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소결분위기 변환온도가 Al<sub>2</sub>O<sub>3</sub>/Cu 나노복합재료의 미세조직과 파괴강도에 미치는 영향
오승탁,윤세중,Oh Sung-Tag,Yoon Se-Joong 한국분말야금학회 2004 한국분말재료학회지 (KPMI) Vol.11 No.5
The microstructure and mechanical property of hot-pressed $Al_2O_3/Cu$ composites with a different temperature for atmosphere changing from H$_{2}$ to Ar have been studied. When atmosphere-changed from H$_{2}$ to Ar gas at 145$0^{\circ}C$, the hot-pressed composite was characterized by inhomogeneous microstructure and low fracture strength. On the contrary, when atmosphere-changed at low temperature of 110$0^{\circ}C$ the composite showed more homogeneous microstructure, higher fracture strength and smaller deviation in strength. Based on the thermodynamic consideration and microstructural analysis, it was interpreted that the Cu wetting behavior relating to the formation of CuAlO$_{2}$ is probably responsible for strong dependence of microstructure on atmosphere changing temperature. The reason for a strong sensitivity of fracture strength and especially of its deviation to atmosphere changing temperature was explained by the microstructural inhomogeneity and by the role of CuAlO$_{2}$ phase on the interfacial bonding strength.
오승탁,이종현 대한금속·재료학회 2014 ELECTRONIC MATERIALS LETTERS Vol.10 No.2
The metallurgical and mechanical properties of the commercial low-temperature solder alloy, Sn-57.6Bi-0.4Ag (wt. %), were altered by doping with each of Pd, Co, Zn, and Ni, through reactive reflow processing by using the appropriate metal-organic compound. The use of metal-acetates resulted in appropriate doping concentrations, while the use of metal-acetylacetonates and -stearates resulted in insufficient doping concentrations. This indicates that the degree of doping is strongly dependent on the nature of the metal-organic compound used in the reactive reflow process. Notably, a concurrent decrease in the melting point and the degree of undercooling were observed only in the case of the Pd-doped alloy. In addition, the Pd-doped alloy exhibited an increase in the fraction of the primary β-Sn phase in its microstructure, and greater wettability as tested on a Cu plate. Meanwhile, the Co-doped alloy exhibited a notable increase in the size and spacing of its lamellar structure, and the Ni-doped alloy showed a refinement of its lamellar structure. Accordingly, doping with Pd and Co mitigated the brittleness of the parent Sn-57.6Bi-0.4Ag alloy, which thereby showed a pronounced increase in its plastic displacement during shear tests. Considering the increase in wettability and reduction in brittleness of the original alloy, Pd is considered to be the most suitable dopant, among all the different doping elements analyzed in this study.
Cu 첨가량이 Al<sub>2</sub>O<sub>3</sub>/Cu 나노복합재료의 미세조직과 기계적 성질에 미치는 영향
오승탁,윤세중,Oh Sung-Tag,Yoon Se-Joong 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.1
The effect of Cu content on microstructure and mechanical properties of nano-sized Cu dispersed $Al_2O_3(Al_2O_3/Cu)$ nanocomposites was investigated. The nanocomposites with Cu content of 2.5 to 10 vol% were prepared by reduction and hot-pressing of $Al_2O_3/CuO$ powder mixtures. The nanocomposites with Cu content of 2.5 and 5vol% exhibited the maximum fracture strength of 820MPa and enhanced toughness compared with monolithic $Al_2O_3$. The strengthening was mainly attributed to the refinement of $Al_2O_3$ matrix grains. The toughening mechanism was discussed by the observed microstructural feature based on crack bridging.
나노크기 Sn 분말의 산화열처리에 의한 SnO<sub>2</sub>분말의 합성 및 미세조직 특성
오승탁,이성일,주연준,Oh, Sung-Tag,Lee, Sung-Il,Joo, Yeon-Jun 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.5
Oxidation behavior and microstructural characteristics of nano-sized Sn powder were studied. DTA-TG analysis showed that the Sn powder exhibited an endothermic peak at $227^{\circ}C$ and exothermic peak at $560^{\circ}C$ with an increase in weight. Based on the phase diagram consideration of Sn-O system and XRD analysis, it was interpreted that the first peak was for the melting of Sn powder and the second peak resulted from the formation of $SnO_2$ phase. Microstructural observation revealed that the $SnO_2$ powder, heated to $1000^{\circ}C$ under air atmosphere, consisted of agglomerates with large particle size due to the melting of Sn powder during heat treatment. Finally, fine $SnO_2$ powders with an average size of 50nm can be fabricated by controlled heat treatment and ultrasonic milling process.
원료분말에 따른 Al<sub>2</sub>O<sub>3</sub>/CuO 분말혼합체의 수소환원 거동 및 미세조직 특성
오승탁,김정남,강계명,Oh Sung-Tag,Kim Jung-Nam,Kang Kae-Myung 한국재료학회 2004 한국재료학회지 Vol.14 No.10
The reduction behavior of $Al_{2}O_3/CuO$ powder mixtures, prepared from $Al_{2}O_3/CuO$ or $Al_{2}O_3/Cu-nitrate$, was investigated by using thermogravimetry and hygrometry. The powder characteristics were examined by BET, XRD and TEM. Also, the influence of powder characteristics on the microstructure and properties of hot-pressed composites was analyzed. The formation mechanism of nano-sized Cu dispersions was explained based on the powder characteristics and reduction kinetics of oxide powders. In addition, the dependence of the microstructure and mechanical properties of hot-pressed composites on powder characteristics is discussed in terms of the initial size and distribution of Cu particles. The practical implication of these results is that an optimum processing condition for the design of homogeneous microstructure and required properties can be established.
A1₂O₂/CuO 혼합분말의 수소환원 거동 및 미세조직 특성
오승탁 서울産業大學校 2005 논문집 Vol.54 No.1
분산상Cu3 CuO 및 Cu-nitrate로 선택하여 제조한 Al₂0₃/Cu0 혼합분말에서의 나노금속 입자 형성기구를 정량적으로 해석하여, 분말제조 공정과 산화물 환원거동의 관계 및 이러한 거동이 최종 소결체의 미세조직과 특성에 미치는 영향에 대하여 고찰하였다. Al₂O₃/Cu-nitrate를 원료분말로 사용한 경우에서, 수소환원 후에 미세한 Cu 입자의 균일한 분포를 갖는 복합분말을 제조할 수 있었으며, 최종 소결체에서도 증가된 파괴강도를 나타내었다. 이러한 차이는 주로 원료분말의 환원특성에 따른 것으로 해석하였다.
나노크기 금속입자가 분산된 Al<sub>2</sub>O<sub>3</sub> 나노복합재료의 제조 및 마모거동
오승탁,윤세중,정영근,Oh Sung-Tag,Yoon Se-Joong,Jeong Young-Keun 한국재료학회 2005 한국재료학회지 Vol.15 No.8
Microstructure and wear behavior of A1203-based nanocomposites with Cu and Ni-Co dispersions were investigated. $Al_2O_3/Cu$ and $Al_2O_3/Ni-Co$ nanocomposites were fabricated by hydrogen reduction and sintering method using metal oxide and metal nitrates. The nanocomposites showed increased mechanical properties compared with monolithic $Al_2O_3$. In particular, high toughness and hardness were measured for the $Al_2O_3/Ni-Co$ nanocomposite consolidated by spark plasma sintering. A minimum value of wear coefficient comparable to the monolithic $Al_2O_3$ was obtained for $Al_2O_3/Ni-Co$ nanocomposite. Wear behavior is discussed in terms of microstructure and mechanical properties of nanocomposites