Designing novel high-entropy alloys (HEAs) with low stacking fault energy has been drawn significant attention for achieving a unique combination of high strength and ductility via transformation-induced plasticity (TRIP) mechanism. However, extensive work hardening of TRIP HEAs have led to the difficulties in metalworking, which required very high thermomechanical processing temperature even to 1000 oC. In this study, we introduced warm multi-pass caliber rolling to Cr20Mn20Fe20Co20Ni20 (Ni20) HEA and Cr20Mn20Fe20Co35Ni5 (Ni5) TRIP HEA to validate the feasibility of thermomechanical processing for TRIP HEAs at 400 oC. Grain growth behavior of annealed HEA bars was analyzed after recrystallization and Vickers hardness test was performed to compare the Hall-Petch relationship for Ni5 and Ni20 HEAs. Ni5 TRIP HEA exhibited higher strain hardening but lower tensile elongation than Ni20 HEA, which was responsible for the poor workability of Ni5 TRIP HEA at room temperature. Tensile tests in temperature range from -180 to 225 oC revealed that Ni5 TRIP HEA showed stress-induced martensitic transformation that had preceded slip deformation of the austenitic phase in 10 – 100 °C, which is the temperature range feasible for shape memory applications. These results demonstrate that the warm multi-pass caliber rolling can be an effective process to fabricate TRIP HEA billets for structural and functional applications.
Developing earth-abundant oxygen-evolution reaction (OER) electrodes that operate efficiently at practical current densities remains a challenge because NiFe layered double hydroxides (LDHs), which are among the most active non-noble catalysts in alkaline media, are limited by poor electronic conductivity, nanosheet restacking, and weak contact with current collectors. Herein, we develop a binder-free, integrated NiFe-LDH/Ni3Se2@nickel foam (NF) electrode fabricated using a sequential hydrothermal route: Ni3Se2 is first grown on NF using Se powder and hydrazine, followed by the in-situ deposition of NiFe-LDH nanosheets. X-ray diffraction verifies the crystalline Ni3Se2 backbone and, after LDH growth, a diagnostic low-angle peak near 2 theta approximate to 11o is observed, assigned to the (003) basal reflection of hydrotalcite-like LDH. Field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy reveal conformal LDH coverage on the selenide scaffold with uniform Ni, Fe, and O signals, whereas X-ray photoelectron spectroscopy shows mixed-valent Ni2+/Ni3+ and Fe3+ in the shell, preserved Se2-from the core, and hydroxyl/ water species in O 1s, consistent with a hydrotalcite-like surface that readily evolves to Ni(Fe)OOH under an anodic bias. Electrochemically, the heterostructure exhibits lower overpotentials at 50-100 mAcm-2, a smaller Tafel slope, and reduced charge-transfer resistance relative to NiFe-LDH@NF and Ni3Se2@NF. The gains correlate with the largest double-layer capacitance and electrochemically active surface area, and the electrode exhibits stable chronopotentiometric operation. We attribute this performance to synergistic interfacial coupling and rapid electron-transport through Ni3Se2, together with abundant, well-wired LDH active sites and improved mass transport in the open 3D foam. This study provides a general strategy for fabricating high-rate alkaline OER electrodes based on LDH/metal selenide heterostructure.
This study investigates and validates the feasibility of a Charpy impact testing methodology conducted at 4K ultra-cryogenic temperatures using liquid helium (LHe). Conventional cryogenic impact tests are primarily performed at 77K using liquid nitrogen; however, with the increasing demand for hydrogen energy systems operating at lower temperatures, evaluating mechanical properties at temperatures below 20K has become essential. In this context, a new approach was developed to cool ISO 148-1 standard 316L stainless steel specimens by directly injecting LHe into a specially designed containment system. The injection was performed at a pressure of 9 psig, and it was experimentally confirmed that the specimen core temperature stabilized at approximately 4K within 45 seconds after LHe exposure. Subsequent Charpy impact testing at this temperature demonstrated reliable and repeatable results, confirming that sufficient thermal equilibrium had been achieved. The study not only demonstrates the technical feasibility of this cooling approach but also provides supporting data on the stability and reproducibility of mechanical property evaluation under ultra-low temperatures. In particular, the results offer significant insight into material behavior relevant for components exposed to cryogenic hydrogen conditions, such as storage tanks, transfer lines, and safety valves. The proposed methodology overcomes practical limitations of traditional testing setups by allowing efficient specimen cooling without requiring full-system cryogenic insulation. Therefore, this work provides a crucial reference framework for future material development and testing in support of next-generation hydrogen infrastructure, where accurate property data under extreme cryogenic conditions is critical for safe and efficient system design.
