• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.377-380
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• 2006

Manufacturing process of Ti-6Al-4V alloy billet was investigated with FEM simulation and experimental analysis. Before the breakdown process of Ti-6Al-4V alloy ingot, FEM simulation for the breakdown processes of Ti-6Al-4V alloy ingot was used to calculate the forging load and state variables such as strain, strain rate and temperature. In order to breakdown the ingot structure and make an equiaxed structure billet, two different processes were employed for a VAR/VAR processed Ti-6Al-4V alloy ingot. Firstly, the ingot was cogged in single-phase $\beta$ field at the temperature of $1,100^{\circ}C$. In the process, the coarse and inhomogeneous structure developed by the double melting process was broken down. The second breakdown was performed by upsetting and cogging processes in $\alpha+\beta$ phase field to obtain the microstructure of fine equixed $\alpha$ structure in the matrix of transformed $\beta$. Finally, the mechanical properties of Ti-6Al-4V alloy billet made in this work were compared with those of other billet and ring product.

• 한국세라믹학회지
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• 제30권1호
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• pp.46-54
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• 1993

$\beta$-SiC was chemically vapor deposited by pyrolysis of MTS＋H2 gas mixture. The experiments were conducted in the temperature range of 1100~150$0^{\circ}C$ with a r.f. induction furnace under atmospheric pressure. The IR, XRD, EDS and AES analysis revealed that the free Si was always codeposited with SiC below 140$0^{\circ}C$, regardless of the total flow rate and MTS concentration, whereas $\beta$-SiC single phase was deposited at 150$0^{\circ}C$. C3H8 or CH2Cl2 as an excess C sources, was supplied with MTS in order to obtain stoichiometric SiC at low temperature. With the addition of C3H8 or CH2Cl2, the deposition rate was increased and $\beta$-SiC single phase could be deposited even at temperature as low as 110$0^{\circ}C$. In the absence of C3H8 or CH2Cl2, the microhardness of the layer was quite low (

• 생명과학회지
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• 제8권6호
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• pp.723-728
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• 1998

$\beta$-lactam계 항생물질에 강한 내성을 가지는 세균 Bacillus subtilis J105는 항생물질 존재 하에서 $\beta$-lactamase를 유도생산하여 내성이 더 강해진다. 배지에 항생물질이 존재하지 않을 때는 내성을 유도하는 $\beta$-lactamase의 생산은 15시간 만에 plateau에 달했다. 그러나 배지 중에 ampicillin(500$\mu\textrm{g}$/$m\ell$)이 존재할 때는 배양 25시간 만에 효소 생산이 plateau에 달하나 항생물질 비존재시와 비교하면 효소 활성은 약 20배인 2,900 units/$m\ell$나 많이 생산하는 것을 알 수 있었다. 또한, ampicillin 처리한 것과 무처리 균주를 여러 $\beta$-lactam계 항생물질에 적용하여 MIC를 비교해 본 결과 ampicillin 처리 균주의 MIC가 2~27배 가량 높은 것을 알 수 있었다. 이것은 본 균주가 ampicillin 처리함으로서 $\beta$-lactamase 생산을 유도하여 내성을 증가시킨 것으로 사료된다. 본 내성균주는 penicillin뿐만 아니라 cephalosporin계 항생물질에 대해서도 $\beta$-lactamase 생산을 유도하는 것을 알았다. 그 중에서도 300$\mu\textrm{g}$/$m\ell$의 cloxacillin이 효소생산유도에 가장 최적 농도였다. 항생물질 첨가 시기를 균의 생육시 기별로 조사한 결과 대수증식기가 가장 효과적인 결론을 얻었다. 이상의 결과로 본 내성균주는 다양한 $\beta$-lactam계 항생물질에 의하여 내성이 강하게 유도되는 특이적인 균주임을 시사한다.

