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The drawing process severely deforms commercial AA1070 alloy for electrical wire, reducing a rod from a diameter of 2.0 mm to 0.4 mm, followed by annealing. The annealing process was conducted at various temperatures ranging from 200℃ to 450℃, with each temperature maintained for 1hour. The effects of increasing annealing temperature on the microstructure, mechanical properties, and electrical properties of the Al wire were investigated in detail. The drawn Al wire showed a severely deformed microstructure and fiber texture that {110}<111> and {112}<111> components strongly developed. As the annealing temperature increased, the deformation structure changed into recrystallization structure over all regions. However, the fiber texture still strongly remained even in the specimens annealed at higher temperatures. The hardness decreased with increasing annealing temperature due to the occurrence of recovery and/or recrystallization. The strength also continued to decrease as the annealing temperature increased. However, elongation gradually increased with increase of annealing temperature to 250℃; above 275℃, it increased particularly sharply. The electric conductivity tended to increase slightly with increasing annealing temperature, reaching a maximum value of 62.2%IACS at 300℃. Changes in microstructure, mechanical properties and electrical conductivity with annealing of commercially drawn AA1070 were compared with those of the previous study.

keyword : AA1070 alloy, wire drawing, annealing, microstructure, mechanical properties, electrical conductivity

Copper is widely utilized in electric vehicle batteries due to its excellent electrical conductivity, lightweight, and excellent corrosion resistance. However, copper has a high reflectivity of about 97% for infrared lasers, which makes it difficult to achieve stable welding quality. This study investigated using a green laser to weld nickel-coated copper and aluminum materials. After performing welding by changing the laser power and scan speed, the weld cross-section was observed with an optical microscope, and it was confirmed that the welding penetration depth and bead width increased as the heat input increased. The spatter on the bead surface and defects such as pores and cracks in the weld were caused by excessive heat input. Analysis of the weld cross-section using SEM-EDS showed that high heat input increased the formation of intermetallic compounds including CuAl2 and Cu9Al4. The mechanical properties of the weld were examined using a shear tensile test. The analysis results showed that intermetallic compounds caused brittleness in the weld joint, which lowered mechanical properties and caused defects such as pores and cracks. P60 (1.2 kW, scan speed: 250 mm/s), P80 (1.6 kW, scan speed: 375 mm/s), and P100 (1.2 kW, scan speed: 375 mm/s) were examples of excellent mechanical quality. The fastest welding condition, P100 (power: 2 kW, scan speed: 450 mm/s), was suggested as the most efficient welding condition.

keyword : Green laser, Nickel coated copper, Electric vehicle, Aluminum, Intermetallic compound

The Rene N5 is a second-generation single crystal superalloy containing 3wt% Re, commonly used in gas turbine blades for power generation at temperatures up to 1600°C due to its excellent creep life. Generally, single crystal (SX) and directionally solidified (DS) blades are not applied to hot isostatic pressing (HIP) because their porosities are lower than conventionally cast (CC) blades, and it causes recrystallization issue. However, in this study, HIP was chosen as a candidate to improve the mechanical properties of the second-generation single crystal superalloy Rene N5. HIP followed by ultra-rapid cooling rate of 660K/minute was applied in an attempt to address this issue. This approach was expected to enhance creep rupture properties through pore reduction and microstructural homogenization. Furthermore, by setting the HIP temperature and time identical to the solution treatment condition, the possibility of replacing solution treatment with HIP was discussed. As results of creep rupture tests, the rupture life was excellent in the order of specimens treated with HIP + solution + aging, solution + aging, and HIP + aging treatments. It is interesting that this is found to be primarily influenced by the size and shape of carbides and γ’ phases, with the effects of crystallographic orientation, shrinkage porosity, and eutectic phase being negligible.

keyword : Single crystal superalloy, investment casting, HIP, creep rupture

Multilayer ceramic capacitors (MLCCs) are essential fundamental components in electronic devices, enabling miniaturization and high capacitance for energy storage and filtering. A key focus in MLCC research is enhancing capacitance density, for which improving the connectivity of Ni internal electrodes is imperative. The primary cause of reduced electrode connectivity in MLCCs is the sintering shrinkage mismatch between Ni internal electrodes and dielectric materials. In this study, we propose a method to mitigate the sintering shrinkage mismatch between the Ni internal electrodes and dielectric materials by incorporating W nanopowder into Ni to retard the sintering shrinkage of the Ni nanopowder. The degree of sintering retardation due to the increase in W content was quantified through measurements of shrinkage rate, density, and porosity, confirming the retarded sintering of Ni. Particularly, microstructural analysis and phase analysis were conducted to elucidate the role of W during the dissolution and sintering processes. Furthermore, the activation energy of each sintering stage was determined, with an analysis of the sintering retardation mechanism induced by W. Additionally, similar sheet resistance values before and after the addition of W were obtained through electrical resistance measurements, and results suggested that the incorporation of W effectively retards the sintering of Ni while enabling its function as an internal electrode in MLCCs.