This study explores the electromagnetic (EM) wave absorption behavior of a bilayer structure comprising BaZnCoFe16O27-epoxy (BZCFO) and BaTiO3-epoxy (BT). BZCFO exhibits magnetic loss via ferromagnetic resonance (FMR) originating from BaZnCoFe16O27 particles, while BT provides high permittivity and dielectric loss due to the ferroelectric nature of BaTiO3 particles. The composite samples were prepared by individually mixing the synthesized single-phase powders of BaZnCoFe16O27 and BaTiO3 with 10 wt% epoxy. The complex permittivity and permeability of each layer were experimentally determined and applied in HFSS simulations across the 0.1–18 GHz frequency range. To ensure the accuracy of the simulation, the reflection loss (RL) results of the single-layer BZCFO structure were compared with experimental measurements and calculations based on transmission line theory. Based on this, various bilayer configurations were examined by adjusting the thicknesses of BZCFO (tBZCFO) and BT (tBT), and applying different BT layer patterns: non-patterned, cross-shaped, and square island types. The non-patterned bilayer exhibited lower performance than the optimized single BZCFO layer, with increased tBT causing reduced absorption due to stronger reflection. In contrast, the cross-shaped pattern exhibited enhanced broadband absorption when tBT = 0.2 mm, tBZCFO = 2.25 mm, and the pattern width was 1.0 mm, achieving an absorption bandwidth (Δf) of 12.51 GHz where RL remained below –10 dB. In the case of the square island pattern, an excellent absorption bandwidth of Δf > 12 GHz was achieved when the BT squares had a side length of 0.75 mm and covered approximately 2–14% of the BZCFO surface. These results highlight the potential of tailored dielectric–magnetic bilayers with patterned structures for broadband EM wave absorption and shielding applications.
Adhesion strength between coatings and substrates is a fundamental property. It determines the reliability, durability, and performance of coated materials in engineering applications. Coating technologies are widely used in semiconductors, displays, automotive, energy, and biomedical industries. However, there is still no universally accepted method to evaluate adhesion strength. This review examines the key factors that influence adhesion, such as surface energy, contact angle, interfacial chemistry, and microstructure. It also classifies adhesion mechanisms into mechanical interlocking, interdiffusion, and compound layer formation. Evaluation methods are critically compared. Adhesive-based tests, such as lap shear, pull-off, and tensile adhesion, are standardized by ASTM and ISO. They provide quantitative values but are limited by the strength of the adhesive itself. In contrast, adhesive-free methods, including scratch, indentation, and peel tests, can directly reveal interfacial failure modes, but their outcomes are markedly influenced by test parameters and specimen preparation. Consequently, no single method can comprehensively characterize adhesion strength. Therefore, a complementary approach using multiple methods is recommended. Reliable evaluation also requires careful specimen preparation, strict compliance with standards, and the use of auxiliary diagnostics such as acoustic emission and microscopy. This review provides researchers and engineers with a clear framework for standardized and reliable evaluation of adhesion strength between coatings and substrates.
Au-ZnO nanostructures derived from zeolitic imidazolate framework-8 (ZIF-8) were rationally designed and investigated as highly efficient chemiresistive sensors for detecting H2S gas. The incorporation of Au nanoparticles markedly enhanced the sensing characteristics relative to pristine ZnO, delivering an extraordinary response of ~419.1 toward 10 ppm H2S at 200 °C—nearly two orders of magnitude higher than that of bare ZnO. The optimized Au-ZnO 2 sensor demonstrated excellent selectivity against interfering gases (NO2, NH3, H2, and volatile organics), fast response/recovery dynamics, and reliable detection down to 0.2 ppm, maintaining stable operation under repeated cycling. Structural and spectroscopic analyses revealed that Au nanoparticles were uniformly anchored on the porous ZnO surfaces, establishing abundant catalytic sites and Au-ZnO Schottky junctions that facilitate charge transfer and accelerate surface reactions. The superior sensing performance arises from the synergistic effects of Au-induced catalytic dissociation, spillover phenomena, and interfacial electronic modulation within the MOF-derived porous framework. This study provides a clear structure–performance correlation and demonstrates a scalable strategy for developing noble-metal/semiconductor hybrid gas sensors with outstanding sensitivity, selectivity, and long-term stability for practical toxic-gas monitoring applications.
