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• The Recycling Process and Powderization Technology of Stellite 6 Scrap: A Thermodynamic and Heat Transfer Analysis
  YongKwan Lee, Hyun-chul Kim, Myungsuk Kim, Soong Ju Oh, Kyoungtae Park, JaeJin Sim
  Journal of Powder Materials.2025; 32(4): 330.     CrossRef

The influence of MgO addition on the densification and microstructure of alumina (Al₂O₃) was studied. Compacted alumina specimens were manufactured using ball-milling and one-directional pressing followed by sintering at temperatures below 1700oC. Relative density, shrinkage, hardness, and microstructure were investigated using analytical tools such as FE-SEM, EDS, and XRD. When the MgO was added up to 5.0 wt% and sintered at 1500°C and 1600°C, the relative density exhibited an average value of 97% or more at both temperatures. The maximum density of 99.2% was with the addition of 0.5 wt% MgO at 1500°C. Meanwhile, the specimens showed significantly lower density values when sintered at 1400°C than at 1500°C and 1600°C owing to the relatively low sintering temperature. The hardness and shrinkage data also showed a similar trend in the change in density, implying that the addition of approximately 0.5 wt% MgO can promote the densification of Al₂O₃. Studying the microstructure confirmed the uniformity of the sintered alumina. These results can be used as basic compositional data for the development of MgOcontaining alumina as high-dielectric insulators.

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• Hardness of Ultra-High-Density Alumina Fabricated using the Aerodynamic Levitation Process
  Ye-Ji Son, Dong-Wook Kim, Seung-Wook Kim, Hyo-Min Kim, Hui-Woong Kang, Min-Yeong Ha, Dae-Yong Jeong
  Korean Journal of Materials Research.2025; 35(9): 436.     CrossRef

In this study, machine learning models are proposed to predict the Vickers hardness of AlSi10Mg alloys fabricated by laser powder bed fusion (LPBF). A total of 113 utilizable datasets were collected from the literature. The hyperparameters of the machine-learning models were adjusted to select an accurate predictive model. The random forest regression (RFR) model showed the best performance compared to support vector regression, artificial neural networks, and k-nearest neighbors. The variable importance and prediction mechanisms of the RFR were discussed by Shapley additive explanation (SHAP). Aging time had the greatest influence on the Vickers hardness, followed by solution time, solution temperature, layer thickness, scan speed, power, aging temperature, average particle size, and hatching distance. Detailed prediction mechanisms for RFR are analyzed using SHAP dependence plots.

The effect of the laser beam diameter on the microstructure and hardness of 17-4 PH stainless steel manufactured via the directed energy deposition process is investigated. The pore size and area fraction are much lower using a laser beam diameter of 1.0 mm compared with those observed using a laser beam diameter of 1.8 mm. Additionally, using a relatively larger beam diameter results in pores in the form of incomplete melting. Martensite and retained austenite are observed under both conditions. A smaller width of the weld track and overlapping area are observed in the sample fabricated with a 1.0 mm beam diameter. This difference appears to be mainly caused by the energy density based on the variation in the beam diameter. The sample prepared with a beam diameter of 1.0 mm had a higher hardness near the substrate than that prepared with a 1.8 mm beam diameter, which may be influenced by the degree of melt mixing between the 17-4 PH metal powder and carbon steel substrate.

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• Mechanical response and microstructural evolution of a composite joint fabricated by green laser dissimilar welding of VCoNi medium entropy alloy and 17-4PH stainless steel
  Hadiseh Esmaeilpoor, Mahdi Aghaahmadi, Hyun Jong Yoo, Chan Woong Park, Tae Jin Jang, Seok Su Sohn, Jeoung Han Kim
  Journal of Materials Science & Technology.2025; 213: 223.     CrossRef
• Laser additive manufacturing of ceramic reinforced titanium matrix composites: A review of microstructure, properties, auxiliary processes, and simulations
  Yuzhou Zeng, Jiandong Wang, Xuanrui Liu, Yu Xue, Lang Tang, Yunxiang Tong, Fengchun Jiang
  Composites Part A: Applied Science and Manufacturing.2024; 177: 107941.     CrossRef
• Study on the Elemental Diffusion Distance of a Pure Nickel Layer Additively Manufactured on 316H Stainless Steel
  UiJun Ko, Won Chan Lee, Gi Seung Shin, Ji-Hyun Yoon, Jeoung Han Kim
  journal of Korean Powder Metallurgy Institute.2024; 31(3): 220.     CrossRef