keyword : MLCC, Ni Internal electrode connectivity, W, Sintering retardation, Master sintering curve, Sintering activation energy

This study investigates the thermoelectric properties of Pb-doped p-type Bi0.5Sb1.5Te3 alloys using the Single Parabolic Band (SPB) model, focusing on optimizing room-temperature performance. We systematically analyze the effects of Pb doping (0, 0.49, 0.65, 0.81, 0.97, and 1.3 at%) on key parameters including density-of-states effective mass (m_d*), non-degenerate mobility (μ₀), weighted mobility (μ_W), and the thermoelectric quality factor (B-factor) at 323 K. The results reveal that m_d* reaches a maximum of 1.37 m_e at 0.97 at% Pb doping, representing a 22.25 % increase over the pristine sample. The highest μ₀ of 234.5 ㎠ V^-1 s^-1 is achieved at 0.65 at% Pb, highlighting the complex relationship between doping and carrier mobility. Notably, 0.97 at% Pb doping optimizes thermoelectric performance, yielding the highest μ_W, power factor, and B-factor. This composition also minimizes lattice thermal conductivity (κ_l) by 44.93 % compared to the undoped sample, significantly reducing phonon heat conduction. The Callaway-von Baeyer model corroborates these findings, indicating maximized point defect scattering at 0.97 at% Pb. A theoretical peak figure-of-merit (zT) of 1.74 is thus predicted at this doping level, demonstrating a possible substantial enhancement in thermoelectric efficiency upon appropriate carrier concentration tuning. The observed trends in Seebeck coefficient, Hall carrier concentration, and Hall mobility with increasing Pb content provide insights into the underlying mechanisms of performance enhancement. This comprehensive study highlights the critical role of precise Pb doping in optimizing the thermoelectric properties of Bi_0.5Sb_1.5Te₃ alloys for room-temperature applications and establishes a framework for future investigations into similar material systems.

keyword : thermoelectric, B-factor, weighted mobility, single parabolic band model, Callaway-von Baeyer model

Bismuth telluride (Bi₂Te₃)-based alloys are widely used for thermoelectric cooling and power generation at low temperatures, and they are the only commercially available materials for thermoelectric applications below 500 K. The rhombohedral unit cell with a large c/a lattice constant ratio consisting of - Te-Bi-Te-Bi-Te- stacked layers inevitably brings about a large anisotropy in transport properties, which is why texturing is very important in polycrystalline Bi₂Te₃ alloys for maximum performance. In this report, p and n-type polycrystalline Bi₂Te₃ alloys were synthesized and hot-deformed to investigate the effects of texturing on thermoelectric properties. Hot deformation (HD) induces the strong alignment of (00l) orientations along the compression direction, and a remarkable increase in the orientation factor F of (00l) orientations is observed after HD in both p and n-type materials. All of the hot-deformed polycrystalline samples showed increased electrical conductivity (σ), power factor (PF), and thermal conductivity (κ) in the in-plane (IP) direction, and vice versa in the out-of-plane (OOP) direction, which makes the IP direction of the hot-deformed bodies more favorable for module fabrication in terms of power factor, for both p and n-type Bi₂Te₃-based alloys. However, due to the different degree of anisotropy of κ and σ, the figures of merit (zT) were maximized in the OOP direction in the p-type materials after HD, whereas the zTs of the n-type materials were higher in the IP direction. This occurs because the anisotropy factor of electron conduction is higher than that of hole conduction, which more than offsets the advantage of the smaller κ in the c-direction of n-type Bi₂Te₃. The maximum zT of 1.33 (OOP) and 0.90 (IP) were obtained after HD from the p and n-type Bi2Te3 alloys, respectively, which were 9.3% and 18.4% higher than those of as-sintered materials.

keyword : thermoelectric, bismuth telluride, hot deformation, texturing, anisotropy

