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•TiAl second phase inhibiting elemental diffusion at grain boundaries to resist LBE corrosion.•AlTi0.75CrFe shows the best performance with the thinnest OL after LBE ...corrosion.•Increased Ti in HEA coating leads to finer grains and better corrosion resistance.
High-entropy alloy (HEA), when used as coating materials for structural steel in lead–bismuth eutectic (LBE) nuclear reactor, faces severe dissolution corrosion due to the diffusion of their constituents along grain boundaries. In order to mitigate dissolution corrosion, a method to enhance the LBE corrosion resistance of HEA is proposed by utilizing a second phase to inhibit elemental diffusion at grain boundaries. Herein, we used the laser cladding technique to prepare a series of biphase AlTixCrFe HEA coating with a body-centered cubic primary phase and a TiAl second phase. During the LBE corrosion process, a single-layer oxide layer (OL) formed on the HEA coating surface, and meanwhile there existed an internal oxidation zone (IOZ) formed beneath the single-layer OL at AlTixCrFe HEA coating interface, which gradually converted into the single-layer OL as the corrosion time prolonged. After 2000 h of corrosion, AlTi0.75CrFe HEA coating exhibited the lowest OL thickness (8.1 μm) and oxidation rate (0.065 μm2/h) because Al, Ti, and Cr acted as protective elements, rapidly forming a protective OL on the surface. Meanwhile, the presence of TiAl second phase at the grain boundaries impeded the mobility of elements, which improved the dissolution corrosion resistance and diminished its destructive impact on the protective OL.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In lead-cooled fast reactor (LFR) systems, the liquid lead-bismuth eutectic (LBE) coolant provides a corrosive environment that damages the steel components during high-temperature operation. This ...study investigated the microstructural deterioration of 9Cr ferritic/martensitic (F/M) steel under thermal aging at 550 °C for 2,000, 10,000, or 20,000 h and its effect on oxidation corrosion in an LBE environment using multiscale characterization techniques. The results indicated that the thickness of the internal oxidation zone (IOZ) increased significantly with extended thermal aging, whereas that of the spinel layer remained relatively constant. The abundant subgrain boundaries that emerged during extensive thermal aging facilitated Fe diffusion, and the enlarged Cr-rich M23C6 carbides contributed to the formation of preferential oxidation regions, accelerating IOZ layer growth. The spinel layer formed from the IOZ was influenced by microstructural defects within the IOZ. A theoretical model describing the accelerated oxide layer growth due to thermal aging was developed. These findings support the advancement of LFR technology.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Material compatibility and corrosion in lead-bismuth eutectic alloy (LBE) systems have been the critical issues to develop the accelerator driven systems (ADS) and the fast reactors (FR). Corrosion ...tests of 410 stainless steel were performed in LBE to study the corrosion behavior at 550 °C with different relative velocities. In the first part of the corrosion test, 410 stainless steel was exposed to flowing LBE with the relative velocities of 0 m/s, 1.70 m/s, 2.31 m/s, 2.98 m/s for 600 h. The second part is to immerse 410 stainless steel in the flowing LBE with the relative velocity of 2.98 m/s for 200 h, 400 h and 600 h. The results show that the oxide layer on the surface of corrosion samples is divided into an outer oxide layer, an inner oxide layer and an internal oxidation zone (IOZ). Specifically, the outer oxide layer is mainly composed of Fe3O4 and partially infiltrated Pb–Bi, the inner oxide layer is mainly made up of spinel (Fe,Cr)3O4, and the IOZ is consisting of Cr-rich oxides at the grain boundaries. Within 600 h, the corrosion degree is enhanced with the increase of corrosion time and relative velocity (0 m/s to 2.98 m/s). Moreover, the effect of prolonging corrosion time is similar to that of enhancing the flow velocity of LBE. Finally, the growth mechanism for the oxide layer of 410 stainless steel in oxygen-saturated LBE at 550 °C is proposed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The oxidation behavior of the nickel superalloy Inconel 740H was studied at 750 °C for 100, 250, 500, 1000, and 2000 h in a steam atmosphere. Microstructure observations were performed using scanning ...electron microscopes and scanning-transmission electron microscope. The phase identification of existing oxidation products was conducted by electron diffraction in transmission electron microscope. The obtained results showed that the microstructure of Inconel 740H was stable during the oxidation process. The kinetic data showed that the superalloy has the ability to form protective oxide layers that are characterized by good adhesion and no tendency to spallation during the test. The oxidation products were mainly composed of external and internal oxides mainly at grain boundaries. The oxides in the external layer were Cr2O3, MnTiO3,, and α-Al2O3 after 2000 h of oxidation. Internal oxides were α-Al2O3 and TiO2. The occurrence of discontinuities in the internal oxidation zone was also observed after 500 h of test. It was found that the thickness of the internal oxidation zone was greater than the thickness of the external oxide layer, which proves the strong tendency of the superalloy to form internal oxides after oxidation in the steam atmosphere.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
To produce high tensile strength steel sheets in cold rolling with good thickness accuracy, it is important to supply material hot bands without harmful fluctuations in their deformation resistance. ...For the purpose, it is effective to set a high coiling temperature in the hot rolling stage. On the other hand, it is well known that the surfaces of steel sheets easily form oxide at a high temperature in the case of steel grade which contains Si and Mn in its chemical composition. To avoid the formation of oxide, it is necessary to set a low coiling temperature in the hot rolling stage. By the conventional hot rolling conditions, it is difficult to satisfy conditions both to get uniform formability in cold rolling and to prevent the surface of hot strips from forming internal oxidation zone. This report describes the improvement on the mechanical property without harmful internal oxidation zone of hot strips by the proper heat histories in manufacturing the hot rolled 0.17C-1.3Si-2.0Mn high tensile steel sheet.
