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CM247LC 초내열합금에서 일방향응고 스타트 블록의 초기 핵생성 조건에 따른 결정립 성장
윤혜영 ( Hye Young Yoon ),이재현 ( Je Hyun Lee ),정형민 ( Hyeong Min Jung ),서성문 ( Seong Moon Seo ),조창용 ( Chang Young Jo ),권석환 ( Seok Hwan Gwon ),장병문 ( Byeong Moon Chang ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.1
The grain size and growth direction of a directionally solidified turbine blade were evaluated by the initial nucleation condition at the start block of directional solidification. The initial nucleation condition was controlled by inserting a Ni foil on the directional solidification plate of the directional solidification furnace. Fine grains with good orientation were obtained in the faster cooling condition at the start block. The nucleus number was compared with the cooling rate of the start block by electron back scattered diffraction (EBSD). DSC (differential scanning calorimeter) analysis was performed to compare the melting point and undercooling for nucleation of the coarse nuclei and fine nuclei of the start block. The faster cooling condition at the start block showed more undercooling for nucleation and smaller size of nuclei which resulted in a fine grain with good orientation in the directional turbine blade.
GTD111M 초내열합금에서 응고속도 및 온도구배가 일방향응고 조직 에 미치는 영향
예대희,김현철,이재현,유영수,조창용,Ye, Dae-Hee,Kim, Cyun-Choul,Lee, Je-Hyun,Yoo, Young-Soo,Jo, Chang-Yong 한국재료학회 2002 한국재료학회지 Vol.12 No.12
Morphological evolution and growth mechanism at the solid/liquid interface during solidification were investigated in the Ni-base superalloy GTD111M by directional soldification and quenching(DSQ) technique. The experiments were conducted by changing solidification rate(V) and thermal gradient(G) which are major solidification process variables. High thermal gradient condition could be obtained by increasing the furnace temperature and closely attaching the heating and cooling zones in the Bridgeman type furnace. The dendritic/equiaxed transition was found in the G/V value lower than $0.05$\times$10{^3}^{\circ}C$s/$\textrm{mm}^2$, and the planar interface of the MC-${\gamma}$ eutectic was found under $17 $\times$ 10{^3}^{\circ}C$ s/$\textrm{mm}^2$. It was confirmed that the dendrite spacing depended on the cooling rate(GV), and the primary spacing was affected by the thermal gradient more than solidification rate. The dendrite lengths were decreased as increasing the thermal graditne, and the dendrite tip temperature was close to the liquidus temperature at $50 \mu\textrm{m}$/s.
수용성 매체에서 뮬라이트의 합성거동 및 입자형상에 미치는 염 및 전구체 pH의 영향
정연길,이재언,신영일,김재원,조창용,Jung, Yeon-Gil,Lee, Jae-Ean,Shin, Young-Ill,Kim, Jae-Won,Jo, Chang-Yong 한국재료학회 2003 한국재료학회지 Vol.13 No.4
The effects of the salt and the precursor pH on the synthesizing behavior and the morphology of mullite have been studied. Two kinds of mullite precursor sols were prepared by the dissolution of two kinds of salt (aluminum nitrate enneahydrate, Al($NO_3$)$_3$ㆍ$9H_2$O; type I and aluminum sulfate 14∼18 water, (SO$Al_4$)$_3$$\cdot$$14∼18H_2$O; type II) into the mixture of colloidal silica sol, respectively. Precursor pH of the sols was controlled to the acidic (pH= 1.5∼2) and basic (pH= 8.5∼9) conditions. The co-products with nitrate and sulfate were completely eliminated at $500^{\circ}C$ and $850^{\circ}C$, respectively, which was confirmed by TG/DTA results. The synthesizing temperature of mullite phase was found to be above $1200^{\circ}C$ for pH= 1.5∼2 and above $1300^{\circ}C$ for pH= 8.5∼9 in type I. However, in type II, the synthesizing temperature of mullite was decreased to $850^{\circ}C$ for pH= 1.5∼2 and $1100^{\circ}C$ for pH= 8.5∼9. The grain size of the mullite synthesized at pH= 8.5∼9 was larger than that at pH= 1.5∼2 in overall heat-treated temperatures, showing smaller grain size in type II. Aspect ratio of the mullite grains was more increased at pH= 1.5∼2 than pH= 8.5∼9 in type I, showing similar aspect ratio at both pH conditions in type II. It was found that the synthesizing temperature and grain size were predominantly governed by the initial precursor pH and decomposition of the salt, with minor effect on the grain morphology.
