• Title/Summary/Keyword: Cr-Al alloy

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Microstructural characterization of accident tolerant fuel cladding with Cr-Al alloy coating layer after oxidation at 1200 ℃ in a steam environment

  • Park, Dong Jun;Jung, Yang Il;Park, Jung Hwan;Lee, Young Ho;Choi, Byoung Kwon;Kim, Hyun Gil
    • Nuclear Engineering and Technology
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    • v.52 no.10
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    • pp.2299-2305
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    • 2020
  • Zr alloy specimens were coated with Cr-Al alloy to enhance their resistance to oxidation. The coated samples were oxidized at 1200 ℃ in a steam environment for 300 s and showed extremely low oxidation when compared to uncoated Zr alloy specimens. The microstructure and elemental distribution of the oxides formed on the surface of Cr-Al alloys have been investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A very thin protective layer of Cr2O3 formed on the outer surface of the Cr-Al alloy, and a thin Al2O3 layer was also observed in the Cr-Al alloy matrix, near the surface. Our results suggest that these two oxide layers near the surface confers excellent oxidation resistance to the Cr-Al alloy. Even after exposure to a high temperature of 1200 ℃, inter-diffusion between the Cr-Al alloy and the Zr alloy occurred in very few regions near the interface. Analysis of the inter-diffusion layer by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) measurement confirmed its identity as Cr2Zr.

Effects of Si Addition on the Microstructure and Properties of Cr-Al alloy for High Temperature Coating (고온 코팅용 Cr-Al합금의 미세조직 및 특성에 미치는 Si 첨가의 영향)

  • Kim, Jeong-Min;Kim, Il-Hyun;Kim, Hyun-Gil
    • Korean Journal of Materials Research
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    • v.29 no.1
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    • pp.7-10
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    • 2019
  • Cr-Al alloys are attracting attention as oxidation resistant coating materials for high temperature metallic materials due to their excellent high temperature stability. However, the mechanical properties and oxidation resistance of Cr-Al alloys can be further enhanced, and such attempts are made in this study. To improve the properties of Cr-Al alloys, Si is added up to 5 wt%. Casting specimens with different amounts of Si content are prepared by a vacuum arc remelting method and isothermally heated under steam conditions at $1,100^{\circ}C$ for 1 hour. The as-cast microstructure of low Si alloys is mainly composed of only a Cr phase, while $Al_8Cr_5$ and $Cr_3Si$ phases are also observed in the 5 % Si alloy. In the high Si alloy, only Cr and $Cr_3Si$ phases remain after the isothermal heating at $1,100^{\circ}C$. It is found that Si additions slightly decrease the oxidation resistance of the Cr-Al alloy. However, the microhardness of the Cr-Al alloy is observed to increase with an increasing Si content.

Effects of Al and Cr Alloying Elements on the Corrosion Behavior of Fe-Al-Cr Alloy System (Fe-Al-Cr계 합금의 부식거동에 미치는 Al 및 Cr 합금원소의 영향)

  • Choe Han-Cheol
    • Journal of the Korean institute of surface engineering
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    • v.38 no.6
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    • pp.241-247
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    • 2005
  • Effects of Al and Cr alloying elements on the corrosion behavior of Fe-Al-Cr alloy system was investigated using potentiodynamic and cyclic potentiodynamic polarization tests(CPPT) in the $H_2SO_4$ and HCI solutions. The corrosion morphologies in Fe-Al-Cr alloy were analysed by utilizing scanning electron microscopy(SEM) and EDX. It was found that the corrosion potential of Fe-20Cr-20Al was highest whereas the critical anodic current density and passive current density were lower than that of the other alloys in 0.1 M $H_2SO_4$ solution. The second anodic peak at 1000 mV disappeared in the case of alloys containing high Al and low Cr contents. Pitting potential increased with increasing Cr content and repassivation potential decreased with decreasing Al content in 0.1 M HCI solution. Fe-Al-Cr alloy containing high Al and Cr contents showed remarkably improved pitting resistance against $Cl^-$ attack from pit morphologies.

