• Title/Summary/Keyword: Pack-cementation

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High temperature properties of surface-modified Hastelloy X alloy (표면처리에 따른 Hastelloy X 합금의 고온물성)

  • Cho, Hyun;Lee, Byeong-Woo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.22 no.4
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    • pp.183-189
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    • 2012
  • Surface treatments and their effects on high temperature properties for the Hastelloy X, which is a promising candidate alloy for high temperature heat-transport system, have been evaluated. For TiAlN and $Al_2O_3$ overlay coatings, the two different PVD (physical vapor deposition) methods using an arc discharge and a sputtering, were applied, respectively. In addition, a different surface treatment method of the diffusion coating by a pack cementation of Al (aluminiding) was also adopted in this study. To achieve enhanced thermal oxidation resistance at $1000^{\circ}C$ by suppressing the inhomogeneous formation of thick $Cr_2O_3$ crust at the surface region, a study for the surface modification methods on the morphological and structural properties of Hastelloy X substrates has been conducted. The structural and compositional properties of each sample were characterized before and after heat-treatment at $1000^{\circ}C$ under air and He environment. The results showed that the Al diffusion coating showed the more enhanced high temperature properties than the overlay coatings such as the suppressed thick $Cr_2O_3$ crust formation and lower wear loss.

Application of ultra-high-temperature ceramics to oxidation-resistant and anti-ablation coatings for carbon-carbon composite (탄소-탄소 복합재의 내삭마 내산화 코팅을 위한 초고온 세라믹스의 적용)

  • Kim, Hyun-Mi;Choi, Sung-Churl;Cho, Nam Choon;Lee, Hyung Ik;Choi, Kyoon
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.29 no.6
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    • pp.283-293
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    • 2019
  • As applications in extreme environments such as aerospace, high-energy plasma and radio-active circumstances increases, the demand for materials that require higher melting points, higher mechanical strength and improved thermal conductivity continues to increase. Accordingly, in order to improve the oxidation/abrasion resistance of the carbon-carbon composite, which is a typical heat-resistant material, a method of using ultra high temperature ceramics was reviewed. The advantages and disadvantages of CVD coating, pack cementation and thermal plasma spraying, the simplest methods for synthesizing ultra-high temperature ceramics, were compared. As a method for applying the CVD coating method to C/C composites with complex shapes, the possibility of using thermodynamic calculation and CFD simulation was proposed. In addition, as a result of comparing the oxidation resistance of the TaC/SiC bi-layer coating and TaC/SiC multilayer coating produced by this method, the more excellent oxidation resistance of the multilayer coating on C/C was confirmed.

Formation of Multi-Component Boride Coatings Containing V and/or Cr and Evaluation of Their Properties (바나듐 및 크롬을 포함하는 다 성분 Boride 코팅의 생성 및 특성 평가)

  • Lee, Euiyeol;Yoon, Sanghyun;Kim, Jongha
    • Journal of the Korean institute of surface engineering
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    • v.49 no.2
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    • pp.211-217
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    • 2016
  • Boride coating applied on steam turbine parts of power plants has provided good particle erosion resistance under temperature of $550^{\circ}C$, but it isn't able to protect the parts effectively any more in ultra super critical (USC) steam turbine which is being operated up to temperature of $650^{\circ}C$. To ensure stable durability for USC steam turbine parts, an alternative coating replacing boride coating should be developed. In this study, multi-component boride coatings containing elements such as chromium (Cr) and vanadium (V) were formed on base metal (B50A365B) using thermochemical treatment method called by pack cementation. The thermochemical treatments involve consecutive diffusion of boron(B) and Cr or/and V using pack powders containing diffusion element sources, activators and diluents. The top layer of Cr-boride coating is primarily consisted of $Cr_2B_3$ and $Cr_5B_3$, while that of V-boride coating is mostly consisted of $VB_2$ and $V_2B_3$. The (Cr,V)-boride coating is consisted of $Cr_2B_3$, $Cr_5B_3$ and $V_2B_3$ mostly. The top surfaces of 3 multi-component boride coatings show hardness of $3200-3400H_v$, which is much higher than that of boride, about $1600-2000H_v$. In 5 wt.% NaCl solution immersion tests, the multi-component boride coatings show much better corrosion resistance than boride coating.

