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Hastelloy X 주조재의 열간 노출에 따른 미세조직 및 인장 특성 변화
최백규,김인수,도정현,정중은,정인용,홍현욱,조창용,Choi, Baig Gyu,Kim, In Soo,Do, Jeonghyeon,Jung, Joong Eun,Jung, In Yong,Hong, Hyun Uk,Jo, Chang Yong 한국주조공학회 2017 한국주조공학회지 Vol.37 No.5
Microstructural evolution of cast Hastelloy X during thermal exposure has been investigated. OM, SEM, and TEM microscopy were carried out on the as-cast, the standard heat treated, and the thermally exposed conditions. Tensile tests were also conducted to understand the effect of microstructural evolution on the degradation of tensile properties. Coarse $M_6C$ and fine $M_{23}C_6$ carbides were found in as-cast Hastelloy X with fine carbides on sub-boundary. Some of $M_{23}C_6$ carbide dissolved into the matrix during solution heat treatment and dislocation network formed at the interface between the carbide and the matrix due to the misfit strain. There was no significant microstructural difference between the exposed specimens at $400^{\circ}C$ and the solution heat treated specimen. A large amount of $M_{23}C_6$ carbides precipitated along and near grain boundaries and sub-boundaries after exposure at $650^{\circ}C$. Exposure at $870^{\circ}C$ of the alloy caused precipitation of $M_6C$ and ${\mu}$. The strength increased and the elongation decreased by thermal exposure at $650^{\circ}C$ and $870^{\circ}C$ because carbides interfere with the movement of the dislocation. It was found that the precipitation of carbide gave significant effects on the tensile properties of Hastelloy X.
니켈기 초내열 합금 GTD 111에서 편석에 의한 합금원소 분포 및 미세조직 변화
최백규 ( Baig Gyu Choi ),김인수 ( In Soo Kim ),도정현 ( Jeong Hyeon Do ),정중은 ( Joong Eun Jung ),조창용 ( Chang Yong Jo ) 한국주조공학회 2015 한국주조공학회지 Vol.35 No.6
Segregation during solidification and homogenization during thermal exposure in GTD 111 were investigated. The microstructures of as-cast, standard heat-treated, and thermally exposed specimens were observed by SEM. A compositional analysis of each specimen was conducted by EDS. The dendrite core was enriched in W and Co, though lower levels of Ti and Ta were observed. An unexpected phase, in this case like the η phase, was observed due to segregation near the γ-γ`` eutectic in the standard heat-treated specimen. Segregation also induced microstructural evolution near the γ-γ`` eutectic during the standard heat treatment. A quantitative analysis and microstructural observations showed that the thermal exposure at a high temperature enhanced the chemical homogeneity of the alloy.
일방향 응고 니켈기 초내열 합금 CM247LC의 온도에 따른 크리프 특성
최백규 ( Baig-gyu Choi ),도정현 ( Jeonghyeon Do ),정중은 ( Joong Eun Jung ),석우영 ( Woo-young Seok ),이유화 ( Yu-hwa Lee ),김인수 ( In Soo Kim ) 한국주조공학회 2021 한국주조공학회지 Vol.41 No.6