일방향 응고된 Co기 초내열합금 FSX-414의 응고속도에 따른 응고조직 및 편석 거동
이현정 ( Hyun Jung Lee ),이재현 ( Je Hyun Lee ),서성문 ( Seong Moon Seo ),조창용 ( Chang Young Jo ),권석환 ( Seok Hwan Gwon ),장병문 ( Byeong Moon Chang ) 대한금속재료학회 ( 구 대한금속학회 ) 2009 대한금속·재료학회지 Vol.47 No.7
Co base superalloys have been widely used for the parts of gas turbine due to their excellent strength, thermal fatigue, oxidation resistance and weldability at high temperature. In this study, directional solidifications were carried out at various solidification rates, including 0.5~300 μm/s in the Co base superalloy FSX-414. The cellular interface were formed at a low solidification rate, 1 μm/s, and the dendritic interface was found at higher solidification rates, 5~300 μm/s. As the spacing of dendrite structure decreased, the size and spacing of eutectics decreased. Dendrite arm spacing decreased with increasing solidification rates and temperature gradient. It was interesting to find the M23C6 eutectic microstructure formed between γ dendrites. Composition analysis showed that Cr and W were segregated severely between the dendrites, which resulted in the formation of Cr-rich M23C6 and W-rich MC carbides.
니켈계 초내열합금의 응고 및 용질원소의 편석 거동에 미치는 레늄 및 루테늄 첨가의 영향
서성문 ( Seong Moon Seo ),정희원 ( Hi Won Jeong ),이재현 ( Je Hyun Lee ),유영수 ( Young Soo Yoo ),조창용 ( Chang Yong Jo ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.11
The influence of rhenium (Re) and ruthenium (Ru) addition on the solidification and solute redistribution behaviors in advanced experimental Ni-base superalloys has been investigated. A series of model alloys with different levels of Re and Ru were designed based on the composition of Ni-6Al-8Ta and were prepared by vacuum arc melting of pure metallic elements. In order to identify the influence of Re and Ru addition on the thermo-physical properties, differential scanning calorimetry analyses were carried out. The results showed that Re addition marginally increases the liquidus temperature of the alloy. However, the γ` solvus was significantly increased at a rate of 8.2℃/wt.% by the addition of Re. Ru addition, on the other hand, displayed a much weaker effect on the thermo-physical properties or even no effect at all. The microsegregation behavior of solute elements was also quantitatively estimated by an electron probe microanalysis on a sample quenched during directional solidification of primary γ with the planar solid/liquid interface. It was found that increasing the Re content gradually increases the microsegregation tendency of Re into the dendritic core and γ` forming elements, such as Al and Ta, into the interdendritic area. The strongest effect of Ru addition was found to be Re segregation. Increasing the Ru content up to 6 wt.% significantly alleviated the microsegregation of Re, which resulted in a decrease of Re accumulation in the dendritic core. The influence of Ru on the microstructural stability toward the topologically close-packed phase formation was discussed based on Scheil type calculations with experimentally determined microsegregation results.
CMSX-10 단결정 초내열합금에서 일방향 응고 공정변수에 따른 응고조직 변화도
구지호 ( Ji Ho Gu ),정형민 ( Hyung Min Jung ),이정석 ( Jeong Seok Lee ),윤혜영 ( Hye Young Yoon ),서성문 ( Seong Moon Seo ),조창용 ( Chang Yong Jo ),이재현 ( Je Hyun Lee ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.3
Directional solidification experiments were carried out on a single crystal Ni base superalloy CMSX-10 over a wide range of growth velocity and temperature gradient conditions. Under the imposed temperature gradients, the primary dendrite arm spacings decreased proportionally with the growth velocity. Microstructural characteristics at the solid/liquid interface were found to depend strongly on the growth velocities and temperature gradients. Based on the experimental observations, a growth velocity versus temperature gradient map was selected for planar to cellular and cellular to dendritic transitions during solidification. As a result, the microstructure selection map for the alloy was established by comparing it to theoretical models. Good agreement was obtained from the results for planarcellular and cellular-dendritic transitions. The columnar-equiaxed transition, however, was calculated using Hunt`s model for castings. The results are discussed in terms of the combined effects of constitutional undercooling and nucleation undercooling ahead of the growing dendrite tips.