The increasing transition to electric vehicles and new Euro 7 standards has intensified the focus on brake-derived particulate emissions. Current braking systems exhibit significant susceptibility to corrosion with an accelerated wear rate. This susceptibility highlights the need for materials that can maintain stable friction coefficients under various operating conditions. Therefore, this study investigated the application of Fe-Cr-based composite coatings on gray cast iron substrates for brake-disc applications, while also developing an automated wear pattern recognition methodology. High-velocity oxygen fuel-sprayed Fe-Cr-based composite coatings were evaluated via ball-on-disk tests against Si3N4 and WC counterfaces under standardized conditions (load: 20 N, sliding distance: 1000 m, speed: 100 RPM). Microstructural analysis revealed that the composite coatings achieved significantly enhanced mechanical properties (hardness: 6.52–7.51 GPa) compared to the gray cast iron substrate (1.98 GPa). Tribological testing demonstrated superior wear resistance, with Composite B exhibiting a specific wear rate of 7.37 × 10−6 m3 N−1 m−1, representing a three-fold improvement over that of conventional materials. Energy-dispersive X-ray spectroscopy analysis identified two distinct tribochemical interactions: SiO2 and WO2 formation with the Si3N4 and WC counterfaces, respectively. A deep ensemble convolutional neural network, trained on 500 scanning electron microscopy images, achieved a superior classification performance (training: 0.947, validation: 1.000, test: 0.960 accuracy) in automated wear pattern recognition. This integrated approach, which combines materials science with machine learning, provides an effective methodology for both material development and automated wear analysis in tribological applications.
The bonding characteristics and high-temperature reliability of gold bonding wires were investigated with respect to the thickness of the aluminum pads and the addition of palladium. Samples of high-purity gold (99.99%, 4N) and gold with 1% palladium added (99% purity, 2N) were processed into 15.3 μm diameter ultra-fine wires through wire drawing and bonded to aluminum pads with thicknesses of 1 μm and 5 μm using ball bonding equipment. The reliability at elevated temperatures was evaluated by annealing at 175oC for up to 1,000 hours. Micro-structural and intermetallic compound (IMC) phase changes at the vertical cross-sections of bonded areas were characterized using SEM-EDS at specific time intervals. For 1 μm aluminum pads, both 4N and 2N gold wires initially exhibited identical bonding ball morphologies. Voids began to form at the lateral sections after 250 hours, accompanied by the formation of Au8Al3 and Au4Al phases. Despite these observations, stable bonding was maintained up to 1,000 hours, with the palladium addition proving advantageous in terms of bonding strength. On the other hand, for 5 μm aluminum pads, IMCs in the 4N wire were stabilized as Au8Al3, maintaining the bond interface for up to 1,000 hours. However, for the 2N wire, significant voids were observed beneath the bond interface as early as 250 hours. These voids were attributed to the incorporation of palladium, which caused the growth of AuAl2 into Au2Al, leading to rapid shrinkage due to phase transformation occurring at a very early stage. Therefore, the addition of palladium is less favorable when using 5 μm thick aluminum pads, as it induces different inter-diffusion phenomena compared to 1 μm pads, resulting in void formation.