Synthesis and Microstructure Analysis of NiO Catalysts Coated on the FeCrAl Metal Alloy Foam for Hydrogen Production (수소제조를 위한 다공성 FeCrAl 금속 합금 Foam의 NiO 촉매 담지 및 미세구조 분석)

  • Lee, Yu-Jin;An, Geon-Hyoung;Park, Man-Ho;Lee, Chang-Woo;Choi, Sang-Hyun;Jung, Ju-Yong;Jo, Sung-Jong;Lee, Kun-Jae;Ahn, Hyo-Jin
    • Korean Journal of Materials Research
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    • v.24 no.8
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    • pp.393-400
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    • 2014
  • NiO catalysts were successfully coated onto FeCrAl metal alloy foam as a catalyst support via a dip-coating method. To demonstrate the optimum amount of NiO catalyst on the FeCrAl metal alloy foam, the molar concentration of the Ni precursor in a coating solution was controlled, with five different amounts of 0.4 M, 0.6 M, 0.8 M, 1.0 M, and 1.2 M for a dip-coating process. The structural, morphological, and chemical bonding properties of the NiO-catalyst-coated FeCrAl metal alloy foam samples were assessed by means of field-emission scanning electron microscopy(FESEM), scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS), X-ray diffraction(XRD), and X-ray photoelectron spectroscopy(XPS). In particular, when the FeCrAl metal alloy foam samples were coated using a coating solution with a 0.8 M Ni precursor, well-dispersed NiO catalysts on the FeCrAl metal alloy foam compared to the other samples were confirmed. Also, the XPS results exhibited the chemical bonding states of the NiO phases and the FeCrAl metal alloy foam. The results showed that a dip-coating method is one of best ways to coat well-dispersed NiO catalysts onto FeCrAl metal alloy foam.

Microstructural Characteristics of Oxidation Resistant Cr-Si-Al alloys in Cast State and after High Temperature Heating (내산화성 Cr-Si-Al합금의 주조상태 및 고온가열 후의 미세조직 특성)

  • Kim, Jeong-Min;Kim, Chae-Young;Yang, Won-Chul;Park, Joon-Sik
    • Korean Journal of Materials Research
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    • v.31 no.3
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    • pp.156-161
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    • 2021
  • Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 ℃, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.

SULFIDATION PROCESSING AND Cr ADDITION TO IMPROVE OXIDATION RESISTANCE OF Ti-Al INTERMETALLIC COMPOUNDS AT ELEVATED TEMPERATURES

  • Narita, Toshio;Izumi, Takeshi;Yatagai, Mamoru;Yoshioka, Takayuki
    • Proceedings of the Korean Institute of Surface Engineering Conference
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    • 1999.05a
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    • pp.5-5
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    • 1999
  • A novel process is proposed to improve oxidation resistance of Ti-Al intermetallic compounds at elevated temperatures by both Cr addition and pre-sulfidation, where TiAl alloys withlor without Cr addition were sulfidized at 1173K for 86.4ks at a 1.3 Pa sulfur partial pressure in a $H_2-H_2S$ gas mixture. The pre-sulfidation treatment formed a thin Cr-Al alloy layer as well as 7~10 micrometer $TiAl_3$ and $TiAl_2$ layer, due to selective sulfidation of Ti. Oxidation resistance of the pre-sulfidation processed TiAl 4Cr alloy was examined under isothermal and heat cycle conditions between room temperature and 1173K in air. Changes in $TiAl_3$ into $TiAl_2$ and then TiAl phases as well as their effect on oxidation behavior were investigated and compared with the oxidation behavior of the TiAl-4Cr alloy as TiAl and pre-sulfidation processed TiAl aHoys. After oxidation for up to 2.7Ms a protective $Al_2O_3$ scale was formed, and the pre-formed $TiAl_3$ changed into $TiAl_2$ and the $Al_2Cr$ phase changed into a CrAlTi phase between the $Al_2O_3$ scale and $TiAl_2$ layer. The pre-sulfidation processed TiAl-4Cr alloy had very good oxidation resistance for longer times, up to 2.7 Ms, in contrast to those observed for the pre-sulfidation processed TiAl alloy where localized oxidation occurred after 81 Oks and both the TiAl and TiAl-4Cr alloys themselves corroded rapidly from the initial stage of oxidation

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Effect of Needle-Like NiO Protecting Layer on NiCrAl Alloy Foam by Controlled Oxygen Concentration (산소 농도 제어를 통한 NiCrAl 합금 폼 표면의 침상 NiO 보호층 효과)

