• 한국분말재료학회지
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• 제18권6호
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• pp.496-501
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• 2011

In this study, the effect of milling time on the microstructure and phase transformation behaviors of Ni-12 wt.%B powders was investigated using vibratory ball milling process. X-ray diffraction patterns showed that the phase transformation of mixed Ni-B elemental powder occurred after 50 hours of milling, with a formation of nickel boride phases. Through the study of microstructures in mechanical alloying process, it was considered that ball milling strongly accelerates solid-state diffusions of the Ni and B atoms during mechanical alloying process. The results of X-ray photoelectron spectroscopy showed that most of B atoms in the powder were linked to Ni with a formation of nickel boride phases after 200 hours of milling. It was finally concluded that mechanical alloying using ball milling process is feasible to synthesize fine and uniform nickel boride powders.

• Transactions on Electrical and Electronic Materials
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• 제15권3호
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• pp.155-158
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• 2014

The phase transformation of Sn-Pb-Bi solder for photovoltaic ribbon during soldering was studied using real-time synchrotron x-ray scattering. At room temperature, Sn and Pb crystal phases in the solder existed separately. By heating to $92^{\circ}C$, a new PbBi alloy crystal phase was formed, which grew further up to $160^{\circ}C$. The Sn crystal phase first started to melt at $160^{\circ}C$, and was mostly melted at $165^{\circ}C$. In contrast, the Pb and PbBi crystal phases started to melt at $165^{\circ}C$, and were mostly melted at $170^{\circ}C$. The useful result was obtained, that the solder's melting temperature decreased from $183^{\circ}C$ to $170^{\circ}C$ by addition of a small amount of Bi atoms to the eutectic Sn62-Pb38 (wt%) solder. Our study first revealed the detailed in-situ phase transformation of Sn-Pb-Bi solder during heating to the eutectic temperature. Considering the results of peel strength and hardness, adding 1 wt% of Bi atoms to the Sn62-Pb38 (wt%) solder produced an appropriate composition.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 춘계학술대회논문집
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• pp.116-119
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• 1999

The effects of secondary phase morphology and carbon content on the plastic deformation of 0.2C-1.5Si-1.5mn TRIP(TRansformed Induced Plasticity) steel have been investigated at various annealing and bainitic transformation temperatures. The morphology of ferrite and secondary phases was controlled by the annealing temperature and the distribution of secondary phase was controlled by the bainitic transformation temperature. The secondary phase contributed to elongation and/or UTS depending on the ferrite morphology which determined deformation mode simple elongation or rotation of secondary phase along the tensile direction In case of the sample containing the granular type retained austenite the elongation was improved as carbon stabilized the austenite phase. If the film-shape retained austenite in acicular ferrite was dominant however UTS was enhanced as the transformed martensite was hardened by carbon.

• 열처리공학회지
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• 제11권3호
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• pp.192-199
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• 1998

This study was carried out to investigate the influence of variations in the temperature and time of isothermal heat treatment, applied stresses and prestrain on the isothermal transformation behavior of ${\gamma}$ and ${\sigma}$ phases and mechanical properties of 25Cr-7Ni-3Mo duplex stainless steel. The precipitation of ${\gamma}$ and ${\sigma}$ phases through isothermal heat treatment showed the type curves with a certain incubation period, the curve migrated to in a short period of time and the amount of precipitation increased with decreasing isothermal heat treatment temperature. Under the state of isothermal transformation, the precipitation of ${\gamma}$ and ${\sigma}$ phases was stimulated by applied stress, with increasing applied stress, the curves migrated to in a short period of time and also observed that the application of stress has a greater influence on the amount of ${\sigma}$ precipitation than that of ${\gamma}$ precipitation. The precipitation of ${\gamma}$ and ${\sigma}$ phases was stimulated by cold and warm rolling before isothermal heat treatment and precipitation of ${\gamma}$ and ${\sigma}$ phases has a greater influence on the warm rolling than cold rolling. The tensile strength and hardness increased with increasing cold and warm rooling reduction ratio.