Novel Ni- and Fe-based alloys are developed to impart improved mechanical properties and corrosion resistance. The designed alloys are manufactured as a powder and deposited on a steel substrate using a high-velocity oxygen-fuel process. The coating layer demonstrates good corrosion resistance, and the thus-formed passive film is beneficial because of the Cr contained in the alloy system. Furthermore, during low-temperature heat treatment, factors that deteriorate the properties and which may arise during high-temperature heat treatment, are avoided. For the heattreated coating layers, the hardness increases by up to 32% and the corrosion resistance improves. The influence of the heat treatment is investigated through various methods and is considered to enhance the mechanical properties and corrosion resistance of the coating layer.

Conventionally, metal materials are produced by subtractive manufacturing followed by melting. However, there has been an increasing interest in additive manufacturing, especially metal 3D printing technology, which is relatively inexpensive because of the absence of complicated processing steps. In this study, we focus on the effect of varying powder size on the synthesis quality, and suggest optimum process conditions for the preparation of AlCrFeNi high-entropy alloy powder. The SEM image of the as-fabricated specimens show countless, fine, as-synthesized powders. Furthermore, we have examined the phase and microstructure before and after 3D printing, and found that there are no noticeable changes in the phase or microstructure. However, it was determined that the larger the powder size, the better the Vickers hardness of the material. This study sheds light on the optimization of process conditions in the metal 3D printing field.

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• Fabrication and Alloying Behavior of Ultra-Lightweight AlTiCrVMg High-Entropy Alloy via Al-Mg Mutual Solubility and Sintering Control
  Eunhyo Song, Hansung Lee, Byungmin Ahn
  Journal of Powder Materials.2025; 32(3): 254.     CrossRef

Zirconia has excellent mechanical properties, such as high fracture toughness, wear resistance, and flexural strength, which make it a candidate for application in bead mills as milling media as well as a variety of components. In addition, enhanced mechanical properties can be attained by adding oxide or non-oxide dispersing particles to zirconia ceramics. In this study, the densification and mechanical properties of YSZ-TiC ceramic composites with different TiC contents and sintering temperatures are investigated. YSZ - x vol.% TiC (x=10, 20, 30) system is selected as compositions of interest. The mixed powders are sintered using hot pressing (HP) at different temperatures of 1300, 1400, and 1500°C. The densification behavior and mechanical properties of sintered ceramics, such as hardness and fracture toughness, are examined.

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• Phase Formation and Mechanical Property of YSZ‒30 vol.% WC Composite Ceramics Fabricated by Hot Pressing
  Jin-Kwon Kim, Jae-Hyeong Choi, Nahm Sahn, Sung-Soo Ryu, Seongwon Kim
  journal of Korean Powder Metallurgy Institute.2023; 30(5): 409.     CrossRef

The effects of different spray angles (90°, 85°, 80°) on the microstructure and mechanical properties of a Y₂O₃ coating layer prepared using the atmospheric plasma spray (APS) process were studied. The powders employed in this study had a spherical shape and included a cubic Y₂O₃ phase. The APS coating layer exhibited the same phase as the powders. Thickness values of the coating layers were 90°: 203.7 ± 8.5 μm, 85°: 196.4 ± 9.6 μm, and 80°: 208.8 ± 10.2 μm, and it was confirmed that the effect of the spray angle on the thickness was insignificant. The porosities were measured as 90°: 3.9 ± 0.85%, 85°: 11.4 ± 2.3%, and 80°: 12.7 ± 0.5%, and the surface roughness values were 90°: 5.9 ± 0.3 μm, 85°: 8.5 ± 1.1 μm, and 80°: 8.5 ± 0.4 μm. As the spray angle decreased, the porosity increased, but the surface roughness did not show a significant difference. Vickers hardness measurements revealed values of 90°: 369.2 ± 22.3, 85°: 315.8 ± 31.4, and 80°: 267.1 ± 45.1 HV. It was found that under the condition of a 90° angle with the lowest porosity exhibited the best hardness value. Based on the aforementioned results, an improved method for the APS Y₂O₃ coating layer was also discussed.