  • Lee, Young-Geun;Shin, Dong-Yo;Ahn, Hyo-Jin
    • Korean Journal of Materials Research
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    • v.28 no.6
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    • pp.324-329
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    • 2018
  • Needle-like NiO protecting layers on NiCrAl alloy foam, used as support for hydrogen production, are introduced through electroplated Ni and subsequent microwave annealing. To improve the stability of the NiCrAl alloy foam, oxygen concentration of microwave annealing to form a needle-like NiO layer with good chemical stability and corrosion resistance is controlled in a range of 20 and 50 %. As the oxygen concentration increases to 50 %, needle-like NiO forms a dense coating layer on the NiCrAl alloy foam; this layer formation can be attributed to accelerated growth of the (200) plane. In addition, the increased oxygen concentration causes increased NiO/Ni ratio of the resultant coating layer on NiCrAl alloy foam due to improved rate of the oxidation reaction. As a result, the introduction of dense needle-like NiO layers formed at 50 % oxygen concentration improves the chemical stability of the NiCrAl alloy foam by protecting the direct electrochemical reaction between the electrolyte and the foam. Thus, needle-like NiO can be proposed as a superb protecting layer to improve the chemical stability of NiCrAl alloy form.

Creep Properties of Plasma Carburized and CrN Coated Ti-6Al-4V Alloy (플라즈마 침탄 및 CrN 코팅된 Ti-6Al-4V 합금의 구조 및 Creep특성)

  • Wey Myeong-Yong;Park Yong-Gwon
    • Korean Journal of Materials Research
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    • v.14 no.8
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    • pp.558-564
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    • 2004
  • In order to improve the low hardness and low wear resistance of Ti-6Al-4V alloy, plasma carburization treatment and CrN film coating were carried out. Effects of the plasma carburization and CrN coating were analyzed and compared with the non-treated alloy by mechanical and creep tests. After plasma carburization and CrN coating treatments, the carburized layer was about 150 ${\mu}m$ in depth and CrN coated layer was about 7.5 ${\mu}m$ in thickness. Hardness value of about $H_{v}$ 402 of the non-treated alloy was improved to $H_{v}$ 1600 and 1390 by plasma carburization and CrN thin film coating, respectively. Stress exponent(n) was decreased from 9.10 in CrN coating specimen to 8.95 in carburized specimen. However, the activation energy(Q) was increased from 242 to 250 kJ/mol. It can be concluded that the static creep deformation for Ti-6Al-4V alloy is controlled by the dislocation climb over the ranges of the experimental conditions.

Effects of Al and Ti Additons on Microstructure in Fe-xCrAlloy for Electrical Resistance Wire. (전기저항선용 Fe-xCr합금의 미세조직에 미치는 Al 및 Ti첨가의 영향)

  • 최수정;박수동;이희웅;김봉서
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2000.07a
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    • pp.108-110
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    • 2000
  • The aim of this paper is to investigate the effect of Al and Ti on microstructure of Fe-Cr-Al alloy systems for applying electrical resistance wires of electrical furnace. From the preliminary study, the amount of recovered addition elements increased in the case of both vacuum and Ar-atmosphere melting than that in the case of air-atmosphere melting. Also, optimum Cr content for good performance at high temperature was approximately 24wt% from the observation of microstucture. The precipitates of Fe-Cr, Al-Cr and Al phases were observed, adding Al and Ti. Especially, Sharp rectangular shapes of precipitates were observed with increasing amount of Ti.

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Microstructural Features of Multicomponent FeCoCrNiSix Alloys

  • Kong, Kyeong Ho;Kim, Kang Cheol;Kim, Won Tae;Kim, Do Hyang
    • Applied Microscopy
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    • v.45 no.1
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    • pp.32-36
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    • 2015
  • The microstructural features of FeCoCrNi, FeCoCrNiAl and FeCoCrNiSix (x=0, 5, 10, 15, 20) alloys have been investigated in the present study. The microstructure of FeCoCrNi alloy changes dramatically with equiatomic addition of Al. The fcc irregular shaped grain structure in the as-cast FeCoCrNi alloy changes into the bcc interconnected structure with phase separation of Al-Ni rich and Cr-Fe rich phases in the as-cast FeCoCrNiAl alloy. The microstructure of FeCoCrNi alloy changes with the addition of Si. With increasing the amount of Si, the fcc structure of the grains is maintained, but new phase containing higher amount of Si forms at the grain boundary. As the amount of Si increases, the fraction the Si-rich grain boundary phase increases.