• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.4
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• pp.460-466
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• 2004

Cast austenitic stainless steel is used for several components, such as primary coolant piping, elbow, pump casing and valve bodies in light water reactors. These components are subject to thermal aging at the reactor operating temperature. Thermal aging results in spinodal decomposition of the delta-ferrite leading to increased strength and decreased toughness. This study shows that ferrite content can be predicted by use of the artificial neural network. The neural network has trained teaming data of chemical components and ferrite contents using backpropagation learning process. The predicted results of the ferrite content using trained neural network are in good agreement with experimental ones.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.456-460
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• 1995

Giant magnetoresistance(GMR) of $Cu_{85-x}Co_{15}Ni_{x}$ melt-spu ribbons is closely correlated with the microstructure produced by the spinodal decomposition. The solid solution range is extanded by the replacement of Cu by Ni in the as-quenched state. The wavelengths obtained by subsequent isothermal aging in Cu-Co-Ni ribbons are shorter than those in Cu-Co binary ribbons, resulting in the increase of the surface-to-volume ratio. The largest MR ratio of 8 % in high field has been achieved in the $Cu_{80}Co_{15}Ni_{5}$ aged ribbon. The field dependence of MR ratio in low fields becomes larger with the Ni content.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.26 no.4
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• pp.333-342
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• 2022

In this paper, we perform a direct comparison study of real experimental data for domain rearrangement and the Cahn-Hilliard (CH) equation on the dynamics of morphological evolution. To validate a mathematical model for physical phenomena, we take initial conditions from experimental images by using an image segmentation technique. The image segmentation algorithm is based on the Mumford-Shah functional and the Allen-Cahn (AC) equation. The segmented phase-field profile is similar to the solution of the CH equation, that is, it has hyperbolic tangent profile across interfacial transition region. We use unconditionally stable schemes to solve the governing equations. As a test problem, we take domain rearrangement of lipid bilayers. Numerical results demonstrate that comparison of the evolutions with experimental data is a good benchmark test for validating a mathematical model.

• Journal of Korean Vacuum Science & Technology
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• v.6 no.2
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• pp.88-91
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• 2002

InGaN/GaN multiple quantum wells (MQWs) were grown by metalorganic chemical vapor deposition and their structural and optical properties were studied. When the average In content was increased by increasing TMIn flow rate, PL measurement showed little change in PL peak position and large increase in PL intensity instead. Large changes in PL peak position could be achieved by changing growth temperature. We propose the formation of fixed In content, highly In-rich quantum dot-like phases in InGaN MQWs driven by spinodal decomposition.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.13 no.1
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• pp.92-100
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• 2017

Due to the presence of ferrite phase in the finished welds, austenitic stainless steel welds (ASSWs) are considered susceptible to the thermal aging embrittlement during long-term service in light water reactor environment. In this study, the thermal aging embrittlement of typical ASSWs, E308 and ER316L welds, were evaluated after the long-term exposure up to 20,000 h at $400^{\circ}C$, which is considered as an accelerated thermal aging condition. After thermal aging, the decrease of tensile ductility and fracture toughness was observed. The microstructure observation with high resolution transmission electron microscopy revealed that spinodal decomposition in ferrite phase of both E308 and ER316L welds would be the main cause of the degradation of mechanical properties. Also, it was shown that the difference of thermal ageing embrittlement between ER316L and E308 welds was significant, such that the reduction of fracture resistance for ER316L weld was much larger than that of E308 weld.

• Bulletin of the Korean Chemical Society
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• v.24 no.10
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• pp.1485-1489
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• 2003

The gelation for di-(2-ethylhexyl) phthalate (DEHP)-plasticized poly(vinyl chloride) was studied by measuring time-resolved small-angle X-ray scattering (SAXS) and a flow of the solutions in test tube. It was found that for the gelation there were three regimes. At Regime I, the solution rapidly changed to a gel, and the SAXS intensity showed a peak and the peak intensity increased, keeping the peak angle constant. Applying the SAXS intensity to the kinetic analysis of the liquid-liquid phase separation, it was revealed that the spinodal decomposition proceeded to develop a periodic length of 29.9 nanometer in size, a hydrogen-bonding-type association in polymer rich phase followed, and then it induced fast gelation rate. At Regime II, the gelation slowly occurred and the SAXS intensity was not observed, suggesting that a homogeneous gel network was formed by a hydrogen-bonding. At regime III, the solution was a homogeneous sol.

