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과공정 Al-Si 합금의 분무성형-압출에 따른 미세조직 변화
라형용,이호인,김상균,석현광,이재철,신돈수 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.10
Microstructural evolutions of both Si particles and matrix grains of hypereutectic Al-Si alloy were investigated by calculating temperature profiles within the preform during spray forming. Based on calculations, the cooling rates were observed to be relatively higher both at the bottom and the top than the inner regions of the preform along the rotation axis of rod. Such trends in temperatures resulted in size variations of Si particles within the preform. The size of Si particles varies from 3㎛ to 13.5㎛ with distance from the surface to the inner of the preform along the rotation axis of rod. Larger Si particles observed from the inner regions of the preform were found to be poly-crystals having irregular surface boundaries. However, such Si particles were fractured after extrusion, indicating a possibile means for fabricating hypereutectic Al-Si alloys with fine Si particles. In addition, the methodology for predicting the matrix grain size in the presence of small Si particles was also demonstrated.
7075 Al 합금/SiCP 복합재료의 마멸특성 (1) : 상온 및 고온 마멸거동 Wear behaviour at room and elevated temperature
라형용,오창선,이영근 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.2
Wear characteristics of 7075 Al/SiC_p composites fabricated by spray forming and extrusion process are studied. This study shows a wear transition from mild to severe wear as a function of applied load, sliding velocity and friction temperature with wear mapping approach. 7075 Al/SiC_p composites exhibit the transition from mild to severe wear when a load, sliding velocity or temperature reaches a critical value respectively. In mild wear regime; wear rate increases with increasing applied load. But wear rate decreases with increasing sliding velocity. At constant load and velocity in mild wear conditions, wear rate decreases with increasing friction temperature. The reasons are that the worn surface of disk was covered with much more iron oxides at elevated temperatures than at room temperature which played a role as solid lubricant. But in severe wean regime, this oxide layer is not stable and fractured, leading to increase wear rate and friction coefficient. Wear transition map of 7075 Al/SiC_p composites is constructed on applied load and sliding velocity axes with elevated temperatures. Severe wear regime is enlarged with increasing temperature on the wear transition map and wear transition conditions move to lower load and velocity at elevated temperatures than at room temperature. Therefore safe operating range of aluminum metal matrix composite parts is reduced at elevated temperatures.
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.
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.
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.
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.