The twin-roll casting (TRC) process has gained significant attention for aluminum sheet production due to its cost-effectiveness and high processing efficiency. However, controlling the initial grain structure of TRC strips remains challenging due to the absence of a hot rolling stage, necessitating an advanced predictive modeling approach. In this study, a cellular automaton-finite element (CA-FE) model was developed to predict the grain structure and texture of aluminum strips fabricated via TRC. Both pure Al and AA7075 alloys were cast under identical conditions using a pilot-scale horizontal twin-roll caster, and their microstructures were characterized experimentally. The developed model incorporated a Gaussian nucleation distribution function and an equivalent binary approach to account for the solidification behavior of multicomponent alloys. The CA-FE simulation results successfully reproduced the key aspects of solidification, grain structure, and texture evolution of TRC strips. The predicted temperature distribution and solid fraction evolution showed distinct differences between the alloys, with pure Al forming columnar grains and AA7075 developing a fully equiaxed structure, which closely matched the experimental findings. Additionally, texture analysis using inverse pole figures (IPFs) and pole figures (PFs) revealed a clear <001> orientation in pure Al, whereas AA7075 exhibited a random texture, both of which were well captured by the CA-FE model. The findings indicate that the developed model offers a reliable prediction of the solidification microstructure and texture evolution in TRC strips, making it a valuable tool for optimizing continuous casting processes.

The twin-roll casting (TRC) process is widely used in the aluminum industry due to its cost efficiency and continuous production capability. However, maintaining consistently high surface quality remains challenging due to complex heat transfer behavior at the roll/strip interface. This study examines the critical influence of roll surface conditions, especially the formation of an Al coating layer, on solidification behavior and resulting strip quality in the TRC of an Al-5Mg alloy. Experimental results demonstrated that casting without an Al coating layer led to surface defects such as hot tears and porosity due to insufficient cooling. In contrast, strips produced with a stable Al coating layer exhibited excellent surface quality with no surface defects. Numerical simulations further indicated that a stable Al coating enhanced the interfacial heat transfer coefficient (up to 30,000 W/m2K), ensuring effective cooling and complete solidification before the strip exited the roll nip. Moreover, simulations validated the feasibility of using steel rolls in industrial applications, provided the coating layer was consistently maintained. This research highlights the significance of roll surface control in improving TRC product quality.

Bronze vessels are manufactured using casting and forging techniques, and various microstructures can be observed depending on the manufacturing process. In this study, we confirmed mechanical properties and microstructural evolution in the manufacturing process by observing the microstructures and composition analysis of 18 bronze vessels in the Goryeo Dynasty excavated from historical sites. The results show that 13 of the bronze vessels were manufactured using a Cu-Sn alloy with a Sn content of 20 to 24 wt%. The a phase and (3(M) phase were observed, indicating that hot forging and quenching treatment were performed after casting. 3 bronze vessels were produced from a Cu-Sn-Pb alloy, and considering that the a phase and a+delta phase were observed, it could be seen that the process was completed by slow cooling after casting. The correlation between the type of bronze vessel and the manufacturing process has not been confirmed, except of ewer. It was confirmed that various microstructures were created depending on the manufacturing process and that the mechanical properties also changed. Bronze vessels composed of the a phase and a+delta phase due to the casting process had lower Vickers hardness values compared to bronze vessels that showed the quenched (3(M) or y phase. Electron backscatter diffraction (EBSD) phase analysis and kernel average misorientation (KAM) were performed using six bronze vessels composed of a and (3(M) phases. The results showed that the factors affecting hardness were the ratio of the (3(M) phase and the KAM value. However, it could not be confirmed to what extent the ratio of the (3(M) phase and KAM value affected the improvement in mechanical properties.

This study examined the feasibility of in situ fabrication of oxide dispersion-strengthened (ODS) Ti-6Al-4V (Ti64) powder through a gas atomization (GA) method. Thermodynamic calculations were performed to design the ODS Ti64 by deriving compositions of yttrium oxide (Y2O3), which is completely dissolved into the molten Ti64 and subsequently reprecipitated during cooling in the GA process. In addition, the changes in the equilibrium phase fractions based on varying the Y2O3 content and oxygen (O) concentration in the Ti64 matrix were investigated. From the thermodynamic calculations, an optimal composition for the ODS Ti64 alloy was determined, involving the addition of 1 wt% Y2O3 to Ti64 with an O concentration of 0.1 wt%. The alloy ingot was prepared via vacuum arc remelting, leading to the precipitation of coarse Y2O3 along grain boundaries because of a slow cooling rate. The ODS Ti64 powder was fabricated through an electrode induction melting GA method, and the resulting ODS Ti64 powder had spherical morphology, with uniformly distributed Y2O3 particles of several tens of nanometers in size. The hardness of a conventional Ti64 powder was 354 HV, significantly increasing to 485 HV in the ODS Ti64 powder due to the Y2O3 nanoparticles' dispersion. This study introduces a novel methodology for fabricating high-quality ODS Ti64 powder by the in situ GA method.