• 한국세라믹학회지
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• 제34권9호
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• pp.957-962
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• 1997

Dicalcium silicate has many polymorphs according to temperature. $\beta$-dicalcium silicate which exists in cement is stabilized by minor components drived from raw materials regardless of temperature, such as high temperature and room temperature. K2O, SO3 and B2O3 are effective stabilizers for $\beta$-dicalcium silicate at room temperature. B2O3 was the most effective stabilizer. Transformation from $\beta$ to ${\gamma}$ phase causes dicalcium silicate to change volume, resulting in dusting phenomenon. When B2O3 was used the phase transformation is the least than any other stabilizers. In addition, the starting temperature of quenching influences phases transformation : low temperature of quenching presented much phase transformation and decreased size of parameter of $\beta$-dicalcium silicate.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제13권1호
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• pp.31-40
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• 2009

In the present work transformation of dimensionless heat diffusion equation for the solution of moving boundary problems have been formulated. The formulation is based on 1-D, 2-D and 3-D, unsteady heat diffusion equations. These equations are rst turned int dimensionless form by using dimensionless quantities and their transformation was formulated in liquid and solid phases. The salient feature of this work is that during the transformation of dimensionless heat diffusion equation there arises a convective term $\tilde{v}$ which is responsible for the motion of interface in liquid as well as solid phase. In the transformed heat equation, a correction factor $\beta$ also arises naturally which gives the correct transformed flux at interface.

• 한국광물학회지
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• 제24권2호
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• pp.63-71
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• 2011

슈베르트마나이트로부터 침철석으로의 전이 시 일어나는 광물학적 변화 및 이와 연관된 중금속의 거동을 알아보기 위하여 달성광산의 광산배수 정화시설 소택지에 침전된 침전물을 대상으로 광물학적 연구와 지구화학적 연구를 수행하였다. XRD 연구결과 초기에 광산배수로부터 침전된 슈베르트마나이트는 대부분 침철석으로 전이되어 상부 일부에서만 슈베르트마나이트가 관찰되었다. SEM으로 광물 전이에 따른 외부형태 변화를 관찰한 결과 눈에 띄는 변화가 없는 것으로 보아 광물전이는 용해-챔전의 과정보다는 고체상에서의 전이가 있었음을 알 수 있었다. 슈베르트마나이트와 침철석에 흡착 또는 공침된 중금속들 중 Pb와 Cu의 경우 광산배수의 중금속 농도에 비교하여 상대적으로 높은 농도를 보였으며 나머지 중금속들은 상대적인 양에 있어서 비슷한 값을 보였다. 상부 슈베르트마나이트에서 하부의 침철석으로 전이가 일어나면서 광물 내 함유된 중금속의 함량은 일부 시료를 제외하고 전체적으로 눈에 띄는 변화를 보이지 않았으며 이는 슈베르트마나이트에서 침철석으로 전이되는 과정에서 고체 상태에서 전이가 일어나면서 추가적인 중금속의 용출이나 흡착이 없었음을 지시한다.

• 열처리공학회지
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• 제18권6호
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• pp.362-368
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• 2005

Formation and thermal stability of a quasicrystalline phases in Al-Fe-Mo alloys were investigated by means of melt-spinning process and subsequent heat treatment test. Thermal decomposition and phase transformation process of the as-spun alloys were studied using X-ray diffraction and electron microscopy. The melt-spun Al-Fe-Mo alloys contained an icosahedral quasicrystalline phase with a quasilattice constant of 0.457 nm. Icosahedral phase formed at a composition of $Al_{82.5}Fe_{14}Mo_{3.5}$ as a metastable phase during rapid solidification was transformed into the stable crystalline phases, cubic 1/0 approximant and monoclinic ${\lambda}$-phase, upon heating. A metastable icosahedral and cubic(a = 0.93 nm) phases in as-spun $Al_{65}Fe_{20}Mo_{15}$ alloy were decomposed into two cubic(a = 0.62, 0.31 nm) phases by heat treatment.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.589-590
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• 2005

BSCCO:2212-2223 thin films were fabricated by using the ion beam sputter with a evaporation method at various substrate temperatures, $T_{sub}$, and ozone gas pressures, $pO_3$. The correlation diagrams of the BSCCO phases with Tsub and $pO_3$ are established in the 2212 and 2223 compositional films. In spite of 2212 compositional sputtering, Bi2201 and Bi2223 as well as Bi2212 phases come out as stable phases depending on Tsub and $pO_3$. From these results, the thermodynamic evaluation of ${\Delta}H$ and ${\Delta}S$, which are related with Gibbs' free energy change for single Bi2212 or Bi2223 phase, was performed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2001년도 학술대회 논문집 전문대학교육위원
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• pp.7-12
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• 2001

A large number of methods for the design optimization have been proposed in recent years. However, it is not easy to apply these methods to practical use because of many iterations. So, in the design optimization, physical and engineering investigation of the given model are very important, which results in an overall increase in the optimization speed. This paper describes a novel optimization procedure utilizing the conformal transformation method. This approach consists of two phases and has the advantage of grasping the physical phenomena of the model easily. Some numerical results that demonstrate the validity of the proposed method are also presented.