• 한국주조공학회지
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• 제33권2호
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• pp.55-62
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• 2013

Effect of Fe and Mn contents on the castability of Al-4wt%Mg-0.9wt%Si system alloy has been studied. According to the analysis of cooling curve for Al-4wt%Mg-0.9wt%Si-0.3wt%Fe-0.3/0.5wt%Mn alloy, ${\alpha}-Al_{15}(Fe,Mn)_3Si_2$ and ${\beta}-Al_5FeSi$ phases crystallized above eutectic temperature of $Mg_2Si$. Therefore, these phases affected both the fluidity and shrinkage behaviors of the alloy during solidification. As Fe and Mn contents of Al-4wt%Mg-0.9wt%Si system alloy increased from 0.1 wt% to 0.4 wt% and from 0.3 wt% to 0.5 wt% respectively, the fluidity of the alloy decreased by 26% and 33%. When Fe content of the alloy increased from 0.1 wt% to 0.4 wt%, 23% decrease of macro shrinkage and 19% increase of micro shrinkage appeared. Similarly, Mn content of the alloy increased from 0.3 wt% to 0.5 wt%, 11% decrease of macro shrinkage and 14% increase of micro shrinkage appeared. Judging from the castability of the alloy, Al-4wt%Mg-0.9wt%Si alloy with low content of Fe and Mn, 0.1 wt% Fe and 0.3 wt% Mn, is recommendable.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1994년도 추계 학술발표 강연 및 논문 개요집
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• pp.1-1
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• 1994

;The electronic state calculations for various types of ceramic materials have beell performed by the use of $DV-X\;{\alpha}$ cluster method. The molecular orbital levels and wave functions for model clusters have been computed to study the electronic properties ami chemical bonding of the ceramics. For ${\beta}-sialon(Si_{6-z}Al_zO_zN_{8-z})$ which is a high temperature structural material based on ${\beta}-Si_3N_4$, we have made model cluster calculations to estimate the strength of chemical bonding between atoms by the Mulliken population analysis. It is found that the covalent bonding between Si and N atoms is very strong in pure ${\beta}-Si_3N_4$, but the covalency around solute atom is considerably weakened when Si atom is substituted by AI. This tendency is enhanced by an additional substitution of oxygen atom for N. The result calculated can well explain the experimental data of changes in mechanical properties such as the reductions of Young's modulus and Vickers hardness with increment of z-value in ${\beta}-sialon$. Various model clusters for transition metal oxides which show many interesting physical and chemical properties have also been calculated. High-valent perovskite-type iron oxides EMFe0_3E(M=Ca and Sr) possess very interesting magnetic and chemical properties. In these oxides, iron exists as $Fe^{4+}$ state, but the experimental measurement of Mossba~er effect suggests that disproportionation $2Fe^{4+}=Fe^{3+}+Fe^{5+}$ takes place for $CaFe0_3$ at low temperatures. The model cluster calculations for these compounds indicated the existence of considerably strong covalent bonding of Fe-O. The calculations of hyperfine interaction at iron neucleus show very good agreement with the experimental Mossbauer measurements. The result calculated also implies that the disproportionation reaction is strongly possible by assuming the quenching of breathing phonon mode at low temperatures.tures.

• 한국가스학회지
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• 제19권5호
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• pp.41-46
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• 2015