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• The Effect of In Situ Laser-Assisted Plasma Spraying on the Plasma Etching Resistance of Yttrium Oxide Coating
  Xutao Zhao, Tian Xie, Panpan Zhang, Zhehe Yao, Qunli Zhang, Jiake Deng, Yongfeng Sui, Jianhua Yao
  Coatings.2024; 14(11): 1427.     CrossRef
• Investigation of contamination particles generation and surface chemical reactions on Al2O3, Y2O3, and YF3 coatings in F-based plasma
  Jongho So, Minjoong Kim, Hyuksung Kwon, Seonjeong Maeng, Eunmi Choi, Chin-Wook Chung, Ju-Young Yun
  Applied Surface Science.2023; 629: 157367.     CrossRef
• Cleaning Effect of Atmospheric-Plasma-Sprayed Y2O3 Coating Using Piranha Solution Based on Contamination Particle Measurement
  Hyuksung Kwon, Minjoong Kim, Jongho So, Seonjeong Maeng, Jae-Soo Shin, Ju-Young Yun
  Coatings.2023; 13(3): 653.     CrossRef
• The effect of powder particle size on the corrosion behavior of atmospheric plasma spray-Y2O3 coating: Unraveling the corrosion mechanism by fluorine-based plasma
  Minjoong Kim, Eunmi Choi, Dongjin Lee, Jungpil Seo, Tae-Sun Back, Jongho So, Ju-Young Yun, Song-Moon Suh
  Applied Surface Science.2022; 606: 154958.     CrossRef
• The Effect of Powder Particle Size on the Corrosion Behavior of Atmospheric Plasma Spray-Y2o3 Coating: Unraveling the Corrosion Mechanism by Fluorine-Based Plasma
  Minjoong Kim, Eunmi Choi, Dongjin Lee, Jungpil Seo, Tae Sun Back, Jongho So, Ju-Young Yun, Song-Moon Suh
  SSRN Electronic Journal .2022;[Epub]     CrossRef

Ti-based alloys are widely used in biomaterials owing to their excellent biocompatibility. In this study, Ti- Mn-Cu alloys are prepared by high-energy ball milling, magnetic pulsed compaction, and pressureless sintering. The microstructure and microhardness of the Ti-Mn-Cu alloys with variation of the Cu addition and compaction pressure are analyzed. The correlation between the composition, compaction pressure, and density is investigated by measuring the green density and sintered density for samples with different compositions, subjected to various compaction pressures. For all compositions, it is confirmed that the green density increases proportionally as the compaction pressure increases, but the sintered density decreases owing to gas formation from the pyrolysis of TiH₂ powders and reduction of oxides on the surface of the starting powders during the sintering process. In addition, an increase in the amount of Cu addition changes the volume fractions of the α-Ti and β-Ti phases, and the microstructure of the alloys with different compositions also changes. It is demonstrated that these changes in the phase volume fraction and microstructure are closely related to the mechanical properties of the Ti-Mn-Cu alloys.

Ti_0.5Al_0.5N/CrN nano-multilayers, which are known to exhibit excellent wear resistances, were prepared using the unbalanced magnetron sputter for various periods of 2–7 nm. Ti_0.5Al_0.5N and CrN comprised a cubic structure in a single layer with different lattice parameters; however, Ti_0.5Al_0.5N/CrN exhibited a cubic structure with the same lattice parameters that formed the superlattice in the nano-multilayers. The Ti_0.5Al_0.5/CrN multilayer with a period of 5.0 nm exceeded the hardness of the Ti_0.5Al_0.5N/CrN single layer, attaining a value of 36 GPa. According to the low-angle X-ray diffraction, the Ti_0.5Al_0.5N/CrN multilayer maintained its as-coated structure up to 700°C and exhibited a hardness of 32 GPa. The thickness of the oxidation layer of the Ti_0.5Al_0.5N/CrN multilayered coating was less than 25% of that of the single layers. Thus, the Ti_0.5Al_0.5N/CrN multilayered coating was superior in terms of hardness and oxidation resistance as compared to its constituent single layers.

