• 한국재료학회지
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• 제8권11호
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• pp.1038-1042
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• 1998

$Nd_5Pr_7Fe_{82}B_6$ 및 $Nd_{12}Fe_{82}B_6$ 조성의 1차 용유된 ingot에 대하여 기계적 분쇄처리 및 열처리를 행하고 결정구조 및 자기적 특성을 측정하였다. Ar 분위기 하에서 330시간 분쇄처리한 결과 $2~3\mu\textrm{m}$크기의 입자가 얻어졌으며, x-선 회절도로부터 각 입자는 미세한 결정립으로 구성되어 있음을 알았다. 330시간 분쇄처리된 분말을 $600^{\circ}C$에서 2시간 열처리함으로써 항자계가 18.36-18.79kOe, 최대에너지적이 8.32-8.38 MGOe인 자기적 특성을 얻었다. 열처리 온도가 높아지면 자기적 특성이 향상되었으나, 기계적 분쇄처리에 의한 ingot의 미세결정화 과정이 최적의 자기적 특성을 얻는데 더욱 중요하였다.

• 한국주조공학회지
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• 제15권5호
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• pp.459-468
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• 1995

For high performance aerospace structures, the properties of highest priority are low density, high strength, and high stiffness(modulus of elasticity). Addition of beryllium decrease the density of the aluminum alloy and increase the strength and the stiffness of the alloy. However it is very difficult to produce the Al-Be alloy having useful engineering properties by conventional ingot casting, because of the extremely limited solid solubility of beryllium in aluminum. So, rapid solidification processing is necessary to obtain extended solid solubility. In this study, rapidly solidified Al-6 at% Be alloy were prepared by twin roll melt spinning process and single roll melt spinning process. Twin roll melt spun ribbons were extruded at $450^{\circ}C$ with reduction in area of 25 : 1 after vacuum hot pressing at $550^{\circ}C and 375^{\circ}C$. The microstructure of melt spun ribbon exhibited a refined cellular microstructure with dispersed Be particles. As advance velocity of liquid/solid interface increase, the morphology of Be particle vary from rod-like type to spherical type and the crystal structure of Be particle from HCP to BCC. These microstructural characteristics of rapidly solidified Al-6at.%Be alloy were described on the basis of metastable phase diagram proposed by Perepezko and Boettinger. The extruded ribbon consisted of recrystallized grains dispersed with Be particles and exhibited improved tensile property compared with that of extruded ingot.

• 대한치과보철학회지
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• 제36권5호
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• pp.772-785
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• 1998

This study was undertaken to clarify the microstructure of the different IPS Empress ingots by etching and to observe the change of leucite crystal structure according to subsequent heat treatment and the crystal distribution according to sprue types(${\phi}2.8mm$, single sprue; ${\phi}1.8mm$, double sprue) by scanning electron microscopy. IPS Empress T1, O1 ingots used for staining technique, and Dentin(A2) ingots used for layering technique were selected for this study. To observe the microstructures of these ingots before pressing, the specimens were prepared in splinters($3{\times}3{\times}3mm$) taken from the original ingots. And to estimate crystal distribution and microstructural change by sprue type and subsequent heat treatment. the specimens($3{\times}3{\times}3mm$) were heat-pressed through the two types of sprues with different diameters and numbers, and all specimens were fired according to the recommended firing schedule. The observed surface was ground with waterproof papers($#800{\sim}#1800$) on the grind polisher and was cleaned ultrasonically. All specimen were etched with 0.5% hydrofluoric acid. After etching, the surface was treated by ion sputter coating for SEM observation at an accelerating voltage of 20kV. In all specimens, the central area of ground surface was observed because there was less difference in microstructure between the peripheral area and the central area. The results were as follows ; 1. In the microstructure according to the ingot type, there was a wide difference between the staining (T1,O1) and layering(Dentin A2) ingots, but there was not a considerable difference between the T1 ingot and the O1 ingot for staining technique. 2. In all specimens, the crystal dispersion of IPS Empress ceramic using double sprue was significantly more scattered than that of IPS Empress ceramic using single sprue. The degree of scattering was strongest in the Dentin(A2) specimen and weakest in the O1 ingot. 3. In the microstructural change according to the subsequent heat treatment, all of ingots had some microcracks in the inside of the leucite crystal and the glass matrix after pressing. The inner splinters of the leucite crystal became smaller, and more microcracks occurred in the glass matrix due to increasing heat treatment times. 4. The size of leucite crystals varied from $1{\mu}m\;to\;5{\mu}m$. The mean size of mature crystals was about $5{\mu}m$. The form of the crystal was similar to a circle when it was smaller and similar to an ellipse when it was larger.

• 열처리공학회지
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• 제26권2호
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• pp.72-79
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• 2013

The effects of homogenization, hot-forging, and annealing condition on microstructure and hardness of a modified STD61 hot-work tool steel were investigated. The ingot specimen had a dendritic structure consisting of bainite and martensite. Spherical VC particles of approximately 50 nm and cuboidal (V,Ti)C particles of about 100 nm were observed in the ingot specimen. After homogenization, the dendritic structure was blurred, and the difference in hardness between martensite and bainite became narrow, resulting in the more homogeneous microstructure. Needle-shaped non-equilibrium $(Fe,Cr)_3C$ particles were additionally observed in the homogenized specimen. The hot-forged specimen had bainite single phase with spherical VC, cuboidal (V,Ti)C, and needle-shaped $(Fe,Cr)_3C$ particles. After annealing at $860^{\circ}C$, the microstructures of specimens were ferrite single phase with various carbides such as VC, $(Fe,Cr)_7C_3$, and $(Fe,Cr)_{23}C_6$ because of relatively slow cooling rates. The size of carbides in annealed specimens decreased with increasing cooling rate, resulting in the increase of hardness.

