In this study, GNPs/FeCoNiCuAl particles synergistically reinforced aluminum matrix composites are developed by friction stir processing (FSP) to explore the effects of different GNPs contents (1, 3, and 5%) on the microstructure, mechanical performance, and wear resistance of the materials. The results show that the incorporation of GNPs affects the formation of the diffusion layer between the FeCoNiCuAl particles and the aluminum matrix. As the content of GNPs increases, the thickness and integrity of the diffusion layer between FeCoNiCuAl particles and aluminum matrix gradually decrease. In addition, the introduction of GNPs is beneficial in enhancing the proportion of high-angle grain boundaries in the composites, but the grain size of the specimen increases slightly to about 5.5 μm at a content of 5% GNPs. When the content of GNPs is 1%, the composites achieve the highest microhardness and the lowest specific wear rate (0.1459 × 10⁻⁶ mm3/ N·m), with the wear mechanism dominated by abrasive wear. Nonetheless, when the GNPs content in the composite increases to 5%, the thickness and integrity of the diffusion layer are minimal, causing the tensile strength of the composite to be reduced to 250 MPa, and the specific wear rate increased to 0.4244 × 10– 6 ( mm3/N·m), with the wear mechanism transformed to abrasive–adhesive mixed wear. This study demonstrates that the appropriate ratio of GNPs and FeCoNiCuAl particles can effectively enhance the mechanical and wear resistance properties of aluminum matrix composites, providing a theoretical basis for the design and development of high-performance aluminum matrix composites.

Poor bonding occurs with resin due to surface inertness of carbon fiber (CF), so CF surfaces were often treated. In some common surface treatments, sizing was a simple and effective modification method. Polyurethane (PU) was used as the main component of sizing agents due to its similar structure to polyamide 6 (PA6). The CF/PA6 composites’ interfacial properties were improved using PU as a sizing agent. Meanwhile, in this paper, glycidol (GLD) was introduced into the PU emulsion so that the epoxy group reacted with the carboxyl group on the acidified CF. After testing, when the content of glycidyl in the sizing agent is 2%, the CF/PA6 composites showed an important improvement in tensile, impact, and flexural strengths, which increased by 49.4%, 94.6%, and 53.2%, respectively. In addition, the effect of modified WPU sizing agents with different GLD contents on the properties of CF/PA6 composites was investigated.

In this study, the effect of welding heat input on the microstructure and mechanical properties of reduced-activation ferritic/martensitic steel weld metal was investigated to provide a basis for developing welding technology for this steel, which is considered a structural material for fusion reactor blankets. Autogenous bead-on-plate gas tungsten arc welding was performed with heat inputs of 0.57, 1.38, and 2.32 kJ/mm, and the microstructural evolution and mechanical properties of the weld metal were analyzed. The fraction of residual δ-ferrite in the weld metal varied depending on the welding heat input, which acted as a primary factor contributing to the reduction in weld metal strength, although it remained higher than that of the base metal. In addition, the effect of post-weld heat treatment (PWHT) at 730 °C for 1 h was evaluated. Before PWHT, the weld metal exhibited significantly higher hardness compared with the base metal. However, after PWHT, its hardness was substantially reduced, thereby minimizing the differences in hardness of the weld and the base metal.

In this study, Cu was added in amounts of 0, 0.5, and 1 wt% to Al-1Zn-0.5MM-0.3Mg alloys to investigate its effects on phase formation, microstructural evolution, recrystallization behavior, and mechanical properties under as-cast and extruded conditions. Additional Al2Cu phases appeared with increasing Cu addition. EBSD (electron backscatter diffraction) analysis of the extruded alloys revealed that the average grain size boundaries [HAGB (high angle grain boundary), > 15°] increased from 0.124 to 0.299, confirming recrystallization was significantly enhanced by the addition of 1 wt% Cu. Furthermore, the maximum ODF(orientation distribution function) intensity decreased from 6.597 to 3.88 (M.R.D.), indicating that the crystallographic texture became more randomized as recrystallization progressed. Tensile testing showed that the yield strength (YS) and ultimate tensile strength (UTS) increased from 56.28 to 62.28 MPa and from 91.58 to 152.73 MPa, respectively, due to grain refinement and both solid-solution and precipitation strengthening by Cu. These findings demonstrate that adding Cu effectively controls phase formation, recrystallization, and mechanical properties in Al-Zn-MM-Mg alloys.