In the development of advanced ceramic tools, material improvements and design freedom are critical in improving tool performance. However, in the die press molding method, many factors limit tool design and make it difficult to develop innovative advanced tools. Ceramic 3D printing facilitates the production of prototype samples for advanced tool development and the creation of complex tooling products. Furthermore, it is possible to respond to mass production requirements by reflecting the needs of the tool industry, which can be characterized by small quantities of various products. However, many problems remain in ensuring the reliability of ceramic tools for industrial use. In this study, alumina inserts, a representative ceramic tool, was manufactured using the digital light process (DLP), a 3D printing method. Alumina inserts prepared by 3D printing are pressurelessly sintered under the same conditions as coupon-type specimens prepared by press molding. After sintering, a hot isostatic pressing (HIP) treatment is performed to investigate the effects of relative density and microstructure changes on hardness and fracture toughness. Alumina inserts prepared by 3D printing show lower relative densities than coupon specimens prepared by powder molding but indicate similar hardness and higher fracture toughness values.

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• A Study on Fabrication of PCD Endmill Holder using PBF Additive Manufacturing Technology
  Min-Woo Sa, Ho-Min Son, Kyung-Hwan Park, Sang-Geun Lee, Dae-Ho Shin, Dong-Gyu Kim
  Journal of the Korean Society of Manufacturing Process Engineers.2024; 23(6): 124.     CrossRef
• Vat photopolymerization-based 3D printing of complex-shaped and high-performance Al2O3 ceramic tool with chip-breaking grooves: Cutting performance and wear mechanism
  Haidong Wu, Wei Liu, Yuerui Xu, Lifu Lin, Yehua Li, Shanghua Wu
  Journal of Asian Ceramic Societies.2023; 11(1): 159.     CrossRef

Nb-Si-B alloys with Nb-rich compositions are fabricated by spark plasma sintering for high-temperature structural applications. Three compositions are selected: 75 at% Nb (Nb0.7), 82 at% Nb (Nb1.5), and 88 at% Nb (Nb3), the atomic ratio of Si to B being 2. The microstructures of the prepared alloys are composed of Nb and T₂ phases. The T₂ phase is an intermetallic compound with a stoichiometry of Nb₅Si_3-xB_x (0 ≤ x ≤ 2). In some previous studies, Nb-Si-B alloys have been prepared by spark plasma sintering (SPS) using Nb and T₂ powders (SPS 1). In the present work, the same alloys are prepared by the SPS process (SPS 2) using Nb powders and hypereutectic alloy powders with composition 67at%Nb-22at%Si-11at%B (Nb67). The Nb67 alloy powders comprise T₂ and eutectic (T₂ + Nb) phases. The microstructures and hardness of the samples prepared in the present work have been compared with those previously reported; the samples prepared in this study exhibit finer and more uniform microstructures and higher hardness.

An artificial neural network (ANN) model is developed for the analysis and simulation of correlation between flake powder metallurgy parameters and properties of AA2024-SiC nanocomposites. The input parameters of the model are AA 2024 matrix size, ball milling time, and weight percentage of SiC nanoparticles and the output parameters are density and hardness. The model can predict the density and hardness of the unseen test data with a correlation of 0.986 beyond the experimental data. A user interface is designed to predict properties at new instances. We have used the model to simulate the individual as well as the combined influence of parameters on the properties. Moreover, we have analyzed the calculated results from the powder metallurgical point of view. The developed model can be used as a guide for further composite development.

The microstructure and mechanical characteristics of SUS630 specimens fabricated using the direct energy deposition (DED) process are investigated. In DED, several process parameters such as laser scan speed, chamber gas flow, powder carrier gas flow, and powder feed rate are kept fixed; the laser power is changed as 150 W, 180 W, and 210 W. As the laser power increases, the surface becomes smooth, the thickness uniformity improves, and the size and number of pores decreases. With the increase in laser power, the hardness deviation decreases and the average hardness increases. The microstructure of the material is columnar; pores are formed preferentially along the columnar interface. The lath-martensite phase governs the overall microstructure. The volumetric fraction of the retained austenite phase is measured to increase with the increase of laser input power.

