• 열처리공학회지
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• 제30권3호
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• pp.99-105
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• 2017

This study was carried out to investigate the effect of heat treatment on the microstructure and mechanical properties in 90% hot forged Incoloy 825 alloy. With increasing solution treatment temperature, the grain size increased and the volume fraction of total precipitates decreased, and the precipitates disappeared at $1,000^{\circ}C$. With increasing aging time at $700^{\circ}C$, the volume fraction of precipitate increased and the precipitates size increased. Most of the precipitates consist $Cr_{23}C_6$ carbide, and a small amount of TiC carbide was also observed. With decreasing solution treatment temperature and increasing aging time, tensile strength and hardness increased, and the elongation and impact value decreased. With increasing aging time, the impact value decreased sharply by the increased of the precipitate size.

• 대한금속재료학회지
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• 제49권2호
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• pp.137-144
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• 2011

Strengthening mechanisms in an ordered intermetallic compound containing coherent precipitates of lower antiphase boundary energy than the matrix were investigated on the basis of the interaction between the deformation induced dislocations and the disordered precipitates in an $Ll_2$ ordered $Ni_3Al$-based alloy. Extra work was needed to pull out the dislocations from the precipitate, which was dependent on the difference in the antiphase boundary energy between the matrix and the precipitate, as well as the size and volume fraction of the precipitate. The strength of the $Ll_2$ ordered ${\gamma}^{\prime}$ phase containing fine precipitates of the disordered ${\gamma}$ phase was examined using the proposed model. The model can explain almost quantitatively the age hardening behavior of the $Ll_2$ ordered ${\gamma}^{\prime}$ phase.

• 소성∙가공
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• 제29권1호
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• pp.37-43
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• 2020

Increasing the critical current density of superconducting wire is one of the difficult challenges in the field of superconductivity. It is well known that the higher volume fraction of uniformly dispersed α-Ti is able to enhance the critical current density of superconducting material NbTi because α-Ti serves as a flux pinning center. The volume fraction of α-Ti highly depends on the grain size of NbTi because α-Ti precipitates at the grain boundaries or triple points. For this purpose, we investigated the effect of initial microstructures of NbTi obtained from hot rolling in various temperature conditions on the critical current density. In addition, subsequent heat treatment was assigned to precipitate α-Ti and groove rolling/cold drawing was adopted to produce a wire with a diameter of about 1.0 mm. It was observed that the band structure was formed after hot rolling at 500~600℃. It was also found that the volume fraction of α-Ti after hot rolling at 500~600℃ was higher and it led to the highest critical current density.

• 한국재료학회지
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• 제28권10호
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• pp.570-577
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• 2018

This study examines the effect of microstructural factors on the strength and deformability of ferrite-pearlite steels. Six kinds of ferrite-pearlite steel specimens are fabricated with the addition of different amounst of Mn and V and with varying the isothermal transformation temperature. The Mn steel specimen with a highest Mn content has the highest pearlite volume fraction because Mn addition inhibits the formation of ferrite. The V steel specimen with a highest V content has the finest ferrite grain size and lowest pearlite volume fraction because a large amount of ferrite forms in fine austenite grain boundaries that are generated by the pinning effect of many VC precipitates. On the other hand, the room-temperature tensile test results show that the V steel specimen has a longer yield point elongation than other specimens due to the highest ferrite volume fraction. The V specimen has the highest yield strength because of a larger amount of VC precipitates and grain refinement strengthening, while the Mn specimen has the highest tensile strength because the highest pearlite volume fraction largely enhances work hardening. Furthermore, the tensile strength increases with a higher transformation temperature because increasing the precipitate fraction with a higher transformation temperature improves work hardening. The results reveal that an increasing transformation temperature decreases the yield ratio. Meanwhile, the yield ratio decreases with an increasing ferrite grain size because ferrite grain size refinement largely increases the yield strength. However, the uniform elongation shows no significant changes of the microstructural factors.

• 한국균학회지
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• 제11권4호
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• pp.147-150
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• 1983

To investigate a possibility of producing the antitumor component by shake culture method, the mycelia of Flammulina velutipes were cultured in flasks on a shaker at $26{\sim}28^{\circ}C$ at 180 rpm for seven days. The extract of the mycelia was concentrated under vacuum. The precipitate obtained by adding a three-fold volume of ethanol was centrifugated and freeze-dried after dialysis. The fraction was tested against sarcoma 180 in the mice. The inhibition ratio of the fraction against the tumor was 68.0% at the dose of 20 mg/kg/day for the period of ten days and the tumors in three of the mice were completely regressed. The results showed, therefore, that the antitumor component was produced by the shake culture method.

• 한국표면공학회지
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• 제42권5호
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• pp.246-249
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• 2009

Cu-Ti alloys with titanium in the range of 0.5-6.0 wt% were developed to evaluate the effect of the titanium content and heat treatment on microstructure, hardness, and electrical conductivity. The hardness of the Ti-added copper alloys generally increased with the increase in titanium content and hardening was effective up to the 2.5 wt%-Ti addition. Microstructural examination showed that the second phase of $Cu_4Ti$ started to precipitate out from the 3.0 wt% Ti-addition, and the precipitate size and volume fraction increased with further Ti addition. Aging of the present Cu-Ti alloys at $450^{\circ}C$ for 1 h increased the hardness; however, the further aging up to 10 h did not much change the hardness. In the present study, it was inferred that in optimal Ti addition and aging condition Cu-Ti alloy could have the hardness and electrical conductivity values which are comparable to those of commercial Cu-Be alloy.

