최신논문

Home > KJMM 논문 > 최신논문

Cast β titanium alloys exhibit low mechanical properties and are therefore suitable for various thermomechanical processing methods, such as forging, hot rolling, and extrusion, before practical applications. Depending on β stability, different deformation mechanisms, including slip, stress-induced martensite (SIM), and twinning, can occur, leading to diverse mechanical properties. Thus, controlling β stability and thermomechanical processing conditions are crucial to tailoring the properties of β titanium alloys. In this study, Ti-5Mo-xFe (x = 1, 2 wt%) alloys were investigated. The β stability was adjusted by varying the Fe content, and hot rolling was performed at 900°C with a 60% reduction in thickness. In the Ti-5Mo-1Fe alloy, due to its relatively low β stability, dynamic strain-induced transformation of the α phase predominantly occurred, accompanied by deformation mechanisms involving slip as well as tensile twins with an 86° misorientation and compressive twins with a 64° misorientation. Conversely, in the Ti-5Mo-2Fe alloy, which exhibited higher β stability, dynamic recrystallization of the β phase was the dominant deformation mechanism, and {332}<112> twins along with α'' martensite formed by stress-induced martensitic transformation adjacent to the twin boundaries were observed. These findings demonstrate that precise control over β stability through compositional tuning effectively tailors the deformation mechanisms, thereby significantly influencing the microstructural evolution and mechanical properties of β titanium alloys. (Received 3 April, 2025; Accepted 16 June, 2025)

keyword : Ti-Mo-Fe alloy, Thermomechanical processing, Stress-induced martensite transformation, Deformation mechanism

Superhydrophobic (SH) coatings have received considerable attention for their potential use in water-repellent, anti-corrosion, and anti-icing applications. However, conventional spray-based SH coatings often suffer from non-uniform hierarchical structures due to uncontrollable nanoparticle aggregation during solvent evaporation, which significantly limits their practical performance and scalability. In this study, we developed a surface chemistry-based strategy to improve the uniformity of SH coatings by precisely controlling the surface polarity and functional group density of the nanoparticles. Specifically, silicon carbide (SiC) nanoparticles, which originally exhibit very low surface hydroxyl content, were chemically modified via acid treatment followed by the grafting of hydroxyl-terminated polydimethylsiloxane (H-PDMS) to tune their surface polarity and interparticle interactions. The modified SiC nanoparticles formed aggregates with optimized size which significantly enhanced uniformity during the spray deposition process, resulting in robust and uniform hierarchical surface structures. Compared to unmodified SiC and conventional SiO₂ nanoparticles, the coatings fabricated with modified SiC exhibited a high water contact angle of 163.5o as well as remarkably reduced contact angle variation across the coated area, confirming the improvement in spatial uniformity. This work demonstrates that precise control over nanoparticle surface functionalization is critical for achieving uniform and scalable superhydrophobic surfaces and provides a foundational strategy for overcoming aggregation-induced non-uniformity, thereby advancing the industrial applicability of spraydeposited SH coatings. (Received 2 May, 2025; Accepted 17 June, 2025)

keyword : Superhydrophobic, Spray method, SiC, Nanoparticle, Coating uniformity

In this study, electrical steel was additively manufactured using the Laser Powder Bed Fusion (LPBF) process with 3.3% Si powder. The effects of varying laser power, scanning speed, and Y-axis scanning angle on the microstructure, density, surface roughness, and hardness were investigated. Machine learning and explainable artificial intelligence (XAI) techniques were employed to model and optimize processing conditions to achieve desirable density, surface roughness, and hardness, and the results were compared with those of commercial electrical steel. Microstructural observations revealed melt pools with cellular structures, dendrites, and porosity along the solidification heat flow direction. As the number of layers increased, primary pores formed and extended continuously along the build direction (BD). Stable values of porosity, surface roughness, and hardness were achieved when the laser power exceeded 250W and the scan speed ranged from 300 to 1000 mm/s. Increasing the Y-axis scanning angle led to a stepped layer structure due to variations in deposition thickness, which negatively affected surface roughness and porosity, although the impact on hardness was minimal―indicating the feasibility of thin-layer fabrication. Optimization using machine learning and XAI reduced porosity to 5.49%, surface roughness to 4.6 μm, and increased hardness to 305.9 HV. The predicted and experimental values showed deviations within 5%, validating the effectiveness of the machine learning approach. By prioritizing high density and low roughness, the optimal processing conditions were suggested to be 260W, 30o, and 700 mm/s. Compared with commercial electrical steel, the additively manufactured samples showed a 2% lower density, fourfold higher roughness, and 10% higher hardness, suggesting that with improved roughness control, L-PBF-based additive manufacturing could become a viable production route for electrical steel. (Received 15 May, 2025; Accepted 19 June, 2025)

