High-entropy alloys (HEA) have emerged as promising structural materials for use in extreme environments where conventional alloys face limitations. In this study, ferritic Fe-Al-Cr-Ni-Ti alloys were developed by employing the HEA design concept to promote coherent L21 precipitation within a BCC matrix. The systematic variation of Al content enhanced lattice coherency, precipitation strengthening, and the rapid formation of protective Al2O3 scales. The alloy with 16 at% Al exhibited superior high-temperature mechanical performance, showing a yield strength of approximately 400 MPa and ~5 % uniform elongation at 700 °C, exceeding the use temperature limit of conventional steels. Steam oxidation tests demonstrated the formation of dense, continuous alumina films, while hot rolling and grain refinement effectively improved room-temperature ductility. These findings indicate that Fe-Al-Cr-Ni-Ti alloys offer a cost-effective pathway to achieve a balanced combination of heat resistance, corrosion resistance, and mechanical processability, suggesting their potential as strong candidates for next-generation energy and high-temperature structural applications.

As science and technology advance, the demand for materials capable of withstanding extreme environments has steadily been increasing. Among them, structural materials that can operate reliably at high temperatures remain a critical field of development. Single-crystal nickel-based superalloys are among the most advanced metallic materials, capable of sustaining stresses at the highest operating temperatures, and are widely used for gas turbine blades. Since the efficiency of a gas turbine increases with higher turbine inlet temperature, the development of alloys capable of operating under such extreme conditions has been a continuing challenge. Significant progress has been achieved by adding refractory elements such as Re and Ru, leading to superalloy generations classified according to their content. While advanced countries initially led the development of 4th and 5th generation alloys containing high amounts of Re and Ru, recent trends have emphasized cost competitiveness, by reducing these expensive elements while maintaining high-temperature performance. Alongside Western countries, China has also invested heavily in optimizing Re and Ru content for material self-reliance. For Korea, the local realization of single-crystal superalloys is essential not only for industrial gas turbines but also for defense-related jet engines. At the Korea Institute of Materials Science, extensive research has been carried out to develop alloys tailored to different conditions. Recently, a Re-free single-crystal superalloy was developed that exhibits superior creep resistance compared to conventional Re-containing alloys, even outperforming TMS-1700, the world-class Re-free alloy developed at NIMS, Japan. Optimization studies toward commercialization are ongoing, contributing to the national goal of self-reliance in extreme high-temperature materials.

The Al-Fe-Mg-Cu-B system aluminum alloy is used for electrical wire, but is severely deformed by the multi-pass drawing process when a rod with a diameter of 12 mm is greatly reduced to 2.0 mm. This study investigated the changes in the microstructure, mechanical properties, and electrical properties of the aluminum wire during the drawing process in detail. The as-drawn aluminum alloy wire exhibited a deformation structure in which the grains were greatly elongated in the drawing direction, particularly in the specimens subjected to more than 80 % reduction in cross-sectional area (RA). For all drawn specimens, the fiber texture of the {110}<111> and {112}<111> components was mainly developed. The hardness tended to increase with increasing RA due to work hardening. In particular, when the RA increased to 97 % a great increase in hardness resulted. The specimen with an RA of 97 % showed the highest tensile strength of 288 MPa, 2.2 times higher than that of the specimen before drawing. The electrical conductivity decreased slightly with increasing RA, even in specimens with extreme increases in RA, and it remained at an average value of 56.6 %IACS.

본 연구는 철계 형상기억합금(Fe-SMA)의 화재 후 성능과 화재 후 구조물의 성능 회복을 위한 프리스트레싱 재료로서의 적용 가능성을 평가하였다. 이를 위해 사전변형률이 2.5%, 5.0%, 7.5%인 Fe-SMA 시편을 최대 가열 온도 400°C, 500°C, 600°C, 700°C 까지 가열한 뒤 냉각 및 인장시험을 수행하였다. 가열 및 냉각 과정에서의 온도–응력 이력 분석 결과, 사전변형률이 높을수록 가열 중 좌굴이 지연되고 냉각 후 더 큰 회복응력이 발현됨을 확인하였다. 특히 7.5% 사전변형률 시편은 500°C 이상에서 500 MPa 이상의 회복응력을 보였으며, 강성 저하 시점의 응력 또한 400°C에서 793 MPa, 700°C에서 735 MPa로 세 조건 중 가장 큰 값을 나타냈다. 2.5%와 5.0% 시편은 600°C 및 700°C에서 5∼10% 더 큰 극한변형률을 나타냈으나, 7.5% 시편은 보강재로서 충분한 극한변형률을 확보함과 동시에 강성 저하 시 더 큰 응력을 유지하여 화재 후 보강재로 사용되기에 가장 적합한 것으로 판단되었다. 본 연구는 500°C 이상의 고온에 노출된 Fe-SMA의 회복응력과 기계적 특성 데이터를 제공함으로써 기존 연구의 공백을 보완하였고, Fe-SMA가 화재 후 구조물 피해 저감과 성능 회복에 기여할 수 있는 보강재로서의 잠재력을 제시하였다.