To produce high tensile strength steel sheets in cold rolling with good thickness accuracy, it is important to supply material hot bands without harmful fluctuations in their deformation resistance. ...For the purpose, it is effective to set a high coiling temperature in the hot rolling stage. On the other hand, it is well known that the surfaces of steel sheets easily form oxide at a high temperature in the case of steel grade which contains Si and Mn in its chemical composition. To avoid the formation of oxide, it is necessary to set a low coiling temperature in the hot rolling stage. By the conventional hot rolling conditions, it is difficult to satisfy conditions both to get uniform formability in cold rolling and to prevent the surface of hot strips from forming internal oxidation zone. This report describes the improvement on the mechanical property without harmful internal oxidation zone of hot strips by the proper heat histories in manufacturing the hot rolled 0.17C-1.3Si-2.0Mn high tensile steel sheet.
This research studies the formation patterns of two-phase regions during the internal oxidation process in weak-alloyed binary alloys. The goal of the research is the creation of a mathematical model ...for the internal oxidation process, which describes the kinetics of the formation and evolution of internal oxidation zones. A theoretical analysis of the two-phase diffusion saturation process with light components applied to binary alloys is given. The simulation and experimental results demonstrate that the distribution of structural parameters in the two-phase area has a complex, non-monotonous nature. The results of the provided research could be used for developing new technologies in thermal and chemical-thermal treatments for dispersed strengthening of materials using internal oxidation.
Surface defects formed on Si-containing steels in hot-rolling process depend largely on the character of the scale composed of FeO and Fe2SiO4 (FeO+Fe2SiO4 oxide scale) during de-scaling. The ...formation of FeO+Fe2SiO4 oxide scale is influence by internal oxide precipitates. In order to elucidate quantitatively the internal oxidation, it is required to analyze the distributions of number, radius and volume of internal oxide precipitates in internal oxidation zone (IOZ). Internal oxidation of Fe–1 mass%Si alloy was examined at 1473K in Ar–17.6%H2–12.2%H2O where an outer scale of FeO does not form. The growth rate of IOZ was obeyed the parabolic rate law, indicating that the rate-determining step was the diffusion of oxygen through alloy. SiO2 precipitated from the internal oxidation front to 0.23±0.02 of normalized thickness of IOZ, and Fe2SiO4 precipitated from the position to the gas/alloy interface, depending on the chemical potential distribution of oxygen. Fe2SiO4 is formed by the reaction between SiO2, Fe and dissolved oxygen in IOZ. The number of precipitates in unit volume is reciprocally proportional to depth in IOZ, suggesting that the grain growth of oxide obviously affected the distribution. The radius of the precipitates was proportional to the cubic root of depth so that the volume of the precipitate was proportional to depth. These results elucidated that the volume fraction of precipitates in IOZ was constant.
Corrosion of a T91 steel tube, used in subcritical conditions in an oil power plant for 157,000 h, was characterized mainly through SEM, TEM, EDX and DRX analyses. Severe oxidation and carburization ...took place in both the outer (boiler) and inner (steam) wall sides. The nature and morphology of the oxide scale multilayer structure (hematite, magnetite and spinel) depended on the environment exposure. Specific attention was given to the internal oxidation zone at the oxide/metal interface. Diffusion of chromium during the oxidation process was determined and was proposed to be responsible for the continuous advancement of oxidation to the core of material, which eventually gave rise to the spinel. Finally, in the bulk material, coarsening of the secondary carbides (M
23
C
6
) was the main form of microstructural evolution.
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