation of locally confined corrosion pockets reaching several microns into the alloy. These nitrided pockets form underneath chromia islands laterally surrounded by the otherwise protective alumina scale. Chromia renders a nitrogen-permeable defect under the given conditions and the presence of aluminum in the alloy. In light of these findings on FeCrAl, a focused ion beam-scanning electron microscope tomography study has been undertaken on an equally nitrided FeNiCrAl sample to characterize its nitridation corrosion features chemically and morphologically. The alloy is strengthened by a high number of chromium carbide precipitates, which are also preferential chromia formation sites. Besides the confirmation of the complete encapsulation of the corrosion pocket from the alloy by a closed and dense aluminum nitride rim, very large voids have been found in the said pockets. Furthermore, metallic particles comprising nickel and iron are deposited on top of the outer oxide scale above such void regions.
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| 12. |
- Lindgren, Mikaela, 1987, et al.
(författare)
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Possible origin and roles of nano-porosity in ZrO2 scales for hydrogen pick-up in Zr alloys
- 2017
-
Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 492, s. 22-31
-
Tidskriftsartikel (refereegranskat)abstract
- A mechanistic understanding of Wagnerian build-up and subsequent non-Wagnerian break-down of barrier oxide upon oxidation of zirconium alloys by water is reiterated. Hydrogen assisted build-up of nano-porosity is addressed. Growth of sub-nanometer wide stalactitic pores owing to increasing aggregation of neutral oxygen vacancies offering a means to permeate hydrogen into the alloy is explored by density functional theory. The Wagnerian channel utilizes charge separation allowing charged oxygen vacancies and electrons to move separately from nominal anode to nominal cathode. This process becomes increasingly controlled by the charging of the barrier oxide resulting in sub-parabolic rate law for oxide growth. The break-down of the barrier oxide is understood to be preceded by avalanching hydrogen pick-up in the alloy. Pore mediated diffusion allows water to effectively short circuit the barrier oxide.
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| 13. |
- Madloch, S., et al.
(författare)
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Development of a metal dusting resistant functional coating by Sn and Al pack cementation
- 2016
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 299, s. 29-36
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Tidskriftsartikel (refereegranskat)abstract
- A new coating against metal dusting is developed by the combination of a catalytic inhibition approach with a classical oxide barrier. Coatings were manufactured by co-deposition of tin and aluminum on nickel plated alloy 800H via powder pack cementation with different dwell times. The resulting coatings consist of two phases, a nickel-aluminide phase as oxide forming reservoir and an underlying nickel-tin phase which catalytically inhibits carbon deposition. Coated samples were exposed to H2-22%CO-10%H2O as a laboratory metal dusting environment as well as air at 620 °C. Cross sectional analysis revealed no sign for metal dusting and the formation of a thin alumina layer at the surface.
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| 14. |
- Meier de Andrade, Ageo, 1990, et al.
(författare)
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Stress-corrosion cracking sensitization by hydrogen upon oxidation of nickel-base alloys by water – An experiment-guided first-principles study
- 2024
-
Ingår i: Journal of Nuclear Materials. - 0022-3115. ; 595
-
Tidskriftsartikel (refereegranskat)abstract
- This work describes a viable hydrogen-induced sensitisation process toward stress corrosion cracking in chromia-forming nickel base alloys owing to oxidation by water. A mechanistic chemical understanding of the stress corrosion based on repeated cracking and re-healing of the oxide scale emerges from experiment-guided first-principles calculations. Piggybacking processes during repeated oxide scale cracking-healing cycles are understood to cause sensitisation towards the formation and growth of macroscopic cracks. Under light-water reactor conditions, the healed oxide scale comprises an outer region composed of chromium depleted nickel ferrite, and non-protective chromia, nickel oxide, and nickel hydroxide. An inner nickel iron chromite layer provides the passivating barrier that controls the oxidation rate at a steady state. Early during the re-healing of a crack in the oxide scale, water is conveyed to the alloy/scale interface by hydration/dehydration of composite nickel oxy-hydroxide Ni(OH)2∙NiO inclusions in the scale. At later stages, Ni(OH)2∙NiO serves as oxidant of preferentially chromium, while hydrogen is released as H2(g) into the primary water or becomes picked up by the alloy, possibly while assisting in the reduction of NiO to form nickel metal particles. Oxidation by water equivalents at the confining alloy/oxide scale interface favours hydrogen pick-up in the alloy that becomes increasingly detrimental owing to enrichment and inward diffusion of hydrogen along alloy grain boundaries. The pinning of alloy vacancies by hydrogen causes mitigation of outward diffusion of chromium, which in turn hampers crack re-healing while promoting alloy embrittlement.
