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초고속 유성형 매체 분쇄기를 이용한 건식분쇄공정에서 Al/CNTs 복합재 제조를 위한 알루미늄분말의 분쇄거동
최희규,이재현,김성수,최경필,배대형,이승백,이웅,Choi, Heekyu,Lee, Jehyun,Kim, Seongsoo,Choi, Gyungpil,Bae, Daehyung,Lee, Sungbak,Lee, Woong 한국재료학회 2013 한국재료학회지 Vol.23 No.2
The study of grinding behavior characteristics on aluminum powders and carbon nano tubes (CNTs) has recently gained scientific interest due to their useful effect in enhancing advanced nano materials and components, which significantly improves the property of new mechatronics integrated materials and components. We performed a series of dry grinding experiments using a planetary ball mill to systematically investigate the grinding behavior during Al/CNTs nano composite fabrication. This study focused on a comparative study of the various experimental conditions at several variations of rotation speeds, grinding time and with and without CNTs. The results were monitored for the particle size distribution, median diameter, crystal structure from XRD pattern and particle morphology at a given grinding time. It was observed that pure aluminum powders agglomerated with low rotation speed and completely enhanced powder agglomeration. However, Al/CNTs composites were achieved at maximum experiment conditions (350 rpm, 60 min.) of this study by a mechanical alloy process for Al/CNTs mixed powders because the grinding behavior of Al/CNTs composite powder was affected by addition of CNTs. Indeed, the powder morphology and crystal size of the composite powders changed more by an increase of grinding time and rotation speed.
CM247LC 초내열합금에서 일방향응고에 따른 응고조직 변화
이정석 ( Jeongseok Lee ),권석환 ( Seokhwan Kown ),윤병관 ( Byunggwan Yoon ),장병문 ( Byungmoon Chang ),정연길 ( Yongil Jung ),이재현 ( Jehyun Lee ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.11
Directional solidification of CM247LC was performed at a constant growth velocity (300 mm/h) using a Bridgman type furnace. Microstructural features, including the number of grains, PDAS, and EBSD IPF map, were investigated with progressive positions from the starter block. As directional solidification proceeded, the number of grains decreased and PDAS increased. These results indicate that the thermal gradient decreases with distance from the starter block. Thermal gradient changes were estimated by dendrite spacing change in the directionally solidified rod. The EBSD IPF map showed that almost all of the grains were close to the < 001 > preferred direction, but with heights of about 300 mm from the starter block, some grains at the center of the specimen exhibited quite different crystallographic directions near the gate instead of the preferred direction. (Received October 5, 2015; Accepted May 24, 2016)
최적 고속화염 용사 코팅 공정기술로 제조된 WC-CrC-Ni 코팅의 마모 특성
주윤곤,윤재홍,이재현,Joo, Yunkon,Yoon, Jaehong,Lee, Jehyun 한국재료학회 2017 한국재료학회지 Vol.27 No.2
WC-CrC-Ni coatings were prepared by nine processes of the Taguchi program with three levels for the four spray parameters: spray distance, flow rates of hydrogen and oxygen, and powder feed rate. The optimal coating process (OCP) was oxygen flow rate of 38 FMR, hydrogen flow rate of 53 FMR, powder feed rate of 25 g/min, and spray distance of 7 inches. Hardness of 1150 Hv and porosity of 1.2 %, were obtained by OCP; these are better results compared with the highest 1033 Hv and the lowest 1.5 % porosity obtained by nine processes of the Taguchi program. Friction coefficient of the WC-CrC-Ni coating decreased from $0.36{\pm}0.07$ at $25^{\circ}C$ to $0.23{\pm}0.07$ at $450^{\circ}C$. These values were smaller than those of the EHC (electrolytic hard chrome) plating at both temperatures due to lubrication from the oxide debris. The wear trace and wear depth of the coating are smaller than those of the EHC at both temperatures. Pitting was not found in the WC-CrC-Ni coating sample, while it did appear in the EHC sample.
