최신논문

Home > KJMM 논문 > 최신논문

This study investigates the effect of electron beam welding (EBW) on SA508 Gr.3 Cl.1 Mn-Mo-Ni low alloy steel, focusing on changes in the microstructural and mechanical properties of the weld and heat-affected zone (HAZ) under various post-weld heat treatment (PWHT) conditions. The rapid cooling inherent in the EBW process led to the formation of coarse columnar structures consisting of Widmanstätten ferrite and bainite in the weld. In the HAZ, finer low-temperature transformation microstructures, such as martensite and lower bainite, were observed, compared to the weld metal. The formation of these microstructures resulted in increased hardness and residual stresses. To address these effects, PWHT was conducted at 610℃ and 630℃. After PWHT, precipitates formed along the laths within the grains, and the softening of the matrix combined with the relaxation of residual stresses led to decreased hardness and strength, accompanied by improved impact toughness. However, as the PWHT temperature increased, the coarsening of precipitates contributed to an increase in the impact transition temperature. Moreover, despite the application of post-weld quality heat treatment, the segregation of solute atoms at the columnar grain boundaries in the weld metal was not completely eliminated. Consequently, the impact transition properties of the weld metal did not fully recover to the level of the base metal. (Received 21 March, 2025; Accepted 13 May, 2025)

keyword : SA508 Gr.3, Electron Beam Welding, Post-Weld Heat Treatment, Post-Weld Quality Heat Treatment, Microstructure, Mechanical Properties

The joining of Ni/Al dissimilar metals to exploit the synergetic effect between the unique properties of Ni and Al alloys has been studied for potential applications in various industrial areas. This study investigates the interfacial reaction between deposited AlSi10Mg and an Inconel 625 substrate during the laser direct energy deposition (L-DED) process. Samples were fabricated with the L-DED process with five different laser process parameters. The effects of the different L-DED process parameters on the microstructure, chemical composition, and mechanical properties of the interface were analyzed. The results showed that as the volumetric energy density (VED) increased, the intermetallic compound (IMC) phase became thicker, and defects such as cracks tended to occur. An energy dispersive spectrometer analysis exhibited the formation of two different IMC phases, Al3Ni5 and NiAl, at the interface. Tensile tests demonstrated that as the VED was decreased, the tensile interfacial strength increased due to the thinner IMC interlayer and fewer interfacial defects. Although the interface showed lower tensile strength compared to L-DED processed AlSi10Mg and Inconel 625, it exhibited reliable tensile interfacial strength, in the range of 11 - 34 MPa. The results demonstrate that an adequately low VED can produce a dissimilar joint between AlSi10Mg and Inconel 625 with a defect-less interface. This approach is expected to be beneficial for the Ni- Al multi-material L-DED process and for producing Ni and Al dissimilar joint structures. (Received 12 March, 2025; Accepted 15 April, 2025)

keyword : Directed Energy Deposition, Dissimilar Metal Joining, AlSi10Mg, Inconel 625, Interfacial Reaction, Mechanical Properties

In this study, during the manufacturing process for SCR420H steel we attempted to measure the atmosphere during gas nitriding and examine the formation of a compound layer accordingly. For the nitriding process, the processing time was changed at K_N (Nitriding potential) 1.2 atm^-1/2 at temperatures of 510 and 540 ℃ for SCR420H steel, and the formation behavior of the compound layer was observed. At the beginning of the nitriding process, the ε phase was formed due to high K_N, and then the γ′ phase formed inside due to the concentration gradient. As the processing time increased, the ε phase and the γ′ phase grew, and the fraction of γ′ phase gradually increased. Meanwhile, at a nitriding process temperature of 540 ℃, the compound thickness grew and then decreased as the nitriding process time increased, and a rapid change in surface hardness was observed. The effective hardening depth was proportional to the square root of time. The formation mechanism of these nitrided compounds could be comparatively and thermodynamically analyzed using the CALPHAD (CALculation of PHAse Diagram) technique. In addition, we were able to confirm the formation mechanism of the ε phase and γ′ phase during the nitriding process through a modified Lehrer diagram. (Received 31 March, 2025; Accepted 29 April, 2025)

keyword : Nitriding, Microstructure, Compound layers, SCR420H, Hardness test

With the growing demand for LIBs (lithium-ion batteries) for EVs (electric-powered vehicles), it will be important to recover valuable metals from spent lithium-ion batteries in the future. The black mass recovered from spent lithium-ion battery contains elements such as Li, Ni, Co, and Mn with C. The carbon in the black mass can act as a reducing agent of oxide. This study investigated the effect of reaction temperature on the reduction behavior and Li recovery from black mass powder mixed with spent NCM (LiNi_xCo_yMn_zO₂) powder and C in an Ar atmosphere. In the isothermal reaction, the weight loss rate increased with an increase of temperature, and the final amount of weight loss also increased. After significant weight loss, the NCM powder was decomposed and nickel and cobalt oxides were reduced to metals. When significant weight loss occurred, a significant amount of CO gas was also emitted. This phenomenon is due to the reduction of nickel and cobalt oxides in the black mass and the reaction of CO₂ with C by the Boudouard reaction. When the isothermally reacted black mass was leached in water, the Li recovery increased with an increase of the reaction temperature, and the Li recovery above 900 ℃ was about 98%. From these results, by heating the black mass in an inert atmosphere lithium can be separated and recovered from valuable metals and C. (Received 21 April, 2025; Accepted 12 May, 2025)

keyword : Lithium-ion battery, Reduction, Boudouard reaction, Recycling, Water leaching

