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To apply the leak-before-break (LBB) concept to the main steam line piping of nuclear power plants, the use of SA508 Gr.1A low-alloy steel is being considered. To increase the LBB safety margin, it is essential to improve the strength and toughness of the material. In this study, intercritical heat treatment (IHT) and pre-tempering were applied to V-added SA508 Gr.1A low-alloy steel, and the effects of heat treatments on mechanical properties and LBB safety margin were analyzed. IHT resulted in the formation of fine grains at the grain boundaries and the decomposition of coarse cementite, which led to an improvement in impact transition toughness and J-R fracture resistance without a significant decrease in strength. The application of pre-tempering promoted the formation of nano-sized precipitates. It increased the strength by approximately 30 MPa or more at room temperature and 286°C, while no significant difference was observed in impact transition toughness and J-R fracture resistance. Both heat treatments increased the LBB safety margin from 1.37 to 1.41 by enhancing yield strength or J-R fracture resistance. However, when IHT and pretempering were applied together, J-R fracture resistance increased but yield strength decreased. As a result, there was no increase in the LBB safety margin.

keyword : Main steam line piping, SA508 Gr, 1A low-alloy steel, Heat treatment, Mechanical property, Leak-beforebreak

7xxx series aluminum alloys possess extremely high cold working yield strength, which make hot working processes essential for component manufacturing. Preheating specimens before or between hot rolling processes significantly affects the mechanical properties of the hot rolled Al alloy sheets, depending on the preheating temperature and time. In this study, we investigated the effects of temperature and time variations in intermediate preheating treatments on the microstructure and mechanical properties of Al-Zn- Mg-Cu-Sc-Zr alloy sheets after hot rolling. Specimens preheated at various temperatures (300, 350, 400℃) after hot rolling showed an increase in hardness with increasing heat treatment time, reaching a peak value before decreasing. Additionally, as the preheating temperature increased, the time to reach the peak hardness decreased. The increase in preheating temperature resulted in an increase in hardness, attributed to the promotion of grain refinement due to recrystallization occurring during hot rolling or subsequent intermediate preheating. When the intermediate preheating time was increased from 15 min to 25 min, the yield strength decreased due to the Orowan mechanism, which resulted from the increase in the size of precipitates and the decrease in their number density. The specimen that underwent heat treatment for 20 min exhibited the highest tensile strength, which was attributed to grain refinement through recrystallization and an increased work hardening rate due to the Orowan mechanism.

keyword : Al alloy, Preheating, Hot rolling, Precipitation, Aging

Fe-based amorphous alloys are promising structural materials that have a disordered lattice structure and metastable state. Due to their advanced properties, including high hardness, high elastic limit, improved wear and corrosion resistance, Fe-based amorphous alloys have a great potential for protective materials in harsh industrial fields. Twin wire arc spray (TWAS), which is a kind of thermal spray process, is a reasonable choice for depositing Fe-based amorphous coating. Industrial advantages of TWAS include simple apparatus, low cost, excellent field usability. Several previous studies of TWAS Fe-based amorphous coating have reported microstructural features, the effect of major element variation, and the effect of postheat treatment. Unfortunately, studies about Fe-based amorphous coating exposed to soluble salt solution are limited. Thus, a Fe-based amorphous coating was fabricated using TWAS in this study, and the effect of 3.5 wt.% NaCl solution exposure on its microstructure and mechanical properties was researched. Single- and multi-layer coatings were fabricated and Al-3%Ti was selected as a bond coat material. The results showed that single- and multi-layer Fe-amorphous coatings were successfully deposited on high strength low alloyed (HSLA) steel, which is a representative structural material for offshore construction. The single-layer coating showed continuous corrosion and the multi-layer coating showed delamination induced by Al-3%Ti bond coat galvanic corrosion. The Vickers hardness of the coating was retained after the long-term salt solution immersion test, thus, the feasibility of single-layer Fe-amorphous coating was confirmed.

keyword : Twin wire arc spray, TWAS, Fe-based amorphous alloy, Bond coating, Soluble salt immersion test, SSIT, Mechanical property

