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Ok, Myoung-Ryul,Suh, Jin-Yoo,Chung, Sung Jae,Ji, Young Su,Hong, Kyung Tae Elsevier 2007 Materials science & engineering. properties, micro Vol.454 No.-
<P><B>Abstract</B></P><P>Bulk metallic glasses are adequate for micro-forming because of the viscous flow in the supercooled liquid state. The deformation behavior of Zr<SUB>41</SUB>Ti<SUB>14</SUB>Cu<SUB>12.5</SUB>Ni<SUB>10</SUB>Be<SUB>22.5</SUB> alloy under compression in the supercooled liquid state were investigated by using DSC and TMA. Based on the deformation behavior, micro-forming process of Zr<SUB>41</SUB>Ti<SUB>14</SUB>Cu<SUB>12.5</SUB>Ni<SUB>10</SUB>Be<SUB>22.5</SUB> alloy was designed and carried out. The surface of the deformed specimens were analyzed by SEM, XRD, and AFM. The roughness of the specimen surface exhibited a correlation with the total deformation and a new parameter reflecting roughness evolution of the deformed surface was suggested as the relative comparison among different forming conditions.</P>
Si 첨가강의 연속주조공정 신뢰성 향상을 위한 고온변형특성에 관한 연구
옥명렬(Myoung-Ryul Ok),서진유(Jin-Yoo Suh),심재혁(Jae-Hyeok Shim),홍경태(Kyung-Tae Hong),이주동(Joo-Dong Lee),임창희(Chang-hee Yim) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.8
A study was made on the high temperature deformation behavior of Si steel to increase the reliability of continuous casting process. In continuous casting process, the cast slab experiences cooling and deformation simultaneously, and various sources for defect formation exist. Of all these defects, cracking has the most deleterious effect on the property of the cast slab. To avoid or minimize transverse cracking, unbending temperature should be chosen carefully. In general, transverse cracks can easily be formed when unbending temperature lies within the ductility minimum temperature range of hot tensile test. Relative ratio of austenite-ferrite and their distribution or morphology have significant effect on the reliability of unbending process. Moreover, inhomogeneous deformation can be the source of defect formation. So, to produce Si steel by continuous casting, deformation behavior of Si steel as well as the relative ratio of austenite-ferrite or phase transformation temperature(Ar₃) should be known. We carried out hot tensile and hot compression test to evaluate the mechanical properties of the Si steel at high temperature. Hot ductility minimum temperature was not found with all Si contents, but inhomogeneous deformation occurred in high Si(1.17% and 3.21%) samples. It can be concluded that to minimize inhomogeneous deformation is the key to the successful unbending process of silicon steel. To analyze the effect of the silicon on the strength of silicon steel, a model was established, by using rule of mixture.
Research on the surface oxidation procedure of Fe-base metallic glass during wet oxidation treatment
Kang, Eun Young,Chung, Young Hoon,Ok, Myoung-Ryul,Baik, Hong Koo Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>Internal structure of magnetic core for high-frequency use could be divided into small insulating units to minimize eddy current loss. Accordingly, the powder size of Fe<SUB>bal.</SUB>Si<SUB>9.6</SUB>B<SUB>14.4</SUB>Nb<SUB>4</SUB> (numbers indicate at.%) amorphous alloy should be small and covered with some degree of insulating layer for producing high-frequency magnetic core. In this investigation, formation of the insulating layer on the surface of Fe-based amorphous alloy powder was studied using wet oxidation method. The size of Fe–Si–B–Nb amorphous alloy powder used in this research was less than 75μm in diameter. Forming mechanism of surface cracks and consecutive oxide layers was explained and the thickness of insulating layer could be controlled by changing treatment time and concentration of HNO<SUB>3</SUB> in the oxidizing solution. Even though the oxide layer on the powder surface was partially flaked off during hot-compacting process, sufficient electrical resistance was maintained to lessen eddy current loss effectively.</P>