In this study, we explore the potential of pulsed ultraviolet (UV)-assisted thermal annealing as an effective low-temperature processing technique for fabricating high-performance indium oxide (In2O3) thin films, with a particular emphasis on their application in thin-film transistors (TFTs). In2O3 films were synthesized using a solution-based method, with indium nitrate hydrate serving as the precursor. The precursor solution was spin-coated onto SiNX/p+-Si substrates to form uniform thin films. To assess the effectiveness of the annealing approaches, we compared conventional thermal annealing at 300 degrees C with pulsed UV-assisted thermal annealing conducted at a reduced temperature of 200 degrees C. Characterization techniques- including UV-Vis spectroscopy, X-ray diffraction, atomic force microscopy, and scanning electron microscopy-revealed that pulsed UV-assisted annealing significantly improved the optical transparency, crystallinity, and carrier concentration of the films, even at lower processing temperatures. Electrical characterization of the resulting TFTs showed enhanced device performance, including higher drain currents and improved field-effect mobility, compared to devices fabricated with conventionally annealed films. Despite the improved electrical properties, the increased hydrophilicity of the UV-annealed films indicates the need for additional surface passivation to ensure long-term device stability. Overall, this work demonstrates that pulsed UV-assisted thermal annealing is a promising low-temperature processing strategy for the development of transparent oxide semiconductors in next-generation electronic devices.
Digital light processing (DLP) 3D printing has emerged as a promising technique for fabricating high-precision ceramic components, including biomedical implants. However, achieving high-strength silicon nitride (Si3N4) spinal implants via DLP remains challenging due to slurry formulation constraints. This study optimizes the formulation of a photocurable Si3N4 slurry to enable DLP-based printing of spinal implant components. The effects of monomer composition and photoinitiator content on slurry viscosity and stability were evaluated. Slurries with only monomer A exhibited post-printing warpage, while those with only monomer B showed rapid polymerization shrinkage, causing delamination. In contrast, a 1:1 weight ratio blend of monomers A and B with 3 wt% photoinitiator (M-AB-3) maintained viscosity stability within 3% over 24 h and showed excellent shape fidelity. The flexural strength of the green body increased to 122 MPa when 8 wt% oligomer A was added, while viscosity rose to similar to 9,100 cP. A low-viscosity oligomer B was added to reduce viscosity. A formulation with 4 wt% oligomer A and 4 wt% oligomer B achieved optimal performance, with similar to 7,000 cP viscosity and 154 MPa green strength. Based on this optimized resin, ceramic solid loading was increased stepwise, and 66 wt% was determined to be the maximum printable content. Printed specimens were sintered under nitrogen (1800 degrees C, 1 MPa), resulting in a relative density exceeding 99%, flexural strength of 1,070 MPa, Vickers hardness of 1,670 HV, and fracture toughness of 7.3 MPa.m(1/2). These results confirm that the developed slurry enables stable high-solid loading and yields high-performance Si3N4 components suitable for spinal implant applications.
This study investigates the fabrication and high-temperature time-dependent deformation of a multi-sheet stacked Ni-Cr-Al superalloy foam. The foam was produced by powder spraying to deposit alloying elements onto a pure Ni preform, followed by transient liquid phase sintering for homogenization and hot rolling for lamination and structural integrity. The fabricated foam exhibited a relative density of 4.55% and a porosity of 95.45%, with an average pore size of 2988.1 mu m in the rolling direction. Microstructural analysis confirmed a gamma(Ni, Cr) matrix and cuboidal gamma '(Ni3Al) precipitates (60.7% volume fraction). Time-dependent deformation tests at 923 K and 1073 K under constant compressive load revealed a significant difference in creep strain. At 923 K, 0.29 MPa (=0.387 sigma Y) stress resulted in a strain of 0.123, whereas at 1073 K, 0.14 MPa (=0.389 sigma Y) stress induced 0.246 strain, approximately twice the creep deformation. Despite higher creep strain at 1073 K, the stress exponent was lower (2.31 vs. 3.76 at 923 K). This is attributed to intersecting struts at sheet interfaces constraining free deformation through friction and interaction effects. Additionally, densification at strains over 30% increased relative density, which altered the initial stress effect and led to continuously decreasing creep deformation rates. Based on these results, the influence of strain hardening, densification, and structural interactions at sheet interfaces on the time-dependent deformation behavior of the block Ni-Cr-Al foam is discussed.