Metallographic analysis of microstructure, chemical composition and hardness was carried out on 7 bronze vessels from Mangduksa temple site in Gyeongju. Result show that the technology of bronze vessels divided into casting and forging followed by quenching. Tin contents of casting bronzes were around 11∼14 wt%, forging bronzes were about 21∼23 wt% tin. Kundika and dish of casting bronzes were Cu-Sn-Pb alloys and 5 bowl samples were produced using Cu-Sn binary alloy materials. These show that the manufacturing technology was applied different depends on the Sn contents. Also 4 bowls of approximately 20 wt% tin were manufactured by forging and quenching at above 520℃ avoid formation of the brittle δ phase. The non-metallic inclusions in the 7 bronze samples are divided into Cu-S and Cu-Fe-S-Se systems, indicating that the copper ore used the production is different. It was confirmed that casting bronze vessels had lower micro-hardness values than forging samples, and that hardness values changed depending on Sn content and processing.

The purpose of this study is to analyze the components and observe the microstructure of 98 bronze vessels excavated from the Korean Peninsula, where such vessels were widely used, to identify the alloy composition and manufacturing process of bronze artifacts by period. In addition, we attempted to confirm the changing processes of bronze manufacturing technology by reviewing previous studies. The analysis results showed that the bronzeware of the Unified Silla period was mainly produced using a Cu-Sn binary alloy containing 20-26 wt% Sn, which was cast and slowly cooled. Also, most bronze vessels from the Goryeo dynasty were made of a Cu-Sn binary alloy, with an Sn content of 20-24 wt%. In the microstructure, a twinned alpha phase and beta(M) phase were observed, indicating that the container was manufactured using the casting-hot forging-quenching process. Bronze vessels from the Joseon dynasty were made using a binary alloy of Cu-Sn and a ternary alloy of Cu-Sn-Pb. In order to confirm the changes in bronze manufacturing technology over time, we investigated the alloy composition and microstructure of a total of 295 vessels, including previous studies, and were able to confirm the dominant production technology for each period. During the Unified Silla period, the shape of the container was made by casting using a Cu-Sn binary alloy, and the process was completed through slow cooling or quenching. During the Goryeo Dynasty, vessels were made using a Cu-Sn binary alloy through a process of casting, hot forging, and quenching, or by casting a Cu-Sn-Pb ternary alloy into a vessel shape and then slowly cooling it. And in the Joseon Dynasty, the use of ternary alloys of Cu-Sn-Pb increased.

Hydrogen embrittlement (HE) resistance is a significant concern in austenitic stainless steel (ASS) used for hydrogen transportation and storage. While microstructure-controlled methods to enhance HE resistance have been extensively studied in ferritic steels, comprehensive research on microstructure effects in ASS is lacking. In this study, two 316L ASSs with different microstructures were evaluated for HE resistance using electrochemical hydrogen charging. The steel with abundant in <111>+<110> orientations showed a significant elongation reduction after hydrogen charging. It revealed that, from the hydrogen permeation and thermal desorption analysis (TDA) results, effective diffusivity and activation energy of hydrogen were changed along the crystallographic orientation distributions. Also, transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) behavior affecting to the HE resistance preferentially formed in grains with <111> and <110> orientations rather than in those with <001> orientation during plastic deformation. Therefore, the study suggests that reinforcing the <001> microstructure is advantageous for improving HE resistance in 316L ASS

In this study, the multi-shell structured Mo-Si-B powder with La2O3 particles (MSB + L powder) was designed to obtain the ideal microstructure of sintered body, and the effects of the La2O3 addition on the microstructural and mechanical characteristics were investigated. Mo-Si-B powder (MSB powder) was prepared via mechanochemical powder metallurgy methods, and MSB + L multi-shell powder was fabricated via chemical methods such as mixing and calcination processes. Using this powder, MSB + L alloys were prepared under cold isostatic pressing followed by pressureless sintering. Our unique powder's architecture allows us to fabricate the ideal microstructure of MSB + L alloys which consist of isolated intermetallic compound phases and uniformly dispersed La2O3 particles in continuous alpha-Mo matrix. This ideal microstructure contributes to the enhancement of fracture toughness of MSB + L alloys by changing fracture behavior, compared to MSB alloys without La2O3 particles. For example, intergranular fracture mode in MSB alloys changed to intragranular fracture mode in MSB + L alloys. In addition, the fracture toughness was enhanced around 26% in MSB with 0.3 wt% La2O3 particle at room temperature (17.0 MPa center dot m1/2) while MSB alloys have around 13.50 MPa center dot m1/2. The addition of La2O3 particles in MSB alloys highly affect the fracture behavior at room temperature through the grain refinement and oxide particle strengthening.