• 열처리공학회지
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• 제31권5호
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• pp.213-219
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• 2018

This study was carried out to investigate the effect of hot forging ratio and solution treatment temperature on the mechanical properties of incoloy 825 alloy. With an increasing of the hot forging ratio, grain size and range of grain size was decreased. With an increasing of the solution treatment temperature after 90% forging, grain size and range of grain size was increased. Cr carbides and Ti nitrides was precipitated at below $900^{\circ}C$ and volume fraction of precipitate was increased with an decreasing of the solution treatment temperature. With an increasing of the hot forging ratio, hardness, tensile strength and elongation, toughness was increased. With an increasing of the solution treatment temperature after 90% forging, hardness and strength was increased, elongation and toughness was decreased by grain refinement. With an increasing of the forging ratio, effect of solution treatment temperature on the hardness, strength and elongation was small, but on the toughness was large.

• 한국주조공학회지
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• 제28권3호
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• pp.113-118
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• 2008

A new approach of producing martensitic structure for guide-roll materials was developed using centrifugal casting instead of classic overlay welding process. Centrifugal casting offered a simpler process, fewer defects and even microstructures. Especially in terms of thermal fatigue cracking which usually occurs in the HAZ of welding beads of used continuous caster guide roll materials made by overlay welding process. A typical tensile strength of 1,600 MPa was obtained by this process and was higher than typical tensile strength($800{\sim}1,200\;MPa$) with overlay welding technique. Tempering at $400{\sim}550^{\circ}C$ for 2 hrs was observed to have significant precipitate hardening effect which increases strength and elongation. Nitrogen content from the Cr-N input in the casting process was found to have positive contribution to decrease the volume fraction of ${\delta}$-ferrite which directly corresponds to increasing strength of the roll materials.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.46.1-46.1
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• 2010

일반적으로 석출물의 석출은 핵생성(Nucleation)-성장(Growth)-조대화(Coarsening)의 단계를 거친다. 핵생성에 의해 생성된 개개의 핵들은 아직 열역학적으로 평형 상태가 아니다. 석출물의 부피 분율은 아직 상태도에서 예측할 수 있는 값까지 도달하지 못했다. 과포화된 기지에서 생성된 핵은 계속적으로 기지로부터 용질 원자를 공급받아 성장하게 된다. 석출물의 성장은 그 부피 분율이 상태도에서 예상되는 값에 도달할 때까지 계속된다. 시간에 따른 석출 분율 계산과 분산된 석출물들이 matrix내에서 어느 정도 용해도를 갖는다면, 보다 작은 크기의 입자들은 용해되어 보다 큰 입자로 석출(성장)하려는 경향이 있다. 이러한 현상의 구동력은 전체 시스템의 계면 에너지 감소에 의해 주어지며, 결국 하나의 큰 입자만이 존재하게 될 것이다. 본 연구에서는 석출분율을 계산하기 위해 상용프로그램인 Pandat을 통해 Mg-Al 2원계합금의 상태도 및 석출분율 계산을 위한 열역학 데이터를 계산하였다. 계산된 열역학 데이터는 C언어로 함수화 하여 입력하고 Excell을 통해 석출분율을 계산하였다. 계산된 석출분율과 실험값의 비교를 통해 fitting parameters를 대입하여 계산값 및 실험값의 오차율을 줄였다. 본 연구에서 계산된 석출분율은 미래의 석출상 크기 및 분포 등을 개발하는 기초데이터로 활용할 수 있을 것이다.

• 한국재료학회지
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• 제8권12호
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• pp.1099-1109
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• 1998

Zr합금에서 V, Sb의 함랗 변화가 Zr 합금의 부식 특성에 미치는 영향을 조사하기 위해 V, Sb함량을 각각 0.1, 0.2, 0.4wt.% 변화시킨 6종의 합금을 제조하고$ 360^{\circ}C$ 물 분위기에서 100일 동안 부식실험을 수행하였다. V이 0.2, 0.4wt% 첨가시편에서는 부식 속도의 천이 현상이 관찰되지 않았으나 0.1wt.% V 첨가 시편의 경우 10일 이후부터 무게증가량이 급격히 증가하는 부식 속도 가속 현상이 발생하였다. V 첨가량이 증가할수록 내식성이 증가하였으며 0.4wt.%V 첨가 합금이 가장 우수한 내식성을 보였다. Sb가 첨가된 삼원계 합금에서는 0.1, 0.4wt.%Sb 첨가 시편의 경우 초기부터 급격히 부식이 가속되는 현상이 발생하였으며 Sb 첨가량이 증가할수록 무게증가량이 감소하다가 다시 증가하여 0.2wt.% Sb 첨가에서 최소 무게증가량을 보였다. V, Sb함량이 증가할수록 석출물의 크기와 석출물의 부피 분율이 증가하는 경향을 보였으며 석출물의 크기가 0.11-0.13$\mu\textrm{m}$의 석출물 크기를 가질 때 가장 우수한 내식성을 보였다. 부식특성과 석출물 크기와의 관계로부터 적절한 크기의 석출물은 음극반응에서 전자의 전도를 제어하고 안정한 산화막 미세구조를 유지하는데 중요한 역할을 한다고 사료된다.