High Temperature Steam Oxidation Research Articles

Mechanical and high-temperature steam oxidation properties of Cr coatings deposited via high-power impulse magnetron sputtering

Applying protective coatings to Zr alloy cladding surfaces is one of the better methods to design fuel tolerant materials. In this study, the surface of a Zr-4 alloy was coated with Cr using high-power impulse magnetron sputtering. Furthermore, the mechanisms by which bias voltages affect the mechanical characteristics, resistance to high-temperature steam oxidation, and coating structure were elucidated. The coating exhibits a strong (200) weave structure with coarse grains at a bias voltage of -100 V. With increasing bias, the energy of deposited particles increases, grains continue to grow, (200) preferential growth orientation disappears, and the coating exhibits a (110) crystal orientation. The growth structure of the coating first shows a tendency to be dense and then loose. For the Cr coating with a (200) crystal orientation, a dense oxide layer is preferentially formed after oxidation, which can effectively block the internal diffusion of O. With increasing oxidation time, coarse Cr grains can effectively block the external diffusion of Zr. Furthermore, the Cr coating exhibiting a (110) crystal orientation was severely oxidized after oxidation, resulting in the formation of cracks at the film base; this accelerated the outward diffusion of Zr.

Fuel performance modelling of Cr-coated Zircaloy cladding under DBA/LOCA conditions

Chromium coatings are being developed for advanced technology fuel (ATF) claddings, offering negligible corrosion during normal operation, improved resistance to high-temperature steam oxidation, and superior high-temperature strength, the latter two being of utmost relevance during design basis accidents (DBAs). Demonstrating the improved response of Cr-coated Zircaloy requires the development or extension of fuel performance codes to coating simulations.In this work, material models and correlations for Cr-coated Zircaloy cladding have been derived or obtained from the literature and implemented into TRANSURANUS and the FRAPTRAN-TUmech suite. These extended tools have been used to simulate two complementary LOCA tests: QUENCH-L1 rod 4 (out-of-pile bundle test on fresh Zircaloy cladding) and IFA-650.10 (in-pile single rod test on high-burnup Zircaloy-UO2 fuel), enabling a gradual cross-verification of results between codes and a comparative performance analysis between coated and uncoated cladding.The results indicate negligible impact of coating properties other than creep on the burst time. While the superior high-temperature creep resistance of coated cladding slightly delays the burst time, additional burst data would be necessary to draw sound conclusions on the balloon size. Regarding the modelling approach, treating the coated cladding as a composite material through the definition of effective properties might result in worse performance relative to uncoated cladding, contradicting experimental observations. Therefore, the separate modelling of the coating and the cladding is recommended.

Steam oxidation of thermally deposited coatings from 304 L and recycled 316 L/Z100 steels: Influence of temperature, coatings microstructure and steel recycling

The application of thermally sprayed stainless steels coatings is a well-established approach to protecting low-alloy steels against high-temperature degradation. In this study, we investigated both: (1) the influence of microstructural features of the coatings and (2) the recycling of stainless steels on the course of high temperature steam oxidation. It was achieved by thermally spraying coatings on C45 steel from 304 L and a new type of 316 L/Z100 steel, obtained as a result of mixed scraps recycling. Steam oxidation tests carried out in the temperature range 600–800 °C for 500 h in pure steam show temperature depended mechanism of oxidation, which was defined and described. The formation of the scales with a multi-layered structure was observed, consisting of Fe2O3, Fe3O4, Cr2O3, Fe- or Cr-rich CrxFex-2O3 and (Mn,Cr,Ni)xFe3-xO4 spinels. The relative ratio of the phases and their presence in particular scale layers varied depending on the material studied and the exposure temperature. The key findings are that recycling of steel deposited as protective coating has led to an unintended change in Si and C concentrations, which may affects course of oxidation. Also, the microstructure of the initial coatings, consisting of porosity and a significant volume of oxides formed during steel deposition, inhibits the formation of a homogeneous layer of protective Cr2O3. As a result, the established values of oxidation kinetics constants (in range of 8.55E-12 to 1.50E-10 g3·cm−6·s−1 for 316 L/Z100 and 2,71E-12 to 4.60E-10 g3·cm−6·s−1 for 304 L coatings) and oxidation activation energies (156.4 kJ·mol−1 for 316 L/Z100 and 211.5 kJ·mol−1 for 304 L coatings) differ significantly from those of bulk steels under the same conditions reported in the literature.