keyword : Magnetic materials, Powder processing, Si steels, Scanning electron microscopy(SEM), Machine learning

As the trend in advanced semiconductor packaging continues toward finer pitch and higher integration, bonding technologies are increasingly expected to meet stricter thermal and mechanical performance requirements. However, conventional methods such as Thermo-Compression Bonding (TCB) often lead to problems including thermal stress, long processing times and limitations of fine-pitch bonding. To overcome these challenges, this study introduces Room-Temperature Laser-Assisted Bonding with Compression (LABC), a next-generation bonding technique that enables localized heating and rapid cooling, minimizing thermal stress while improving alignment accuracy and process efficiency. To further enhance the electrical and mechanical reliability of LABC, we developed two types of Laser Non-Conductive Paste (LNCP), designated LNCP-(A) and LNCP-(B). These eco-friendly materials, flux-free and solvent-free, not only prevent void formation and fume generation but also eliminate the need for post-bond cleaning and underfill processes. The bonding experiments were conducted on 30 μm-pitch daisy-chain bump structures formed on 11 mm × 7 mm silicon chips, simulating High Bandwidth Memory (HBM). The glass transition temperatures (Tg) of LNCP-(A) and LNCP-(B) were measured to be 36.27 °C and 51.23 °C, respectively, via Differential Scanning Calorimetry (DSC). Following the bonding process, electrical resistance measurements, cross-sectional microstructural analysis, and temperature cycling (TC) tests were performed. LNCP-(B), with its higher Tg, exhibited improved thermal stability and lower resistance variation compared to LNCP-(A). Furthermore, the LABC process effectively suppressed intermetallic compound (IMC) growth, resulting in consistently thinner IMC thickness compared to those formed by TCB. In addition, shear strength testing confirmed the mechanical robustness of the bonded joints. These results demonstrate the effectiveness of LABC with optimized LNCP materials as a promising solution for high-reliability, fine-pitch interconnections in next-generation semiconductor packaging. (Received 24 April, 2025; Accepted 23 June, 2025)

keyword : Laser-Assisted Bonding with Compression (LABC), Laser Non-Conductive Paste (LNCP), 30 μm-pitch interconnection, Reliability, Room Temperature Bonding

This study explores the influence of microwave (MW) irradiation time on the NO₂ gas sensing performance of ZnO nanoparticles (NPs). ZnO NPs were subjected to MW irradiation for 1, 3, 5, and 7 minutes to assess the effects of defect engineering via MW irradiation on their sensing behavior. Phase and morphological characterizations using XRD and SEM confirmed that MW irradiation did not induce significant changes in the crystalline phase or surface morphology of the ZnO NPs. However, PL, XPS, TEM, and EDS results revealed the generation of defects, which were particularly pronounced after five minutes of MW exposure. The pristine ZnO NPs sensor displayed a response of 6.0 to 2 ppm NO₂ at 250 °C. After five minutes of MW irradiation, the response nearly doubled to 11.25 under the same conditions and reached 34.63 at 10 ppm NO₂. The improved sensitivity was attributed to the formation of defect sites, ZnO-ZnO homojunctions, and ZnO-Zn(OH)₂ heterojunctions. Notably, the sensor irradiated for five minutes also demonstrated excellent selectivity toward NO₂ in the presence of interfering gases. These results demonstrate that MW-assisted defect modulation is a promising and scalable strategy to boost sensing features of ZnO NPs. It is anticipated that high-efficiency sensors tailored for specific environmental and industrial applications could be developed with further optimization of MW parameters and integration with surface modification techniques. (Received 16 April, 2025; Accepted 15 June, 2025)

keyword : ZnO nanoparticles, Microwave irradiation, NO2 gas, Selectivity, Gas sensor, Sensing mechanism