다양한 매체형 분쇄기를 이용한 건식 분쇄공정에서 장비의 표준화를 위한 분쇄실험의 비교 연구
보르암갈란,사꾸라기시오리,이재현,최희규,Bor, Amgalan,Sakuragi, Shiori,Lee, Jehyun,Choi, Heekyu 한국재료학회 2015 한국재료학회지 Vol.25 No.6
The study of grinding behavior characteristics on the metal powders has recently gained scientific interest due to their useful applications to enhance advanced nano materials and components. This could significantly improve the property of new mechatronics integrated materials and components. So, a new evaluation method for standardizing grinding equipment and a comparative study for the grinding experiment during the grinding process with various grinding mills were investigated. The series of grinding experiments were carried out by a traditional ball mill, stirred ball mill, and planetary ball mill with various experimental conditions. The relationship between the standardization of equipment and experimental results showed very significant conclusions. Furthermore, the comparative study on the grinding experiment, which investigated changes in particle size, particle morphology, and crystal structure of materials with changes in experimental conditions for grinding equipment, found that the value of particle size distribution is related to the various experimental conditions as a revolution speed of grinding mill and media size.
초고속화염용사 WC-CoFe 코팅층의 레이저 표면 열처리 효과
주윤곤,윤재홍,이재현,Joo, Yunkon,Yoon, Jaehong,Lee, Jehyun 한국재료학회 2019 한국재료학회지 Vol.29 No.1
The microstructure, hardness, and wear behaviors of a High Velocity Oxygen Fuel(HVOF) sprayed WC-CoFe coating are comparatively investigated before and after laser heat treatments of the coating surface. During the spraying, the binder metal is melted and a small portion of WC is decomposed to $W_2C$. A porous coating is formed by evolution of carbon oxide gases formed by the reaction of the free carbon and the sprayed oxygen gas. The laser heat treatment eliminates the porosity and provides a more densified microstructure. After laser heat treatment, the porosity in the coating layer decreases from 1.7 % to 1.2 and the coating thickness decreases from $150{\mu}m$ to $100{\mu}m$. The surface hardness increases from 1440 Hv to 1117 Hv. In the wear test, the friction coefficient of coating decreases from 0.45 to 0.32 and the wear resistance is improved by the laser heat treatment. The improvement is likely due to the formation of oxide tribofilms.
세 가지 매체형 분쇄기를 이용한 분쇄공정에서 다양한 실험 조건에 대한 입자형상변화
사꾸라기시오리,보르암갈란,이재현,최희규,Sakuragi, Shiori,Bor, Amgalan,Lee, Jehyun,Choi, Heekyu 한국입자에어로졸학회 2015 Particle and Aerosol Research Vol.12 No.3
This study investigated the effects of ball mill operation condition on the morphology of raw powders in the dry-type milling process using three types of ball mills traditional ball mill, stirred ball mill and planetary ball mill. Furthermore, since spherical powders offer the best combination of high hardness and high density, the optimum milling condition to produce sphere-shaped powders was studied. The applied rotation speed ranged from 200rpm (low rotation speed) to 700rpm (high rotation speed). The used ball size ranged from 1mm to 5mm. The metal powder morphology was studied using SEM, XRD and PSA. The aimed spherical powders could be obtained under the optimum experimental conditions: traditional ball mill(200rpm, 1mm ball), planetary ball mill (500rpm, 1mm ball) and also planetary ball mill (700rpm, 1 and 3 mm ball). The results show to the development of new material using spherical type copper powder/CNT composites for air-craft and automotive applications.
CMSX-10 단결정 초내열합금에서 거시편석에 따른 γ/γ' 응고조직 형성
윤혜영,성창훈,신종호,한승전,이재현,Yoon, Hyeyoung,Sung, Changhoon,Shin, Jongho,Han, Seong Zeon,Lee, Jehyun 한국재료학회 2015 한국재료학회지 Vol.25 No.9
The ${\gamma}/{\gamma}^{\prime}$ two-phases, commonly known as a eutectic structure, are observed in the ${\gamma}$ interdendritic region of a Ni-base superalloy. However, the growth behavior of the ${\gamma}/{\gamma}^{\prime}$ two-phases, whether it is of eutectic or peritectic nature, has not been decidedly established. Directional solidifications were, thus, performed with the planar interface at a low growth rate of $0.5{\mu}m/s$ in order to promote macro segregation. Directional solidification started with the ${\gamma}$ planar interface and the ${\gamma}^{\prime}$ phase nucleated on the ${\gamma}$ planar interface at the solidification fraction of 0.75. The ${\gamma}/{\gamma}^{\prime}$ two-phases showed the ${\gamma}^{\prime}$ rod structure as major phase and the ${\gamma}$ minor phase between ${\gamma}^{\prime}$ rods, and the volume fraction of the ${\gamma}$ phase changed continuously with an increasing solidification fraction. The two-phase ${\gamma}/{\gamma}^{\prime}$ is seen as the coupled peritectic.
