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1
Content available Structural Deformation of Tungsten Diselenide Nanostructures Induced by Ozone Oxidation and Investigation of Electronic Properties Change
Kim Eunjeong, Lee Sangyoeb, Je Yeonjin, Lee Dong Park, Park Sang Jun, Jeong Sanghyun, Park Joon Sik, Ahn Byungmin, Park Jun Hong
Archives of Metallurgy and Materials
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2022
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Vol. 67, iss. 4
1469--1473
EN
Tungsten diselenide (WSe2) is one of the promising transition metal dichalcogenides (TMDs) for nanoelectronics and opto-electronics. To enhance and tune the electronic performance of TMDs, chemical functionalization via covalent and van der Waals approaches has been suggested. In the present report, the electric and structural transition of WSe2 oxidized by exposure to O3 is investigated using scanning tunneling microscopy. It is demonstrated that the exposure of WSe2/high-ordered pyrolytic graphite sample to O3 induces the formation of molecular adsorbates on the surface, which enables to increase in the density of states near the valence band edge, resulting from electric structural modification of domain boundaries via exposure of atomic O. According to the work function extracted by Kelvin probe force microscopy, monolayer WSe2 with the O3 exposure results in a gradual increase in work function as the exposure to O3. Therefore, the present report demonstrates the potential pathway for the chemical functionalization of TMDs to enhance the electric performance of TMDs devices.
2
Content available Sintering Behavior and Mechanical Property of Cu-Sn Alloy with Ag Addition Produced by Pulsed Electric Current Sintering
Lee Se Hwan, Ahn Byungmin
Archives of Metallurgy and Materials
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2022
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Vol. 67, iss. 4
1475--1479
EN
This work mainly focuses on the sintering behavior of the Cu-Sn alloy with the addition of Ag up to 4 wt% after pulsed electric current sintering (PECS) process for ultra-fast sintering. The microstructural evolution was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and density measurements. The mechanical properties were evaluated via measurements of transverse rupture strength (TRS) and Rockwell hardness. The mechanism during the sintering process has been discussed thoroughly, and the effect on porosity with the addition of the Ag is also correlated. The results showed that the growth of porosity progressed with the amount of Ag up to 2 wt%, and further addition of Ag leads reduction in porosity. The effect on mechanical properties were improved slowly as the amount of Ag increased.
3
Content available Synthesis of the Nickel-Cobalt-Manganese Cathode Material Using Recycled Nickel as Precursors from Secondary Batteries
Jung Hang-Chul, Han Deokhyun, Kim Dae-Weon, Ahn Byungmin
Archives of Metallurgy and Materials
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2021
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Vol. 66, iss. 4
987--990
EN
As the amount of high-capacity secondary battery waste gradually increased, waste secondary batteries for industry (high-speed train & HEV) were recycled and materialization studies were carried out. The precipitation experiment was carried out with various conditions in the synthesis of LiNi0.6Co0.2Mn0.2O2 material using a Taylor reactor. The raw material used in this study was a leaching solution generated from waste nickel-based batteries. The nickel-cobalt-manganese (NCM) precursor was prepared by the Taylor reaction process. Material analysis indicated that spherical powder was formed, and the particle size of the precursor was decreased as the reaction speed was increased during the preparation of the NCM. The spherical NCM powder having a particle size of 10 μm was synthesized using reaction conditions, stirring speed of 1000 rpm for 24 hours. The NCM precursor prepared by the Taylor reaction was synthesized as a cathode material for the LIB, and then a coin-cell was manufactured to perform the capacity evaluation.