The cathode active materials of lithium-ion batteries (LIBs) contain critical metals including Ni, Co, Mn, and Li. Since these metals are only produced in a few countries, it is necessary to recover them from spent lithium-ion batteries. The concentrated electrode materials of lithium-ion batteries are referred to as black mass (B/M), which contains a large amount of carbon used as the anode material, along with metal oxides used in the cathode. In this study, the effect of roasting temperature in an Ar+CO gas atmosphere on the reduction behavior of NCM (LiNixCoyMn1-x-yO2)-based black mass powder and the recovery of Li was investigated. In the thermogravimetric analysis, the CO2 concentration increased sharply from about 430 degrees C to a maximum value and then decreased, during which a weight gain due to the formation of Li2CO3 was also observed. Above approximately 700 degrees C, the concentration of CO increased due to the reaction of CO2 with the C in the B/M due to the Boudouard reaction. In the isothermal roasting in an Ar+CO 50 vol.% atmosphere, the weight of the sample decreased significantly above 696 degrees C, and the final weight loss amount also increased with increasing temperature. Most of the significant weight loss is thought to be due to the Boudouard reaction. Li2CO3 was generated regardless of temperature. Above 696 degrees C, most of the Ni and Co oxides were reduced to metals, and above 900 degrees C, some of the MnO was also reduced and is thought to have been dissolved in the Ni-Co alloy. At temperatures above 696 degrees C, where the NiO was fully reduced, the recoveries rate of lithium was approximately 90 % with no significant difference.
strength and heat resistance compared to conventional carbon steels, making them widely utilized in the automotive, machinery, and aerospace industries for high-strength fastening and precision-formed components. However, such high-strength steels often suffer from die wear and cracking during cold forming processes. To address these issues, optimization of spheroidizing annealing conditions through appropriate microstructural control via heat treatment is essential. In this study, spheroidizing annealing conditions were optimized for two steel grades: the widely used CHQ-grade SCM435 and a newly developed 1600 MPa-grade ultra-high-strength Cr-Mo alloy steel. A series of spheroidizing heat treatment conditions were applied to both steels, and their spheroidization behavior and mechanical characteristics were comparatively analyzed based on initial microstructural differences. Intercritical Annealing (IA) and Subcritical Annealing (SA) cycles were designed based on Ac1 and Ac(3 )transformation temperatures determined via DSC analysis. The results revealed that both steels exhibited optimal spheroidization and hardness reduction when subjected to IA conditions with a second heating temperature approximately 20-40 degrees C below Ac-1. The lowest Vickers hardness was observed at 113 HV for SCM435 and 171 HV for the developed alloy, corresponding to an average decrease of 55% and 54.5% from their initial hardness, respectively. Microstructural observations showed that SCM435, which primarily consists of pearlite in a ferrite matrix, underwent effective spheroidization under both IA and SA conditions. In contrast, the bainitic structure of the developed alloy required prior austenitization under IA conditions to enable successful spheroidization. A quantitative evaluation using the morphological shape factor (F) confirmed there was a clear inverse relationship between hardness and F values, indicating that this factor can serve as a reliable metric for assessing cold formability and the effectiveness of spheroidizing heat treatment.
The effects of Mn on pitting corrosion resistance for Fe-22Cr-9Ni-3Mo-(0, 2, 4)Mn (wt%) duplex stainless steels (DSSs) were investigated, by considering the microstructural change and the Mn content in the solid solution state. By fabricating the ingots under carefully controlled conditions and performing hot rolling and solution treatments, three DSSs were prepared to have similar microstructural features in terms of phase fraction, grain size, and volume fraction of nonmetallic inclusions (NMIs). The NMIs in the DSS without Mn were found to be Cr2O3, and those in the DSSs containing Mn were (Cr,Mn)(2)O-3. Accordingly, the Mn content in the solid solution state and the type of NMI were considered as the primary factors affecting pitting resistance. Potentiodynamic polarization tests in neutral NaCl solution showed that the pitting resistance decreased as the Mn content increased. After the polarization tests, it was found that the (Cr,Mn)(2)O-3 in the DSSs containing Mn acted as pitting initiation sites, whereas Cr2O3 in the DSS without Mn remained uncorroded. In addition, the critical dissolution rate of the DSSs measured in strongly acidic HCl solution increased with increasing Mn content, suggesting that the pit propagation rate was accelerated by Mn addition. In conclusion, the Mn addition to DSSs reduced pitting resistance by providing more pit initiation sites and also increasing the pit propagation rate.