Effect of surface treatment on oxidation film of 55SiCr spring steel wire

Abstract In this work, the surface pretreatments of 55SiCr spring steel wire rods were conducted using shot blasting and phosphating. After drawing, the steel wire was heated at 950°C × 15 s, followed by oxidation treatment with high-temperature steam or air for 3 seconds, and tempering treatment at 520°C. The effects of different surface treatment methods on the surface oxide film of spring steel wire were studied using stereomicroscopy, SEM, EDS, and XRD. The results showed that the steel wire surface oxide film with phosphating pretreatment was thicker and easy to fall off. The thickness of the oxide film formed by phosphating pretreatment samples increased by 2.1 um (high-temperature steam) and 0.3 um (air) compared to the shot-blasting samples under different oxidation atmospheres. High-temperature steam oxidation treatment significantly increased the thickness of the oxide film by 0.65 um (shot blasting) and 2.45 um (phosphating) under different surface pretreatment conditions. The outer surface of the oxide film turned black with high-temperature steam oxidation treatment and turned yellowish brown with air oxidation treatment. By both above oxidation treatments, the oxide film showed a multilayer structure, with enrichment of Cr and Si on the inner side.

Exploring the impact of microstructure refinement on high temperature steam oxidation behavior of FeCrAl alloy

Microstructure refinement is an effective way to improve the mechanical properties and radiation resistance of FeCrAl alloy, which may also increase the susceptibility to high temperature steam oxidation (HTSO) due to the increased surface chemical activity. To investigate the microstructural effects on the HTSO behavior, a FeCrAl alloy was subjected to controlled annealing strategies to produce three types of microstructures: “fine sub-grains + fine precipitates”, “coarse grains + fine precipitates” and “coarse grains + coarse precipitates”. The three alloys were exposed to high temperature steam during a heating and holding procedure. Large oxide nodules and rough multilayer-structured oxide films were formed during heating, which subsequently evolved into a single α-Al2O3 layer during the isothermal oxidation. Microstructure refinement can promote the oxidation and slightly increase the weight gain. However, the variation of isothermal oxidation parabolic rate constants brought by the microstructure refinement is 1-2 orders of magnitude lower than that brought by alloying. Microstructure refinement can improve other service performance of FeCrAl alloy without significantly deteriorating the HTSO resistance, indicating its advantages for engineering applications.

High-Temperature Steam Oxidation Behavior of VDM Alloy 699 XA Produced by Laser Powder Bed Fusion

AbstractVDM alloy (AM) 699 XA (AM-XA) produced by laser powder bed fusion (LPBF) was subjected to steam oxidation at different high temperatures. Initial studies on mass gain of AM-XA at 650 °C after 500 hours revealed insignificant changes. Typical to high temperatures, a wide range of oxides were obtained at 750 and 950 °C associated with mass gain. To fully understand AM-XA material behavior at high temperatures, hot-rolled 699 XA (HR-XA) was also fabricated and tested under similar conditions. At 750 °C, HR-XA showed a higher mass gain in comparison with AM-XA, whereas at 950 °C mass gain of AM-XA overtook HR-XA. This anomalous behavior was related mostly to carbide formation. In-depth anomalous behavior of AM-XA is explained by investigating the microstructure and phase composition of the oxidation products formed.