초내열합금 René 80의 응고 조직과 열처리 후 인장특성의 변화
우한별,신종호,주윤곤,이재현,Woo, Hanbyeol,Shin, Jongho,Joo, Yunkon,Lee, Jehyun 한국재료학회 2020 한국재료학회지 Vol.30 No.12
Microstructural characteristics of directionally solidified René 80 superalloy are investigated with optical microscope and scanning electron microscope; solidification velocity is found to change from 25 to 200 μm/s under the condition of constant thermal gradient (G) and constant alloy composition (Co). Based on differential scanning calorimetry (DSC) measurement, γ phase (1,322 ℃), MC carbide (1,278 ℃), γ/γ' eutectic phase (1,202 ℃), and γ' precipitate (1,136 ℃) are formed sequentially during cooling process. The size of the MC carbide and γ/γ' eutectic phases gradually decrease with increasing solidification velocity, whereas the area fractions of MC carbide and γ/γ' eutectic phase are nearly constant as a function of solidification velocity. It is estimated that the area fractions of MC carbide and γ/γ' eutectic phase are determined not by the solidification velocity but by the alloy composition. Microstructural characteristics of René 80 superalloy after solid solution heat-treatment and primary aging heat-treatment are such that the size and the area fraction of γ' precipitate are nearly constant with solidification velocity and the area fraction of γ/γ' eutectic phase decreases from 1.7 % to 0.955 %, which is also constant regardless of the solidification velocity. However, the size of carbide solely decreases with increasing solidification velocity, which influences the tensile properties at room temperature.
최적 고속화염용사법으로 제조된 Diamalloy4006 코팅의 내마모 특성
주윤곤,윤재홍,정연길,이재현,Joo, Yunkon,Yoon, Jaehong,Jung, Yeongil,Lee, Jehyun 한국재료학회 2015 한국재료학회지 Vol.25 No.9
The effects of coating parameters were investigated in wear resistance coatings of Diamalloy-406 on Inconel 718 to obtain an optimum coating condition by high velocity oxy-fuel spraying. The coating parameters, the flow rates of source gases (hydrogen and oxygen), the powder feed rate, and the spray distance, were designed by the Taguchi method. The optimal conditions were determined: oxygen flow rate 34 FRM, hydrogen flow rate 57 FRM, powder feed rate 35 g/min, and spray distance 7 inch. Friction coefficients of the coating and the substrate decreased with an increasing sliding surface temperature from $25^{\circ}C$ to $450^{\circ}C$. The friction coefficient of Diamalloy-4006 coating decreased as the sliding surface temperature increased from $0.43{\pm}0.01$ at $25^{\circ}C$ to $0.29{\pm}0.01$ at $450^{\circ}C$. The wear trace and wear depth of the coating were smaller than the substrate at all temperatures tested. The relationship between spray parameters and wear resistance was discussed extensively, based on the measured roughness, hardness, and porosity in each coating.
티타늄이 첨가된 알루미나 분산강화 동합금의 산화물 형성 거동
조홍래,한승전,안지혁,이재현,손영국,김광호,Joh, Hongrae,Han, Seung Zeon,Ahn, Jee Hyuk,Lee, Jehyun,Son, Young Guk,Kim, Kwang Ho 한국재료학회 2015 한국재료학회지 Vol.25 No.4
Alumina dispersion strengthening copper(ADSC) alloy has great potential for use in many industrial applications such as contact supports, frictional break parts, electrode materials for lead wires, and spot welding with relatively high strength and good conductivity. In this study, we investigated the oxidation behavior of ADSC alloys. These alloys were fabricated in forms of plate and round type samples by surface oxidation reaction using Cu-0.8Al, Cu-0.4Al-0.4Ti, and Cu-0.6Al-0.4Ti(wt%) alloys. The alloys were oxidized at $980^{\circ}C$ for 1 h, 2 h, and 4 h in ambient atmosphere. The microstructure was observed with an optical microscope(OM) and a scanning electron microscope(SEM) equipped with energy-dispersive X-ray spectroscopy(EDS). Characterization of alumina was carried out using a 200 kV field-emission transmission electron microscope(TEM). As a result, various oxides including Ti were formed in the oxidation layer, in addition to ${\gamma}$-alumina. The thickness of the oxidation layer increased with Ti addition to the Cu-Al alloy and with the oxidation time. The corrected diffusion equation for the plate and round type samples showed different oxidation layer thickness under the same conditions. Diffusion length of the round type specimen had a value higher than that of its plate counterpart because the oxygen concentration per unit area of the round type specimen was higher than that of the plate type specimen at the same diffusion depth.