We employed electrophoretic deposition (EPD) using AC voltage to prepare lithium iron phosphate (LFP) Li-ion battery electrodes with varying the LFP thickness, to compare bulk-limited electro chemical reaction with the surface-limited electrochemical reactions. We analyzed the electrochemical performances of the thin and thick LFP electrodes at various scan rates. They revealed that with increasing scan rates, both electrode types showed a greater reliance on surface capacitive effects for charge storage. Significantly, the thin LFP electrode predominantly exhibited capacitive charge storage, surpassing diffusion-based storage mechanisms. This was in contrast to the performance of the thicker electrode, which had a lower capacitive contribution. Quantitative assessment using the Randles-Sevcik equation further confirmed the superior performance of the thin LFP electrode. The Li-ion diffusion coefficient of the thin LFP electrode was substantially higher (9.6×10^-9 cm²·V^-1·s^-1) compared to the thick electrode (2.0×10-9 cm²·V^-1·s^-1), indicating enhanced ionic mobility in the surface-limited electrochemical reaction. These findings emphasize the significant advantages of thinner LFP electrodes, and induced surface limited electrochemical reaction, in high-rate applications, including higher capacitive charge storage and more favorable ion diffusion characteristics. The advantages conferred by the enhanced capacitive charge storage and superior ion diffusion in thin LFP electrodes have profound implications for the design and optimization of next-generation high-rate batteries. By focusing on tailoring electrode thickness, we can harness the full potential of surfacelimited reactions, pushing the boundaries of what is currently achievable in terms of power density, charging speed, and cycle life in LFP-based energy storage technologies. These enhancements align with the growing need for high-performing, reliable energy storage solutions in an increasingly electrified and energy-conscious world.

keyword : Lithium Iron Phosphate, Bulk, Surface-limited, Li-ion Battery, Cathode

Nitrogen diO_xide (NO₂) is a highly dangerous gas, mostly emitting emitted from fossil fuels, and a major contributor to air pollution. It has negatively effects affects on the human health as well asand contributes to environmental issues like acid rain. In this study, mesoporous CuO_x nanoparticles (NPs) were successfully synthesized using a low-temperature inverse micelle sol-gel method. Subsequently, the synthesized NPs were annealed at temperatures of 250, 350, and 450 ℃. Advanced characterization of the synthesized samples revealed that upon with increasing the annealing temperature, the sizes of the NPs increased, whileereas their surface areas decreased. The sample annealed at 250℃ showed a remarkably higher surface area (161.85 m²/g) compared with the samples annealed at 350 ℃ (39.88 m2/g) and 450 ℃ (22.52 m²/g) thanks to finer particle sizes and a mesoporous nature. Resistive gas sensors incorporating these samples were successfully fabricated and tested for sensitivity towards both NO₂ (O_xidizing gas) and H₂S (reducing gas) at 200 ℃. The sensor with the mesoporous CuO_x NPs annealed at the lowest temperature (250 ℃) exhibited an enhanced response to NO₂ gas but no response to H₂S. The strong response to NO₂ gas is considered to be due to the high surface area of the sensing layer which provides plenty of adsorption sites for gas molecules and the O_xidizing nature of NO₂ gas with high affinity to electrons. These findings highlight the effectiveness of the inverse micelle sol-gel method forin synthesizing mesoporous CuO_x NPs for gas sensing, as well as the need for to optimizing optimize the annealing temperature to maximize the sensor response.

keyword : mesoporous CuO_{x, inverse micelle, gas sensor, NO₂ gas, sensing mechanism}

In recent years, extensive research has been conducted on wearable smart garments incorporating various materials and technologies, among which heating garments with the ability to generate heat through battery-powered circuits have gained significant attention. However, traditional methods utilizing heating wires suffer from drawbacks such as increased weight, lack of flexibility due to embedded wires, and limited heating distribution. To address these challenges and enhance user convenience, research efforts are actively focused on developing smart textile technologies that maintain lightweight properties while offering sufficient flexibility and low electrical resistance. This study explores the fabrication of heating fibers by applying silver nanowires, known for their excellent electrical and thermal conductivity, onto polyester fabric, a commonly used textile known for its durability and heat resistance. A dispersion and drying method utilizing isopropyl alcohol is employed to ensure uniform distribution of nanowires on the fabric surface. The impact of nanowire concentration and deposition cycles on the electrical properties and structure of the fabric is investigated, demonstrating high heating stability and reproducibility, thus indicating potential applications in various industries. Experimental results reveal that the fabricated heating textiles exhibit rapid heating response times, reaching target temperatures within seconds, and maintaining stable temperatures with minimal fluctuations even after prolonged usage. Furthermore, the textiles demonstrate excellent reproducibility under repeated heating cycles and show promising performance even under various deformation conditions, highlighting their suitability for practical usage scenarios.