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| 15. |
- Mohamedin, Esraa Hamdy, 1991, et al.
(författare)
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Additional data and experimental setups, for a comparative study of alloys in contact to eutectic melts for thermal storage
- 2021
-
Ingår i: Data in Brief. - : Elsevier BV. - 2352-3409. ; 38
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Tidskriftsartikel (refereegranskat)abstract
- Three different eutectic salt mixtures have been brought into contact with three different high temperature alloys to assess corrosion damages for next-generation CSPs. This article contains additional material to support findings and assessments reported on our main article in the Solar Energy Journal [https://doi.org/10.1016/j.solener.2021.06.069]. Five sections, A-E, provide data to ensure reproducibility and confidence in our claims in the main article. A newly designed experimental setup for high temperature exposures is described as well as impurities within used chemicals. Material thickness measurements document alloy consumption by eutectic salts. Reaction enthalpies are listed illustrating individual metal species in contact with salt species at relevant temperatures. Thermodynamic single point equilibrium calculations have extended environmentally induced Laves phase precipitation found for alloy Kanthal APMT in contact with molten chlorides.
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| 16. |
- Mohamedin, Esraa Hamdy, 1991, et al.
(författare)
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Differentiation in corrosion performance of alumina forming alloys in alkali carbonate melts
- 2021
-
Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 192
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Tidskriftsartikel (refereegranskat)abstract
- Alkali carbonate melts are promising high temperature thermal storage media. In this work five alumina forming alloys have been exposed to a ternary LiNaK carbonate melt and CO2 at 800 °C. The corrosion propagation was found to depend on the formation of a slow-growing LiAlO2 scale. Furthermore, the two polymorphs contributing to the LiAlO2 phase were monitored for up to 1000 h: a dense α-LiAlO2 scale and γ-LiAlO2 crystallites. We suggest a growth stress assisted formation of α-LiAlO2 relaxing into the outwards growing γ-LiAlO2 phase. This implies a deceleration of the α-LiAlO2 scale growth towards a steady state-thickness.
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| 17. |
- Mohamedin, Esraa Hamdy, 1991, et al.
(författare)
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Direct and indirect contact of an austenitic high-temperature alloy to eutectic chloride melts with possible consequences for inhibitor strategies
- 2023
-
Ingår i: Engineering Failure Analysis. - 1350-6307. ; 150
-
Tidskriftsartikel (refereegranskat)abstract
- There is an inevitable difference between direct and indirect contact of metals with eutectic chloride melts defined by the gas phase impurity content, here, humidity and oxygen in argon. The impurities-to-salt ratio will always be higher in the gas phase allowing for a more aggressive attack on metal components. This effect has been studied on a decommissioned metal container from an experimental high-temperature setup, which has never been in direct contact with a chloride melt but with its evaporated species; the vessel lasted only a short time, 700 h. It was found that the vessel suffered more severe damage when exposed to evaporated salt species than in direct contact with the salt melt; the estimated metal thickness loss per year is higher by almost three-fold than the direct contact. In contrast to 253MA fully immersed in MgCl2-KCl, magnesium has not been the most-active cationic species causing corrosion in the vessel wall exposed to evaporated salt species; instead, it has been potassium. Consequently, this unexpected observation needs to be carefully considered in the design of a Gen3-CSP storage tank and the applied inhibitor strategy.
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| 18. |
- Mohamedin, Esraa Hamdy, 1991, et al.