High Temperature Air and Steam Oxidation and Fireside Corrosion Behavior of 304HCu Stainless Steel: Dichotomous Role of Grain Boundary Engineering

High Temperature Air and Steam Oxidation and Fireside Corrosion Behavior of 304HCu Stainless Steel: Dichotomous Role of Grain Boundary Engineering

Effects of nitrogen content on the phase composition and high-temperature steam oxidation resistance of Cr0.5Al0.5Nx (x = 0.33, 0.81, 1.23) coatings on Zry-4 alloy

Cr0.5Al0.5Nx (x = 0.33, 0.81, 1.23) coatings were deposited on Zry-4 alloy using magnetron reaction sputtering technique to investigate their application as accident-tolerant fuel materials. The effects of nitrogen (N) content on the phase composition and high-temperature steam oxidation resistance of the coatings were systematically investigated. With the increasing N content, the phase composition of the coatings is mainly transformed from Cr(Al) to the cubic-CrAlN phase, which may be due to the formation of a greater number of CrN bonds and AlN bonds. The high-N content of the Cr0.5Al0.5Nx coating can significantly enhance the high-temperature steam oxidation resistance of zirconium alloy. Compared to the bare Zr alloy, the weight gain oxidation of the Cr0.5Al0.5N1.23 coating is reduced by 45 % after oxidation at 1200 °C for 1 h. The oxide layer thickness of the bare Zry-4 alloy is as high as 350 μm, while the oxide layer thickness of the Cr0.5Al0.5N1.23 coating is only about 12 μm. The complex oxide layer structure and an internal continuous Al2O3 layer are formed, effectively preventing the inward diffusion of O2−. In addition, with the increase of N content in the coatings, the degree of interdiffusion between the coating and the substrate is weakened. The formation of α-Zr(N) layer in the Cr0.5Al0.5N1.23 coating significantly inhibits the interdiffusion between the coating and the substrate.

A thermogravimetric comparative study of the high temperature steam oxidation of bare and pre-oxidized Zircaloy-4, M5Framatome and Optimized ZIRLO™

For Loss of Coolant Accident (LOCA) analysis, high-temperature oxidation kinetics in steam of Zircaloy-4 and the two Nb-bearing alloys used in French Pressurized Water Reactors (PWRs), M5Framatome11M5 and M5Framatome are trademarks or registered trademarks of Framatome or its affiliates, in the USA or other countries. and Optimized ZIRLO™22Optimized ZIRLO is a trademark or registered trademark of Westinghouse Electric Company LLC, its affiliates and/or its subsidiaries in the United States and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited. Other names may be trademarks of their respective owners., have been studied using Thermo-Gravimetric Analysis (TGA) technique in the temperature range of 900–1200 °C. A specific test procedure allowing the use of a high steam flow rate and good steam supply to the whole specimen surface, as well as fast heating of the specimen, has been developed. Clean kinetic data, not affected by steam starvation, were obtained on the bare, as-received alloys. For as-received claddings, oxidation kinetics are comparable and close to parabolic for the three alloys at 1100 °C and above. Below 1100 °C, a significant deviation from the parabolic kinetic regime was observed, and M5 Framatome oxidizes slower than Zircaloy-4 and Optimized ZIRLO. Thanks to the fast-heating protocol, the influence of pre-oxidation, simulating corrosion in normal reactor operation, could be investigated, avoiding evolution of the pre-oxidation scale during a slow, long heating phase. Pre-oxidized Zircaloy-4 and M5 Framatome were investigated. A strong protective effect is observed below 1200 °C, while at 1200 °C, the pre-oxidation layer appears to be much less protective, possibly due to the monoclinic to tetragonal zirconia phase transformation.

Reflood oxidation performances of Cr-coated Zr-Sn-Nb alloy cladding tubes at 1000 °C∼1200 °C

Reflood plays an important role in preventing the serious accident process. In this paper, the reflood oxidation performances of Cr-coated Zr-Sn-Nb alloy cladding tubes at 1000 °C, 1100 °C and 1200 °C were studied by high-temperature steam oxidation followed by in-situ water quenching. The oxidation kinetics, macroscopic morphology, phase transformation and microstructural evolution were investigated. Cr coating can provide excellent anti-reflood oxidation protection for Zr-Sn-Nb alloy, resulting in an oxidation rate constant of only 1/4–1/7 of that of uncoated Zr-Sn-Nb alloys. However, the cladding tube degraded into fragments due to excessive thermal stress during the in-situ water quenching after reflood oxidation at 1200 °C for 4000 s. After reflood oxidation at 1000 °C and 1100 °C, the most prominent feature of the surface is a porous flocculation structure main due to the formation of volatile products, while after 1200 °C, it is a fine mackerel scale-like structure accompanied by protruding whiskers main owing to Cr3+ rapidly migrates outward to the outer surface via short circuit paths. After oxidation, the cross-section of Cr-coated Zr-Sn-Nb alloys exhibits a multi-layer structure. The thickness of each layer changes approximately linearly with oxidation time. However, due to the redox reaction, compared to that after oxidation for 2000s, the Cr2O3 layer becomes thinner and the residual Cr coating becomes thicker after oxidation at 1200 °C for 4000 s.