알루미늄 6061-T6는 $Mg_2Si$와 ${\beta}-Al_5FeSi$로 구성되며, 피로 손상도가 증가하면 ${\beta}-Al_5FeSi$주변에서 기공이 발생하고 성장하는 것으로 알려져 있다. 본 연구에서는 우선 알루미늄 6061-T6 시편에 대한 SEM 촬영을 통해 이러한 현상을 확인하였다. 이후, 피로 손상도에 따라 이 시편의 전위댐핑 (dislocation damping), 정합변형률 (coherency strain), 및 기공 (void)이 감쇠계수와 비선형인자에 미치는 영향을 실험적으로 관찰하였다. 그 결과 비선형인자는 피로 손상도가 증가에 따라 증가하다가 피로수명 75% 이후에서는 감소하는 것을 확인하였다. 이는 전위댐핑과 정합변형률이 증가할수록 비선형인자는 증가하지만, 기공이 증가하면 초음파의 산란이 커져 비선형인자가 감소하는 것으로 해석할 수 있다. 따라서, 피로에 따라 조직변화가 복잡하게 나타나는 재료의 열화 평가에 있어서는 비선형인자를 주의하여 활용하여야 한다는 결론을 얻었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 1998년도 제14회 학술발표회 논문개요집
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• pp.152-153
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• 1998

• 한국주조공학회지
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• 제18권5호
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• pp.431-438
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• 1998

Microstructure of A356 aluminum alloys cast in the permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. Beryllium addition improved tensile properties and impact toughness of the A356 aluminium alloy, due to the formation of a script phase or a Be-rich phase instead of a needlelike ${\beta}-phase$. The DSC tests indicated that the presence of Be could increase the amount of Mg which is available for $Mg_2Si$ precipitate hardening, and enhance the precipitation kinetics by lowering the ternary eutectic temperature.

• 한국재료학회지
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• 제23권12호
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• pp.702-707
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• 2013

High-quality ${\beta}$-silicon carbide (SiC) coatings are expected to prevent the oxidation degradation of carbon fibers in carbon fiber/silicon carbide (C/SiC) composites at high temperature. Uniform and dense ${\beta}$-SiC coatings were deposited on carbon fibers by low-pressure chemical vapor deposition (LP-CVD) using silane ($SiH_4$) and acetylene ($C_2H_2$) as source gases which were carried by hydrogen gas. SiC coating layers with nanometer scale microstructures were obtained by optimization of the processing parameters considering deposition mechanisms. The thickness and morphology of ${\beta}$-SiC coatings can be controlled by adjustment of the amount of source gas flow, the mean velocity of the gas flow, and deposition time. XRD and FE-SEM analyses showed that dense and crack-free ${\beta}$-SiC coating layers are crystallized in ${\beta}$-SiC structure with a thickness of around 2 micrometers depending on the processing parameters. The fine and dense microstructures with micrometer level thickness of the SiC coating layers are anticipated to effectively protect carbon fibers against the oxidation at high-temperatures.

• 자원리싸이클링
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• 제12권5호
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• pp.29-35
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• 2003

국내의 화력발전소에서 발생되는 Fly ash와 활성탄을 원료로 사용하여 환원질화방법에 의해 $\beta$-Sialon 분말을 합성하였다. 분말합성은 $1,450^{\circ}C$에서 10시간 동안 질소분위기에서 합성하였으며, 또한 소결체 제조는 $1,550^{\circ}C$에서 3시간 동안 관상로에서 소결하였다. 본 실험에서 합성된 $\beta$-Sialon의 z value는 2.15이었으며 XRD 분석결과 $\beta$-Sialon 이외에 소량의 $SiO_2$와 $_FeSi{x}$ 가 일부 확인되었다. $\beta$-Sialon 소결체는 20시간 동안의 고온산화 결과 1,31$0^{\circ}C$까지는 열적으로 매우 안정하나 $1,360^{\circ}C$ 부근에서는 급격한 무게의 증가를 나타냈다. $1,360^{\circ}C$에서 10시간 고온산화 후 산화층은 mullite로 상전이가 일어났다.