(författare)
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Evaporated Alkali Carbonate Effect on an Aluminum Diffusion Coated 253MA Vessel after 4000 h Discontinuous Operation— Lessons Learned
- 2022
-
Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 15:9
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Tidskriftsartikel (refereegranskat)abstract
- A vessel of a laboratory setup for hosting molten alkali carbonate immersion experiments was recently decommissioned after about 4000 h discontinuous operation at 800 °C. In this article, we want to describe the long‐term damage of the vessel caused by evaporated alkali carbonate spe-cies in a carbon dioxide gas environment. The vessel is made of alloy 253MA and coated by an aluminum powder pack diffusion process. The degree of material loss and internal degradation did not correlate with the temperature profile across the vessel but rather with the vicinity to the gas and salt evaporation source. One millimeter of the vessel’s initial 5 mm wall thickness was com-pletely consumed at the strongest attacked location plus another 800 μm of internal attack beneath the metal–oxide interface.
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| 19. |
- Mohamedin, Esraa Hamdy, 1991, et al.
(författare)
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Perspectives on selected alloys in contact with eutectic melts for thermal storage: Nitrates, carbonates and chlorides
- 2021
-
Ingår i: Solar Energy. - : Elsevier BV. - 0038-092X. ; 224, s. 1210-1221
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Tidskriftsartikel (refereegranskat)abstract
- Increasing the operating temperature of molten salt-based concentrated solar power plants is of paramount importance to enable next-generation gas turbines and an overall increase in power conversion efficiency. The issue is how to mitigate the degradation of necessary metallic components in highly corrosive salt environments. In this study, three eutectic salt mixture candidates, nitrates, carbonates, and chlorides, are brought into contact with stainless steel (316H or 304L) and the FeCrAl alloy Kanthal® APMT. The post-exposure analysis is discussed in terms of the overall performance of each alloy as concerns mass change, scale growth, internal attack, and leaching. Significant reduction of corrosion is realised through the ability of Kanthal® APMT to form aluminium oxide species at the surface in contact with alkali nitrates and carbonates. On the other hand, aluminium is leached most efficiently in contact with chlorides, which causes a deeper attack on Kanthal® APMT than alloy 304L. The overall conclusion is that only by employing a holistic perspective on all individual measurements can a long-term performance estimation be formulated.
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| 20. |
- Mohamedin, Esraa Hamdy, 1991, et al.
(författare)
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Superior protection by α-Al2O3/α-LiAlO2 double oxide scales against alkali carbonate corrosion
- 2023
-
Ingår i: Corrosion Science. - 0010-938X. ; 218
-
Tidskriftsartikel (refereegranskat)abstract
- Ferritic alumina-forming alloys showed high corrosion resistance to molten carbonates by forming a protective α-LiAlO2 scale at their surface. In this work, four ferritic alumina-forming alloys were pre-oxidised before exposure to (Li,Na,K)2CO3-melt at 800 °C for 1000 h. Only outer transient alumina, such as γ-alumina, reacts with the melt, forming LiAlO2. At the same time, the innermost α-Al2O3 scale remains intact. α-Al2O3, as well as α-LiAlO2, are slow-growing compressive stress-stabilised oxide scales. Thus, the combined presence of α-Al2O3/α-LiAlO2 improves the corrosion protection of materials investigated in this study, compared to non-pre-oxidised ones, by forming a superior double oxide scale.
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| 21. |
- Mortazavi, A. N., et al.
(författare)
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Exploring failure modes of alumina scales on FeCrAl and FeNiCrAl alloys in a nitriding environment
- 2020
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454. ; 201, s. 131-146
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Tidskriftsartikel (refereegranskat)abstract
- Two high-temperature FeCrAl and FeNiCrAl alloys were exposed in a strongly nitriding environment at 900 °C and the morphology of nitridation was studied. Quasi-in-situ experiments revealed that nitridation started at specific surface sites directly related to the alloy microstructure where the alumina scale was permeable to nitrogen. FeCrAl alloy grains with (112) orientation formed outward-growing alumina scales and were susceptible to nitridation. Outward-growing scales and substrate nitridation was also observed at chromium carbide precipitates in the FeNiCrAl alloy. Both alloys suffered nitridation at reactive element-rich (Y and Zr) inclusions larger than a certain critical size. The latter type of attack is caused by cracks and pores in the scale. The findings open new avenues of research for developing the next generation of high temperature alloys with superior properties.