일방향응고로 제조된 니켈기 초내열합금 CM247LC의 다양한 온도 및 응력조건에서 크리프 특성에 대해 고찰하였다. 열처리 후 일부 공정조직이 남아 있었으며 비교적 균일한 육면체의 γ'이 수지상 내부와 수지상간 영역에서 관찰되었다. 상대적 저온인 750℃의 고응력 크리프 영역에서는 1차 크리프 동안 많은 변형이 발생하였으나 고온으로 갈수록 3차 크리프 구간이 크리프 변형시간의 대부분을 차지함을 알 수 있었다. 저온 고응력에서는 부분 전위가 γ'으로 진입하며 적층결함을 γ'내에 생성시켰으며 초기 크리프변형속도가 증가하는 부분이 있었으나 850℃ 이상의 온도에서는 γ' 내부에서 적층결함이 관찰되지 않았으며 이는 적층결함에너지의 온도의존성 때문인 것으로 판단된다. 고온이어서 확산속도가 빠른 950℃와 1000℃에서는 γ'의 래프팅이 관찰되었다. 온도가 좀 더 낮은 850℃에서는 변형기구가 응력에 따라 다르게 나타나서 상대적으로 크리프 시간이 긴 저응력에서만 래프팅이 관찰되었다. Creep properties of directionally solidified Ni-based superalloy CM247LC under various temperature and stress conditions have been investigated. In the heat-treated specimen, some portion of eutectic γ-γ' remained, and uniform cubic γ' was observed in the dendrites. At low temperature (750℃) and high stress condition, a large amount of deformation occurred during the primary creep, while the tertiary creep region accounted for most of the creep deformation under high temperature and low stress condition. γ' particles are sheared by dislocation dissociated into super lattice partial dislocations separated by stacking faults at 750℃. No stacking faults in γ' were found at and above 850℃ due to the temperature dependence of the stacking fault energy. Raft structure of γ' was found after creep test at high temperature of 950℃ and 1000℃. At 850℃, the deformation mechanism was shown to be dependent on the stress condition, and so rafting was observed only under low stress condition.
니켈기 초내열합금의 열간노출에 따른 미세조직 및 기계적 특성 변화
김인수 ( In-soo Kim ),최백규 ( Baig-gyu Choi ),정중은 ( Joong-eun Jung ),도정현 ( Jeong-hyeon Do ),정인용 ( In-yong Jung ),조창용 ( Chang-yong Jo ) 한국주조공학회 2016 한국주조공학회지 Vol.36 No.5
The microstructural evolution of a cast Ni base superalloy, IN738LC, has been investigated after long term exposure at several temperatures. Most of the fine secondary γ` particles resolved after 2000 hour exposure at 816℃. At higher temperatures of 871℃ and 927℃, secondary γ` resolved after 1000 hours of exposure, and cuboidal primary γ` grew with exposure time. During the ther-mal exposure, σ phase formed at all tested temperatures, and η phase was observed around interdendritic regions due to carbide degeneration. The influence of microstructural evolution during thermal exposure on the mechanical properties has been analyzed. The effects of γ` particle growth are more pronounced on the high temperature creep properties than on the room temperature tensile properties.
논문 : 니켈기 초내열합금 Alloy 263의 고온인장 및 크리프 변형기구
김인수 ( In Soo Kim ),최백규 ( Baig Gyu Choi ),홍현욱 ( Hyun Uk Hong ),조창용 ( Chang Yong Jo ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.7
The tensile and creep behaviors of Alloy 263, which is a wrought Ni-base superalloy used for gas turbine combustion systems, was studied. Anomalous increase of yield strength and abrupt decrease of elongation with increasing temperature were observed after tensile testing at an intermediate temperature. Elongation of the superalloy decreased as the temperature increased to and above 540℃, and it reached a minimum value at 760℃. It was found that creep strain was also very low at the same temperature. Inhomogeneous deformation with intensive slip bands was observed in the specimens tested at low temperature. A thermally-assisted dislocation climb process was regularly conducted at high temperature. Twinning was found to be an important mechanism of both tensile and creep deformations of the superalloy at an intermediate temperature where ductility minimum was observed.