4
Content available Microstructural Evolution of AlCuFeMnTi-0.75Si High Entropy Alloy Processed by Mechanical Alloying and Spark Plasma Sintering
Kim Minsu, Sharma Ashutosh, Chae Myoung Jin, Lee Hansung, Ahn Byungmin
Archives of Metallurgy and Materials
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2021
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Vol. 66, iss. 3
703--707
EN
In this work, we have designed a new high entropy alloy containing lightweight elements, e.g., Al, Fe, Mn, Ti, Cu, Si by high energy ball milling and spark plasma sintering. The composition of Si was kept at 0.75 at% in this study. The results showed that the produced AlCuFeMnTiSi0.75 high entropy alloy was BCC structured. The evolution of BCC1 and BCC2 phases was observed with increasing the milling time up to 60 h. The spark plasma sintering treatment of milled compacts from 650-950°C showed the phase separation of BCC into BCC1 and BCC2. The density and strength of these developed high entropy alloys (95-98%, and 1000 HV) improved with milling time and were maximum at 850°C sintering temperature. The current work demonstrated desirable possibilities of Al-Si based high entropy alloys for substitution of traditional cast components at intermediate temperature applications.
5
Content available Development of Admixed Lubricant for Warm Die and Warm Compaction of High-Density PM Iron
Oh Min Chul, Ahn Byungmin
Archives of Metallurgy and Materials
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2021
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Vol. 66, iss. 3
679--682
EN
The objective of the present research is to develop new admixed lubricants which can be used for high-density sintered iron when processed using warm die and warm compaction. Depending on various lubricants, the effect of compaction temperature on the ejection behavior and sintered properties was studied. Lubricants were prepared by mixing of Zn-stearate and ethylene bis stearamide (EBS) in various compositions. The iron powders blended with lubricants were compacted under the pressure of 700 MPa at various temperatures. The green compacts were sintered at 1120°C for 30 min. Microstructure, density, hardness, and transverse rupture strength of sintered materials with different lubricants were investigated in detail.
6
Content available Effect of Al/Cu Weight Fraction on the Mechanical and Electrical Properties of Al-Cu Conductors for Overhead Transmission Lines
Han Deokhyun, Kim Geon-Hong, Kim Jaesung, Ahn Byungmin
Archives of Metallurgy and Materials
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2020
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Vol. 65, iss. 3
1019--1022
EN
In the past few years, overhead copper transmission lines have been replaced by lightweight aluminum transmission lines to minimize the cost and prevent the sagging of heavier copper transmission lines. High strength aluminum alloys are used as the core of the overhead transmission lines because of the low strength of the conductor line. However, alloying copper with aluminum causes a reduction in electrical conductivity due to the solid solution of each component. Therefore, in this study, the authors attempt to study the effect of various Al/Cu ratios (9:1, 7:3, 5:5) to obtain a high strength Al-Cu alloy without a significant loss in its conductivity through powder metallurgy. Low-temperature extrusion of Al/Cu powder was done at 350ºC to minimize the alloying reactions. The as-extruded microstructure was analyzed and various phases (Cu9Al4, CuAl2) were determined. The tensile strength and electrical conductivity of different mixing ratios of Al and Cu powders were studied. The results suggest that the tensile strength of samples is improved considerably while the conductivity falls slightly but lies within the limits of applications.
7
Content available Brazeability and Microstructure of Ag-28Cu Microjoining Filler Produced by High Energy Ball Milling
Sharma Ashutosh, Chae Myoung Jin, Ahn Byungmin
Archives of Metallurgy and Materials
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2020
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Vol. 65, iss. 4
1323--1327
EN
In this paper, we have studied the evolution of morphology and brazing behavior of Ag-28Cu alloy filler processed by high energy ball milling. The milling of the powder mixture was carried out for 40 h. The structural and morphological analyses were performed by the X-ray diffraction and scanning electron microscopy. The melting temperature of the braze filler was determined by differential thermal analysis. The filler wetting properties were assessed from the spread area ratio measurements on various Ti substrates. The results indicate that the ball milling can effectively depress the filler melting point and enhance the brazeability. The milled powder mixture showed Ag(Cu) solid solution with a crystallite size of 174-68 nm after 40 h. It was shown that the high energy ball milling can be a potential method to develop low temperature brazing fillers for advanced microjoining applications.