This study investigated the effect of degree of ordering in Alloy 600 steam generator (SG) tube material on the initiation of primary water stress corrosion cracking (PWSCC), using a slow strain rate test (SSRT). The material was cooled in air from 1,100℃ to 550℃, and below 550℃ the cooling rate was varied by water quench (WQ), air cooling (AC), and furnace cooling (FC). The change in cooling rate was intended to control the degree of ordering. The PWSCC initiation experiment was conducted using a double tube compact tension (DTCT) specimen at a constant load in the primary water environment of a nuclear reactor. The results of the PWSCC initiation tests showed that the materials cooled at a fast rate were more susceptible. This experiment showed that cracking probability was higher when the degree of order was low due to a fast cooling rate. This can be interpreted to mean that a higher residual entropy is formed by fast cooling, since the higher entropy provides a greater driving force for crack initiation. The nature of the PWSCC activation process can be well explained by the ordering reaction of Alloy 600 (Q= 190 kJ/mol). For the first time, crack formation during the ordering reaction in Alloy 600 was detected using an acoustic emission sensing method. To explain the PWSCC resistance of Alloy 690, the kinetics of the ordering reaction of Alloy 600 and Alloy 690 were compared based on their activation energy. (Received 25 March, 2025; Accepted 30 May, 2025)

keyword : PWSCC initiation, Acoustic emission(AE), Alloy 600, Alloy 690, Ordering reaction, Cooling rate, Degree of order, Residual entropy, Driving force

Water electrolysis is an efficient and environmentally friendly hydrogen production technology that emits no greenhouse gases. However, its overall efficiency is significantly constrained by the high overpotential associated with the oxygen evolution reaction (OER), and this remains the bottleneck in water splitting. Among various OER catalysts, NiFe-layered double hydroxide (NiFe-LDH) has emerged as a promising candidate due to its low cost and high intrinsic activity. Its catalytic performance, however, is limited by the strong binding of OH intermediates, which inhibits rapid reaction kinetics and restricts further improvements in efficiency. In this study, we designed and synthesized PANI@NiFe-LDH by coating polyaniline (PANI) onto the surface of NiFe-LDH to modulate its electronic structure and alleviate the adsorption strength of reaction intermediates. The intimate interfacial interaction between PANI and NiFe- LDH effectively redistributed the electronic density. This in turn optimized the OH adsorption energy and led to faster OER kinetics. As a result, the PANI@NiFe-LDH exhibited significantly enhanced catalytic activity compared to pristine NiFe-LDH. Furthermore, when applied as anode catalyst in an anion exchange membrane water electrolysis (AEM electrolyzer), PANI@NiFe-LDH demonstrated excellent performance under alkaline conditions, confirming its practical applicability in sustainable hydrogen production systems. This work not only demonstrates an effective strategy to improve the OER performance of non-platinum group metal (non-PGM) based catalysts but also provides insights into the role of polymer coatings in tuning the surface electronic structure for AEM electrolyzer. (Received 2 June, 2025; Accepted 17 June, 2025)

keyword : Anion exchange membrane water electrolysis, Oxygen evolution reaction, NiFe-LDH, PANI