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• Optimization of Additive Manufacturing of Precipitation Hardening Type STS630 by DED (Direct Energy Deposition) Process
  Yongjae Kwon, SeongSeon Shin, SangEun Joo, JongHoon Lee, JunHo Hwang, HyunDeok Kim
  Journal of Welding and Joining.2021; 39(6): 590.     CrossRef
• Effects of pre- and post-repair heat treatments on microstructure and tensile behaviors of 630 stainless steel repaired by metal additive manufacturing
  Do Sik Shim, Hyub Lee, Yong Son, Wook Jin Oh
  Journal of Materials Research and Technology.2021; 13: 980.     CrossRef
• Solution annealing and precipitation hardening effect on the mechanical properties of 630 stainless steel fabricated via laser melting deposition
  Wook Jin Oh, Yong Son, Seung Yeong Cho, Seung Weon Yang, Gwang Yong Shin, Do Sik Shim
  Materials Science and Engineering: A.2020; 794: 139999.     CrossRef
• Spheroidization of Pure-vanadium Powder using Radio Frequency Thermal Plasma Process
  Nana Kwabena Adomako, Seungmin Yang, Min Gyu Lee, N. S. Reddy, Jeoung-Han Kim
  Journal of Korean Powder Metallurgy Institute.2019; 26(4): 305.     CrossRef
• Joint Properties of Stainless Steel and Titanium Alloys Additive Manufactured on Medium Entropy Alloys
  Chan Woong Park, Nana Kwabena Adomako, Min Gyu Lee, Jeoung Han Kim
  Journal of Korean Powder Metallurgy Institute.2019; 26(4): 319.     CrossRef

SiAlON-based ceramics are some of the most typical oxynitride ceramic materials, which can be used as cutting tools for heat-resistant super-alloys (HRSA). SiAlON can be fabricated by using gas-pressure reactive sintering from the raw materials, nitrides and oxides such as Si₃N₄, AlN, Al₂O₃, and Yb₂O₃. In this study, we fabricate Yb_m/3Si_12-(m+n)Al_m+nO_nN_16-n (m=0.3, n=1.9, 2.3, 2.7) ceramics by using gas-pressure sintering at different sintering temperatures. Then, the densification behavior, phase formation, microstructure, and hardness of the sintered specimens are characterized. We obtain a fully densified specimen with β- SiAlON after gas-pressure sintering at 1820°C for 90 min. under 10 atm N₂ pressure. These SiAlON ceramic materials exhibited hardness values of ~92.9 HRA. The potential of these SiAlON ceramics for cutting tool application is also discussed.

In this study we manufacture a Ni-Cr-B-Si +WC/12Co composite coating layer on a Cu base material using a laser cladding (LC) process, and investigate the microstructural and mechanical properties of the LC coating and Ni electroplating layers (reference material). The initial powder used for the LC coating layer is a powder feedstock with an average particle size of 125 μm. To identify the microstructural and mechanical properties, OM, SEM, XRD, room and high temperature hardness, and wear tests are implemented. Microstructural observation of the initial powder and LC coating layer confirm the layer is composed mainly of γ-Ni phases and WC and Cr₂₃C₆ carbides. The measured hardness of the LC coating and Ni electroplating layers are 653 and 154 Hv, respectively. The hardness measurement from room up to high temperatures of 700°C result in a hardness decrease as the temperature increases, but the hardness of the LC coating layer is higher for all temperature conditions. Room temperature wear results show that the wear loss of the LC coating layer is 1/12 of the wear level of the Ni electroplating layer. The measured bond strength is also greater in the LC coating than the Ni electroplating.