8
Content available A Facile Method for the Production of Sn-Ag Alloy by High Energy Ball Milling
Sharma Ashutosh, Ahn Byungmin
Archives of Metallurgy and Materials
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2020
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Vol. 65, iss. 4
1329--1333
EN
In this study, we have developed Sn-Ag alloy by a simple high energy ball milling technique. We have ball-milled the eutectic mixture of Sn and Ag powders for a period of 45 h. The milled powder for 45 h was characterized for particle size and morphology. Microstructural investigations were carried out by scanning electron microscopy and X-ray diffraction studies. The melting behavior of 45 h milled powder was studied by differential scanning calorimetry. The resultant crystallite size ofthe Sn(Ag) solid solution was found to be 85 nm. The melting point of the powder was 213.6°C after 45 h of milling showing depression of ≈6°C in melting point as compared to the existing Sn-3.5Ag alloys. It was also reported that the wettability of the Sn-3.5Ag powder was significantly improved with an increase in milling time up to 45 h due to the nanocrystalline structure of the milled powder.
9
Content available Novel Technique to Produce Hybrid P/M Components Using Dissimilar Ferrous Alloys
Oh Min Chul, Seok Hyunjoo, Jo Yeongcheol, Ahn Byungmin
Archives of Metallurgy and Materials
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2019
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Vol. 64, iss. 2
613--616
EN
The objective of the present research is to develop the novel multi-compaction technology to produce hybrid structure in powder metallurgy (P/M) components using dissimilar Fe-based alloys. Two distinct powder alloys with different compositions were are used in this study: Fe-Cr-Mo-C pre-alloyed powder for high strength and Fe-Cu-C mixed powder for enhanced machinability and lower material cost. Initially, Fe-Cu-C was pre-compacted using a bar-shaped die with lower compaction pressure. The green compact of Fe-Cu-C alloy was inserted into a die residing a half of the die, and another half of the die was filled with the Fe-Cr-Mo-C powder. Then they subsequently underwent re-compaction with higher pressure. The final compact was sintered at 1120°C for 60 min. In order to determine the mechanical behavior, transverse rupture strength (TRS) and Vickers hardness of sintered materials were measured and correlated with density variations. The microstructure was characterized using optical microscope and scanning electron microscope to investigate the interfacial characteristics between dissimilar P/M alloys.
10
Content available Microstructural Evolution of Sinter-Forged Fe-Cr-Mo-C Alloy Depending on Cu Addition
Oh Min Chul, Kim Moontae, Lee Jisung, Ahn Byungmin
Archives of Metallurgy and Materials
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2019
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Vol. 64, iss. 2
539--542
EN
Pre-alloyed Astaloy CrLTM (Fe-1.5 wt% Cr-0.2 wt% Mo), a commercial Fe-based alloy powder for high strength powder metallurgy products, was sintered and hot forged with additions of 0.5 wt% C and 0~2 wt% Cu. To investigate the influence of various Cu contents, the microstructural evolution was characterized using density measurements, scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). Transverse rupture strength (TRS) was measured for each composition and processing stage. The correlation between Cu additions and properties of sinter-forged Fe-Cr-Mo-C alloy was discussed in detail.
11
Content available Correlation between Microstructure and Exothermic Reaction Kinetics of Al-CuO Thermite Nanocomposite Powders Fabricated by Cryomilling
Oh Minseok, Kim Kwanil, Ahn Byungmin
Archives of Metallurgy and Materials
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2019
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Vol. 64, iss. 3
931--934
EN
Al-CuO is a thermite material exhibiting the exothermic reaction only when aluminum melts. For wide spread of its applica-tion, the reaction temperature needs to be reduced in addition to the enhancement of total reaction energy. In the present study, a thermite nanocomposite with a large contact area between Al and CuO was fabricated in order to lower the exothermic reaction temperature and to improve the reactivity. A cryomilling process was performed to achieve the nanostructure, and the effect of composition on the microstructure and its reactivity was studied in detail. The microstructure was characterized using SEM and XRD, and the thermal property was analyzed using DSC. The results show that as the molar ratio between Al and CuO varies, the fraction of uniform nanocomposite structure was changed affecting the exothermic reaction characteristics.
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