• 한국재료학회지
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• 제24권4호
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• pp.201-206
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• 2014

TiC-21 mol% Mo solid solution (${\delta}$-phase) and TiC-99 mol% Mo solid solution (${\beta}$-phase), and TiC-(80~90) mol% Mo hypo-eutectic composite were deformed by compression in a temperature range from room to 2300 K and in a strain rate range from $4.9{\times}10^{-5}$ to $6.9{\times}10^{-3}/s$. The deformation behaviors of the composites were analyzed from the strengths of the ${\delta}$- and ${\beta}$-phases. It was found that the high strength of the eutectic composite is due primarily to solution hardening of TiC by Mo, and that the ${\delta}$-phase undergoes an appreciable plastic deformation at and above 1420 K even at 0.2% plastic strain of the composite. The yield strength of the three kinds of phase up to 1420 K is quantitatively explained by the rule of mixture, where internal stresses introduced by plastic deformation are taken into account. Above 1420 K, however, the calculated yield strength was considerably larger than the measured strength. The yield stress of ${\beta}$-phase was much larger than that of pure TiC. A good linear relationship was held between the yield stress and the plastic strain rate in a double-logarithmic plot. The deformation behavior in ${\delta}$-phase was different among the three temperature ranges tested, i.e., low, intermediate and high. At an intermediate temperature, no yield drop occurred, and from the beginning the work hardening level was high. At the tested temperature, a good linear relationship was held in the double logarithmic plot of the yield stress against the plastic strain rate. The strain rate dependence of the yield stress was very weak up to 1273 K in the hypo-eutectic composite, but it became stronger as the temperature rose.

• 한국재료학회지
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• 제25권8호
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• pp.403-409
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• 2015

Metastable phase characteristics of beta Ti alloys were investigated to consider the relationship of the microstructure and diffraction pattern in TEM. TEM analysis showed that the microstructure was mottled as a modulated structure, and the diffraction pattern was composed of spot streaks between the main spots of a stable beta phase with a specific lattice relationship. The modulated structure may be induced by short distance slip or atom movement during a very short interval of solution treated and quenched (STQ) materials. The athermal ${\omega}$ phase, which could be precipitated at low temperature aging, is also analysed by the metastable phase. The metastable phases including athermal ${\omega}$ phase had a common characteristic of hardened and brittle behavior because the dislocation slip was restricted by a super lattice effect due to short distance atom movement at the metastable state.

• 한국분말재료학회지
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• 제17권6호
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• pp.443-448
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• 2010

The $\beta$ phase Ti-Nb-Sn-HA bio materials were successfully fabricated by high energy mechanical milling and pulse current activated sintering (PCAS). Ti-6Al-4V ELI alloy has been widely used as biomaterial. But the Al has been inducing Alzheimer disease and V is classified as toxic element. In this study, ultra fine sized Ti-Nb-Sn-HA powder was produced by high energy mechanical milling machine. The $\beta$ phase Ti-Nb-Sn-HA powders were obtained after 12hr milling from $\alpha$ phase. And ultra fine grain sized Ti-Nb-Sn-HA composites could be fabricated using PCAS without grain growth. After sintering, the microstructures and phase-transformation of Ti-Nb-Sn-HA biomaterials were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The relative density was obtained by Archimedes principle and the hardness was measured by Vickers hardness tester. The $\beta$-Ti phase was obtained after 12h milling. As result of hardness and relative density, 12h milled Ti-Nb-Sn-HA composite has the highest values.

• 열처리공학회지
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• 제24권3호
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• pp.133-139
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• 2011

This study has been investigated for tensile properties with lead-free brass containing 1 wt.% of Bi. And also characteristic of corrosion resistance was analyzed by polarization test. An increase of tempering temperature was found to tend to decrease tensile strength, and percentage of elongation was shown to be the lowest value at $300^{\circ}C$. On the other hand, the elongation was increased with an increase of tempering temperature after $300^{\circ}C$. The change of mechanical properties was closely related with the content and shape of acicular Witmanst$\ddot{a}$tten ${\alpha}$ formed at the interface of ${\beta}$ phase as well as in ${\beta}$ phase. Tensile strength had a tendency to be decreased with an increase of test temperature. The elongation was shown to be the lowest value at around $300^{\circ}C$, while it began to increase as test temperature rose after $300^{\circ}C$. It might be speculated that the reason that elongation was decreased was found to form bismuth film at the interface of ${\alpha}/{\beta}$ phase leading to be easily brittle when loaded by tensile stress. The lead-free brass containing 1 wt.% of Bi had similar characteristic of corrosion resistance with a free-cutting brass with 3.4 wt. % of Pb in spite of higher fraction of ${\beta}$ phase.