A cold roll-bonding process using AA1050 and AA6061 sheets, in which the initial strain of AA1050 is higher than that of AA6061, was employed to fabricate an AA1050/AA6061 layered sheet. The sheet was then annealed at various temperatures ranging from 200 to 400 °C. The as-roll-bonded sheet exhibited a typical deformation structure in which the grains were elongated along the rolling direction. The evolution of the microstructure in the layered sheets varied significantly depending on the location, resulting in an inhomogeneous distribution of hardness along the thickness direction. After annealing up to 300 °C, both the AA1050 and AA6061 regions still mainly exhibited a deformed structure. Complete recrystallization occurred in the specimens annealed at temperatures above 350 °C. The hardness decreased with increasing annealing temperature in both AA1050 and AA6061, but the decrease was greater in the AA6061 region than in the AA1050 region. Resultantly, at 350 °C or higher, hardness was almost the same in all regions. The specimen annealed at 350 °C exhibited the best mechanical properties in terms of the balance between tensile strength and elongation. It is concluded that AA1050/AA6061 layered Al sheets with excellent mechanical properties can also be fabricated by CRB when AA1050 has a higher initial strain than AA6061, and subsequent annealing.

In this study, we investigated the effects of aging treatment on the physicochemical, mechanical, and barrier properties of edible composite films prepared from shellac (Sh) and cellulose nanofiber (CNF) with different blending ratios. Sh–CNF films (0%, 20%, and 50% CNF) were fabricated and subjected to aging for 7 days at 40°C and 53% relative humidity. Film thickness was found to decline with both CNF incorporation and aging, whereas there were corresponding increases in opacity, particularly in Sh-rich films. In addition, the moisture content and water solubility of films declined at higher CNF ratios, and aging contributed to further reductions in moisture content, although had no significant effects on water solubility. Color analysis revealed that aging promoted the yellowing of pure Sh films, whereas the addition of CNF mitigated these changes. The findings of mechanical analysis revealed that CNF enhanced tensile strength, yield stress, Young’s modulus, and work of break, although reduced elongation at break. Aging contributed to further enhancements of strength and stiffness, along with a reduction in flexibility, although the magnitude of change diminished at higher CNF contents. Furthermore, the findings of gas barrier analysis indicated that CNF was associated with reductions in oxygen permeability, although promoted increases in water vapor permeability, with aging having the opposite effects. Collectively, these findings revealed that the functional properties of Sh–CNF films can be tailored via controlled aging and blending, thereby highlighting the potential utility of these films as edible packaging 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.

The aromatization degree of coal liquefaction pitch is closely related to its molecular structure evolution and the properties of derived carbon fibers. Using refined coal direct liquefaction pitch (RCLP) as raw material, pitches with different aromatization degrees were prepared by the self-pressurization/N₂ blowing two-stage thermal condensation method. Carbon fibers were then produced through melt spinning, oxidative stabilization, and carbonization. As the aromatization degree advanced, the C/H atomic ratio rose from 1.55 to 2.01, with the mesophase content nearing 100%. During RCLP thermal polymerization, large toluene-insoluble molecules were readily generated, yet the enrichment of the mesophase was comparatively sluggish. The spinnable pitch from RCLP had a relatively high aliphatic hydrogen content (33.40% ~ 13.69%) and a lower aromaticity (91.62% ~ 96.90%). Increasing aromatization made the carbon fiber cross-section’s radial transverse texture more distinct and ordered. The carbon layers stacked closely and parallelly, leading to a continuously rising tensile modulus. Due to the inhomogeneity from isotropic and anisotropic component changes, the carbon fiber tensile strength first decreased and then increased. When the spinnable pitch C/H ratio was 1.84, the mesophase pitch-based carbon fiber had an average diameter of 14.78 μm, a tensile strength of 1140 MPa, and a tensile modulus of 209 GPa.

WC–Mo₂C–Co cemented carbides were fabricated to investigate the effects of Mo₂C addition on microstructure and mechanical properties. Dual hard-phase design using WC and Mo₂C was employed to optimize the balance between hardness and toughness. Spark plasma sintering (SPS) was conducted at various temperatures after ball milling, and 1300 °C for 5 min was identified as the optimized sintering condition, achieving complete densification and phase stability. The addition of Mo₂C refined the microstructure by suppressing abnormal WC grain growth through preferential dissolution of Mo₂C into the Co binder. Hardness increased up to 1769 Hv30 due to grain refinement and solid-solution strengthening, while promoted η-phase formation and reduced fracture toughness.The 27Mo₂C composition exhibited the most balanced combination of hardness and toughness. These results demonstrate that controlled Mo₂C addition enables dual hard-phase strengthening and microstructure optimization in WC–Mo₂C–Co carbides for advanced cutting and forming applications.

