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변형지도 모델링을 통한 몰리브데늄의 고온 변형에 따른 미세조직 변화 연구
김영무,이성호,이성,노준웅,Kim, Young-Moo,Lee, Sung-Ho,Lee, Seong,Noh, Joon-Woong 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.6
The hot deformation characteristics of pure molybdenum was investigated in the temperature range of $600{\sim}1200^{\circ}C$ and strain rate range of $0.01{\sim}10.0/s$ using a Gleeble test machine. The power dissipation map for hot working was developed on the basis of the Dynamic Materials Model. According to the map, dynamic recrystallization (DRX) occurs in the temperature range of $1000{\sim}1100^{\circ}C$ and the strain rate range of $0.01{\sim}10.0/s$, which are the optimum conditions for hot working of this material. The average grain size after DRX is $5{\mu}m$. The material undergoes flow instabilities at temperatures of $900{\sim}1200^{\circ}C$ and the strain rates of $0.01{\sim}10.0/s$, as calculated by the continuum instability criterion.
김영무,김은표,이성,노준웅,Kim, Young-Moo,Kim, Eun-Pyo,Lee, Seong,Noh, Joon-Woong 한국분말야금학회 2007 한국분말재료학회지 (KPMI) Vol.14 No.4
이상에서 살펴본 바와 같이, 내열재료들은 고밀도를 이용하여 비행하는 물체의 운동에너지를 극대화 시킬 수 있기 때문에 군사적으로 각종 무기체계의 성능 향상에 매우 중요하다. 또한 유도 무기 및 항공기의 경우 고온, 고압 등의 환경에서 운용되기 때문에, 이러한 조건에서 견딜 수 있는 소재 개발이 필수적이다. 따라서 무기 선진국에서는 고밀도 재료인 텅스텐, 몰리브덴, 탄탈륨, 텅스텐-구리 감손우라늄을 활용하기 위한 연구를 활발하게 진행하고 있다. 이중, 텅스텐, 몰리브덴, 텅스텐-구리 라이너에 관한 연구는 괄목할 만한 연구 성과를 거두고 있다. 이러한 연구성과는 기존 탄의 관통 성능을 크게 증가시켜, 이에 대응하고자 하는 방어 체계 연구자들을 바쁘게 할 것으로 판단된다. 한편 내열 금속의 경우, 초고온 및 고압과 같은 극한 환경에서의 고온 강도 및 내삭마성이 우수하기 때문에, 각종 유도 무기 체계의 구성 부품, 즉 터빈, 밸브, 노즐, 제트 베인 등에 적용되고 있으나 대부분의 내열 재료들은 제조 방법이 까다롭고, 가공성이 나쁘며, 고가라는 단점들이 있어 이를 극복하는 연구들이 현재 진행 중에 있다.
열간 등압 성형된 니켈기 초내열 합금 IN 713C 분말 소결체의 특성 평가
김영무,김은표,정성택,이성,노준웅,이성호,권영삼,Kim, Youngmoo,Kim, Eun-Pyo,Chunga, Seong-Taek,Lee, Seong,Noh, Joon-Woong,Lee, Sung Ho,Kwon, Young-Sam 한국분말야금학회 2013 한국분말재료학회지 (KPMI) Vol.20 No.4
Nickel-based superalloy IN 713C powders have been consolidated by hot isostatic pressing (HIPing). The microstructure and mechanical properties of the superalloys were investigated at the HIPing temperature ranging from $1030^{\circ}C$ to $1230^{\circ}C$. When the IN 713C powder was heated above ${\gamma}^{\prime}$ solvus temperature (about $1180^{\circ}C$), the microstructure was composed of the austenitic FCC matrix phase ${\gamma}$ plus a variety of secondary phases, such as ${\gamma}^{\prime}$ precipitates in ${\gamma}$ matrix and MC carbides at grain boundaries. The yield and tensile strengths of HIPed specimens at room temperature were decreased while the elongation and reduction of area were increased as the processing temperature increased. At $700^{\circ}C$, the strength was similar regardless of HIPing temperature; however, the ductility was drastically increased with increasing the temperature. It is considered that these properties compared to those of cast products are originated from the homogeneity of microstructure obtained from a PM process.
이성,홍문희,김은표,이성호,노준웅,Lee, Seong,Hong, Moon-Hee,Kim, Eun-Pyo,Lee, Sung-Ho,Noh, Joon-Woong 한국분말야금학회 2003 한국분말재료학회지 (KPMI) Vol.10 No.6
The reduction mechanism of the composite powders mixed with $WO_3$ and CuO has been studied by using thermogravimetry (TG), X-ray diffraction, and microstructure analyses. The composite powders were made by simple Turbula mixing, spray drying, and ball-milling in a stainless steel jar with the ball to powder ratio of 32 to 1 at 80 rpm for 1 h without process controlling agents. It is observed that all the oxide composite powders are converted to W-coated Cu composite powder after reducing treatment under hydrogen atmosphere. For the formation mechanism of W-coated Cu composite powder, the sequential reduction steps are proposed as follows: CuO contained in the ball-milled composite powder is initially reduced to Cu at the temperature range from 20$0^{\circ}C$ to 30$0^{\circ}C$. Then, $WO_3$ powder is reduced to W $O_2$ via W $O_{2.9}$ and W $O_{2.72}$ at higher temperature region. Finally, the gaseous phase of $WO_3(OH)_2$ formed by reaction of $WO_2$ with water vapour migrates to previously reduced Cu and deposits on it as W reduced by hydrogen. The proposed mechanism has been proved through the model experiment which was performed by using Cu plate and $WO_3$ powder.