In this study, a micro/nano core-shell molybdenum powder was synthesized by mechanochemical process to improve its microstructural uniformity and density by pressureless sintering the core-shell powder. The micro-sized spherical Mo powder, prepared through an electrode induction melting inert gas atomization process, was mixed with MoO3 powder and ball-milled using a three-dimensional shaker mixer. A mechanochemical process involving hydrogen reduction was employed to prepare the core-shell Mo powder. The prepared powders were sintered through the compacting and pressureless sintering. The density was measured using a densitometer to analyze the properties of sintered specimens. Phase analysis was performed using X-ray diffraction. In addition, microstructure analysis was conducted using scanning electron microscopy and electron backscatter diffraction. Comparing the sintered core-shell powder to the sintered conventional mixing powder under the same conditions, we observed that the former exhibited a uniform microstructure and higher density. Furthermore, we experimentally demonstrated the dependence of sintering properties on mixing ratio.

The impact of drought is intensifying due to climate change, leading to significant environmental consequences, particularly concerning river water quality. While drought is typically classified as meteorological or hydrological, studies assessing its environmental impacts remain limited. Drought-induced hydrological alterations in rivers often degrade water quality, necessitating the development of an environmental drought index. This study introduces a novel methodology for calculating an index to evaluate the effects of drought on river water quality, specifically applied to tributaries of the Nakdong River in South Korea. The index was constructed by reviewing existing water quality and drought indices, selecting relevant parameters, and weighting each factor following the National Sanitation Foundation Water Quality Index (NSFWQI) methodology. Factors integrated into the index encompass both meteorological and hydrological indicators, with priority given to variables measurable in real time. Real-time parameters—such as flow rate, cumulative precipitation, days without rainfall, and sensor-based metrics (pH, electrical conductivity [EC], dissolved oxygen [DO], and total organic carbon [TOC])—were incorporated. Additionally, for rivers with upstream dams, dam discharge data were included to reflect its influence on flow conditions. The applicability of the calculated index was assessed by comparing index values to observed water quality data. A class interval structure was implemented to enhance the index’s usability across diverse riverine conditions. Furthermore, the utility of the index was validated by comparing it to the basin’s target water quality, thereby assessing its sensitivity to drought-induced water quality deterioration. The environmental drought index proposed in this study enables the proactive and real-time monitoring of water quality under drought conditions. When applied to 10 tributaries of the Nakdong River, the index demonstrated a clear correlation between drought conditions and water quality deterioration. This index provides a practical tool for river management, facilitating early response strategies to mitigate water quality impacts associated with environmental drought.

Traditional Water Quality Indices (WQIs) often fail to capture the significant impact of flow velocity on water quality, especially under varying hydrological conditions. In this study, an Integrated Water Quality Index (IWQI) was developed by combining water quality parameters and flow rate, providing a more comprehensive assessment under various flow conditions. Compared to traditional indices, the IWQI showed slightly lower correlations in individual parameter performance, but it performed well in evaluating water quality changes associated with flow variations. Parameters such as Total Phosphorus (TP), Total Coliforms (TC), and Fecal Coliforms (FC), which are prevalent pollutants in the Cheongmi River, significantly influenced IWQI scores. River water quality was evaluated using input data simulated under a climate change scenario. When precipitation was abundant, the IWQI score remained relatively stable even with reduced flow rates. However, during periods of insufficient rainfall, water quality deteriorated sharply. While general water quality parameters exhibited approximately a 10% change as flow decreased, TC and FC showed rapid deterioration, with change rates ranging from 20% to 60%. These findings underscore the importance of managing TC and FC, particularly when insufficient rainfall is predicted, as they are major sources of pollution.