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| 22. |
- Mortazavi Seyedeh, Nooshin, 1986, et al.
(författare)
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Interplay of water and reactive elements in oxidation of alumina-forming alloys
- 2018
-
Ingår i: Nature Materials. - : Springer Science and Business Media LLC. - 1476-4660 .- 1476-1122. ; 17:7, s. 610-617
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature alloys are crucial to many important technologies that underpin our civilization. All these materials rely on forming an external oxide layer (scale) for corrosion protection. Despite decades of research on oxide scale growth, many open questions remain, including the crucial role of the so-called reactive elements and water. Here, we reveal the hitherto unknown interplay between reactive elements and water during alumina scale growth, causing a metastable ‘messy’ nano-structured alumina layer to form. We propose that reactive-element-decorated, hydroxylated interfaces between alumina nanograins enable water to access an inner cathode in the bottom of the scale, at odds with the established scale growth scenario. As evidence, hydride-nanodomains and reactive element/hydrogen (deuterium) co-variation are observed in the alumina scale. The defectrich alumina subsequently recrystallizes to form a protective scale. First-principles modelling is also performed to validate the RE effect. Our findings open up promising avenues in oxidation research and suggest ways to improve alloy properties.
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| 23. |
- Tari, Dogac, 1995, et al.
(författare)
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Reaction Capsule Design for Interaction of Heavy Liquid Metal Coolant, Fuel Cladding, and Simulated JOG Phase at Accident Conditions
- 2024
-
Ingår i: JOURNAL OF NUCLEAR ENGINEERING. - 2673-4362. ; 5:1, s. 57-73
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Tidskriftsartikel (refereegranskat)abstract
- High temperature corrosion of fuel cladding material (15-15Ti) in high burn-up situations has been an important topic for molten metal-cooled Gen-IV reactors. The present study aims to investigate the simultaneous impact of liquid lead (coolant side) and cesium molybdate (fuel side) on the cladding tube material. A capsule was designed and built for experiments between 600 degrees C and 1000 degrees C. In order to simulate a cladding breach scenario, a notch design on the cladding tube was investigated pre- and postexposure. Material thinning by corrosion and leaching at temperatures >= 900 degrees C caused breaches at the notches after 168 h exposure. The temperature dependent cladding thinning phenomenon was used for kinetic interpretation. As the first of a two-part study, this paper will focus on the exposure capsule performance, including metallographic cross-section preparation and preliminary results on the interface chemistry.
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| 24. |
- Ulrich, Anke S., et al.
(författare)
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Pt accelerated coarsening of A15 precipitates in Cr-Si alloys
- 2022
-
Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- The effect of alloying Cr-rich Cr-Si alloys with Pt was investigated by a combination of complementary experimental methods and atomic scale modelling. The investigated Cr-Si and Cr-Si-Pt (Cr ⩾86 at.%) alloys developed a two-phase microstructure consisting of Cr solid solution (Crss) matrix and strengthened by A15 precipitates during annealing at 1200°C. It was found that additions of 2 at.% Pt increase the coarsening rate by almost five times considering annealing times up to 522 h. Pt was found to change the precipitate matrix orientation relationship, despite its low influence on the Crss matrix/A15 precipitate misfit. Through this experimental and modelling approach new insight has been gained into mechanisms of enhanced coarsening by Pt addition. The increased coarsening is principally attributed to a change in interface composition and structure resulting in different thermodynamic stabilities: Pt-containing A15 phase was found to have a broader compositional range if both elements, Pt and Si, are present compared to only Si. Additionally, the Crss phase was found to have a higher solubility of Pt and Si over just Si. Both factors additionally facilitated Ostwald ripening.
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