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• Microstructure and Room Temperature Wear Properties of a Ni-Cr-B-Si-C Coating Layer Manufactured by the Laser Cladding Process
  Tae-Hoon Kang, Kyu-Sik Kim, Soon-Hong Park, Kee-Ahn Lee
  Korean Journal of Metals and Materials.2018; 56(6): 423.     CrossRef
• Microstructural and Wear Properties of WC-based and Cr₃C₂-based Cermet Coating Materials Manufactured with High Velocity Oxygen Fuel Process
  Yeon-Ji Kang, Gi-Su Ham, Hyung-Jun Kim, Sang-Hoon Yoon, Kee-Ahn Lee
  Journal of Korean Powder Metallurgy Institute.2018; 25(5): 408.     CrossRef

In this study, Fe-Cu-Ni-Mo-C low alloy steel powder is consolidated by spark plasma sintering (SPS) process. The internal structure and the surface fracture behavior are studied using field-emission scanning electron microscopy and optical microscopy techniques. The bulk samples are polished and etched in order to observe the internal structure. The sample sintered at 900°C with holding time of 10 minutes achieves nearly full density of 98.9% while the density of the as-received conventionally sintered product is 90.3%. The fracture microstructures indicate that the sample prepared at 900°C by the SPS process is hard to break out because of the presence of both grain boundaries and internal particle fractures. Moreover, the lamellar pearlite structure is also observed in this sample. The samples sintered at 1000 and 1100°C exhibit a large number of tiny particles and pores due to the melting of Cu and aggregation of the alloy elements during the SPS process. The highest hardness value of 296.52 HV is observed for the sample sintered at 900°C with holding time of 10 minutes.

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• Fabrication of Fe-Si-B Based Amorphous Powder Cores by Spark Plasma Sintered and Their Magnetic Properties
  Liang Yan, Biao Yan, Yin Jian
  Materials.2022; 15(4): 1603.     CrossRef
• Effect of Milling Time and Addition of PCA on Austenite Stability of Fe-7%Mn Alloy
  Seung-Jin Oh, In-Jin Shon, Seok-Jae Lee
  Journal of Korean Powder Metallurgy Institute.2018; 25(2): 126.     CrossRef
• Sintering and Microstructures of SUS 316L Powder Produced by 3D Printing Process
  W.J. Kim, H.-H. Nguyen, H.Y. Kim, M.-T. Nguyen, H.S. Park, J.-C. Kim
  Archives of Metallurgy and Materials.2017; 62(2): 1215.     CrossRef
• Fabrication and Mechanical Property of Fe-20Cu-1C Compacts by SPS process with Different Heating Rate
  Jung-Han Ryu, Soo-Sik Shin, Byung-Rok Ryu, Kyung-Sik Kim, Jun-Ho Jang, Ik-Hyun Oh, Kap-Tae Kim, Hyun-Kuk Park
  Journal of Korean Powder Metallurgy Institute.2017; 24(4): 302.     CrossRef

Microstructural examination of the Nb-Si-B alloys at Nb-rich compositions is performed. The Nb-rich corner of the Nb-Si-B system is favorable in that the constituent phases are Nb (ductile and tough phase with high melting temperature) and T₂ phase (very hard intermetallic compound with favorable oxidation resistance) which are good combination for high temperature structural materials. The samples containing compositions near Nb-rich corner of the Nb- Si-B ternary system are prepared by spark plasma sintering (SPS) process using T₂ and Nb powders. T₂ bulk phase is made in arc furnace by melting the Nb slug and the Si-B powder compact. The T₂ bulk phase was subsequently ballmilled to powders. SPS is performed at 1300°C and 1400°C, depending on the composition, under 30 MPa for 600s, to produce disc-shaped specimen with 15 mm in diameter and 3 mm high. Hardness tests (Rockwell A-scale and micro Vickers) are carried out to estimate the mechanical property.