This study presents a cost-effective approach to fabricating near β-Ti alloys via in-situ alloying during laser powder bed fusion (L-PBF). A blend of non-spherical pure Ti, 3 wt.% Fe, and 0.1 wt.% SiO2 nanoparticles was used to induce β-phase stabilization and improve flowability. Twenty-five process conditions were evaluated across a volumetric energy density range of 31.75-214.30 J/mm3, achieving a maximum relative density of 99.21% at 89.29 J/mm3. X-ray diffraction analysis revealed that the β-Ti phase was partially retained at room temperature, accompanied by lattice contraction in the α’-Ti structure, indicating successful Fe incorporation. Elemental mapping confirmed that the Fe distribution was homogeneous, without significant segregation. Compared to pure Ti, the Ti-3Fe sample exhibited a 49.2% increase in Vickers hardness and notable improvements in yield and ultimate tensile strengths. These results demonstrate the feasibility of in-situ alloying with low-cost elemental powders to produce high-performance near β-Ti alloys using L-PBF.

This study examined process–structure relationships in laser powder bed fusion of Al0.1CoCrFeNi + Cu composites, focusing on densification, elemental distribution, and solidification cracking. Mechanically mixed Al0.1CoCrFeNi and Cu powders were processed across a range of laser powers (100–250 W) and scan speeds (200–800 mm/s). Increased volumetric energy density (VED) improved densification, with a plateau near 200 J/mm3 yielding ~96% relative density; however, this value was still below application-grade thresholds. At low VED, insufficient thermal input and short melt pool residence times promoted Cu segregation, while higher VED facilitated improved elemental mixing. Elemental mapping showed partial co-segregation of Ni with Cu at low energies. Solidification cracks were observed across all processing conditions. In high VED regimes, cracking exhibited a minimal correlation with segregation behavior and was primarily attributed to steep thermal gradients, solidification shrinkage, and residual stress accumulation. In contrast, at low VED, pronounced Cu segregation appeared to exacerbate cracking through localized thermal and mechanical mismatch.

This study investigated the effects of Fe and Cr contents on ω phase formation and transformation during solution treatment and the subsequent aging process, for which four model alloys with varying Fe and Cr contents but keeping Mo equivalent of ~ 12.6 were prepared by plasma arc melting and fabricated into plates by hot forging followed by hot-rolling. The atherrmal ω phase was observed in all Ti alloys after solution treatment followed by water quenching through XRD and TEM analysis. The largest volume fraction of athermal ω phase is formed in Ti alloy with only Fe 4 wt.% among all Ti alloys, leading to the highest Vickers value due to hardening effect ω phase. It was found that not only Mo equivalent but also each characteristic of β stabilizing elements should be considered to understand a microstructure evolution and mechanical properties.

High-entropy alloys (HEAs) incorporating low-melting-point elements (Mg and Al) and high-melting-point elements (Ti, Cr, and V) were fabricated via mechanical alloying and spark plasma sintering. Sintering temperatures were varied to investigate phase behavior and microstructural evolution. X-ray diffraction was used to identify phase structures, scanning electron microscopy to analyze microstructures, X-ray fluorescence to determine elemental composition, and a gas pycnometer to measure density. Micro-Vickers hardness testing was conducted to evaluate mechanical properties. Mechanical-alloyed HEAs exhibited a body-centered cubic (BCC) phase and lamellar structures with element-enriched regions. Sintering introduced additional BCC and Laves phases, while higher temperatures promoted Mg liquid-phase sintering, increasing density and hardness. This study highlights the effects of sintering on HEAs containing elements with differing melting points to optimize their properties.

Ti-6Al-4V alloy is widely utilized in aerospace and medical sectors due to its high specific strength, corrosion resistance, and biocompatibility. However, its low machinability makes it difficult to manufacture complex-shaped products. Advancements in additive manufacturing have focused on producing high-performance, complex components using the laser powder bed fusion (LPBF) process, which is a specialized technique for customized geometries. The LPBF process exposes materials to extreme thermal conditions and rapid cooling rates, leading to residual stresses within the parts. These stresses are intensified by variations in the thermal history across regions of the component. These variations result in differences in microstructure and mechanical properties, causing distortion. Although support structure design has been researched to minimize residual stress, few studies have conducted quantitative analyses of stress variations due to different support designs. This study investigated changes in the residual stress and mechanical properties of Ti-6Al-4V alloy fabricated using LPBF, focusing on support structure design.

