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과냉각과 성장시간에 따른 (TbBi)3(FeAlGa)5O12 Garnet 단결정 후막의 성장속도변화
오규환,이완규,라형용 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.10
The change of growth rate with supercooling and growth time was investigated in the thick film growth of (TbBi)₃(FeAlGa)_5O_(12) garnet single crystal. At the degree of supercooling smaller than critical supercooling having maximum growth rate, growth rate was kept constant and the film composition did not change until the supersaturated garnet solute was depleted. After depletion the Bi concentration profile was decreased with the film thickness. At the degree of supercooling larger than critical supercooling, growth rate was decreased with growth time because of nucleation and growth of garnet microcrystals at the Pt crucilble wall. Bi concentration profile was decreased with the film thickness but concentration of Fe, Al, Ga was kept constant. The variation of Bi concentration with the film thickness is proportion to the film growth rate. It is found out that the interfacial supersaturation βi is decreased with growth time even though growth temperature is kept isothermally.
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Fe-20Cr-5Al-xLa 합금 극박판의 고온 산화에 의한 변형 거동
박원욱,오규환,이기선,라형용,김강오 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.12
Fe-20Cr-5Al(-0.06La) alloy thin strip was spontaneously strained by growth stress which was developed during isothermal high temperature oxidation. The activation energy, Q, for high temperature strain(creep) was determined from the relation between oxidation temperature and stain rate. In La free alloy, the activation energy was calculated to about 332.6 kJ/㏖. The compressive stress of about 651.9 ㎫ and tensile stress of about 10.1 ㎫ was developed in α-alumina oxide film and metal substrate respectively. The high growth stress was relaxed through the not only creep of metal substrate but also local detachment of α-alumina oxide film from the metal substrate. In La added alloy, the activation energy was calculated to about 263.6 kJ/㏖. which was seriously lower than the activation energy for La free alloy. In this case, α-alumina oxide film was not spalled or fractured. The addition of La contributed to not only the decrease of growth stress but also the stress relaxation through creep. It was concluded that easy stress relaxation process was crucial to enhance the adherence between α-alumina film and metal substrate.
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저탄소강에 접합된 Fe-13Cr-5V-1.2C 합금의 초기 응고층 조직 변화
오규환,이희춘,조규섭,라형용 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.9
Liquid Fe-13Cr-5V-1.2C alloy and solid low carbon steel were solidified and bonded in a tube after holding at temperatures for 285sec. The effects of mutual diffusion between two alloys on the microstructural change was investigated. Primary solidified layer bonded on the low carbon steel surface was formed as planar type. Alloy contents and hardness values droped nearby the bonded interface within primary solidified layer. Reaction layer formed in the vicinity of the bonded interface within 30∼40㎛ distance had lower alloy contents than cellular type structure. It is suggested that uphill diffusion of carbon from low carbon Fe-0.2C steel into the Fe-13Cr-5V-1.2C alloy at 1200℃ had produced low Cr content austenite. The austenite was transformed to auto-tempered martensite, which were identified as reaction layer.
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급냉 응고된 Al-Li-Cu합금의 열처리, 미세조직 및 기계적 성질에 관한 연구(I)
許明日,南勝義,李範圭,羅亨用,金錫胤 弘益大學校 1988 弘大論叢 Vol.20 No.2
Effect of aging condition on the microstructure and hardness properties of Al-3Li, Al-3Li-2Cu, Al-3Li-2Cu-0.3Zr have been studied. The alloy ribbons have been prepared by means of Single Roll Melt Spinning by rapid solidification technique. In rapidly solidified Al-3Li-2Cu, Al-3Li-2Cu-0.3Zr alloy ribbons show the icosahedral intermetallic compound of five-fold symmetry which is placed in cell-bound-ary and matrix. In the matrix precipitated fine δ'(Al₃Li) phase. Heat-treated at 250℃ 1hr. In this condition, δ'(Al₃Li) phase started decompose. The icosahedral intermetallic compound has been grown. When heat-treated at 300℃ 1 hr, the δ' phase has been decomposed all. In the matrix, icosahedral intermetallic compound has been grown greatly. The micro-hardness has been obtained more high Al-Li-Cu-(Zr) alloy than Al-Li alloy. Strength-hardended phenomena showed to solution hardning by the addition of Cu. When the heat-treated at 250℃ 1 hr, in the alloy of Zr addition, delayed decomposed δ' phase. In the case, micro-hardness gradually decreased. When the heat-treatment have done at 300℃ 1 hr, the micro-hardness has been decreased because δ' phase decomposed all.
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Fe-15Cr-5V-1.2C 합금의 응고 및 상변태에 따른 용질원자의 분배
오규환,조규변,김창섭,라형용 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.2
Transformation sequence and subsequent solute redistribution behaviors of Fe-15Cr-5V-1.2C alloy during solidification have been discussed. Specimens were quenched interruptly, as they were solidified and transformed. Primary δ-ferrite was not completely transformed into γ-austenite during δ→γ peritectic reaction. During the peritectic reaction V was enriched to the retained δ-ferrite, but Cr was not. When the retained δ-ferrite was directly changed into α-ferrite. V was diffused from δ-ferrite into the surrounding γ-austenite due to the decrease of V-solubility in the α-ferrite. As heating the as-cast specimen up to 1000℃, precipitated iron complex carbides were dissolved into the newly formed γ-austenite. The iron carbides were inferred as M_(23)C_6 carbides from the mole fraction change of each phases existing at the heating temperatures and microstructure change with increasing heating temperatures.
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