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 compares pure Ni coatings deposited on type 316H stainless steel using high-velocity oxy-fuel (HVOF) and directed energy deposition (DED) processes. Microstructural analysis showed that DED produced more uniform claddings with fewer pores, while HVOF resulted in incomplete melting and cracks. Elemental diffusion of Cr and Fe from the substrate into the cladding was evident in DED samples, especially at higher laser power, but minimal in HVOF due to low heat input. Vickers hardness testing revealed that DED claddings had higher hardness near the interface, which was attributed to solid solution strengthening and reduced porosity. Although HVOF better suppressed diffusion, it exhibited inferior mechanical properties due to internal defects. Overall, the DED process demonstrated superior coating quality and mechanical performance, suggesting its suitability for corrosion-resistant applications requiring both structural integrity and thermal stability, such as molten salt reactors.

건설 자재와 건설 폐기물의 환경적 영향에 대한 사회적 관심이 높아지고 있다. 고강도 콘크리트의 필요성이 점차 커짐에 따라, 본 연구에서는 서로 연관된 환경 문제에 대한 두 가지 잠재적 해결책을 검토하였다. 첫째는 재활용 콘크리트 골재의 사용량 증가 가능성이고, 둘째는 고로 슬래그를 시멘트로 활용(재활용)할 가능성이다. 일반적으로 재활용 골재를 사용하면 고강도 콘크리트의 강도 가 저하되는 것으로 알려져 왔다. 따라서, 본 연구에서는 재활용 골재 콘크리트의 배합비와 함량 변화를 분석하여 고층 건축에 재활용 골재가 실용적인지, 그리고 어떤 방식으로 활용되는지를 규명하고자 하였다.

This study examines the effect of delayed quenching (DQ) temperature on the microstructure and mechanical properties of API X70 linepipe steels. Three types of steels were fabricated by varying the DQ conditions: Base (without DQ), LDQ (low-temperature delayed quenching at 700 °C), and HDQ (high-temperature delayed quenching at 740 °C). The microstructures were characterized using optical microscopy, scanning electron microscope (SEM), and electron back-scattered diffraction (EBSD), and their mechanical properties were evaluated through tensile and Charpy impact tests. The Base specimen exhibited the finest effective grain size and the highest bainite fraction, resulting in superior yield strength and impact toughness. In contrast, the LDQ specimen showed increased pearlite content and coarser grains, leading to the highest tensile strength due to work hardening, but reduced impact properties due to crack initiation at the pearlite regions. The HDQ specimen, with the highest ferrite fraction, showed the best ductility and acceptable strength, as well as improved lowtemperature toughness owing to increased resistance to cleavage propagation. EBSD analysis confirmed that finer grains and higher fractions of high-angle grain boundaries play a crucial role in enhancing impact energy and lowering the ductile-to-brittle transition temperature (DBTT). These findings highlight the importance of optimizing DQ parameters to achieve a balanced combination of strength–toughness in high-strength linepipe steels.

In this study, we analyzed the structural and mechanical properties of aluminum foams fabricated using aluminum powders of varying sizes and mixtures. The effects of sintering and pore structure at each size on the integrity and mechanical properties of the foams were investigated. Structural characteristics were examined using scanning electron microscopy and micro–computed tomography, while mechanical properties were evaluated through compression testing. The experimental results demonstrated that smaller powder sizes improved foam integrity, reduced porosity and pore size, and resulted in thinner cell walls. In combination, these effects increased compressive strength as the powder size decreased. The findings of this study contribute to the understanding and improvement of the mechanical properties of aluminum foams and highlight their potential for use in a wide range of applications.

In this paper, the uniaxial tensile mechanical characteristics after synchronous biaxial pre-tension analysis are investigated on a ETFE film crown model. After the biaxial pre-stretching is completed, the rectangular specimens are cut along the MD and TD directions of the biaxially pre-stretched ETFE film to conduct the uniaxial stretching test. The uniaxial tensile mechanical properties of the ETFE film after biaxial pre-stretching are investigated, the specific uniaxial tensile mechanical property parameters of the biaxially pre-stretched film are determined, and the influence of biaxial pre-stretching on the uniaxial tensile mechanical properties of the ETFE film is analyzed.

To further increase the mechanical properties of polyacrylonitrile-based carbon fibers, a multiple stretching technique was applied. Carbon fibers were multiple stretched at 2200 °C and characterizations such as SEM, Raman, XRD, and TEM were used to investigate the evolution of microstructure of carbon fibers. It was found that the grooves on the surface of carbon fibers along the fiber axis direction became more obvious and the cross-section of fibers were twisted from nearly circular to elliptical after multiple stretching. Growth and slippage of graphite microcrystals along the fiber axis direction resulted decrease in disordered structure and defects in the carbon fibers and increase in the degree of graphitization. The multiple stretching effectively enhanced the length-to-width ratio of microcrystals. An increase of 75 GPa in tensile modulus and a retention rate of 0.95 in tensile strength were realized for carbon fibers multiple stretched at 2200 °C.

