• Corrosion Science and Technology
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• v.7 no.4
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• pp.233-236
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• 2008

Halide-activated pack cementation was utilized to deposit B-doped silicide coating. The pack powders were consisted of $3Wt.c/oNH_4Cl$, 7Wt.c/oSi, $90Wt.c/oAl_2O_3+TiB_2$. B-doped silicide coating was consisted of two layers, an outer layer of $NbSi_2$ and an inner layer of $Nb_5Si_3$. Isothermal oxidation resistance of B-doped silicide coating was tested at $1250^{\circ}C$ in static air. B-doped silicide coating had excellent oxidation resistance, because continuous $SiO_2$ scale which serves as obstacle of oxygen diffusion was formed after oxidation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.201-201
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• 2012

탄소 탄소 복합재료(C/C composite)는 고온도 영역에서 강도저하가 없으며 화학적으로 더욱 안정되어 지기 때문에 고온 구조재료로서 널리 사용되어지고 있다. 모재의 성분이 모두 탄소로 구성되어 있어 약 $500^{\circ}C$의 산화분위기에서 부터는 산화되는 결점을 가지고 있다. 본 연구에서는 이러한 결점을 보완하기 위해 Pack Cementation과 Dipping 방법을 통해 내산화 코팅층을 형성 하여 $1300^{\circ}C$에서의 내산화성을 향상 시킬 수 있었다.

• Corrosion Science and Technology
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• v.2 no.1
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• pp.53-57
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• 2003

The MarM247 based superalloy (8wt.%Cr- 9wt.%Co- 3wt.%Ta- 1.5wt.%Hf- 5.6%wt.Al- 9.5wt.%W- Bal. Ni) specimens were diffusion aluminized by for types of pack cementation methods, and their coating structure and their high temperature oxidation resistance were investigated. The coated specimens treated at 973K in high aluminum concentration pack had a coating layer containing large hafunium rich precipitates, which were originally included in substrate alloy. After the high temperature oxidation test in air containing 30 vol.% $H_2O$ at 1273K ~ 323K, the deep localized corrosion which reached to the substrate were observed along with these hafnium rich precipitates. On the other hand, the coated specimens treated at 1323K using low aluminum concentration pack showed the coating layer without the large hafunium rich precipitates, and after the high temperature oxidation test at 1273K for 1800 ksec, it did not show the deep localized corrosion. The nickel electroplating before the aluminizing forms thick hafnium free area, and its high temperature oxidation resistance were comparable to platinum modified aluminizing coatings at 1273K.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.1 s.1
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• pp.127-138
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• 2001

Although Carbon/Carbon Composites(CFRCs) have excellent mechanical properties at high temperature, the disadvantage of combustion in air restricts their applications. Thus a lot of investments have been studied to improve the drawback of CFRCs. In this study, SiC used as a thermal protective coating material possesses almost the same expansion coefficient compared to that of carbon, so SiC was coated on 4D (directional) CFRCs by Pack-Cementation process. For the 4D CFRCs coated with SiC, optical microscopy observations were performed to estimate the coating mechanism involved and TGA tests were also performed to evaluate the improvement of combustion resistance. And their high temperature combustion properties were investigated by the arc torch plasma test. From the results, it is found that the mechanical properties and high temperature combustion properties of the 4D(directional) CFRCs coated with SiC were much better than bare 4D CFRCs.

• Korean Journal of Materials Research
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• v.13 no.2
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• pp.126-132
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• 2003

In order to evaluate the corrosion resistance at the anode side separator for molten carbonate fuel cell, STS316 and SACC-STS316 (chromium and aluminum were simultaneously deposited by diffusion into STS316 authentic stainless steel substrate by pack-cementation process) were applied as the separator material. In case of STS316, corrosion proceeded via three steps ; a formation step of corrosion product until stable corrosion product, a protection step against corrosion until breakaway occurs, a advance step of corrosion after breakaway. Especially, STS316 would be impossible to use the separator without suitable surface modification because of rapid corrosion rate after formation of corrosion product, occurs the severe problem on stability of cell during long-time operation. Whereas, SACC-STS316 was showed more effective corrosion resistance than the present separator, STS316 due to the intermetallic compound layer such as NiAl, Ni3Al formed on the surface of STS316 specimen. And it is anticipated that, in order to use SACC-STS316 alternative separator at the anode side, coating process, which can lead to dense coating layer, has to be developed, and by suitable pre-treatment before using it, very effective corrosion resistance will be achieved.