• 열처리공학회지
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• 제32권4호
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• pp.168-174
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• 2019

The microstructural features and relative room temperature mechanical properties were investigated in various compositions of Mg-xAl-yZn alloys by thxiomolding process. The microstructure was composed of ${\alpha}$-Mg particles and mixture of ${\alpha}$-Mg and ${\beta}-Mg_{17}Al_{12}$ eutectic phase. The amount of ${\beta}-Mg_{17}Al_{12}$ eutectic phase in mixture was increased with increasing Al and Zn contents without grain refinement. After adding Ti content, however, the morphology of ${\beta}-Mg_{17}Al_{12}$ eutectic phase transformed from net-like to discontinuous shape and the average grain size reduced. To determine the relationship between microstructural features and their mechanical properties, a tensile test was performed at room temperature. As a result, it was found that the mechanical properties were improved in all of Ti contained alloys due to increased elongation and the mechanisms are discussed in terms of microstructural evolution.

• 한국작물학회지
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• 제53권2호
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• pp.137-143
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• 2008

조기 초관폐쇄성(rapid canopy closure, RCC) 또한 벼의 유전적인 잠재수량성을 향상시킬 수 있는 생리적 특성 중 하나이다. EGV(early growth vigor)가 상이한 22개 품종을 선정하여 EGV와 초관의 조기폐쇄성(RCC)과의 관계, RCC와 생육 및 수량간의 관계를 평가하고자 포장실험(이앙재배)을 실시하였다. 초관이 폐쇄되기 전의 생장은 $y\;=\;{\alpha}{\cdot}{\exp}({\beta}{\cdot}t)$와 같은 지수생장함수로 표현되는데, y는 엽면적지수(LAI) 또는 지상부건물중(DW)이고, t는 적산온도이며, $\alpha$는 지수생장초기의 LAI나 DW 값이고, $\beta$는 지수생장이 일어나는 시기의 LAI 또는 DW의 상대생장률(relative growth rate, RGR; $^{\circ}C^{-1}$)이다. 1. 벼의 지수생장 초기단계에는 품종의 LAI나 DW가 $\alpha$와 높은 정의 상관이 있었고 또한 종자 무게(천립중)와 정의 상관이 있어 종자무게에 의하여 생육이 크게 영향을 받았으며, 그 후의 시기는 품종의 LAI 및 DW가 $\beta$와 높은 상관을 보였다. 2. $\alpha$와 $\beta$는 모두 품종간에 유의적인 차이가 있었다. 3. $\beta$는 단위면적당 영화수 및 수량과 높은 정의 상관을 보였다. 4. 결론적으로 EGV 및 RCC는 상호 밀접한 관련이 있고, EGV가 크면, RCC도 커서 수량에 정의 방향으로 영향을 하는 것으로 판단되었다.

• 천문학회지
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• 제29권1호
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• pp.9-18
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• 1996

We have analyzed vector magnetograms and $H\beta$ filtergrams of two sunspot groups, one in a growing phase and the other in a decaying phase. In this study, the temporal evolution of their magnetic morphology has been investigated in association with solar activity. The morphological variations of the growing and decaying phase of these sunspots revealed in detail the coalescence of small spots into a large spot and the fragmentation of a large spot into many small spots, respectively. Numerous small flares were detected in the spot group during the decaying phase. This seems to be intimately associated with the shearing motions of many spots with different polarities created by fragmentation of a large sunspot. The magnetic flux and the average shear angle are found to be substantially reduced during the decaying phase, especially in the course of the flarings. This implies that the decaying phase of the sunspot is, to some degree, involved with magnetic field cancellation. The growing spot group has not shown any large activities, but numerous small spots have grown into a typical bipolar sunspot.