Archaeological excavations in Buyeo had revealed Bronze vessels interred within a hole in the building at the Gwanbuk-ri site. These bronze vessels are dated to the Unified silla period (9-10th centuries). To identify the bronze vessels’ manufacturing technology, metallurgical analyses were carried out using Optical Microscopy, SEM-EDS and EPMA. The results allowed a reconstruction of the manufacturing process of bronze vessels in the Unified silla. It proved that bronze vessels were manufactured with Cu-Sn alloy with varying tin contents, which may be related to the application of uncontrolled procedures in making the bronze alloys. Also a casting process was used to shape the bronze vessels and the strength and hardness of the container were improved through a quenching process. Twins were observed in one of the samples, so it was assumed that hot working had been attempted. Non-metallic inclusions in bronze vessels have circular or polygonal shapes, and Cu and S were detected. The presence of Cu-S inclusions showed the probable use of copper sulphide ores for metal production and smelting. Se and Te in the inclusions of the bronze vessels show that the copper ore is different. From the results of metallurgical analyses of bronze vessels excavated from other regions of the same era, casting and quenching treatments were confirmed, and the sequential relationship of the technological system was revealed.

Composition analysis and lead isotope ratio analysis were conducted to determine the coloring machanism on lead glaze used in Gyeongbokgung Palace and the provenance of the lead used as a flux. 31 blue tiles were classified into green, blue, and yellow. The chemical analysis of lead glazes on the blue tiles revealed that Pb, Si, and Cu were the main components, and trace amounts of Fe, Ca, Mg, and Al were detected. The Cu content was high in blue lead glaze, while Cu was not detected in yellow or brown lead glaze which instead had high Fe content. Therefore, it was found that lead was used as a flux and copper oxide as a coloring agent in the production of lead glaze. In addition, the lead isotope ratios of the lead glaze used in the blue tiles of Gyeongbokgung palace were plotted in zone 3 on the distribution map of lead isotope ratios on the Korean Peninsula, which includes Chungcheong-do and Jeolla-do. It is presumed that the flux for the lead glaze was sourced from galena found in these regions. The lead isotope ratios of the green glaze from the Three Kingdoms and Unified Silla period were mostly located outside the Korean Peninsula, showing that the provenance of lead had changed. In particular, the lead isotope ratios of the green glaze from the Three Kingdoms and Unified Silla period suggest exchange with neighboring countries. Also the lead isotope ratios of the green glazes from the same temple are different, so it is believed that they were made at different times or in different workshops.

The directed energy deposited (DED) alloys show higher hardness values than the welded alloys due to the finer microstructure following the high cooling rate. However, defects such as microcracks, pores, and the residual stress are remained within the DED alloy. These defects deteriorate the wear behavior so post-processing such as heat treatment and hot isostatic pressing (HIP) are applied to DED alloys to reduce the defects. HIP was chosen in this study because the high pressure and temperature uniformly reduced the defects. The HIP is processed at 1150oC under 100 MPa for 4 hours. After HIP, microcracks are disappeared and porosity is reduced by 86.9%. Carbides are spherodized due to the interdiffusion of Cr and C between the dendrite and interdendrite region. After HIP, the nanohardness (GPa) of carbides increased from 11.1 to 12, and the Co matrix decreased from 8.8 to 7.9. Vickers hardness (HV) decreased by 18.9 % after HIP. The dislocation density (10-2/m2) decreased from 7.34 to 0.34 and the residual stress (MPa) changed from tensile 79 to a compressive -246 by HIP. This study indicates that HIP is effective in reducing defects, and the HIP DED Stellite 6 exhibits a higher HV than welded Stellite 6.

In this study, the hydrogen reduction mechanism of MoO3 was analyzed in detail using Ti–Mo core–shell powder manufactured through a milling and reduction process. MoO3 and Ti powders were ball-milled to refine the MoO3 powder and coat it onto the Ti powder to fabricated core-shell structure. Subsequently, the milled powder was heat-treated at 600°C in a hydrogen atmosphere to reduce MoO3 to nano-sized Mo. In addition, the reduction behavior of MoO3 was analyzed by varing the reduction times to 1, 10, 30 min and 1, 3, 5 h. Phase analysis was conducted using X-ray diffraction, and oxidation state analysis was conducted using X-ray photoelectron spectroscopy. Morphology analysis was performed using scanning electron microscopy, and elemental analysis was conducted using electron probe micro-analysis. It was confirmed that Mo9O26 and Mo4O11 intermediate phases were formed sequentially as MoO3 was reduced to MoO2, and Mo9O26 had a plate shape with a thickness of sub-70 nm, and Mo4O11 exhibited a thickness of sub-300 nm. Especially, the Mo2O3 intermediate phase, previously studied only theoretically, was experimentally confirmed for the first time in the reduction process from MoO2 to Mo. Furthermore, the analysis of Mo-oxide intermediate phases was explained by the structural characteristics of the core–shell. The shell of Mo oxide was thick and dense, making it difficult for the vapor phase necessary for CVT reduction to penetrate and diffuse into the shell. As a result, the rapid CVT reduction occurred outside the shell, while relatively slower reduction occurred inside the shell where intermediate phases were observed.