Erosion Behavior of SiC Coated C/C Composites with Condition of Combustion Test

  • Joo, Hyeok-Jong;Min, Kyung-Dae;Lee, Jae-Won
    • Carbon letters
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    • v.4 no.3
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    • pp.133-139
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    • 2003
  • Carbon/carbon composites are ideal candidates for a number of aerospace applications including structural materials for advanced vehicles, leading edges, structures of re-entry and hypersonic vehicles and propulsion systems. One serious defect for such application of the carbon/carbon composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating was employed to protect the composites from oxidation. It is mechanically and chemically stable under extreme thermal and oxidative environments, provides good adhesion to the substrate, and offers good thermal shock resistance. The SiC layer on the nozzle machined from the carbon/carbon composites was formed by pack-cementation method. Then, erosion characteristic of SiC coated carbon/carbon nozzle was examined by combustion test using a liquid rocket motor. The erosion rates were measured as function of combustion pressure, ratio of oxygen to fuel, combustion time, density of the composites and geometry of reinforced carbon fibre in the composites. The morphology change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.

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Oxidation Resistant Improvement of Mo-based Feeding Pipe for Zn-Mg Plating System (아연-마그네슘 도금을 위한 Mo 계 Feeding Pipe의 내산화 특성 향상 연구)

  • Bang, Su-Ryong;Byeon, Jong-Min;Kim, Hyeon-U;Kim, Tae-Yeop;Jeong, U-Seong;Kim, Yeong-Do
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 2015.11a
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    • pp.142-142
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    • 2015
  • 아연-마그네슘 합금은 마그네슘 첨가로 인한 뛰어난 내식성과 아연의 자원 고갈에 대한 갈등을 해소할 수 있다는 장점을 가지고 있으므로 차세대 강판 도금 소재로서 주목받고 있다. 그러나 아연-마그네슘의 도금 공정은 상대적으로 높은 융점을 지닌 마그네슘 첨가로 인해 기존의 아연 도금 공정에 비해 고온에서 이루어지므로 용융 금속에 의한 도금 설비의 빠른 손상이 발생하게 된다. 따라서 이와 같이 고온 환경에서도 사용 가능한 수준의 내구성을 지닌 소재의 개발이 반드시 필요한 상황이다. 선행 연구에 의하면 Mo은 아연-마그네슘 용탕에서 우수한 내침식 특성을 보이는 것으로 확인되었지만 pure Mo의 경우 고온 산화에 취약한 단점을 가지고 있어 내구성에 한계를 보인다. 따라서 본 연구에서는 이러한 문제를 해결하기 위해 pack cementation 공정을 통해 Mo 표면에 내산화 특성이 우수한 Mo 금속간화합물($MoSi_2$, $Mo_3Si$, $Mo_5SiB_2$)을 형성시켰고 이를 대상으로 아연-마그네슘 용탕에 대한 내산화 거동을 평가하였다.

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Characterization of Coating Layer formed on the Metal Surface by Calorizing (Calorizing(Aluminizing) 코팅 층의 표면특성 고찰)

  • 하진욱
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.1 no.1
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    • pp.49-54
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    • 2000
  • The effect of Particle size of coating Powder and coating temperature on the Properties of coating layer was studied by calorizing(or aluminizing). The surface properties of coating layer were fully characterized, using SEM and EDXS. Coating powders were separated according to the particle size by 3 steps and the coating temperature was varied from $950^{\circ}C$ to $980^{\circ}C$. Calorizing with pack cementation method carried under Ar atmosphere for 5 hrs. Results show that the thickness and Al content of coating layer increased as the size of coating powder decreased and coating temperature increased. And pores formed on the coating layer reduced and homogeneity of coating layer increased with smaller particle size of coating powder.

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The Aluminizing of Boronized Low Carbon Steel (침붕처리한 저탄소강의 알루미늄 확산처리에 관한 연구)

  • 윤영식;김한삼;김수식
    • Journal of the Korean institute of surface engineering
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    • v.29 no.2
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    • pp.120-131
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    • 1996
  • In order to improve the mechanical properties and the high temperature oxidation resistance, aluminizing was carried out at a temperature range between $850^{\circ}C$ and $1050^{\circ}C$. The pack cementation process was used to produce uniform layer. After each treatment, the microhardness and the characteristics of high temperature oxidation were tested to evaluate the properties of the aluminide layer. The aluminide layer consisted of FeAl above $1000^{\circ}C$, and $Fe_2Al_5$ below $900^{\circ}C$, and the mixed phase of FeAl and $Fe_2Al_5$ between 90$0^{\circ}C$ and $1000^{\circ}C$ in case of the mixture powder consisted of 5%Al+5%$NH_4Cl+90%AL_2O_3$. The microhardness of $Fe_2Al_5$ was obtained much as the twice as that of FeAl. As the aluminizing temperature and time increased, the thickness of aluminide increased. After aluminizing, the high temperature oxidation resistance was remarkably improved. The high temperature oxidation resistance of FeAl was superior to the resistance of high temperature oxidation of $Fe_2Al_5$.