In this study, the effect of build orientation on the mechanical properties of Hastelloy X fabricated by laser powder bed fusion (LPBF) process was investigated. Initial microstructural analysis revealed an equiaxed grain structure with random crystallographic orientation and annealing twins. Intragranular precipitates identified as Cr-rich M23C6 and Mo-rich M6C carbides were observed, along with a dense dislocation network and localized dislocation accumulation around the carbides. Mechanical testing showed negligible variation in yield strength with respect to build orientation; however, both ultimate tensile strength and elongation exhibited a clear increasing trend with higher build angles. Notably, the specimen built at 90° exhibited approximately 22% higher tensile strength and more than twice the elongation compared to the 0° specimen.

The economical manufacturing of high-quality graphene has been a significant challenge in its large-scale application. Previously, we used molten Sn and Cu as the heat-transfer agent to produce multilayer graphene on the surface of gas bubbles in a bubble column. However, element Sn and Cu have poor catalytic activity toward methane pyrolysis. To further improve the yield of graphene, we have added active Ni into Sn to construct a Sn–Ni alloy in this work. The results show that Sn–Ni alloy is much more active for methane pyrolysis, and thus more graphene is obtained. However, the graphene product is more defective and thicker because of the faster growth rate. By using 300 ml molten Sn–Ni alloy (70 mm height) and 500 sccm source gas ( CH4:Ar = 1:9), this approach produces graphene with a rate of 0.61 g/hr and a conversion rate of methane to carbon of 37.9% at 1250 ℃ and ambient pressure. The resulting graphene has an average atom layer number of 22, a crumpled structure and good electrical conductivity.

The AlSi10Mg alloy has garnered significant attention for its application in laser powder bed fusion (L-PBF), due to its lightweight properties and good printability using L-PBF. However, the low production speed of the L-PBF process is the main bottleneck in the industrial commercialization of L-PBF AlSi10Mg alloy parts. Furthermore, while L-PBF AlSi10Mg alloy exhibits excellent mechanical properties, the properties are often over-specified compared to the target properties of parts traditionally fabricated by casting. To accelerate production speed in L-PBF, this study investigated the effects of process parameters on the build rate and mechanical properties of the AlSi10Mg alloy. Guidelines are proposed for high-speed additive manufacturing of the AlSi10Mg alloy for use in automotive parts. The results show a significant increase in the build rate, exceeding the conventional build rate by a factor of 3.6 times or more, while the L-PBF AlSi10Mg alloy met the specifications for automotive prototype parts. This strategy can be expected to offer significant cost advantages while maintaining acceptable mechanical properties of topology-optimized parts used in the automobile industry.

The hydrogen embrittlement could lead to big damages in bolt/nut, fittings, especially, high pressure valve and high leak-proof valve and so on. Thus, special alloy, for instance, such as Monel and Inconel, is recently used to suppress the problems of hydrogen embrittlement in semiconductor facilities, FCEV(fuel cell electric vehicle) and hydrogen gas stations. The purpose of this study is to investigate the characteristics according to ratio change between drawing and extrusion of Monel material within elastic limit through numerical analysis. As the results, the possibility of plastic deformation in case of drawing was greater than that of extrusion. Consequently, the safety factor related to plastic deformation shows the results depending on the ratio change of force between drawing and extrusion.

This study investigated the optimal process conditions and mechanical properties of Cu-10Sn alloys produced by the powder bed fusion (PBF) method. The optimal PBF conditions were explored by producing samples with various laser scanning speeds and laser power. It was found that under optimized conditions, samples with a density close to the theoretical density could be fabricated using PBF without any serious defects. The microstructure and mechanical properties of samples produced under optimized conditions were investigated and compared with a commercial alloy produced by the conventional method. The hardness, maximum tensile strength, and elongation of the samples were significantly higher than those of the commercially available cast alloy with the same chemical composition. Based on these results, it is expected to be possible to use the PBF technique to manufacture Cu-10Sn products with complex 3D shapes that could not be made using the conventional manufacturing method.

We investigated the microstructure of an FeCrMnNiCo alloy fabricated by spark plasma sintering under different sintering temperatures (1000–1100°C) and times (1–600 s). All sintered alloys consisted of a single face-centered cubic phase. As the sintering time or temperature increased, the grains of the sintered alloys became partially coarse. The formation of Cr7C3 carbide occurred on the surface of the sintered alloys due to carbon diffusion from the graphite crucible. The depth of the layer containing Cr7C3 carbides increased to ~110 μm under severe sintering conditions (1100°C, 60 s). A molten zone was observed on the surface of the alloys sintered at higher temperatures (>1060°C) due to severe carbon diffusion that reduced the melting point of the alloy. The porosity of the sintered alloys decreased with increasing time at 1000°C, but increased at higher temperatures above 1060°C due to melting-induced porosity formation.

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 Yi2Ti2O7 in a nano Mo-ODS alloy using TiH2. The alloy compositions were determined to be Mo-0.5Ti-0.5Yi2O3 and Mo-1.0Ti-0.5Yi2Oi2. 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 TiHi2 effectively improved the mechanical properties.