• 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 the Korean Ceramic Society
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• v.31 no.8
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• pp.874-878
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• 1994

To increase the anti-oxidation and anti-wear properties of graphite for the propellant-burning environment, SiC, Pt and Al2O3 multi-layer coatings were conducted succesisvely and the optimum condition was researched. The SiC layer was produced by pack cementation and SiC layer in thickness of 30 ${\mu}{\textrm}{m}$ coating was produced after coating for 6 hours. Pt layer was coated by sputtering, and the Al2O3 layer was coated by reactive sputtering. the thickness of Pt layer and Al2O3 layer was less than one-tenth of that of SiC layer. The pack coated specimens and multi-layer coated specimens were made using above conditions and test-fired. The test result showed that the wear rate of SiC layer is approximately 1/10 compared to that of uncoated graphite.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2013.05a
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• pp.100-101
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• 2013

가스 터빈, 석유 화학 공장 등에 널리 사용되고 있는 합금들은 IGCC 분위기에서 심각한 부식이 야기된다. 특히 고온에서 가스터빈 재료로 사용되는 초내열 합금 등도 열악한 고온 황화분위기에서는 열악한 내부식성을 보였다. 따라서 이러한 조건에서 견딜 수 있는 재료의 개발이 필요하다. 일반적으로 알려진 내부식성 증가 방법은 내부식성 합금원소 첨가와 재료 표면에 직접 코팅을 하는 방법이 있으며, 본 연구에서는 고온의 $H_2S$ 가스 분위기에서 Pack cementation으로 Al과 Cr 확산코팅 시킨 시편을 이용하여 부식실험을 실시하여 부식 특성을 살펴보았다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.59.1-59.1
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• 2011

Ni기 초내열합금을 사용하는 터빈엔진의 효율향상 및 다양한 초고온함금에 대한 관심이 높아지면서, 이를 대체할 수 있는 초고온합금으로 Mo기지 복합재료에 대한 연구가 활발히 진행되고 있는 가운데 실질적으로 Mo 합금은 취약한 산화성으로 인하여 내산화성이 문제가 되고 있다. Mo-Si-B합금이 초고온에 노출될 경우 산화물의 점도가 매우 낮아 산화층을 형성하기 곤란하고, 저온에서는 산화층이 합금을 보호하지 못한다고 알려져 있다. 따라서, 본 연구에서는 Mo-Si-B 합금기지에 Si 확산코팅을 수행하여 내산화성을 높이고자 하였다. $1,100^{\circ}C$와 $800^{\circ}C$의 온도에서 시간에 따른 코팅 층의 두께 및 성장거동을 속도론적으로 고찰하였고, 내산화성을 평가하였다. 코팅된 시험편의 XRD 및 SEM 분석 및 무게측정 결과 내산화성이 크게 개선된 것으로 나타났으며, 내산화성에 대한 기구를 고찰하였다.

• Applied Chemistry for Engineering
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• v.18 no.3
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• pp.227-233
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• 2007

Carbon/carbon (C/C) composites as unique materials possess exceptional thermal resistance with light weight, high stiffness, and strength even at high temperature. However, one serious obstacle for application of the C/C composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating has been employed to protect the composites from oxidation. This study explored combustion characteristics of 4-directional (4D) carbon/carbon composites using liquid fuel rocket engine to investigate ablative motion of the materials. C/C composites were made of coal tar pitch as a matrix precursor, and heat-treated at $2300^{\circ}C$. Throughout repeated densification process, the density of the material reached $1.903g/cm^3$. After machining 4D C/C composites, the nozzle surface was coated by a SiC layer by pack-cementation method to improve oxidation resistance. Erosion characteristics of SiC-coated C/C composites were measured as function of the ratio of oxygen to fuel. The morphological change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.