keyword : Silver, Nanowires, Fabric, Joule heating

Mn, Zn, Ni-substituted Z-type hexaferrites, Sr₃Co₂Fe₂₄O₄₁ (Sr₃Co₂Fe₂₄-_xM_nxO₄₁, Sr₃Co₂-yZnyFe24O41, Sr₃Co_1-zNizZnFe₂₄O₄₁), were prepared by sol-gel synthesis processes and their high-frequency magnetic, dielectric and electromagnetic (EM) wave absorption characteristics were investigated. Substituting Mn for Fe by x = 0.5 maintained the single-phase Z phase while shifting the μ’, μ″ spectra towards lower frequencies. Substituting Zn for Co by y = 1.0 resulted in the single-phase Z phase and effectively shifted the μ’, μ″ spectra towards lower frequencies. Additionally, substituting Ni by z = 0.5, 1.0 gradually shifted the μ’, μ″ spectra towards higher frequencies. The Sr₃Co₂Fe₂₄O₄₁ with a single Z-type hexaferrite phase and epoxy (10 wt.%) composite showed strong ferromagnetic resonance (FMR) at 3.05 GHz and exhibited primary and secondary strong EM wave absorption characteristics at the thicknesses where impedance matching occurred near the FMR frequency and at frequencies higher than this. Substitution of Mn and Zn tended to decrease the FMR frequency, while substitution of Ni tended to increase it. The samples with substituted compositions also showed changes in the primary and secondary strong EM wave absorption frequency regions, depending on the FMR frequency changes. They demonstrated excellent EM wave absorption performance with the absolute value of the minimum reflection loss (RLmin) ranging from 42 to 58 dB. The FMR-tunable Z-type hexaferrite is a promising EM wave absorption material that can modulate EM wave absorption characteristics by cation substitution in in L-S-band (1~4 GHz) and X-band (8~12 GHz) ranges.

keyword : Z-type hexaferrite, sol-gel method, permittivity, permeability, reflection loss, electromagnetic wave absorption

Aluminum-Zinc-Magnesium (Al-Zn-Mg) alloys are extensively utilized in aerospace and automotive industries because of their exceptional mechanical properties and light weight. These properties of Al-Zn-Mg alloys are significantly influenced by the morphology, distribution, and size of the precipitates within the alloy, which result from the formation of numerous nanoscale precipitates. Among the various types of precipitates, η precipitates are the most representative, with the η1 variant comprising approximately 50% of the total η precipitates. In this study, we investigated the atomic-scale growth mechanism of η1 precipitates in Al-Zn- Mg alloys using high-resolution scanning transmission electron microscopy (STEM). The investigation revealed that the growth of η1 precipitates is driven by the separation of Mg and Zn atomic columns along the aluminum atomic arrangement near the interface, which facilitates the stepwise growth of the precipitates. Additionally, it was observed that a unique interfacial segregation layer forms in the direction of η1 precipitate growth, and energy-dispersive X-ray spectroscopy (EDS) confirmed that this layer is composed of Mg and Zn. These findings provide critical insights into the microscopic interactions and transformations that govern the precipitate formation process. This research offers valuable information for optimizing the microstructure and enhancing the mechanical performance of Al-Zn-Mg alloys for various high-performance applications.

keyword : Al-Zn-Mg alloy, Scanning Transmission Electron Microscopy, Energy Dispersive Spectroscopy, Precipitates, Growth Mechanism

This study investigates the influence of {10-12} twins on the aging behavior of an extruded Mg- 8Al-0.5Zn (AZ80) alloy during aging at 150 ℃. The extruded AZ80 alloy is subjected to a compressive strain of 6% along the transverse direction and is subsequently aged at 150 ℃. The sample with {10-12} twins (referred to as the twinned sample) exhibits a finer grain size and higher internal strain energy compared to the extruded sample. The peak-aging time of the twinned sample is 32 h, which is significantly shorter than that of the extruded sample without twins (200 h). Moreover, the peak-aged hardness of the twinned sample (96.3 Hv) is slightly higher than that of the extruded sample (93.6 Hv), despite the substantially shorter peak-aging time in the former. The high internal strain in the twinned sample, especially within the twins, promotes the formation of continuous precipitates (CPs) during the early stages of aging. As the aging time increases, the number density of fine CPs in the twins increases through additional precipitation. In the extruded sample, the area fraction of discontinuous precipitates (DPs) rapidly increases with increasing aging time. In contrast, the formation and growth of DPs are substantially suppressed in the twinned sample, because CPs predominantly form and twin boundaries act as barriers to DP growth. As a result, the area fraction of the peak-aged twinned sample (5.1%) is significantly lower than that of the peak-aged extruded sample (60.2%). Consequently, the introduction of {10-12} twins in the extruded AZ80 alloy results in the promotion of CP formation, suppression of DP formation, and significant reduction in peak-aging time under the 150 ℃ aging condition.

keyword : AZ80 Mg alloy, twin, aging, precipitate, hardness