Torsional Kolsky Bar 를 이용한 텅스텐 중합금의 동적 비틀림특성 연구
김동국,이성학,노준웅,박경진 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.4
Dynamic deformation behavior of a 93W-4.9Ni-2.1Fe heavy alloy was investigated using torsional Kolsky bar in order to evaluate its adiabatic shear banding behavior. Dynamic (γ˙∼10³/sec) torsional tests were conducted for four samples fabricated by the different processing conditions, i.e., sintered, heat-treated, swaged, and aged, and then the test data were compared with those of the quasi-static(γ˙10^(-4)/sec) tests. Dynamic test results showed that the maximum shear stress was increased in the order of the sintered, the heat-treated, the swaged, and the aged samples. In the swaged and the aged samples, the shear stress dropped abruptly after it reached to the maximum shear stress point and the shear strain to the maximum shear stress point were considerably small compared to those of the sintered and the heat-treated samples. The phenomena indicated the higher possibility of forming adiabatic shear bands in the swaged and the aged samples than the sintered and the heat-treated samples. The observation of the deformed areas of the fractured torsional specimens indicated that shear deformation was concentrated to the center of the gage section in the case of the swaged and the aged samples, whereas it was homogeneously distributed in the case of the sintered and the heat-treated samples. This deformation behavior correlated well with the shear stress-shear strain curves, suggesting that the torsional Kolsky bar technique is a good tool for evaluating the adiabatic shear banding behavior of the tungsten heavy alloys.
High Energy Ball Mill에 의해 제조된 75w-25Cu 의 치밀화 거동에 관한 연구
이성,송흥섭,노준웅,홍문희,김근표,김용우 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.2
Solid and liquid phase sintering behaviors of ball-milled 75W-25Cu have been studied by using a dilatometry technique. The ball-milled 75W-25Cu was prepared by high energetic ball milling under argon atmosphere of 1 atm with duration times of 50 to 400 hrs. The sintering was performed in the dilatometer under flowing hydrogen atmosphere with a heating rate of 3℃/min. To compare with the ball milled 75W-25Cu, blended 75W-25Cu was also prepared and sintered. Sintering shrinkage, dl/1, increased with increasing milling time from 50 to 400 hrs. The shrinkage versus temperature plots of the ball-milled 75W-25Cu can be divided into three regions, while for that of the blended 75W-25Cu two regions. The characteristics of ball-milled 75W-25Cu were analyzed by energy dispersive spectroscopy (EDS), differential scanning calorimeter(DSC) and scanning electron microscopy (SEM). The considerable grain growth of W particles was observed during the liquid phase sintering of the ball-milled 75W-25Cu. From these results, the solid and liquid phase sintering behaviors were discussed in terms of the size, the stored energy, and the distribution of W and Cu particles embedded in the ball-milled 75W-25Cu composite powders. (Received August 18, 1992)
텅스텐 중합금 관통자에서 고속충돌에 의해 형성된 단열성 전단밴드의 관찰
김동국,이성학,노준웅 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.11
The objective of the present study is to investigate the adiabatic shear banding behavior in a tungsten heavy alloy penetrator. The penetrator was highly deformed at high strain rate by high speed impact, and after the high speed impact testing, metallurgical observation of the impacted penetrator specimen was conducted using an optical microscope and a scanning electron microscope. Heavily elongated tungsten grains and reaction products such as tungsten oxides were observed on the specimen surface presumably due to the local temperature rise occurring during high speed impact. A few adiabatic shear bands including elongated tungsten grains were observed in the regions near the surface cracks, and their width was wide in comparison to the shear band in armor plates. The cracks had trends to propagate along the shear bands, but sometimes changed their propagation path along the interfaces between adhering tungsten grains. These findings suggested that the minimization of the interfacial area of tungsten grains was required in order to improve the penetration performance of the tungsten heavy alloy.
W-Ni-Fe 중합금에서 바인더 조성에 따른 미세조직 및 기계적 성질의 변화
이성,백운형,김은표,송흥섭,노준웅,천길성 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.8
W heavy alloys with different composition of matrix were sintered at various temperatures to investigate the microstructure and mechanical properties. The Ni/Fe ratios in the composition of 93W-7 (Ni-Fe) heavy alloys were varied from 7/3 via 8/2 to 9/1 by weight. The results showed that, with increased in Ni contents, the volume fraction of matrix was increased due to increased solubility of W in the matrix. In trun, it lowered dihedral angle and facilitated matrix peneratration along the grains to lower contiguity. The increased volume fraction of ductile matrix and decreased contiguity contributed to a higher ductility and toughness. The specimen with 9/1 of Ni/Fe ratio showed the lowest impact energy even though it had the largest volume fraction of matrix and the lowest contiguity. This was attributed to the highly dissolved W in the matrix. The optimum composition in the matrix is 80% Ni and 20Fe.