Oxidation of Metals最新文献

The performance of solid oxide electrolyzer cells (SOEC) can be improved through the development of coatings applied to the surface of ferritic steel interconnects in view of mitigating chromium evaporation and reducing the growth rate of low conductive oxides in oxidizing environments. This work investigated the oxidation and area specific resistance (ASR) of two electrodeposited nickel coatings on preoxidized and non-preoxidized AISI 441 ferritic stainless steel substrates. The nickel coating effectively restricted the outward diffusion of chromium after 100 h of exposure at 700 °C in air but led to nickel/iron interdiffusion between the substrate and coating forming an iron-nickel-rich spinel on the surface, with NiO underneath and Cr₂O₃ at the coating-substrate interface and at the coating grain boundaries. The application of a LSM ((La_0.80Sr_0.20)_0.95MnO_3−x) coating on top of the Ni electrodeposited coatings resulted in the same type of oxides but the oxidation kinetics were slower. Interdiffusion continued with the exposure at 700 °C for 2400 h resulting in the growth of a thick iron-rich oxide layer on top of Cr₂O₃, steadily raising the interconnect ASR to 25 mΩ cm². The addition of a preoxidation step before the electrodeposit of nickel helped to limit iron-nickel interdiffusion, leading to the formation of a thicker NiO layer on a Cr₂O₃ layer between substrate and coating. While the ASR was higher than without preoxidation at the beginning of the test, it stabilized at about 33 mΩ cm² after 1750 h. Despite displaying a higher electrical resistance, the coatings effectively limited the outward chromium diffusion throughout exposure compared to the bare substrate.

As part of advancing oxygen–hydrogen combustion power generation technology, a study was carried out to evaluate the oxidation behavior of a novel developed Ni–Cr–W alloy as the structural material candidate. Tungsten is utilized in the alloy as a solid solution-strengthened element and as an α₂-W precipitate former. The examination involved exposing the developed alloy and commercial alloys, Hastelloy X and Nimonic 263, to air and steam environments at 1273 K. The results show a different oxidation behavior of the developed alloy. Considering the air oxidation kinetics, the performance of the developed alloy was on par with that of Hastelloy X and superior to Nimonic 263. A single outer chromia scale was established with an intergranular oxide. Whereas steam exposure resulted in the formation of outer and inner chromia scales with a deeper intergranular oxide penetration. Thicker chromia formation with a lower mass gain indicates the evaporation of chromia under a steam atmosphere.

A study on the effect of bond coating (BC) surface modifications prior to ceramic deposition is presented. Grit blasting and polishing were used to modify the BC surface finish. Thermal barrier coating (TBC) systems were made of a commercial yttria-stabilized zirconia (YSZ) deposited by electron beam physical vapor deposition on a β-(Ni,Pt)Al-coated Ni-based single crystal superalloy. Surface roughness measurements and scanning electron microscopy observations, before and after thermal cycling at 1100 °C, were performed to investigate the influence of the initial surface treatment on the YSZ/BC interface morphology and top coat spallation resistance. Surface states enhancing TBC spallation resistance have been found. In particular, it is shown that rumpling can be avoided even in the presence of phase transformations in the BC, by grinding samples with P600 SiC paper or by applying an “heavy” grit blasting leading to a thinner BC.

To address the significant commercial interest in fusion energy, it will be necessary to accelerate the compatibility research associated with liquid breeders including Li, eutectic Pb–Li and LiF-BeF₂ (FLiBe) molten salt. Particularly for FLiBe, compatibility understanding is limited especially for fusion relevant materials such as reduced activation ferritic-martensitic steels, SiC and V alloys. The historical knowledge associated with molten salt reactors (MSRs) and recent work to commercialize MSRs can benefit fusion research. Recent experimental and modeling work has improved understanding and this knowledge can be applied to fusion relevant materials. For liquid metals (LMs), the comparisons to Li and Pb–Li are less direct but nevertheless can help guide the pathway toward commercialization. For Pb–Li, Al-rich coatings have been shown to inhibit dissolution and potentially increase operating temperatures. For commercialization, the experience with sensors and on-line cleanup can help guide future developments. Thus, it is worth considering the potential for fission-related research with LMs and molten salts to help accelerate fusion research.