Microstructural characteristics of multilayers and interfaces of Cr-coated Zircaloy-4 cladding based on elemental diffusion under high-temperature steam oxidation

A dense and well-adhered Cr coating was prepared on the surface of Zircaloy-4 cladding by arc ion plating. Oxidation tests on Cr-coated Zircaloy-4 claddings were conducted in steam at 700-1300 °C. The surface morphology and cross-sectional microstructure were investigated using SEM, EBSD, FIB and TEM techniques. The results showed that no significant cracking or spalling was observed after oxidation. The oxidized cross-sections showed characteristics of multilayers and interfaces. From the outer to the inner layer, these are, in order, a Cr oxide film and Sn precipitates on its grain boundaries, an amorphous structural layer, a residual Cr coating and (Zr,Cr)xOy oxides on its grain boundaries, a C15-type Zr(Cr,Fe)2 intermediate layer, and a (Cr,O)-rich substrate Zr. The multilayers and interfaces alter the oxygen diffusion path and reduce the oxygen diffusion rate, thus slowing down the oxidation process of the substrate. In addition, the location and cause of amorphous structures and Kirkendall cavities and their effect on microstructure and adhesion properties were discussed.

Effects of Al and Si elements on oxidation behavior in 1000–1200 °C steam for PEO/CrAlSi composite coating on Zr alloy

A PEO/CrAlSi composite coating of ~10 μm thick on Zr–2 alloy was prepared by duplex plasma electrolytic oxidation (PEO) and filtered cathode vacuum arc deposition (FCVAD) techniques. The high temperature steam oxidation behavior of bare and PEO/CrAlSi–coated Zr alloys was performed in 1000–1200 °C. Their morphologies, microstructures, compositions and phase components were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X–ray diffraction (XRD) and glow discharge optical emission spectrometer (GDOES). The effects of Al and Si elements on multilayers microstructure evolution of coated Zr–2 alloy at steam atmosphere were discussed. It was found that the composite coating significantly improved the high–temperature steam oxidation resistance of Zr–2 alloy. The mass gains of the PEO/CrAlSi–coated Zr–2 alloy after 3600 s exposure in 1000 °C, 1100 °C and 1200 °C steam were 28 %, 29 % and 44 % of the bare alloy. Through the oxidations, Al diffused both inward and outward to the substrate and the surface regions, respectively. Formation of a top oxide layer (Al2O3, Cr2O3) greatly suppressed the inward oxygen diffusion. The Si enrichment in the PEO interlayer formed a Zr2Si layer, which inhibited the Cr-Zr interdiffusion at 1000 °C and 1100 °C. At 1200 °C, the Zr2Si layer was oxidized and the CrZr2 phase was formed in the Zr alloy substrate especially at the β–Zr/α–Zr(O) interface.

Oxidation resistance of Mo/Cr bilayer coating on Zr alloy in a 1200 °C steam environment

The Cr-coated Zr alloys demonstrate excellent resistance to high-temperature steam oxidation. However, the rapid diffusion pathways for oxygen formed by the inter-diffusion between the coating and alloy at high temperatures significantly affect the steam oxidation resistance of the coated alloys. To address this issue, we developed a Mo/Cr bilayer coating on Zr alloy by a combination of dc-MS and HiPIMS surface treatments. The coating exhibits outstanding steam oxidation resistance at high temperatures, resulting in a mass gain approximately 86.6% and 44.1% lower than that of the bare Zr alloy and Cr coating, respectively, after 30 min of steam oxidation at 1200 °C. This is mainly because, during the oxidation process, the Mo interface layer undergoes a transformation into a thin and high-quality double diffusion layer structure, effectively avoiding high-temperature inter-diffusion between the Cr coating and Zr alloy, thereby inhibiting the formation of oxygen diffusion pathways.