• 한국산학기술학회논문지
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• 제16권7호
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• pp.4835-4841
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• 2015

n형 FeSi2의 열전물성에 미치는 입자크기 및 성형압력의 영향에 대해 조사하였다. 입자크기가 다른 출발 분말을 각각 가압성형(성형압력; $70{\sim}220kg/cm^2$) 하였고, 제작한 성형체를 Ar 분위기 1473 K에서 7시간 소결한 후, 반도체상인 ${\beta}$상을 얻기 위해 1103 K에서 100시간 소둔처리 하였다. XRD, SEM 및 EDS를 이용해서 시편들의 미세구조 및 상분석을 행하였다. 동일 시료를 가지고 Ar 분위기 상온~1023 K에서 도전율과 Seebeck 계수를 동시에 측정하였다. 입자크기가 작을수록 소결밀도와 잔존 ${\varepsilon}$-FeSi 금속전도상 증가에 의해 도전율이 상승하였으며, Seebeck 계수는 700~800 K에서 최고값을 나타내었고, 입자크기가 작을수록 잔존 ${\varepsilon}$-FeSi 금속전도상 증가에 의해 감소하였다. 반면에 성형압력의 변화는 도전율 및 Seebeck 계수에 그다지 큰 영향을 미치지 않았다. 결과적으로 power factor는 성형압력 보다 입자크기에 큰 영향을 받았다.

• 한국주조공학회지
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• 제18권4호
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• pp.357-363
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• 1998

Microstructure of A356 aluminium alloys cast in a permanent mold was investigated by optical microscope and image analyzer, with particular respect to the shape and size distribution of iron intermetallics known as ${\beta}-phase$ ($Al_5FeSi$). Morphologies of the ${\beta}-phase$ was found to change gradually with the Be:Fe ratio like these. In Be-free alloys, ${\beta}-phase$ with needlelike morphology was well developed, but script phase was appeared when the Be:Fe ratio is above 0.2:1. With the Be:Fe ratios of 0.4:1-1:1, script phase as well as Be-rich phase was also observed. In case of higher Be addition, above 1:1, Be-rich phase was observed on all regions of the specimens, and increasing of the Be:Fe ratios gradually make the Be-rich phase coarse. It was also observed that the ${\beta}-phase$ with needlelike morphology was coarsened with increase of the Fe content in Be-free alloys. However, in Be-added alloys, length and number of these ${\beta}-phases$ were considerably decreased with the increased Be:Fe ratio. It was concluded that Fe impurity element to be crystallized into needlelike intermetallics was tied up by Be addition element, and new phases were crystallized into script or Be-rich intermetallics.

• 한국주조공학회지
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• 제38권6호
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• pp.111-120
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• 2018

In this study, the effects of two different casting methods (gravity casting and, diecasting) and various solid-solution conditions on the mechanical properties of ASC (Al-10.5wt%Si-1.75wt%Cu) and ALDC12 (Al-10.3wt%Si-1.72wt%Cu-0.76wt%Fe-0.28wt% Mn-0.32wt%Mg-0.9wt%Zn) alloys were investigated. A thermodynamic solidification analysis program (PANDAT) was used to predict the liquidus, solidus, and phases of the used alloys. In the results of an XRD analysis, ${\beta}$-AlFeSi peaks were observed only in the ALDC12 alloy regardless of the casting method or SST (solid-solution treatment) conditions. However, according to the results of a FE-SEM observation, both ${\theta}(Al_2Cu)$ and ${\beta}$-AlFeSi were found to exist besides ${\alpha}$-Al and eutectic Si in the gravity-casted ASC alloy at $500^{\circ}C$ after a SST of 120min. The ${\alpha}$-AlFeSi and ${\beta}$-AlFeSi phases including the eutectic phases were also found to exist in the ALDC12 alloy. The results of a microstructural observation and analyses by XRD, FE-SEM and EDS were in good agreement with the PANDAT results. The gravity-casted ALDC12 and ASC specimens showed the highest Y.S. and UTS values after aging for three hours at $180^{\circ}C$ after a SST at $500^{\circ}C$ for 30min. At longer solid-solution treatment times at $500^{\circ}C$ in the gravity-casted ALDC12 and ASC specimens, the elongations of the ASC alloys increased, whereas they decreased slightly in the ALDC12 alloys.