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논문 : 에틸렌 글리콜 용액에서 물 함량에 따른 티타늄 양극산화 나노튜브의 성장거동
이병관 ( Byung Gwan Lee ),이성은 ( Seong Eun Lee ),최진욱 ( Jin Wook Choi ),정용수 ( Yong Soo Jeong ),오한준 ( Han Jun Oh ),이오연 ( Oh Yeon Lee ),지충수 ( Choong Soo Chi ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 대한금속·재료학회지 Vol.46 No.11
TiO2 nanotubes fabricated in aqueous HF-based electrolytes have been generally grown only to about 500nm in length because of the strong dissolubility of HF acid. In this paper, ethylene glycol solution has been applied for increasing the length of the anodic TiO2 nanotubes, and the growth behaviors of the nanotubes according to water contents has been investigated. Anodization of Ti in ethylene glycol+1 wt% NH4F (EG solution) with water additions up to 10 wt% were carried out at the constant voltage of 20 V. The results show that a thin titanium oxide layer is formed in the initial stage and the nanotube structure grows underneath the initial layer. And the length of TiO2 nanotubes decreases with the increasing water content in the solution. It can be ascribed to the locally acidified circumstance around the barrier layer inside the nanopore due to H+ ion originated from water. The XPS for the nanotubes suggests that the spectra of Ti2p and O1s are the major chemical bonding states of the TiO2, and those for F1s, N1s and C1s come from the compound of (NH4)2TiF6.
아공정 (亞共晶) Cr 주철의 (鑄鐵) 기지조직에 (基地組織) 미치는 Si 의 영향
김석원,이오연,김동건 ( Sug Won Kim,Oh Yeon Lee,Dong Keon Kim ) 한국주조공학회 1984 한국주조공학회지 Vol.4 No.2
The morphologies of eutectic cell formed during solidification affect on the mechanical properties in high Cr cast iron. In order to investigate the influence of Si on the structure, five kinds of specimen containing 16.42% Cr with varying amount of Si (0.51%, 1.17%, 2.22%, 2.71%, 3.56%) were poured into shell mould preheated 330℃ at 1510℃. The effect of Si on matrix in hypo-eutctic Cr cast iron (2.48% C, 16.42%) were studied through its mechanical tests and observation of microstructure using of metallurgical microscope, EPMA, SEM and Image analyzer systematically. The results obtained from the above studies are as follows: 1. Because of ΔT decreasing with increasing Si content, the morpologies of colony change into uniform bar-type carbide from plate-type ones, moreover eutectic colony size (Ew) becomes narrow and spacing of carbide wider. 2. As Si content increases, the amount of carbides also increases and most of Cr were dissolved in carbides while Si in matrix. 3. The hardness, tensile strength and wear resistance were increasing while impact value decreased with increasing Si content. 4. In fracture section, small amount of dimple pattern was observed in less than 1.17% Si but more than 2.22% Si river pattern was presented.
정종구,이오연,박영구,김동은,진광근,Jung, Jong-Ku,Lee, Oh-Yeon,Park, Young-Koo,Kim, Dong-Eun,Jin, Kwang-Geun 한국재료학회 2008 한국재료학회지 Vol.18 No.7
The hydrogen embrittlement susceptibility of high strength TRIP/TWIP steels with the tensile strength of 600Mpa to 900Mpa grade was investigated using cathodically hydrogen charged specimens. TWIP steels with full austenite structure show a lower hydrogen content than do TRIP steels. The uniform distribution of strong traps throughout the matrix in the form of austenite is considered beneficial to reduce the hydrogen embrittlement susceptibility of TWIP steels. Moreover, an austenite structure with very fine deformation twins formed during straining could also improve the ductility and reduce notch sensitivity. In Ubend and deep drawing cup tests, TWIP steels show a good resistance to hydrogen embrittlement compared with TRIP steels.
도전체 매개반응(EMR)법에 의한 미세 Ta 분말 제조
박일,이철로,이오연,Park Il,Lee Chuel Ro,Lee Oh Yeon 한국재료학회 2004 한국재료학회지 Vol.14 No.10
Production of fine tantalum powder by calciothermic reduction of tantalum oxides ($Ta_{2}O_5$) pellet through an electronically mediated reaction (EMR) has been investigated. $Ta_{2}O_5$ pellet feed and reductant calcium-nickel (Ca-Ni) alloy were charged into electronically isolated locations in a molten $CaCl_2$ bath. The current flow through an external path between the feed (cathode) and reductant (anode) locations was monitored. The current approximately 4.7A was measured during the reaction in the external circuit connecting cathode and anode location. Tantalum powder with approximately 99 $mass\%$ purity was readily obtained after each experiment. Tantalum powder by EMR using $Ta_{2}O_5$ pellet feed was fine compared with that of metal powder by metallothermic reduction and EMR using $Ta_{2}O_5$ powder feed.
이현우,전우용,이오연,설경원,Lee Hyun-Woo,Jeon Woo-yong,Lee Oh-yeon,Seol Kyeong-won 한국분말야금학회 2004 한국분말재료학회지 (KPMI) Vol.11 No.5
The purpose of the present study is to determine an optimum composition using cheaper powders keeping with high performance of hard rock cutting diamond saw blade. With 50Fe-20(Cu . Sn)-30Co specimen, a part of Co was replaced by Ni(5%, 10%, and 15%, respectively). These specimens were hot pressed and sintered for predetermined time at various temperature. Sintering is performed by two different methods of temperature controlled method and specimen dimension controlled method. In order to determine the property of the sintered diamond saw blade, 3 point bending tester, X-ray diffractometer, and SEM were used. As the Co in the bond alloy was replaced by Ni, the hardness of the specimen increased. Thus the 50Fe-20(CuㆍSn)-15Co-15Ni specimen showed the maximum hardness of 104(HRB). The results of 3 point bending test showed that flexure strength decreased along with increase in Ni content. This is attributed to the formation of intermetallic compound(Ni$_{x}$Sn) determined by X-ray diffraction. The fracture surface after 3 point bending test showed that diamond was fractured in the specimen containing 0%, 5%, and 10%Ni, and the fracture occurred at the interface between diamond and matrix in the specimen containing 15%Ni. The cutting ability test showed that the abrasive property was not changed in the specimen containing 0%, 5%, and 10%Ni. The optimum composition determined in this study is 50Fe-20(CuㆍSn)-20Co-10Ni.