This study investigated the localised corrosion behaviour of UNS A93003 alloy in a chloride environment, employing potentiodynamic polarisation, electrochemical impedance spectroscopy (EIS), and surface analysis techniques. Potentiodynamic polarisation results indicated that, as the chloride concentration increased, the alloy surface exhibited higher anodic current densities at the same overpotential, suggesting an accelerated rate of localised corrosion. During the initial immersion period, electrochemical reactions on the alloy surface were dominated by protective mechanisms such as passivation and re-passivation, resulting in an increase in surface resistance. However, as immersion time progressed, localised corrosion became the dominant process, leading to a significant reduction in surface resistance. With prolonged exposure, extensive localised corrosion was observed with corrosion products such as aluminium oxide and hydroxide accumulating around the affected areas. These corrosion products acted as intermediaries that promoted further electrochemical reactions, potentially accelerating the propagation of localised corrosion. These findings confirm that the corrosion behaviour of the UNS A93003 alloy surface evolved dynamically over time, highlighting its susceptibility to localised corrosion in chloride environments. The results provide essential insights that could support efforts to enhance alloy durability and effective corrosion prevention strategies for industrial applications.
To protect gas turbine hot section components from operating temperatures exceeding 1100 oC, thermal barrier coating systems are used. Although yttria-stabilized zirconia (YSZ) is commercially used as a thermal barrier coating material, it is destabilized by phase transformations when exposed to extremely high-temperature operating environments (>1200 oC). In efforts to resolve this critical issue, Gd2O3- and Yb2O3-doped YSZ species have been developed as candidate alternative materials. Compared with conventional YSZ, however, GdYb-YSZ exhibits reduced thermal cycling resistance performance under 1400 oC thermal cycling test conditions. To overcome this drawback, a bilayer TBC structure was designed and prepared using conventional YSZ and rare-earth-oxide-modified GdYb-YSZ in the current study. The thermal conductivity and high-temperature thermal cycling durability were subsequently evaluated for bilayer coatings with various thickness ratios of YSZ (bottom layer) and GdYb-YSZ (top layer). Additionally, YSZ derivatives respectively doped with Sc2O3, Gd2O3, Dy2O3, and TiO2 (developed in our previous research) were prepared in both single-layer and bilayer structures and the thermal conductivity and thermal cycling durability were compared for both structures. All bilayerstructured TBC samples respectively exhibited lower thermal conductivity than the single-layer YSZ baseline value of 1.1 W/(mK). Moreover, in high-temperature thermal cycling durability assessments, the bilayer structures exhibited equivalent or superior durability compared with the single-layer YSZ coating. These findings highlight the potential of these materials for use as advanced TBC materials in gas turbines.
Lithium-ion batteries (LIBs) are valued for their lightweight nature, long cycle life, and high energy density, which make them ideal for use in electric vehicles and portable electronics. Recently, red phosphorus (P) has been identified as a potential anode material with a theoretical specific capacity of 2,596 mAh g-1. However, its low conductivity (10-12 Sm-1) and significant volumetric expansion during cycling limit its effectiveness. On the other hand, silicon (Si) has a theoretical capacity of approximately 3,579 mAh g-1 but is problematic because it experiences over 400% volume expansion during lithiation and delithiation. This study presents a silicon and nitrogen-doped carbon nanotube (CNT) composite integrated with red phosphorus, prepared using a simple and scalable process. The P/Si/NCNT composite mitigates harmful electrode/electrolyte reactions, while stabilizing performance during charge-discharge cycles. By combining high-capacity silicon and red phosphorus, the composite achieves enhanced capacity and conductivity while minimizing volume fluctuations by hybridization with CNTs. Electrodes displayed an initial discharge capacity of 2025 mAhg-1 at 100 mAg-1 with a high reversible capacity of 515/521 mAh g-1 after 100 cycles. The prepared composite exhibited good rate capability with 342 mAh g-1 discharge capacity at 1000 mAg-1 after a long 200 cycles, demonstrating excellent rate capability. The enhanced electrochemical performance can be attributed to the synergistic effects of the P/Si blend and the conductive nitrogen-doped CNT framework, highlighting potential advancements in sustainable energy storage solutions.