• Nuclear Engineering and Technology
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• v.51 no.7
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• pp.1816-1821
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• 2019

This research investigates the feasibility of using the thermoelectric power to monitor the thermal embrittlement in 2507 super duplex stainless steel (SDSS) exposed to a temperature between $280^{\circ}C$ and $500^{\circ}C$. It is well known that the precipitation of Cr-rich ${\alpha}^{\prime}$ phase as a result of the spinodal decomposition is the major cause of the embrittlement and the loss of corrosion resistance in this material. The specimens are thermally aged at $475^{\circ}C$ for different holding times. A series of mechanical testing including the tensile test, Vickers microhardness measurement, and Charpy impact test are conducted to determine the property changes with holding time due to the embrittlement. The mechanical strengths and ferrite hardness exhibit very similar trends. Scanning electron microscopy images of impactfractured surfaces reveal a ductile to brittle transition in the fracture mode as direct evidence of the embrittlement. It is shown that the thermoelectric power is highly sensitive to the thermal embrittlement and has an excellent linear correlation with the ferrite hardness. This paper, therefore, demonstrates that the thermoelectric power is an excellent nondestructive evaluation technique for detecting and evaluating the $475^{\circ}C$ embrittlement of field 2507 SDSS structures.

• Korean Journal of Materials Research
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• v.9 no.9
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• pp.905-912
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• 1999

Tensile properties of powder metallurgy (PM) processed Cu-7.5Ni-5Sn alloys, either as-received or additionally solution heat treated, were examined as a function of aging time. It was found that the as-received Cu-7.5Ni-5Sn alloys showed an abrupt increase in tensile strength after aging at $350^{\circ}C$ for 20 minutes, due to the metastable ${\gamma}$\\` precipitation and a marginal Spinodal decomposition. The resolutionized PM Cu-7.5Ni-5Sn alloys, on the other hand, showed a gradual increase in tensile strength from the very early stage of aging. The overall tensile strength of resolutionized PM Cu-7.5Ni-5Sn alloys, however, was lower than that of the as-received and aged counterparts, due to the grain growth during resolutionization. Afterprolonged aging for the as-received PM Cu-7.5Ni-5Sn alloys, a considerable amount of discontinuous precipitates formed along the grain boundaries. The formation and growth kinetics of such discontinuous precipitates appeared to be dependent on the heat treatment conditions, and affect the mechanical properties greatly.

• Applied Microscopy
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• v.32 no.3
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• pp.257-263
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• 2002

Microstructural investigations of $(Li_{1/2}Pr_{1/2})TiO_3$ (LPT) complex perovskite compounds were carried out using X-ray diffractometry and transmission electron microscopy. LPT has not only the ordering of A-site cation deficiencies but also has the antiphase and inphase tilting of oxygen octahedron and the antiparallel shift of cations. Both the antiphase boundaries and the ferroelastic domains are present in the microstructure. Spinodal decomposition is found in the microstructure. The measured dielectric properties were ${\varepsilon}_r=84.6,\;Q\;{\Large f}_o=776\;GHz,\;{\tau}_{f}=-233.66ppm/^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.229.1-229.1
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• 2013

초격자는 동종의 III-V 삼원 합금층을 성장하는 동안 스피노달 분해(spinodal decomposition)로 인한 원자배열(atomic ordering)과 상분리phase separation)에 의해서 발생하는데 MBE (molecular beam epitaxy)과 MOVPE (metalorganic vapor phase epitaxy)를 이용하여 성장시킬 때 주로 발생한다. 본 논문에서는 성장온도에 따른 InP/GaP SPS (short-period superlattices) 구조의 광학적 특성 변화를 시료의 온도와 여기광의 세기를 이용하여 분석하였다. 시료는 MBE 장비를 이용하여 성장하였으며, SPS층은 659쌍의 GaP(2.9 ${\AA}$)과 InP(3.1 ${\AA}$)로 이루어져 있고, GaP 층을 처음에 증착한 뒤, InP 층을 증착 하였다. 성장시 온도를 $400^{\circ}C$, $425^{\circ}C$, $460^{\circ}C$ 그리고 $490^{\circ}C$로 변화를 주어 성장하였다. 이들 시료를 GT400, GT425, GT460 그리고 GT490이라 하였고 이에 대한 광학적 특성을 PL (photoluminescence)를 이용하여 분석하였다. 10 K에서 PL 피크는 GT400 시료는 634 nm, GT425 시료는 636 nm, GT460 시료는 680nm, 그리고 GT490 시료는 692 nm에서 나타났으며, GT425 시료의 PL 세기가 가장 강하게 나타나고 GT400 시료의 PL 세기가 가장 약하게 나타났다. 그러나 260 K에서 PL 세기는 GT460 시료가 가장 강하게 나타나고 GT425 시료가 가장 약하게 나타났다. 성장온도가 증가함에 따라 밴드갭이 감소하는 것은 특정 성장온도($460^{\circ}C$) 이상에서 LCM (lateral composition modulation)이 형성되는 것으로 설명할 수 있다. GT400 시료와 GT425 시료의 PL 피크가 1.94 eV와 1.95 eV로 비슷하고, GT460 시료와 GT490 시료의 PL 피크가 1.82 eV과 1.79 eV로 비슷하게 나타난 것은 $460^{\circ}C$이상에서 성장한 시료에서 LCM 구조 형성으로 설명할 수 있다.