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• Fabrication of Nb-Si-B Alloys Using the Pulverized Nb-T₂ Alloy Powder
  Min-Ho Cho, Sung-Jun Kim, Hyun-Ji Kang, Sung-Tag Oh, Young Do Kim, Seong Lee, Myung Jin Suk
  Journal of Korean Powder Metallurgy Institute.2019; 26(4): 299.     CrossRef
• Mechanical properties of Mo-Nb-Si-B quaternary alloy fabricated by powder metallurgical method
  Jong Min Byun, Su-Ryong Bang, Se Hoon Kim, Won June Choi, Young Do Kim
  International Journal of Refractory Metals and Hard Materials.2017; 65: 14.     CrossRef
• Mechanical properties of Mo-Si-B alloys fabricated by using core-shell powder with dispersion of yttria nanoparticles
  Jong Min Byun, Su-Ryong Bang, Won June Choi, Min Sang Kim, Goo Won Noh, Young Do Kim
  Metals and Materials International.2017; 23(1): 170.     CrossRef
• Fabrication of Ta2O5 Dispersion-Strengthened Mo-Si-B Alloy by Powder Metallurgical Method
  Jong Min Byun, Won June Choi, Su-Ryong Bang, Chun Woong Park, Young Do Kim
  JOM.2017; 69(4): 683.     CrossRef
• Rapid consolidation of nanostuctured WC-FeAl3 by pulsed current activated heating and its mechanical properties
  In-Jin Shon, Seok-Jae Lee
  International Journal of Refractory Metals and Hard Materials.2017; 65: 69.     CrossRef

In this study, the effect of the friction stir welding (FSW) was compared with that of the gas tungsten arc welding (GTAW) on the microstructure and microhardness of Cu-Ni alloy weldment. The weldment of 10 mm thickness was fabricated by FSW and GTAW, respectively. Both weldments were compared with each other by optical microstructure, microhardness test and grain size measurement. Results of this study suggest that the microhardness decreased from the base metal (BM) to the heat affected zone (HAZ) and increased at fusion zone (FZ) of GTAW and stir zone (SZ) of FSW. the minimum Hv value of both weldment was obtained at HAZ, respectively, which represents the softening zone, whereas Hv value of FSW weldment was little higher than that of GTAW weldment. These phenomena can be explained by the grain size difference between HAZs of each weldment. Grain size was increased at the HAZ during FSW and GTAW. Because FSW is a solid-state joining process obtaining the lower heat-input generated by rotating shoulder than heat generated in the arc of GTAW.

The 304 stainless steel powders were prepared by high energy ball milling and subsequently sintered by spark plasma sintering, and the microstructural characteristics and micro-hardness were investigated. The initial size of the irregular shaped 304 stainless steel powders was approximately 42 μm. After high energy ball milling at 800 rpm for 5h, the powders became spherical with a size of approximately 2 μm, and without formation of reaction compounds. From TEM analysis, it was confirmed that the as-milled powders consisted of the aggregates of the nano-sized particles. As the sintering temperature increased from 1073K to 1573K, the relative density and micro-hardness of sintered sample increased. The sample sintered at 1573K showed the highest relative density of approximately 95% and a micro-hardness of 550 Hv.

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• Investigating molybdenum’s sulphur scavenging ability for MoS2 formation in preventing pitting corrosion of stainless steels
  Kai Xiang Kuah, Daniel J. Blackwood
  npj Materials Degradation.2023;[Epub]     CrossRef

Bulk nanostructured copper was fabricated by a shock compaction method using the planar shock wave generated by a single gas gun system. Nano sized powders, average diameter of 100 nm, were compacted into the capsule and target die, which were designed to eliminate the effect of undesired shock wave, and then impacted with an aluminum alloy target at 400 m/s. Microstructure and mechanical properties of the shock compact specimen were analyzed using an optical microscope (OM), scanning electron microscope (SEM), and micro indentation. Hardness results showed low values (approximately 45~80 Hv) similar or slightly higher than those of conventional coarse grained commercial purity copper. This result indicates the poor quality of bonding between particles. Images from OM and SEM also confirmed that no strong bonding was achieved between them due to the insufficient energy and surface oxygen layer of the powders.

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• Compressibility of hierarchic-architectured agglomerates of hydrogen-reduced copper nanopowders
  Dong-Hyun Ahn, Wooyeol Kim, Eun Yoo Yoon, Hyoung Seop Kim
  Journal of Materials Science.2016; 51(1): 82.     CrossRef
• Analysis of the Change in Microstructures of Nano Copper Powders During the Hydrogen Reduction using X-ray Diffraction Patterns and Transmission Electron Microscope, and the Mechanical Property of Compacted Powders
  Dong-Hyun Ahn, Dong Jun Lee, Wooyeol Kim, Lee Ju Park, Hyoung Seop Kim
  Journal of Korean Powder Metallurgy Institute.2014; 21(3): 207.     CrossRef