액체로켓 연소기용 Inconel 718 주조 및 단조 합금의 전자빔 용접부 미세조직 및 극저온 특성
홍현욱,배상현,권순일,이재현,도정현,최백규,김인수,조창용,Hong, Hyun-Uk,Bae, Sang-Hyun,Kwon, Soon-Il,Lee, Je-Hyun,Do, Jeong-Hyeon,Choi, Baig-Gyu,Kim, In-Soo,Jo, Chang-Yong 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.6
Characterization of microstructures and cryogenic mechanical properties of electro beam (EB) welds between cast and forged Inconel 718 superalloys has been investigated. Optimal EBW condition was found in the beam current range of 36~39 mA with the constant travel speed of 12 mm/s and arc voltage of 120 kV for 10 mm-thick specimens. Electron beam current lower than 25 mA caused to occur the liquation microfissuring in cast-side heat affected zone (HAZ) of EB welds. The HAZ liquation microfissure was found on the liquated grain boundaries with resolidified ${\gamma}/Laves$ and ${\gamma}/NbC$ eutectic constituents. EBW produced welds showing a fine dendritic structure with relatively discrete Laves phase due to fast cooling rate. After post weld aging treatment, blocky Laves phase and formation of ${\gamma}^{\prime}+{\gamma}^{{\prime}{\prime}}$ strengtheners were observed. Presence of primary strengthener and coarse Laves particles in PWHT weld may cause to reduce micro-plastic zone ahead of a crack, leading to a significant decrease in Charpy impact toughness at $-196^{\circ}C$. Fracture initiation and propagation induced by Charpy impact testing were discussed in terms of the dislocation structures ahead of crack arisen from the fractured Laves phase.
니켈기 초내열합금의 파형 결정립계 구조가 보론 편석과 재현 열영향부 액화균열거동에 미치는 영향
홍현욱,최준우,배상현,윤중근,김인수,최백규,김동진,조창용,Hong, Hyun-Uk,Choi, June-Woo,Bae, Sang-Hyun,Yoon, Joong-Geun,Kim, In-Soo,Choi, Baig-Gyu,Kim, Dong-Jin,Jo, Chang-Yong 대한용접접합학회 2013 대한용접·접합학회지 Vol.31 No.3
The transition of serrated grain boundary and its effect on liquation behavior in the simulated weld heat-affected zone (HAZ) have been investigated in a wrought Ni-based superalloy Alloy 263. Recently, the present authors have found that grain boundary serration occurs in the absence of adjacent coarse ${\gamma}^{\prime}$ particles or $M_{23}C_6$ carbides when a specimen is direct-aged with a combination of slow cooling from solution treatment temperature to aging temperature. The present study was initiated to determine the interdependence of the serration and HAZ property with a consideration of this serration as a potential for the use of a hot-cracking resistant microstructure. A crystallographic study indicated that the serration led to a change in grain boundary character as special boundary with a lower interfacial energy as those terminated by low-index {111} boundary planes. It was found that the serrated grain boundaries are highly resistant to boron enrichment, and suppress effectively grain coarsening in HAZ. Furthermore, the serrated grain boundaries showed a higher resistance to susceptibility of liquation cracking. These results was discussed in terms of a significant decrease in interfacial energy of grain boundary by the serration.
주조 합금 Alloy 718에서 미세조직과 인장특성에 미치는 열처리의 영향
도정현 ( Jeong-hyeon Do ),김인수 ( In-soo Kim ),최백규 ( Baig-gyu Choi ),정중은 ( Joong-eun Jung ),정인용 ( In-yong Jung ),조창용 ( Chang-yong Jo ) 한국주조공학회 2016 한국주조공학회지 Vol.36 No.5
The effect of various types of heat-treatment on the mechanical properties of cast Alloy 718 has been investigated. Cast Alloy 718 bars were subjected to ‘standard heat-treatment`_(SHT), ‘HIP (Hot Isostatic Pressing) heat-treatment`_(HHT), and ‘HIP-sim-ulated heat-treatment`_(HS). In the absence of long time high temperature heat-treatment, a small amount of Laves phase remained in the ‘SHT` specimen, and needle shaped δ precipitated in the vicinity of the Laves phase. Due to the formation of the Laves and δ phases in the ‘SHT` specimen, it exhibited lower tensile properties than those of the others_specimens. On the other hand, the Laves phase was completely dissolved into the matrix after ‘HHT` and ‘HS` treatments. It is known that isostatic pressure reduces the self-diffusion coefficient, because of the lower self-diffusivity under HIP conditions in the interdendritic region, Nb segregation and the high amount of γ” precipitation that occurs. Due to the higher fraction of coarse γ” phases, the ‘HHT` treated Alloy 718 showed excellent tensile strength.