In this paper, poly(glycolic acid–co-DL–lactic acid) (PGDLLA)/poly(ɛ-caprolactone) (PCL) incompatible nanocomposites were combined with multiscale modeling (MSM) in a ratio of 80/20. Since the behavior and mechanical properties of blends depend significantly on the interphase region, the compatibilizer poly(l,l-lactic acid–co-ɛ-caprolactone) (P(lLA-co-ɛ-CL)) was used to improve compatibility and graphene oxide (GO) was used to increase the interphase strength of PGDLLA matrix/PCL. This work was done by mixing solvent to achieve the optimum disperse of GO in the matrix. The investigation of interfacial phenomenon by the theoretical interfacial models is important. Under the assumption of constant modulus and elastic deformation in the zero interface region, the predictions in this region are more unreliable when the calculations of experimental mechanical properties are analyzed in detail. In this study, PGDLLA/P(lLA-co-ɛ-CL)/PCL compounds were compared with the MSM approach to predict the plastic deformation in the stress–strain behavior. In contrast to the hypothesis that a simple look at the interphase area in nanocomposites, a finite element code is proposed to evaluate the efficiency of the interphase area. Both experimental results and FEM analysis showed that Young’s modulus increases by incorporating GO into GO/PGDLLA/P(lLA-co-ɛ-CL)/PCL nanocomposites; the amount of increase for incorporating 1 phr GO is about 61%.

본 연구는 아민화 셀룰로오스 나노섬유(CNF)를 시멘트 복합체에 적용하여 기계적 및 미세구조적 성능 향상을 도모하고자 하였다. CNF는 (3-aminopropyl) triethoxysilane (APTES)를 활용해 화학적으로 개질하였으며, 이는 시멘트 수화 생성물과의 계면 결합력 및 분산성을 향상시키기 위한 목적이다. 표면 개질의 성공 여부는 주사전자현미경(SEM)과 X-선 회절 분석(XRD)을 통해 확인 하였다. 다양한 함량의 개질 및 비개질 CNF를 혼입한 모르타르를 제작하여 압축강도 및 휨강도를 평가하였다. 그 결과, 아민화 CNF는 0.2% 혼입 시 압축강도 향상 효과가 가장 두드러졌으며, 휨강도는 0.3%에서 가장 우수한 성능을 나타내었다. 미세구조 분석을 통해, 아민화 CNF가 시멘트 수화물과의 상호작용을 통해 내부 조직을 치밀하게 형성하고 공극률을 저감시키는 것으로 확인되었다. 본 연구는 화학적으로 개질된 CNF가 지속가능하고 고성능인 시멘트 복합재료 개발에 있어 유효한 기능성 첨가제로 활용될 수 있음을 시사한다.

전 세계 이산화탄소 배출량이 지속적으로 증가하면서, 환경 개선 및 탄소 격리를 위한 다양한 연구들이 진행되고 있 다. 건설 산업에서도 탄소를 줄이기 위한 연구로 바이오차를 건설 자재에 사용하여, 탄소 격리를 위한 방법으로 진행되고 있다. 바이오차는 바이오매스를 열분해하여 생성한 숯으로, 높은 탄소 함량과 다공성 구조가 특징이며, 탄소 격리를 위한 물질로 떠오 르고 있다. 본 연구에서는 시멘트 사용량을 줄이고 바이오차를 혼입한 콘크리트를 건설 자재로써 가능성을 확인하고자 하였다. 이를 위해 시멘트의 일부를 바이오차로 치환하여 혼입한 콘크리트의 역학적 특성(슬럼프, 공기량, 압축강도)과 질량 기반 특성 (흡수율, 밀도, 공극률)을 평가하였다. 바이오차의 시멘트 치환율은 0%, 5%, 10%로 설정하였다. 바이오차의 수분 흡수 및 보유 력에 따라 바이오차의 시멘트 치환율이 증가할수록 슬럼프는 감소하였다. 바이오차의 다공성 구조를 SEM 실험으로 확인하였으 며, 이에 따라 콘크리트에서의 공극 형성으로 바이오차의 시멘트 치환율이 증가할수록 공기량과 흡수율이 증가하였다. 바이오차 의 시멘트 치환율 5%에서 압축강도와 비강도가 가장 높은 값으로 나타났으며, 탄소 격리를 위한 방법으로 건설 자재 활용의 가능성을 확인하였다.