Gas sensors are crucial devices in various fields such as industrial safety, environmental monitoring, gas infrastructure including hydrogen use, and medical diagnostics. These sensors precisely measure the presence of gases on-site in different environments to ensure operational safety and efficiency. Designed for high sensitivity, stability, and reliability, gas sensors are often required to be cost effective and compact while providing a rapid response. To address these diverse needs, we have developed two types of gas sensors based on volumetric and manometric methods. These two sensors are operated by measuring the gas volume and the pressure changes, respectively, by emitted gas. They are capable of determining the values of gas transport parameters, such as gas uptake, solubility, and diffusivity, for polymers exposed to gas under a high pressure environment. The sensors provide rapid responses within one second and can measure gas uptake in a range from 0.01 wt·ppm to 1500 wt·ppm with adjustable sensitivity and measurement ranges. Performance evaluations demonstrate the sensors' reliability, adaptability to varying measurement ranges, and stability under temperature/pressure fluctuations. The results demonstrate that this sensor system provides real-time detection and analysis of gas transport properties in gases, including H₂, He, N₂, O₂, and Ar, and that it is suitable for pure gas sensing. (Received 6 February, 2025; Accepted 10 May, 2025)

keyword : Gas sensors, Volumetric measurement, Manometric measurement, Gas emission, Diffusivity, Polymer

This study systematically investigates the microstructure, mechanical, and corrosion properties of hot-extruded Al3102 alloy flat tube, with direct comparisons to as-cast equivalents. Microstructural analysis revealed that both materials primarily consist of an aluminum matrix, with widespread distribution of Al₆(Mn,Fe)-type precipitates in their initial structures. The flat tube exhibited an average grain size of 77.3 μm, which is substantially reduced compared to the billet's 243.0 μm, reflecting an effective refinement of the microstructure. Additionally, the flat tube exhibited a slightly lower precipitate volume fraction and a marginally coarser particle size, suggesting that dynamic recrystallization during hot extrusion not only promotes grain refinement but also induces precipitate coarsening. Corrosion resistance was assessed using electrochemical testing procedures based on the ASTM G69 standard. Although the corrosion potentials (Ecorr) of the flat tube (-639.6 mV) and the billet (-657.7 mV) are comparable, the flat tube demonstrated a notably reduced corrosion current density (25.2 μA/cm²) and corrosion rate (0.27 mm/year), implying enhanced resistance to corrosion. This improvement is primarily attributed to the reduced quantity and more homogeneous distribution of precipitates, which effectively suppress galvanic corrosion. In terms of mechanical properties, the flat tube exhibited a marginally greater ultimate tensile strength (UTS) of 91.7 MPa, compared to 77.9 MPa for the billet, presumably due to the Hall-Petch strengthening effect induced by grain refinement. The hot extrusion process enhances the overall performance of Al3102 alloy by tailoring its microstructure and precipitate morphology, thereby providing both theoretical and technical foundations for its application in lightweight systems such as automotive heat exchangers. (Received 8 April, 2025; Accepted 12 May, 2025)

keyword : Al3102 alloy, Hot extrusion, Flat tube, Microstructure, Corrosion resistance, Mechanical property

Metal additive manufacturing (AM), often referred to as metal 3D printing, is a promising and widely adopted approach for fabricating intricate components without conventional molds or casting processes. Although powder-based metal AM processes have gained significant recognition for their ability to realize complex shapes, their cost remains a major barrier to broader commercialization. To address these cost-related challenges, the use of wire-feed directed energy deposition (DED) has emerged as a potential alternative. In particular, laser-based wire directed energy deposition (LW-DED) offers an effective balance between resolution, build rate, and materials flexibility. This review first outlines the limitations of powder-based metal AM processes, highlighting issues such as low powder yield and material cost. Subsequently, it explores the fundamental operating principles of LW-DED, including laser-beam types, deposition head configurations, and their impact on process efficiency. In particular, the review highlights coaxial LW-DED, which enables more uniform material deposition and improved precision. Additionally, it examines the advantages of LW-DED (e.g., reduced material loss, lower raw-material costs, and multi-material flexibility) as well as its shortcomings (including lower resolution and potential need for post-processing). Finally, recent research trends of coaxial LW-DED systems and ongoing advancements in process monitoring, microstructure control, and machine learning-driven optimization are presented to illustrate the potential of LW-DED as a rapidly evolving, commercially viable AM technology. (Received 4 April, 2025; Accepted 1 May, 2025)

keyword : LW-DED, Laser Wire Directed Energy Deposition, Additive Manufacturing, 3D printing