• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.88-94
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• 1997

The oxidation behavior of the NiCrAlY bond coat and thermal fatigue failure in the plasma-sprayed thermal barrier coating system, ZrO2.8wt%Y2O3 top coat/Ni-26Cr-5Al-0.5Y bond coat/Hastelloy X superalloy substrate, in commercial use for finned segment of gas turbine burner were investigated. The main oxides formed in the bond coat were NiO, Cr2O3, and Al2O3. It divided the oxide distribution at this interface into two types whether an Al2O3 thin layer existed beneath ZrO2/bond coat interface before operation at high temperature or not. While a continuous layer of NiO was formed mainly in the region where the Al2O3 thin layer was present, the absence of it resulted in the formation of mixture of Cr2O3 and Al2O3 beneath NiO layer. Analyses on the fracture surface of specimen spalled by thermal cycling showed that spalling occurred mainly along the ceram-ic coat near ZrO2/bond coat oxide layer interface, but slightly in the oxide layer region.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1289-1295
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• 2012

A process heat exchanger (PHE) in a nuclear hydrogen system is a key component for transferring the considerable heat generated in a very high temperature reactor (VHTR) to a chemical reaction that yields a large quantity of hydrogen. A performance test on a small-scale PHE prototype made of Hastelloy-X is underway in a small-scale gas loop at the Korea Atomic Energy Research Institute. Previous research on the high-temperature structural analysis of the small-scale PHE prototype had been performed using base material properties. In this study, a high-temperature structural analysis considering the mechanical properties in the weld zone was performed, and the obtained results were compared with those of the previous research.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.10
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• pp.1283-1288
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• 2012

A process heat exchanger (PHE) in a nuclear hydrogen system is a key component for transferring the considerable heat generated in a very high temperature reactor (VHTR) to a chemical reaction that yields a large quantity of hydrogen. A performance test on a medium-scale PHE prototype made of $Hastelloy^{(R)}$-X is scheduled in a small-scale gas loop at the Korea Atomic Energy Research Institute. In this study, as a preliminary study before carrying out the performance test in the gas loop, high-temperature structural analysis modeling and macroscopic thermal and structural analysis of the medium-scale PHE prototype by imposing the established displacement boundary constraints were carried out under the gas loop test condition. The results obtained in this study will be compared with the performance test results of the medium-scale PHE prototype in the gas loop.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1249-1255
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• 2011

A PHE (Process Heat Exchanger) is a key component required to transfer heat energy of $950^{\circ}C$ generated in a VHTR (Very High Temperature Reactor) to a chemical reaction that yields a large quantity of hydrogen. A small-scale PHE prototype made of Hastelloy-X was scheduled for testing in a small-scale gas loop at the Korea Atomic Energy Research Institute. In this study, as a part of the evaluation of the high-temperature structural integrity of the PHE prototype, high-temperature structural analysis modeling, and macroscopic thermal and elastic-plastic structural analysis of the PHE prototype were carried out under the gas-loop test conditions as a preliminary qwer123$study before carrying out the performance test in the gas loop. The results obtained in this study will be used to design the performance test setup for the modified PHE prototype.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.9
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• pp.1095-1101
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• 2012

A process heat exchanger (PHE) in a nuclear hydrogen system is a key component that transfers the large amount of heat generated in a very high temperature reactor (VHTR) to a chemical reaction that yields a large quantity of hydrogen. A performance test on a small-scale and a medium-scale PHE prototype made of Hastelloy$^{(R)}$-X is being conducted on in a small-scale nitrogen gas loop at the Korea Atomic Energy Research Institute. Previous research on the macroscopic high-temperature structural analysis of PHE prototypes had been performed using base material properties owing to a lack of weld material properties. In this study, macroscopic high-temperature structural analyses considering the weld material properties were performed and the results were compared with those of a previous study.