Ji, Young Su,Chung, Sung Jae,Ok, Myoung-Ryul,Hong, Kyung Tae,Suh, Jin-Yoo,Byeon, Jai Won,Yoon, Jin-Kook,Lee, Kyung Hwan,Lee, Kyung Sub Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>The crystallization behavior of Cu<SUB>43</SUB>Zr<SUB>43</SUB>Al<SUB>7</SUB>Ag<SUB>7</SUB> (numbers indicate at.%) bulk metallic glass was investigated using the isothermal electrical resistivity measurements at 450°C in the supercooled liquid region. The crystallization process is a single step phase transformation. To analyze the electrical resistivity reduction, microstructure evolutions were analyzed using differential scanning calorimetry, X-ray diffraction, transmission electron microscopy and small-angle X-ray scattering. The Avrami parameter of the electrical resistivity reduction step was 1.73, indicating that the crystallization process is a diffusion-controlled growth of intermetallic compounds with decreasing nucleation rate.</P>
Molecular dynamics simulation of cytotoxicity of graphene nanosheets to blood-coagulation protein
Jo, Byeong Cheol,Yoon, Hyun Jung,Ok, Myoung-Ryul,Wu, Sangwook American Vacuum Society 2017 Biointerphases Vol.12 No.1
<P>Graphene is a nanomaterial that is widely used in electronics, biomedicine, and drug-delivery systems. Although it has many industrial applications, the cytotoxicity of graphene has not been sufficiently studied. In this study, the authors used molecular dynamics simulation to investigate how a graphene nanosheet affects a blood-coagulation protein, namely, a tissue factor/FVIIa binary complex bound to a lipid bilayer membrane, in a 4: 1 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2oleoyl-sn-glycero-3-phospho-l-serine lipid bilayer mixture. Based on the results, the authors suggest a mechanism for the cytotoxicity of graphene nanosheets to blood-coagulation protein at the molecular level. (C) 2017 American Vacuum Society.</P>
Terleeva, O. P.,Oh, Young-Joo,Ok, Myoung-Ryul,Slonova, A. I.,Kireenko, I. B.,Lee, Dong-Heon The Japan Institute of Metals 2006 MATERIALS TRANSACTIONS Vol.47 No.7
<P>The structure and phase composition of microplasma coatings formed on a Ti-6Al-4V alloy using the alternating current mode in solutions with different concentrations of KOH, NaAlO<SUB>2</SUB> and Na<SUB>6</SUB>P<SUB>6</SUB>O<SUB>18</SUB> were investigated using XRD analysis, microscope analysis and microhardness testing. The thickness and weight gain were measured with electronic thickness gage and correspondingly, with the gravimetric method. The crystal structure of the microplasma electrolytic coatings had amorphous, rutile, α-Al<SUB>2</SUB>O<SUB>3</SUB> and Al<SUB>2</SUB>TiO<SUB>5</SUB> phase. The coating morphology may be presented as 3 layers—the external amorphous layer, the internal layer, and the barrier layer.</P>
Jaeho Park,Yu-Chan Kim,Myoung-Ryul Ok,Wonryung Lee,Hyung-Seop Han,Jeong-Yun Sun,Hojeong, Jeon 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
As the increasing demand for semiconductor, it has been studied for high integration, and miniaturization. Therefore, a more sophisticated process is essential such as plasma etching within high vacuum system. However, the inner wall of the etching equipment can be easily damaged since the surface is exposed to highly reactive atmosphere, so the surface should be coated with high corrosion resistant property. Currently, yttrium-based ceramic materials with excellent corrosion resistance (e.g, Y2O3, YOF) are synthesized and widely used as coating materials. The materials are used to apply in high-temperature and pressure system. However, residual stress, cracks, pores, and low coating strength of the coating layer inevitably exist. In this study, it is not only does not require pretreatment, but also coat simultaneously a plasma-resistant material on substrate via a pulsed laser heat source. The surface was selectively coated with Y2O3 or YOF by modifying the solution concentration used as a precursor. The coating process in this study is simple compared to the existing method. In addition, it can form a high-density layer that minimizes cracks and pores with improved process efficiency and plasma resistance. It is expected that the ceramic material of the desired composition can be selectively applied to various products by utilizing the highly integrated energy of the laser beam.