The oxidation of a titanium (Ti)-modified Mo-Si-B alloy designed for aerospace applications was investigated. Test samples were produced using arc melting and laser powder bed fusion (LPBF) additive manufacturing methods. To address high-temperature oxidation, a three-step coating strategy was employed, comprising a Mo precoat, Si and B co-deposition, and a conditioning step for the formation of a self-healing coating. The study evaluates the oxidation resistance of both uncoated and coated Mo-Si-B-Ti alloys at temperatures ranging from 1100 to 1300 °C. Uncoated alloys exhibited catastrophic mass loss within 10 hours at temperatures between 800 and 1300 °C. In contrast, the coated samples demonstrated minimal mass loss at 1300 °C after 50 hours, with only minor mass gain observed under cyclic thermal loading after 300 cycles. Microstructural analysis revealed distinct differences between arc-melted and LPBF samples, with the latter displaying an ultrafine dendritic microstructure. The applied coating effectively prevented oxygen diffusion into the substrate, even at elevated temperatures, showcasing its protective capabilities. During cyclic tests, the coating exhibited a self-healing mechanism, with cracks filled with borosilica contributing to prolonged environmental resistance.

Graphical Abstract

The objective of this study was to investigate the oxidation resistance and area specific resistance at high temperature of Ni/Co–W and Cu/Co–W electroplated type 445 stainless steels using co-electrodeposition. Coated samples were exposed to oxidation at a high temperatures 800 °C in air containing 3 vol.% water vapour for 96 h. X-ray diffraction analysis revealed that the oxidation process resulted in the formation of CoWO₄ and Co₃O₄ on the Ni/Co–W sample, and CoWO₄, Co₃O₄, CuWO₄ and CoCr₂O₄ on the Cu/Co–W sample. The Ni/Co–W coated sample effectively suppressed the outward diffusion of chromium. The Cu/Co–W coated sample exhibited a higher oxidation rate than the Ni/Co–W coated sample. The oxidation kinetics of the coated samples obeyed the parabolic rate law. The Cu/Co–W coated sample exhibited a lower area specific resistance compared to the Ni/Co–W coated sample.

The oxidation of δ-stabilized plutonium alloy was studied under dry oxygen exposures for temperatures varying from 100 up to 300 °C and oxygen partial pressures varying from 10^–4 up to 500 mbar. The coupling of X-ray diffraction, Raman spectroscopy and FIB-SEM has allowed to show that the oxide scale is composed of an outer layer of PuO₂ and an inner mixed layer of α + β-Pu₂O₃ platelets propagating into a metallic zone corresponding to the stable phase of unalloyed Pu. Furthermore, the analysis of Pu oxidation kinetics has displayed first a parabolic growth governed by the diffusion of interstitial oxygen. This step consists of the thickening of the Pu₂O₃ layer with a decrease in α-Pu₂O₃ ratio in favor of β-Pu₂O₃. Then, a second step occurs consisting of a linear growth of the PuO₂-layer with the formation of thick nodules which tend to cover the whole oxide surface. Based on the results of this work, a general oxidation mechanism for δ-Pu alloy is provided.

Understanding of the hot corrosion behavior of each constitutive phase of the new Pt-enriched γ/γ′ nickel-based single-crystal TROPEA superalloy is of significant interest for further optimization. Therefore, single-phase γ and γ′ materials containing a low content of Pt (0.13% at.) were manufactured by inductive melting and their behavior was investigated at 900°C with 1 mg/cm² of Na₂SO₄ deposit using thermogravimetry in air and air + 400 ppm of SO₂. After 24 h in air, the scale grown on the γ′ model alloy consisted of an outer heterogeneous NiO layer and of an internal porous α-Al₂O₃ layer. The addition of 400 ppm of SO₂ to air did not really change the nature and morphology of the oxides formed for γ′, but the measured linear rate was tenfold higher than that recorded in air. The γ alloy underwent an incubation period during which the corrosion rate was limited, followed by a propagation stage. In air, the alloy developed an external continuous NiCr₂O₄ spinel layer and a thin internal Cr₂O₃ subscale. The γ alloy was able to efficiently re-passivate after the propagation period. With 400 ppm SO₂, only a thin protective layer Cr₂O₃ formed on the surface of γ, with large Cr₂O₃ crystals growing within the residual Na₂SO₄. The occurrence of Cr-rich sulfides was also greater in the γ′ model alloy compared to the γ counterpart both in air and in air + 400 ppm of SO₂. Therefore, the results clearly evidenced the effect of SO₂ on the type I hot corrosion.