Gas sensors play a crucial role by monitoring hazardous gas concentrations and air quality in real-time, thus preventing accidents, protecting health and ensuring environmental and industrial safety. They are also essential in various applications for improving energy efficiency and environmental protection. With the increasing demand for hydrogen refueling stations and hydrogen fuel cell vehicles in the active hydrogen economy, the need for precise sensing technology to detect hydrogen concentration is critical given hydrogen's broad explosion range. To ensure safety and efficiency, the gas sensors must accurately detect various gas concentrations in real-world environments. To meet these requirements, we propose gas sensors that are not only highly sensitive and stable but also cost-effective, fast-responding, and compact. This study presents two types of gas sensors based on the principles of volume analysis and pressure analysis. These sensors can measure gas charge quantities, solubility, diffusivity, and leakage rates of hydrogen, helium, nitrogen, and argon gases charged in nitrile butadiene rubber under high-pressure conditions. Performance evaluation results showed that the two sensors have a stability of 0.2 %, a resolution within 0.12 wt·ppm, and can measure gas concentrations from 0.1 wt·ppm to 1400 wt·ppm within one second. Additionally, the sensitivity, resolution, and measurement range of the gas sensors are adjustable. The measurement results of the four gases’ charge quantities and diffusivities obtained from both sensors are consistent within the uncertainty range. This system possesses the capability to detect and characterize gases in real-time, making it applicable to hydrogen infrastructure facilities and to help realize a safe hydrogen society in the future. (Received 14 April, 2025; Accepted 17 June, 2025)

keyword : Volumetric Analysis, Manometric Analysis, Gas uptake, Diffusivity, Diffusion analysis program, Polymer

Cuprous oxide (Cu₂O) particles have attracted significant attention due to their low cost, nontoxicity, and abundance with applications spanning solar energy conversion, photocatalysis, sensing, and antimicrobial fields. The antibacterial activity of Cu₂O particles is strongly influenced by their morphology, which determines the exposure of specific crystal facets with distinct surface properties. In this study, the morphological evolution of Cu₂O particles was systematically investigated by varying the water content in an ethanol-water mixed solvent and adjusting the NaCl concentration during synthesis. Increasing the water content (0-20 vol%) favored growth along the [100] direction while exposing the (111) facets, resulting in the formation of octahedra. In contrast, the addition of NaCl (Cl:Cu = 1:70-1:40) led to preferential chemisorption of Cl- ions on the (100) planes, inhibiting the growth of these planes and ultimately inducing the formation of cubes. Morphological changes were confirmed by X-ray diffraction and scanning electron microscopy. Antibacterial assays against S. aureus and E. coli at a concentration of 150 μg/mL verified the morphology-dependent antibacterial performance. In particular, octahedral Cu₂O particles (Cl:Cu = 1:70) exhibited excellent antibacterial activity with an 88.4% reduction of E. coli. These findings demonstrate that the proposed approach provides a scalable and controllable synthesis strategy for precise morphological control that enables the modulation of exposed crystal planes and enhances the functional performance of Cu₂O particles. (Received 16 May, 2025; Accepted 20 June, 2025)

keyword : Solvothermal synthesis, Cuprous oxide, Morphology control, Antibacterial activity

With the recent advances in modern technologies, the mass production and widespread use of electronic devices have led to a considerable increase in electronic waste (E-waste), creating a crucial need for efficient and environmentally sustainable E-waste recycling. Conventional metal recovery techniques, including pyrometallurgical and hydrometallurgical processes, often suffer from low economic efficiency and severe environmental burdens, necessitating the development of alternative recovery strategies. Metal recovery using deep eutectic solvents (DESs), which are formed through hydrogen bonding interactions between hydrogen bond donors (HBDs) and acceptors (HBAs), has emerged as a promising alternative to traditional leaching media due to their tunable physicochemical properties, low toxicity, and cost-effectiveness. DESs are environmentally friendly solvents that have recently gained increasing attention due to their various advantages, including mild design, property adjustment, and high solubility. In this review, we summarize the current status of technologies applied to lithium-ion battery recycling and rare earth element recovery using DESs. First, we provide the concept and principles of deep eutectic solvent technology and analyze key factors affecting their efficiency, including hydrogen bonding, coordination interactions, redox behavior, density, and viscosity. In addition, we summarize industrial applications and the current status of related technology development, analyze technological developments in key unit operations of DES-based metal recovery, such as leaching, precipitation, electrodeposition and solvent extraction, and provide available information on recycling of waste lithium-ion batteries and rare earth metals recovery using DESs, presenting prospects for the technology and industry. (Received 20 May, 2025; Accepted 13 June, 2025)

keyword : Deep eutectic solvents, Lithium-ion battery recycling, Rare earth metals recovery, Hydrometallurgy, Metal leaching