• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.103-108
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• 2001

Wear test has been performed to evaluate the wear mechanism of Inconel alloys against ferritic stainless steels in room temperature water. By means of scanning electron microscopy (SEM), the worn surface and microstructure of subsurface layer have been examined. The wear at steady state conditions result in the formation of 5∼7${\mu}$m thick layers with fragmented microstructure. The thickness of these layers seems to depend on the ability of work hardening and deformation accommodation at the contact areas during wear. Therefore, in room temperature water, the wear rate is closely related with the wear resistance of these fragment microstructure which are generated after severe subsurface deformation.

• 소성∙가공
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• 제22권8호
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• pp.456-462
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• 2013

Compression tests were conducted at the various temperatures and strain rates to investigate void formation and microstructures behavior of a 1.9wt%C ultrahigh carbon steel used in forged workrolls. The microstructure, grain size and volume fraction of cementite were determined using specimens deformed in the temperature range from 800 to $1150^{\circ}C$ and strain rates from 0.01 to 10/s. It was found from the microstructural analysis that the grain size is larger at higher temperatures and lower strain rate deformation conditions. In addition, a higher volume fraction of cementite was measured at lower temperatures. The brittle blocky cementite was fractured at $800^{\circ}C$ and $900^{\circ}C$ regardless of strain rate. As a result, numerous new micro voids were formed in the fragmented blocky cementite. It was also found that local melting can occur at temperatures of more than $1130^{\circ}C$. Therefore, the forging temperature should be controlled between $900^{\circ}C$ and $1120^{\circ}C$. The temperature rise, which depends on the anvil stroke and velocity, was estimated through cogging simulation to find the appropriate forging temperature and to prevent local melting due to plastic work.

• International Journal of Advanced Culture Technology
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• 제3권2호
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• pp.132-137
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• 2015

The purpose of this paper was to investigate the effects of solution treatment time and Sr-modification on the microstructure and property of the Al-Si piston alloy. It was found that as-cast microstructures of unmodified and Sr-modified Al-Si alloys consisted of a coarse acicular plate of eutectic Si, $Cu_3NiAl_6$ and $Mg_2Si$ phases in the ${\alpha}$-Al matrix but different in size and morphology. Both size and inter-particle spacing of Si particles were significantly changed by increasing of the solution treatment time. After a short solution treatment, the coarse acicular plate of the eutectic Si appears to be fragmented. Fully modified microstructure of Sr-modified alloy can reduce the solution treatment time to shorter compared to unmodified alloy. The maximum of a peak hardness value is found in the very short solution treatment of both Al-Si piston alloys. Compared to 10 h solution treatment, the solution treatment of 2-4 h is sufficient to achieve appropriate microstructures and hardness. The short solution treatment is very useful to increase the productivity and to reduce the manufacturing cost of the Al-Si piston alloys.

• 열처리공학회지
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• 제31권3호
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• pp.97-103
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• 2018

The objective of this study is to develop the mechanical properties of AlSiCu aluminum alloy by the two-step solution heat treatment. The microstructure of gravity casting specimen represents a typical dendrite structure having a secondary dendrite arm spacing (SDAS) of 40 mm. In addition to the Al matrix, a large amount of coarsen eutectic Si phase, $Al_2Cu$ intermetallic phase, and Fe-rich phases are generated. The eutectic Si phases are fragmented and globularized with solution heat treatment. Also, the $Al_2Cu$ intermetallic phase is resolutionized into the Al matrix. The $2^{nd}$ solution temperature at $525^{\circ}C$ might be a optimum condition for enhancement of mechanical properties of AlSiCu aluminum alloy.