High-temperature steam oxidation experiment of molten zirconium alloy

In this study, we investigate the steam oxidation behaviors of molten zirconium alloy at exceptionally high temperatures of 1870 ℃ and 1970 ℃. A specialized high-temperature steam oxidation apparatus was established to conduct the steam oxidation experiment. The experiments yielded crucial data including oxidation weight gain results, macroscopic appearance of the oxide surface, and section morphology. Several new phenomena: α-Zr(O) precipitates and two-layer oxide structure, were observed in this study. Based on these observations, a complete mechanism of molten zirconium oxidation in steam was developed, providing an interpretive framework for the oxidation observed in this experiment. This newly proposed mechanism reevaluates the formation process of nonceramic precipitates in the molten bulk and its consequential impact on oxidation kinetics at temperatures below 2000 ℃.

High-temperature steam oxidation behavior and failure mechanisms of Al alloyed Cr coatings on Zr-4 alloy

In this work, the Al content-dependent microstructure evolution and oxidation behavior of co-sputtered CrAl alloyed coatings on Zr-4 alloy were systematically investigated in 1000 ℃ steam. Experimental results demonstrated that the microstructure of generated oxide scale transformed from a Cr2O3 oxide layer with embedding discrete α-Al2O3 particles at low Al contents to a continuous outer (α, θ)-Al2O3 and inner Cr2O3 bi-oxide layer at high Al contents. However, there appeared a unique eutectoid-like Cr2O3/α-Al2O3 multilayered oxide scale in Cr-18.3Al coating, which conferred the sample with optimal oxidation resistance. The underlying oxidation mechanisms were rationalized by revealing the Al content dominated selective oxidation behavior.

High-Temperature Steam and Atmospheric Oxidation Characteristic of a Heat-Resistant SP2215 Steel

The high-temperature oxidation performance of SP2215 has become an important issue when they were used as superheaters and reheaters exposed to two different high-temperature environments. In this study, the oxidation behavior of SP2215 steel was investigated under steam and an atmosphere of 650–800 °C for 240 h. The microstructural and chemical characterization of the samples were performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), a glow discharge optical emission spectrometer (GD-OES), and atomic force microscope (AFM). The kinetic curves of oxidation revealed excellent oxidation resistance under both environments, but significant different oxidation characteristics, oxide film composition, and structure were obvious. In the steam experiment, selective intergranular oxidation was evident at relatively low temperatures, which was attributed to the preference absorption of supercritical water molecules at the grain boundary. Conversely, a double-layer structure of outer Fe2O3 and a small amount of Fe3O4 and inner Cr2O3 was formed uniformly at 800 °C. In the high-temperature atmosphere experiment, a protective chromium film was dominant at 650–700 °C, and a loose multicomponent oxide film was formed at 750–800 °C, primarily consisting of Cr2O3, spinel FeCr2O4, and CuO.

Steam oxidation properties of graphene reinforced bioinspired laminated CoCrFeNiMn high-entropy alloy matrix composites at 1000 ℃

Laminated CoCrFeNiMn high-entropy alloy (HEA) matrix composites reinforced with 1.0 wt% graphene nanoplatelets (GNPs) were fabricated by mechanical ball milling and flake powder metallurgy, and were isothermal oxidized at 1000 ℃ for 100 h. Vacuum hot-pressure sintering (VHPS) shows a distinct nacre structure with the microstructure composed of FCC matrix phase, Cr23C6, CrMn1.5O4 precipitated phases, numerous dislocations and twins. High-temperature oxidation tests showed that the composites had mass gains at 12 h intervals from 12 to 100 h respectively. The oxidation kinetic curve changes from a linear pattern in the early stages to an exponential pattern in the later stages, which demonstrates better long-term oxidation resistance. The anisotropy of the laminated structure results in excellent resistance to high-temperature steam oxidation in the vertical lamellar direction. Observation of the cross-section reveals that although Cr2O3 (inner layer) is present, (Mn, Cr)3O4 and Mn3O4 are the dominant oxides (outer layer). Elemental depletion zones for Mn and Cr exist in the region of the matrix near the oxide scales. The results show that the oxidation resistance of the laminated GNPs/CoCrFeNiMn composites is mainly influenced by the diffusion of Mn and Cr elements, the microstructure of the laminations and the internal oxidation.