Stellite 6 is a Co-based alloy with excellent wear and corrosion resistance, resulting in it frequently being used as a hard-facing material. The main defect that occurs in the hard-facing process is the peeling of the hard-facing layer, which is caused by thermal stress due to differences in thermal expansion coefficients. This peeling phenomenon can be prevented by using a material with an intermediate coefficient of thermal expansion as a buffer layer. Component surfaces are strengthened through a technique called hard-facing, which increases the components’ resistance to wear. In order to increase the wear and corrosion resistance of metal components, a high-hardness substance is usually coated onto their surface. Grinding is carried out to smooth the surface after the material is welded onto the base component. Small pieces, also referred to as “scrap”, are frequently produced during this surface machining procedure. In the hard-facing process, scrap containing a mixture of base material and Stellite 6 is generated during material processing. If this scrap can be used as a buffer layer, the cost of raw materials can be reduced through the recycling of resources, and the overall energy consumption for recycling can be reduced because the process of separating Stellite 6 from the scrap is eliminated. In this study, the physical properties of Stellite 6 with Fe added were explored to determine whether the scrap produced could be used as a buffer layer. When iron was added to the mixture, the amount of carbide decreased, in addition to the wear resistance and hardness decreasing. Regarding the thermal expansion coefficient, the thermal expansion coefficient of Stellite 6 was found to be 15.879 μm/m·°C at 300 °C, and that of Stellite 6 with 40% Fe added was found to be 14.313 μm /m·°C at 300 °C. The thermal expansion coefficient of carbon steel is reported to be 12.8 μm /m·°C at 300 °C; thus, Stellite 6 with 40% Fe can be used as a buffer layer for Stellite 6 and carbon steel because of its suitable thermal expansion coefficient.

Mo-ODS alloys have excellent mechanical properties, including an improved recrystallization temperature, greater strength due to dispersed oxides, and the ability to suppress grain growth at high temperatures. In ODS alloys, the dispersed Y2O3 and added Ti form Y-Ti-O complex oxides, producing finer particles than those in the initial Y2O3. The complex oxides increase high-temperature stability and improve the mechanical properties of the alloy. In particular, the use of TiH2 powder, which is more brittle than conventional Ti, can enable the distribution of finer oxides than is possible with conventional Ti powder during milling. Moreover, dehydrogenation leads to a more refined powder size in the reduction process. This study investigated the refinement of Y2Ti2O7 in a nano Mo-ODS alloy using TiH2. The alloy compositions were determined to be Mo-0.5Ti-0.5Y2O3 and Mo-1.0Ti-0.5Y2O3. The nano Mo-ODS alloys were fabricated using Ti and TiH2 to explore the effects of adding different forms of Ti. The sintered specimens were analyzed through X-ray diffraction for phase analysis, and the microstructure of the alloys was analyzed using scanning electron microscopy and transmission electron microscopy. Vickers hardness tests were conducted to determine the effect of the form of Ti added on the mechanical properties, and it was found that using TiH2 effectively improved the mechanical properties.

Nutrient runoff into rivers caused by human activity has led to global eutrophication issues. The Nakdong River in South Korea is currently facing significant challenges related to eutrophication and harmful algal blooms, underscoring the critical importance of managing total nitrogen (T-N) levels. However, traditional methods of indoor analysis, which depend on sampling, are labor-intensive and face limitations in collecting high-frequency data. Despite advancements in sensor allowing for the measurement of various parameters, sensors still cannot directly measure T-N, necessitating surrogate regression methods. Therefore, we conducted T-N predictions using a water quality dataset collected from 2018 to 2022 at 157 observatories within the Nakdong River basin. To account for the water quality characteristics of each location, we employed a clustering technique to divide the basin and compared a Gaussian mixture model with K-means clustering. Moreover, optimal regressor for each cluster was selected by comparing multiple linear regression (MLR), random forest, and XGBoost. The results showed that forming four clusters via K-means clustering was the most suitable approach and MLR was reasonably accurate for all clusters. Subsequently, recursive feature elimination cross-validation was used to identify suitable parameters for T-N prediction, thus leading to the construction of high-accuracy T-N prediction models. Clustering was useful not only for improving the regressors but also for spatially analyzing the water quality characteristics of the Nakdong River. The MLR model can reveal causal relationships and thus is useful for decision-making. The results of this study revealed that the combination of a simple linear regression model and clustering method can be applied to a wide watershed. The clustering-based regression model showed potential for accurately predicting T-N at the basin level and is expected to contribute to nationwide water quality management through future applications in various fields.