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Effect of Heat Treatment on the Microstructural Evolution of Pt-aluminide Coated Ni-based Superalloy (Pt-Aluminide로 코팅된 초내열합금의 열처리에 따른 미세조직변화)

  • Joo, D.;Park, S.H.;Jung, Y.G.;Lee, K.H.;Kim, C.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.19 no.2
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    • pp.103-108
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    • 2006
  • Microstructural evolution of Pt-aluminide coated Ni-based superalloy has been investigated with ductilization heat treatment. The Pt coat was prepared on the superalloy and then aluminide coating was conducted using a pack cementation process. Samples were heat-treated at $1050^{\circ}C$ for 2 hrs and the microstructure and element analysis were preformed. A various precipitated compounds were observed within the coating layer and the diffusion region in the Pt-aluminide coating and heat treatment, indicating that the bi-phase compounds of $PtAl_2$ and NiAl were performed during the Pt-aluminide coating, whereas $M_{23}C_6$, MC, $Ni_3Al$ and ${\sigma}$ phases were precipitated in the inter-diffusion region. The bi-phase compounds of $PtAl_2$ and NiAl were transformed into the single phase compound of $PtAl_2$ with the heat treatment, increasing the amount of carbide and ${\sigma}$ phase.

Effect of the Heat treatment and Boron on the Hot Corrosion Resistance of the Al Diffusion Coating (Al 확산피복층의 고온 내식성에 미치는 후열처리와 B첨가의 영향)

  • 김태원;윤재홍;이재현;김현수;변응선
    • Journal of the Korean institute of surface engineering
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    • v.32 no.1
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    • pp.67-77
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    • 1999
  • The Ni base superalloy Mar-M247 substrate was aluminized or aluminized after boronizing by the pack cementation under Ar atmosphere. The hot corrosion resistance and after-heat-treatment effect of aluminized specimens were studied by the cyclic hot corrosion test in $Na_2SO_4$-NaCl molten salt. XRD analysis showed that the $Ni_2Al_3$ phase was formed between the coated layer and substrate below 1273K but the NiAl phase above 1273K. The peak of the NiAl phase was developed after heat treatment. Corrosion test showed that corrosion resistance of the specimen with the NiAl phase was better than that with the $Ni_2Al_3$ phase. Corrosion resistance could be improved by heat treatment to form ductile NiAl phase, where cracks were not formed by thermal shock on coating layer. Moreover, it appeared that heat treatment played a role to improve corrosion resistance of Al diffusion coating above 1273K. The existence of boron in the Al diffusion coating layer obstructed outwared diffusion of Cr from the substrate, and it influenced on corrosion resistance of the coating layer by weakening adherence of the oxide scale.

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TREATMENT OF IMPACTED MANDIBULAR FIRST MOLAR BY SURGICAL EXPOSURE : A CASE REPORT (매복된 하악 제1대구치의 외과적 노출술을 이용한 치험례)

  • Cho, Yun-Jung;Park, Young-Ok;Kim, Tae-Wan;Kim, Hyun-Jung;Kim, Young-Jin;Nam, Soon-Hyeun
    • Journal of the korean academy of Pediatric Dentistry
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    • v.34 no.2
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    • pp.322-328
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    • 2007
  • The first molar is important for mastication and also it plays roles to formation of vertical occlusion and growth of jaw bone after mixed dentition. Impaction of mandibular first molar can result in a short lower facial height, formation of a follicular cyst, pericoronal inflammation, resorption of the roots of neighboring teeth and malocclusion. The options of treatment plans are as follows; observation, surgical exposure, orthodontic traction, surgical relocation and extraction. Surgical exposure could be considered as a basic treatment plan. For surgical exposure it is important to maintain patent channel between the crown and the normal eruptive path into the oral cavity, many techniques including cementation of a celluloid crown, packing with zinc oxide-eugenol surgical pack are used. In these cases, we could observe spontaneous eruption of mandibular first molar using surgical exposure with or without removal of odontoma. Also we could obtain the main patency effectively and conveniently by using surgical pack and translucent retainer.

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