High-temperature steam oxidation study of irradiated FeCrAl defueled specimens

Post irradiation examinations (PIE) were performed on irradiated iron-chromium-aluminum (FeCrAl) specimens. These FeCrAl specimens were fabricated at the US Department of Energy's Oak Ridge National Laboratory (ORNL). The experimental setup involved subjecting FeCrAl cladding, along with UO2 pellets, to irradiation in the Idaho National Laboratory Advanced Test Reactor (ATR). In parallel, the FeCrAl alloy tubing without UO2 pellets was irradiated at ORNL's High Flux Isotope Reactor (HFIR). After irradiation, the ATR-irradiated rodlet was transported to an ORNL hot cell, where it was sectioned into multiple samples for the PIE and severe-accident testing. The sectioning process revealed that the fuel was not bonded to the cladding and could be easily detached from sectioned cladding slices. Microstructural analysis of the fuel cross sections demonstrated no significant interaction between the fuel and the cladding. Additionally, high-temperature steam oxidation tests on defueled cladding segments showed minimal oxygen uptake even at 1200 °C. The ATR-irradiated specimens began to exhibit signs of enhanced oxidation upon reaching a temperature of 1300 °C. Furthermore, enhanced oxidation was observed on the inner surface of the ATR-irradiated FeCrAl specimen, which had been subjected to 1300 °C for a duration of 1 min. By contrast, high-temperature steam oxidation experiments indicated that the HFIR-irradiated FeCrAl cladding provided good thermal stability when exposed to 1300 °C for up to 4 h. Comparative analysis encompassing the oxidation behavior of the ATR-irradiated fueled FeCrAl, HFIR-irradiated unfueled FeCrAl, and unirradiated FeCrAl suggests that the fuel–cladding interaction, although not visible via standard microscale electron microscopy measurements, may accelerate the deterioration of FeCrAl cladding in beyond-design-basis accident scenarios.

Microstructure, high-temperature corrosion resistance and oxidation properties of (TiVZrCrAl)N high entropy nitride coatings with different N2/Ar ratios

The (TiVZrCrAl)N high-entropy nitride coatings were prepared on Zr-4 alloy substrates by reactive magnetron sputtering with different N2/Ar pressure ratios I values. The microstructure, nanohardness, high-temperature corrosion and steam oxidation resistance properties of the coatings were investigated. The results showed that the thickness of the coating first decreaseds and then increaseds with decreasing N2/Ar pressure ratio, but the hardness first increaseds and then decreaseds. All the coatings exhibited B1-NaCl structure. When I = 1/12, the (TiVZrCrAl)N coating had excellent high-temperature corrosion resistance and steam oxidation performance. The high-temperature steam oxidation mechanisms of the (TiVZrCrAl)N coatings were analyzed in detail.

Effect of grain refinement on high temperature steam oxidation of an FeCrAl alloy

FeCrAl alloys are promising candidates to replace Zr alloys as fuel cladding materials in nuclear light-water reactors. Grain refinement has been indicated to improve irradiation resistance. To enhance corrosion resistance as well, the effects of grain refinement on steam corrosion behavior were investigated in this work. Samples of Kanthal D alloy (Fe-21Cr-5Al) with two different grain sizes (coarse-grained and ultrafine-grained) were exposed to steam at 1200 °C for 2 hrs. Results indicate improved steam corrosion resistance in ultrafine-grained Kanthal D with formation of a thinner protective Al oxide layer and the presence of a thin underlying Cr oxide layer.