Laser directed energy deposition (L-DED) is a metal additive manufacturing technique that provides high design flexibility and enables the fabrication of complex geometries. However, the rapid and localized thermal cycles inherent to the process lead to the formation of residual stresses, which degrade mechanical properties and dimensional accuracy of the fabricated parts. In this study, the effect of L-DED process parameters on residual stress formation was investigated using AISI 316L powder. Experiments were conducted by depositing material onto substrates fixed at both ends, and bending deformation after constraint removal was measured to evaluate the residual stress. The influences of key process parameters, including laser power, scan speed, and scanning strategy, were systematically examined. A finite element method (FEM) simulation based on the birth and death technique was developed to replicate the thermal and mechanical behavior during the L-DED process. The simulation incorporated the temperature gradient mechanism (TGM) and thermal strain of deposited layers to improve prediction accuracy. The FEM model successfully reproduced the experimental trends, accurately predicting both the bending height and residual stress distributions under various processing conditions. In particular, the model effectively captured the influence of different scanning strategies on the stress profile, demonstrating its ability to simulate processinduced thermal and mechanical behaviors with high fidelity. These findings provide a quantitative basis for optimizing L-DED parameters and contribute to process design strategies aimed at minimizing residual stress and enhancing dimensional stability in metal additive manufacturing.
Zinc oxide (ZnO) is a multifunctional material extensively used in ceramics, electronics, pigments, and pharmaceuticals. The increasing global demand for ZnO, coupled with growing environmental concerns, necessitates the development of resource-efficient and eco-friendly manufacturing methods. This study investigates a dry metallurgical approach for recovering high-purity ZnO powder from zinc ferrite-rich fume dust, a byproduct generated during the roasting of zinc sulfide concentrates. Fume dust samples obtained from industrial zinc roasters were characterized using X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM), which revealed a composition dominated by ZnO, ZnFe2O4, Zn2SiO4. A reductive volatilization process was conducted using a laboratory-scale rotary kiln at temperatures ranging from 1,100oC to 1,300oC, employing carbon and aluminum powders as reducing agents. The volatilized zinc was condensed and subsequently oxidized to form ZnO particulates. The process achieved zinc recovery efficiencies of up to 96% under optimized conditions, and the final ZnO purity exceeded 99.3% by weight. The produced ZnO powder exhibited particle sizes ranging from tens to hundreds of μm and was recovered in an amorphous form. The residual slag contained less than 1% Zn, and most of the Fe remained in a solid state, suggesting the possibility of reuse as an iron source in metallurgical fields. In addition, zinc could be purified and recovered as spherical zinc oxide of approximately 300 nm through a wet smelting process. Finally, nanosized zinc oxide with a purity of approximately 99.84% could be recovered. This work demonstrates that dry metallurgical processing of zinc fume dust offers a sustainable route to high-value ZnO production, minimizing wastewater generation and enabling the circular utilization of metallurgical byproducts.
This study investigates the mechanical behavior and deformation characteristics of Inconel 718 lattice structures with different unit cell sizes fabricated by laser powder bed fusion (LPBF). Two body-centered cubic (BCC) lattice structures with unit cell sizes of 2 mm (BCC 2) and 4 mm (BCC 4) were designed while maintaining a constant strut diameter. The measured relative densities were 31.48% for BCC 2 and 8.67% for BCC 4, indicating a significant reduction in density as the lattice size increased. Although the relative densities differed considerably, both lattices exhibited similar microstructural features such as columnar grains, melt pool boundaries, and surface-attached partially melted powders. No distinct thermal influence was observed with varying unit cell size, demonstrating that uniform build quality was maintained regardless of geometric scale under the given LPBF conditions. Compressive testing revealed that BCC 2 exhibited substantially higher compressive strength (58.47±3.23 MPa) than BCC 4 (1.78±0.11 MPa), which was attributed to enhanced structural stability and a higher number of struts and nodes. Digital Image Correlation (DIC) analysis and cross-sectional microstructure observations confirmed that BCC 2 displayed progressive densification and buckling-dominated deformation, while BCC 4 predominantly exhibited bending-dominated failure with localized deformation. Notably, despite the narrower strut spacing in BCC 2, no discernible thermal influence—such as melt pool distortion or grain coarsening—was identified, indicating that the effect of unit cell size on thermal behavior during LPBF processing remained negligible under the given conditions. These findings were discussed in terms of the effects of lattice unit cell size on microstructure, compressive properties, and deformation behavior.