• Nuclear Engineering and Technology
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• v.41 no.1
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• pp.107-112
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• 2009

Corrosion of nickel-base alloys (Hastelloy C-276, Inconel 625, and Inconel X-750) in $500^{\circ}C$, 25MPa supercritical water (with 10 wppb oxygen) was investigated to evaluate the suitability of these alloys for use in supercritical water reactors. Oxide scales formed on the samples were characterized by gravimetry, scanning electron microscopy/energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The results indicate that, during the 1000h exposure, a dense spinel oxide layer, mainly consisting of a fine Cr-rich inner layer ($NiCr_{2}O_{4}$) underneath a coarse Fe-rich outer layer ($NiFe_{2}O_{4}$), developed on each alloy. Besides general corrosion, nodular corrosion occurred on alloy 625 possibly resulting from local attack of ${\gamma}$" clusters in the matrix. The mass gains for all alloys were small, while alloy X -750 exhibited the highest oxidation rate, probably due to the absence of Mo.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.11a
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• pp.35-50
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• 2012

$900^{\circ}C$이상 초고온 He-gas 분위기 또는 용융불화염 (molten salts, FLINAK) 환경에서 사용될 VHTR(Very High Temperature Reactor)의 IHX(Intermediate heat exchanger)용 열수송 구조재료로 가장 가능성이 높은 합금인 Inconel 617 및 Hastelloy X 상에 습식화학적, 물리적기상합성법(Vacuum arc-plasma과 RF magnetron sputtering) 및 pack cementation에 의한 표면개질 및 마이크로 초내열(refractory ceramics) 코팅층(TiN, TiCN, TiAlN, $Al_2O_3$, $TiO_2$)을 형성시켰다. 고온 장기사용 시 문제가 될 수 있는 고온에서의 조직변화, 미세구조와 상(phase)형성, 고온 부식 및 그에 따른 마모(wear resistance) 손상 등 이들 소재의 내열, 내식 및 내마모 물성을 개선하는 연구를 수행하였다. TiAlN 박막의 경우 공기분위기에서 N이 분해되나 치밀한 산화물($TiO_2/Al_2O_3$ layer)을 형성하여 내식성 있는 보호피막을 형성함으로 기판과의 열팽창 계수로 인한 박리가 발생하지 않아 보호피막으로 적합하였다. Pack cementation법에 의한 aluminiding(Al-Ni합금)도 He 및 공기분위기에서 고온물성의 저하를 가져오는 $Cr_2O_3$의 생성을 충분히 억제하고 있었으며 He 및 air 분위기에서 사용이 가능한 박막으로 여겨진다. 내열 및 내식성에 대한 실험을 종합한 결과, 공기분위기에서 사용할 수 없는 박막은 He-gas 및 FLINAK(LiF-NaF-KF) 용융염 분위기에서도 사용할 수 없었으며, He-gas, FLINAK 및 air 분위기에서 모두 사용이 가능한 박막으로는 Inconel 617에서는 $(TiO_2-)Al_2O_3$, TiAlN 및 Al-Ni이었고 Hastelloy에서는 Al-Ni 및 $Al_2O_3$가 가장 적당하였다.

• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.105-112
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• 1992

The main purpose of this study is to derive a law of fatigue crack growth rate in the region of elastic or elasto-plastic fracture mechanics at elevated temperatures through the application of dimensional analysis. An equation of elasto-plastic fatigue crack growth rate at elevated temperatures appeared a new Arrhenius type equation containing J-integral range and absolute temperature. The elastic or elasto-plastic crack growth rate equation shows a fairly good agreement with the experimental results for Cr-Mo-V rotor steel and Hastelloy-X alloy in the comparatively wide temperature ranges.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.1
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• pp.1-7
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• 2012

A PHE (Process Heat Exchanger) is a key component required to transfer heat energy of $950^{\circ}C$ generated in a VHTR (Very High Temperature Reactor) to the chemical reaction that yields a large quantity of hydrogen. A small-scale PHE prototype made of Hastelloy-X is being tested in a small-scale gas loop at Korea Atomic Energy Research Institute. In order to properly evaluate the high-temperature structural integrity of the small-scale PHE prototype, it is very important to impose a proper constraint condition on its structural analysis model. For this effort, we tried to impose several constraint conditions on the structural analysis model and consequently fixed a proper and effective displacement constraints.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.8 no.2
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• pp.1-6
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• 2012

A PHE (Process Heat Exchanger) in a nuclear hydrogen system is a key component required to transfer heat energy of $950^{\circ}C$ generated in a VHTR (Very High Temperature gas cooled Reactor) to the chemical reaction that yields a large quantity of hydrogen. A small-scale PHE prototype made of Hastelloy-X is being tested in a small-scale gas loop at Korea Atomic Energy Research Institute. Previous research on the high-temperature structural analysis of the small-scale PHE prototype had been performed only using parent material properties. In this study, high-temperature structural analysis using weld properties in weld zone was performed and the analysis results compared with the previous research.