Residual antibiotics in natural aquatic environments pose a critical threat to humans and other organisms. However, most sewage treatment plants fail to remove them. Photocatalytic nanomaterials can efficiently destroy these persistent organic pollutants in wastewater. In this study, we developed a series of cobalt-doped SrTiO₃ (Co-STO) catalysts with different doping amounts (3, 5, 7, and 9 wt%) for the effective photocatalytic degradation of ciprofloxacin (CIP). The nanostructures were characterized using X-ray diffraction, field-emission scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, UV-visible diffuse reflectance spectroscopy, and Brunauer-Emmett-Teller N₂ adsorption isotherms. The Co-STO particles have a mesoporous diameter of ~30.8 nm, and the Co-doped nanostructures have a rhombohedral hopper-like shape. Co-doping decreased the bandgap of pure STO from 3.61 to 3.42 eV, which enabled it to absorb visible light. Among the catalysts, 7 wt% Co-STO showed the highest CIP degradation activity (90.6%) during 120 min of visible-light irradiation. Radical scavenging experiments revealed that superoxide (O₂^·-) is the primary reactive species during degradation. These Co-doped nanostructures have potential applications in the remediation of hazardous pollutants in pharmaceutical wastewater. Moreover, the crystal and energy band structure, density of states, and Bader charge of these molecules were analyzed.

keyword : Perovskite, drug degradation, anthropogenic waste degradation, photocatalysis, visible light irradiation

This study investigates the effect of adding Al to Mg molten metal on the microstructural characteristics and hardness of Mg-Ti composites fabricated via a liquid metal dealloying (LMD) process. The addition of Al to the Mg melt significantly reduces the dealloying rate of Cu in a Ti₃₀Cu₇₀ precursor during LMD. The rapid reaction of Al atoms with Ti results in the formation of a Ti₃Al phase, which in turn inhibits the spinodal decomposition of Ti and Cu. This inhibition decreases the formation rate of α-Mg channels, thereby slowing down the dealloying process of Cu. As a result, as the Al content in the Mg melt increases from 0 to 3 to 6 wt%, the residual Cu content in the composite substantially increases from 0 to 42 wt%. The main phases comprising the composite change from Mg and Ti for the composite using a pure Mg melt to Ti_xCu_y, Ti_xAl_y, and Mg_xCu_y for the composites using Mg-Al melts. The hardnesses of the composites fabricated using the Mg-3Al and Mg-6Al melts are 344 and 354 Hv, respectively, which are more than twice that of the composite fabricated using the pure Mg melt (116 Hv). These results demonstrate that adding small amounts of Al to Mg melt considerably influences the dealloying behavior during LMD as well as the resultant microstructure and mechanical properties of the Mg-Ti composite.

keyword : Liquid metal dealloying, Mg-Ti composite, Al addition, Microstructure, Hardness

This study investigated the high-temperature wear characteristics of Ta-10W alloy, composed of 90% tantalum and 10% tungsten, known for its high melting point, excellent corrosion resistance, and oxidation resistance. Wear tests were conducted using a ball-on-disc method with alumina balls at temperatures of 200℃, 400℃, 600℃, and 700℃. The results indicated that wear loss decreased (increasing wear resistance) from 200℃ to 600℃ due to the lubrication effect by oxide particles induced by Ta₂O₅, which enhanced wear resistance. However, at 700℃, a significant increase in wear loss was observed due to excessive oxide formation and the occurrence of cracks. Calculation of the wear rate revealed that it decreased as the temperature increased to 2.12×10^-4 ㎣· N^-1· m^-1 at 200 ℃, 2.67×10^-5 ㎣·N^-1·m^-1 at 400 ℃, and 4.21×10^-6 ㎣· N^-1· m^-1 at 600 ℃. On the other hand, the wear rate increased at 700 ℃ to 3.87×10^-4 ㎣· N^-1· m^-1. The wear track analysis results revealed distinct wear mechanisms at different temperatures. At 200℃, abrasive wear characterized by pits and furrows was dominant. At 400℃, adhesive wear became more prevalent with cleavage worn surfaces compared to the wear pattern at 200℃. At 600℃, fragmented oxides indicating pest oxidation were noted, while at 700℃, deep pits and cracks along with fragmented oxides were prevalent. X-ray diffraction (XRD) analysis results showed the presence of the α-Ta phase at 200℃, 400℃, and 600℃, with peak shifts indicating lattice expansion. In contrast, at 700℃, Ta₂O₅ peaks were present. Based on the findings, the high-temperature wear mechanism of Ta-10W alloy was also discussed.

keyword : Ta-10W alloy, High temperature wear, Ball-on-disc wear, Oxidation, Wear mechanism