• 한국주조공학회지
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• 제36권3호
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• pp.81-87
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• 2016

In this study, the effect of scrap ratio on the mechanical properties of Zr alloys was studied. Oxygen content in the ingot cake increased rapidly with increasing fraction of scrap, which can be attributed to the surface oxide of scrap including small pieces of turning, chips, etc. Iron content did not increase much with the increasing addition of scrap, suggesting scrap materials was well reserved in the iron-free container. As-cast structure of Zr alloy with the scrap:sponge ratio displayed plate/or needle ${\alpha}$ phase and no appreciable change of the cast structure was observed with change of scrap fraction. The strength increases with increasing fraction of scrap, which can be attributed to the increase of oxygen content. The ductility decreased slightly with increase of scrap fraction. Dislocation-oxygen interaction is known to increase the strength at the expense of ductility. Ingot cake with intentionally added $Fe_2O_3$ exhibited the drastic decrease of the formability, even exhibited the brittle fracture behavior during rolling. The oxidation resistance, however, increased with the increase of scrap fraction because of high oxygen content, which may prevent more penetration and diffusion of oxygen into matrix.

• 한국결정성장학회지
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• 제10권1호
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• pp.42-47
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• 2000

일반적인 쵸크랄스키(CZ)방법으로 성장된 실리콘 단결정봉(Ingot)을 가공하여 경면 연마한 후 RTA법으로 수소 분위기에서 열처리하여 실리콘 웨이퍼 표면 및 표면 근처의 특성 변화에 대하여 고찰하였다 수소 열처리를 통하여 표면의 COP (결정결함)가 현저히 감소하는 것을 확인하였고 깊이 5um까지의 영역에서도 결정결함의 밀도가 감소하였다. 또한 수소 열처리에 의해 실리콘 웨이퍼 표면이 에칭 및 실리콘의 재배열에 의해 형성되는 테라스(Terrace) 형태도 관찰되었다.

• 한국재료학회지
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• 제21권6호
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• pp.334-340
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• 2011

Saw wires have been widely used in industries to slice silicon (Si) ingots into thin wafers for semiconductor fabrication. This study investigated the microstructural and mechanical properties, such as abrasive wear and tensile properties, of a saw wire sample of 0.84 wt.% carbon steel with a 120 ${\mu}M$ diameter. The samples were subjected to heat treatment at different linear velocities of the wire during the patenting process and two different wear tests were performed, 2-body abrasive wear (grinding) and 3-body abrasive wear (rolling wear) tests. With an increasing linear velocity of the wire, the tensile strength and microhardness of the samples increased, whereas the interlamellar spacing in a pearlite structure decreased. The wear properties from the grinding and rolling wear tests exhibited an opposite tendency. The weight loss resulting from grinding was mainly affected by the tensile strength and microhardness, while the diameter loss obtained from rolling wear was affected by elongation or ductility of the samples. This result demonstrates that the wear mechanism in the 3-body wear test is much different from that for the 2-body abrasive wear test. The ultra-high tensile strength of the saw wire produced by the drawing process was attributed to the pearlite microstructure with very small interlamellar spacing as well as the high density of dislocation.

• 한국주조공학회지
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• 제21권4호
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• pp.246-252
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• 2001

Variation in the microstructure of Mg-5%Al semi-solid slurry during isothermal heating was investigated in relation to initial microstructure, holding time, and holding temperature. Specimens with three different initial microstructures were isothermally heated. Dendritic structure in as-cast ingot was decomposed into solid globules in the semi-solid slurry during isothermal holding, while in the recrystallized specimens prepared by extrusion or rolling the size of solid particles was continuously increased during the heating. Effects of mold temperature and liquid fraction of slurry on the mold filling ability were also studied. Very thin section (0.4 mm) could be successfully filled up to 50 mm by 60% liquid slurry when the mold was heated to $600^{\circ}C$.

• 한국주조공학회지
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• 제22권6호
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• pp.293-298
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• 2002

The effects of alloying elements added on the microstructure and high temperature oxidation behavior of the electro-slag remelted Fe-22Cr-5Al alloy were investigated. The amount of casting defect was makedly reduced by the electro-slag remelting. The electro-slag remelted ingot had a directionally solidified structure and cleaner surface than that of air-melted one. The high temperature oxidation reststance was greatly improved by the addition of Be and Zr.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 하계학술대회 논문집 D
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• pp.2089-2092
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• 2002

The PID controller have the simple structure and show the comparatively good control performance. Crystal Grower(FF-CZ150) melt polycrystalline silicon at the temperature of about 1450$^{\circ}C$, then grow it into a single crystalline ingot. The automatic diameter control system of the Crystal Grower has a good performance with only PD control. But it contain the integrator in the plant which has a long time delay. In this paper, we show the secondary approximate model and applies time delay controller which has good performance for the plant with long time delay. It will be able to improve the response characteristic against a standard input and a load disturbance.