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주연준,이정국,김병철,신동혁 漢陽大學校 工學技術硏究所 1999 工學技術論文集 Vol.8 No.1
자동차 산업 등에서 활용성이 높은 Al-Zn-Mg계인 5083 Al 합금에서 우수한 초소성을 얻고, 이의 초소성 변형특성을 분석하여 미세한 결정립을 갖는 알루미늄 합금의 고온 변형특성을 보다 명확하게 이해하고자 하였다. 초소성을 얻기 위한 가공열처리 시 압연온도를 상온으로 낮추어 우수한 초소성 성질을 나타내는 5083 Al 합금을 얻을 수 있었다. 이때 결정립 크기는 압하량에 의존되는데, 약 9㎛까지의 미세한 결정립을 얻을 수 있었다. 이와 같이 얻어진 초소성 5083 Al 합금의 경우, 기존에 알려진 바와 달리 초소성 변형시 상당한 결정립 성장 및 연신이 일어남을 관찰할 수 있었다. 이들은 초소성 변형의 조건과 밀접한 관계가 있음을 확인하였는데, 즉 변형속도가 감소하고 변형량이 증가함에 따라 상대적으로 큰 결정립 성장이 관찰되었다. 또한 미세조직 관찰 결과 이러한 결정립 성장 및 연신은 제 2 상의 종류 및 분포와 밀접한 관계가 있었다. In the present investigation, a simple thermomechanical route was developed to obtain fine-grained superplasticity from a commercial 5083 Al alloy. The grain size of the alloy, obtained after such treatments, was about 9㎛. The superplastic properties of the alloys were evaluated in the temperature range of 480 to 565℃ over the strain-rate range of 10-5 to 10-2s-1. A maximum tensile elongation was about 700% at a strain rate of 2.1×10-4s-1. The microstructral evoluation during superplastic deformation of the 5083 Al alloy was also observed. Considerable gratin growth and grain elongation were obtained to occur during the superplastic deformation. Dynamic grain growth showed a tendency to occure more extensively at low strain rate and large strain. Present results reveal that the microstructral evolution is associated with the existence of a second phase.
발전 설비용 CrMo강의 탄화물 구조와 조성 변화에 미치는 열화 및 크리프 손상의 영향
주연준,홍경태,이현웅,신동혁,김제원,Ju, Yeon-Jun,Hong, Gyeong-Tae,Lee, Hyeon-Ung,Sin, Dong-Hyeok,Kim, Je-Won 한국재료학회 1999 한국재료학회지 Vol.9 No.10
Sn-3.5Ag 무연합금을 Cu 및 Alloy42 리드프레임에 납땜접합 (solder joint)하고 미세조직, 젖음성, 전단강도, 시효효과를 측정하여 비교하였다. Cu의 경우, 땜납의 Sn기지상안에 Ag(sub)3Sn과 Cu(sub)6Sn(sub)5상이, 그리고 땜납/리드프레임의 경계면에서는 1∼2㎛ 두께의 Cu(sub)6Sn(sub)5상이 형성되었다. Alloy42의 경우, 기지상내에 있는 낮은 밀도의 Ag(sub)3Sn상만이, 그리고 계면에는 0.5∼1.5㎛ 두께의 FeSn(sub)2이 형성되었다. 한편, Cu에 비해 Alloy42 리드프레임에서 퍼짐면적은 크고 접촉각은 작아 더 우수한 젖음성을 나타내었으나, 전단강도는 35%, 연신율은 75%로 낮았다. 180℃에서 1주일간 시효처리 후, Cu 리드프레임에는 계면에 η-Cu(sub)6Sn(sub)5 층외에 ξ-Cu(sub)3Sn층이 성장하였고, Alloy42 리드프레임에는 기지상내에 Ag(sub)3Sn이 구형으로 조대하게 성장하였고, 계면에는 FeSn(sub)2층만이 약 1.5㎛로 성장하였다. The effects of operating temperature and stress on degradation of components in high temperature steam generator were investigated. Several 2.25CrlMo tubes which had operated over 20 years and an unused 9CrlMoVNb tube were tested. For the former samples, the amount of $\textrm{M}_{6}\textrm{C}$ carbide and its size are increased with the aging or operating time. The precipitation behavior of carbides ($\textrm{M}_{2}\textrm{O}$, $\textrm{M}_{6}\textrm{C}$) is changed with the operating temperature of the tubes. However, unused 9CrlMoVNb samples show a different carbide precipitation process due to high chromium, vanadium, and niobium contents. The amount of Cr-rich $\textrm{M}_{23}\textrm{C}_{6}$ carbide is significantly increased with aging time, but that of $\textrm{M}_{6}\textrm{C}$ type carbide is rarely changed with aging time at elevated temperatures.
이근재,주연준,소용대,김남훈,이재성,좌용호,Lee Kun-Jae,Joo Yeon-Jun,So Yong-Dae,Kim Nam-Hoon,Lee Jai-Sung,Choa Yong-Ho 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.1
Through the volume change of Sn in a low-temperature phase transformation, the Sn nanopowder with high, purity, was fabricated by an economic and eco-friendly process. The fine cracks were spontaneously generated. in, Sn ingot, which was reduced to powders in the repetition of phase transformation. The Sn nanopowder with 50 run in size was obtained by the 24th repetitions of phase transformation by low-temperature and ultrasonic treatments. Also, the $SnO_2$ powder was fabricated by the oxidation of the produced Sn powder to the ingot and milled by the ultrasonic milling method. The $SnO_2$ nanopowder of 20 nm in size was fabricated after the milling for 180 h.
맹선재,신동혁,주연준,조종원,이동헌 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.7
Superplastic properties of 7475 Al alloy were evaluated at 516℃ over the strain-rate range of 6.3×10^(-5) to 2.1×10^(-2)s^(-1). The strain-rate sensitivity(m) was determined either from the true stresses and the true strain rates at the points of maximum load, or from change in strain rates. The latter method shows clear distinction between Region I(low stress region) and Region II (superplastic region). Observation of 7475 Al alloy after superplastic deformation was done by optical, scanning electron and transmission electron microscopy. Optical micrographs revealed that at low stress($lt;2 MPa) dispersoidfree zones(DFZ) formed at grain boundaries, primarily normal to the tensile direction. This result demonstrates the importance of diffusional flow at low stress. Also, scanning electron micrographs revealed that cavitation was reduced in the DFZ. Finally, transmission electron micrographs showed that dispersoid particles were accumulated at grain boundaries during the superplastic deformation. This result suggested that the deformation behavior at low stress was most likely a consequence of the existence of a thershold stress.
맹선재,신동혁,주연준,하종신 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.2
The superplastic properties of fine-grained 7475 Al alloy were investigated at 516℃ over the strain-rate range of 2.8 × 10^(-4)s : to 1.7 × 10^(-2)s^(-1). A significant improvement in superplastic elongation was achieved by adopting two-stage strain-rate deformation compared to a usual single strain-rate test. The initially higher strain-rate deformation in the first stage caused rapid microstructural changes including the conversion of subboundaries to high angle grain boundaries, The optimum stain-rate in the first stage was found to be 8.3 × 10^(-3)s^(-1). The specimens tested at lower strain-rates, revealed the dispersoid-free zones(DFZs) near grain boundaries normal to the stress axis. When a higher strain-rate was applied to the specimens with DFZs, the grain refining was not observed. This absence of grain refining was due to the concentration of plastic deformation in the weak DFZs.