• 한국기계가공학회지
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• 제17권3호
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• pp.102-108
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• 2018

The objective of this study is to develop the mechanical properties of an AlSiCu aluminum alloy using the two-step solution heat treatment. The microstructure of the gravity casting specimen represents a typical dendrite structure with a secondary dendrite arm spacing (SDAS) of 40 um. In addition to the Al matrix, a large amount of coarsen eutectic Si phase, $Al_2Cu$ intermetallic phase, and Fe-rich phases is generated. The eutectic Si phases are fragmented and globularized with the solution heat treatment. The $Al_2Cu$ intermetallic phase is also resolutionized into the Al matrix. The $2^{nd}$ solution temperature at $525^{\circ}C$ may be an optimal condition to enhance the mechanical properties of the AlSiCu aluminum alloy.

• 대한금속재료학회지
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• 제47권7호
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• pp.397-405
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• 2009

The high strain rate deformation behavior of ultra-fine grained 5083 aluminum alloys prepared via equal channel angular (ECA) extrusion was investigated in this study. The microstructure of ECA extruded specimens consisted of ultra-fine grains, and contained a considerable amount of second phase particles, which were fragmented and distributed homogeneously in the matrix. According to the dynamic torsion test results, the maximum shear stress and fracture shear strain of the route A (no rotation) specimen were lower than those of route C ($180^{\circ}$ rotation) specimen since that adiabatic shear bands of $100{\mu}m$ in width were formed in the route A specimen. The formation of adiabatic shear bands was addressed by concepts of critical shear strain, deformation energy required for void initiation, and microstructural homogeneity associated with ECA operations.

• 한국식품영양학회지
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• 제22권3호
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• pp.387-395
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• 2009

본 연구는 칡 전분 젤의 제조 조건에 따른 젤의 특성을 알아보기 위하여 여러 가지 pH(2.0, 4.0, 7.0 및 10.0)와 칡 전분 농도 (7%, 8% 및 9%), 가열조건($70^{\circ}C$, $80^{\circ}C$, $90^{\circ}C$, $100^{\circ}C$, $110^{\circ}C$ 및 $120^{\circ}C$) 및 가열시간(10 min, 20 min 및 30 min)을 달리하여 칡 전분 젤을 제조하여 초기의 특성(강도, 호화도, 미세구조)과 24시간 저장한 후의 특성을 측정하고 이를 비교 분석하였다. pH 2.0 및 7%의 조건에서는 젤이 형성되지 않았으며, 그 외의 농도에서는 pH 2.0에서 최소의 강도를 나타내었으며, pH 4.0과 10%의 조건에서 최대값(약 94 N)을 보였다. pH 7.0과 10.0에서는 전분 농도가 7%에서 9%까지는 농도 증가에 따라 젤 강도가 증가하였으나, 10%의 경우에는 오히려 감소하는 경향을 나타내었다. 그리고 여러 가지 가열조건에서 7%, 8% 및 9%의 칡 전분 농도로 제조한 시료의 경우 가열온도 및 가열시간에 관계없이 $80^{\circ}C$에서 제조된 젤이 가장높은 강도(hardness)를 나타내었으며, 상대적으로 $100^{\circ}C$ 이상의 높은 농도에서 제조된 젤의 강도의 값이 작았다. $70^{\circ}C$와 $80^{\circ}C$에서는 가열시간이 길어질수록 젤의 강도가 증가하는 경향을 보였으나, $90^{\circ}C$ 이상의 온도에서는 가열시간이 길어 질수록 젤의 강도가 감소하였다. 그리고 24시간 저장한 후의 젤의 강도는 $100^{\circ}C$ 미만의 온도에서는 저장 전보다 감소하는 경향을 보였으나, $100^{\circ}C$ 이상에서는 오히려 증가하는 경향을 나타내었다. 젤의 호화도는 가열온도 및 시간이 증가할수록 전분 농도에 관계없이 증가하였으며, $80^{\circ}C$와 9%에서 제조한 젤의 강도와 호화도가 높은 상관성(r > 0.95)을 보였다. 한편, 젤의 미세구조는 그물망 구조로 저장 후 빈 공간이 더욱 뚜렷한 구조(ghost structure)로 변화되는 양상을 나타내었다.