직접Quenching 열간 단조용 비조질강의 기계적 성질에 미치는 Quenching온도 및 냉각속도의 영향
신정호,류영주,김병옥,고인용,이오연,Shin, Jung-Ho,Ryu, Young-Joo,Kim, Byung-Ok,Ko, In-Yong,Lee, Oh-Yeon 한국재료학회 2012 한국재료학회지 Vol.22 No.10
Recently, automobile parts have been required to have high strength and toughness to allow for weight lightening or improved stability. But, traditional micro-alloyed steel cannot be applied in automobile parts. In this study, we considered the influence of quenching temperature and cooling rate for specimens fabricated by vacuum induction furnace. Directly quenched micro-alloyed steel for hot forging can be controlled according to its micro structure and the heat-treatment process. Low carbon steel, as well as alloying elements for improvement of strength and toughness, was used to obtain optimized conditions. After hot forging at $1,200^{\circ}C$, the ideal mechanical properties (tensile strength ${\geq}$ 1,000 MPa, Charpy impact value ${\geq}\;100\;J/cm^2$) can be achieved by using optimized conditions (quenching temperature : 925 to $1,050^{\circ}C$, cooling rate : ${\geq}\;5^{\circ}C/sec$). The difference of impact value according to cooling rate can be influenced by the microstructure. A fine lath martensite micro structure is formed at a cooling rate of over $5^{\circ}C/sec$. On the other hand, the second phase of the M-A constituent microstructure is the cause of crack initiation under the cooling rate of $5^{\circ}C/sec$.
원자력 압력용기용강 SA508Gr. 3의 기계적 특성과 템퍼 파라메타에 관한 연구
김병옥 ( Byoung Ok Kim ),이오연 ( Oh Yeon Lee ) 한국열처리공학회 2012 熱處理工學會誌 Vol.25 No.3
The large forgings used in chemical plants or nuclear power plants are produced by complex heat treatment. because of thickness up to 200 ~300mm and weight up to 200~300ton, setting proper heat treatment cycle is so difficult. In addition, defects of products make companies wasting large money and valuable time. In this study, to reduce try & err, when setting heat treatment of reactor pressure vessel steel SA508Gr.3, carrying out the basic mechanical property test of SA508 Gr.3 and testing hardness of SA508Gr.3 in various tempering temperature. and calculating temper curve with Hollomon-Jaffe.
Fe-Mn-C계 TWIP강의 재질특성에 미치는 소둔온도와 첨가원소의 영향
정종구,김남규,윤여선,김현호,이오연,Jung, Jong-Ku,Kim, Nam-Kyu,Yeon, Yeo-Sun,Kim, Hyun-Ho,Lee, Oh-Yeon 한국재료학회 2010 한국재료학회지 Vol.20 No.7
Twinning-induced plasticity (TWIP) steels have attracted great attention due to their excellent mechanical properties of high tensile strength (over 800MPa) and high ductility (over 50%), which result from the high strain hardening due to the mechanical twin formation during plastic deformation. The purpose of this study is to investigate the effect of annealing temperature and alloying elements on the mechanical properties of Fe-18Mn-0.6C TWIP steel. In 1.5%Al TWIP steel with 0.123%Ti content, the average recrystallized grain size was reduced to 2.5 ${\mu}m$ by cold rolling and annealing at $800^{\circ}C$ for 5 min, because of the pinning effect of the fine TiC carbides on grain coarsening. The tensile strength was decreased and the ductility was improved with the increase of the annealing temperature. However, a reversion of hardness and yield strength happened between $750^{\circ}C$ and $800^{\circ}C$ due to TiC and $M_3C$ type precipitation. 0.56% Ni added TWIP steel exhibited relatively lower yield strength, because Ni precipitates were not formed during the annealing process. When this specimen was annealed at $800^{\circ}C$ for 5min, the tensile strength and elongation were revealed at 1096MPa and 61.8%, respectively.
박일,추용호,이철로,이오연,Park Il,Chu Yong Ho,Lee Chul Ro,Lee Oh Yeon 한국재료학회 2004 한국재료학회지 Vol.14 No.12
Production of titanium powder directly from tantalum oxides ($TiO_2$) pellet through an electronically mediated reaction (EMR) by calciothermic reduction has been investigated. Feed material ($TiO_2\;pellet$) and reductant (Ca-Ni alloy) were charged into electronically isolated locations in a molten calcium chloride ($CaCl_2$) bath at $950^{\circ}C$. The current flow through an external circuit between the feed (cathode) and reductant (anode) locations was monitored during the reduction of $TiO_2$. The current approximately 3.2A was measured during the reaction in the external circuit connecting cathode and anode location. After the reduction experiment, pure titanium powder with low nickel content was obtained even though Ca-Ni alloy was used as a reductant. These results demonstrate that titanium powder can be produced without direct physical contact between the feed and reductant. In certain experimental conditions, pure titanium powder with approximately $99.5\;mass\%$ purity was successfully obtained.