• Nuclear Engineering and Technology
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• v.53 no.8
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• pp.2629-2639
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• 2021

Within the frame of the EMPIrE test, four monolithic mini-plates were irradiated in the ATR reactor. In two of them, the monolithic U(Mo) foil had been PVD-coated with Zr before the plate manufacturing. Extensive microstructural characterizations were performed on a fresh archive mini-plate, using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectroscopy (EDS), Electron Backscattered Diffraction (EBSD) and Focused Ion Beam (FIB)/Transmission Electron Microscopy (TEM) with nano EDS. A particular attention was paid to the examination of the U(Mo) foil, the PVD coating, the cladding/Zr and Zr/U(Mo) interfaces. The Zr coating has a thickness around 15 ㎛. It has a columnar microstructure and appears dense. The cohesion of the cladding/Zr and Zr/U(Mo) interfaces seems to be satisfactory. An almost continuous layer with a thickness of the order of 100-300 nm is present at the cladding/Zr interface and corresponds to an oxidized part of the Zr coating. At the Zr/U(Mo) interface, a thin discontinuous layer is observed. It could correspond to locally oxidized U(Mo). This work provides a basis for interpreting the results of characterizations on EMPIrE irradiated plates.

• Transactions of Materials Processing
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• v.27 no.6
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• pp.339-346
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• 2018

This study investigated the microstructure and wear properties of extruded hyper-eutectic Al-Si (15wt.%) alloy in an engine oil environment. The wear mechanism of the material was also analyzed and compared to conventional gray cast iron. In microstructural observation results of Al-15wt.%Si alloy, primary Si phase ($45.3{\mu}m$) and eutectic Si phase ($3.1{\mu}m$) were found in the matrix, and the precipitations of $Mg_2Si({\beta}^{\prime})$, $Al_2Cu({\theta}^{\prime})$ and $Al_6(Mn,Fe)$ were also detected. In the case of gray cast iron, ferrite and pearlite were observed. It was also observed that flake graphite ($20-130{\mu}m$) were randomly distributed. Wear rates were lower in the Al-Si alloy as compared to those of gray cast iron in all load conditions, confirming the outstanding wear resistance of Al-15wt.%Si alloy in engine oil environment. In the $4kg_f$ condition, the wear rate of gray cast iron was $6.0{\times}10^{-5}$ and that of Al-Si measured $0.8{\times}10^{-5}$. The microstructures after wear of the two materials were analyzed using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The primary Si and eutectic Si of Al-Si alloy effectively mitigated the abrasive wear, and the Al matrix effectively endured to accept a significant amount of plastic deformation caused by wear.

• Transactions of Materials Processing
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• v.27 no.6
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• pp.347-355
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• 2018

This study investigated the effects of the processing number of multi-axial diagonal forging (MADF) on the microstructural changes of OFC fabricated by MADF processes. The as-extruded OFC was cut to $25mm^3$ cube for the MADF processes. The MADF process consists of plane forging with a thickness reduction of 30% and diagonal forging with a diagonal forging angle of $135^{\circ}$. In order to analyze the microstructural evolutions according to the number of repetitions, 1, 2, 3 and 4 cycles of the MADF process were performed. OFC specimens were successfully deformed without surface cracking for up to 4 cycles of MADF. The grain size, average misorientation and average grain orientation spread (GOS) of MADF processed materials were analyzed using EBSD technique and their Vicker's hardness were also measured. The results showed that MADF process effectively refined the microstructure of OFC with initial average grain size of $84.2{\mu}m$. The average grain sizes of specimens MADF processed for 1, 2, 3, 4 cycles were refined to be $8.5{\mu}m$, $2.2{\mu}m$, $1.5{\mu}m$, $1.1{\mu}m$, respectively. The grain refinement seemed to be saturated when OFC was MADF processed over 2 cycles. In the case of specimens subjected to two or more cycles of MADF, the degree of decrease in average grain size was drastically reduced as the number of cycles increased due to softening phenomena such as dynamic recovery or dynamic recrystallization during processing. The degree of increase in average Vicker's hardness was also dramatically reduced as the number of cycles increased due to the same reason.

• Transactions of Materials Processing
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• v.28 no.2
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• pp.63-70
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• 2019

This study investigates the effects of multi-axial diagonal forging (MADF) processing number on the microstructures of AA1100 fabricated using MADF processes. The cast AA1100 was annealed at $400^{\circ}C$ for 3hrs in $N_2$ atmosphere and cut into $25mm^3$ cubes for the MADF processes. The MADF process consist of plane forging with a thickness reduction of 30% and a diagonal forging with a diagonal forging angle of 135 degrees. In order to analyze the microstructural variations based on the number of repetitions, 1, 2, 3 and 4 cycles of the MADF process were performed. AA1100 specimens were successfully deformed without cracking of the surface for up to 4 cycles of MADF. The grain size, average misorientation and average grain orientation spread (GOS) of MADF processed materials were analyzed using EBSD technique. The results showed that MADF process effectively refined the microstructure of AA1100 with an initial average grain size of $337.4{\mu}m$. The average grain sizes of specimens which were MADF processed for 2, 3, 4 cycles were refined to be $1.9{\mu}m$, $1.6{\mu}m$, $1.4{\mu}m$, respectively. The grain refinement appeared saturated when AA1100 got MADF processed over 2 cycles. When the specimen was subjected to two or more cycles of MADF, the degree of decrease in the average grain size drastically decreased with an increase in the number of cycle due to the softening phenomena such as dynamic recovery or dynamic recrystallization during processing.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.282-287
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• 2023

The effect of stress relief heat treatment temperature and duration time on the microstructure, residual stress and Vickers hardness of additively manufactured Ti-6Al-4V alloy using laser powder bed fusion process was clarified. As a result of stress relief heat treatment for 240 minutes at 823 K and 60 minutes or more at 873 K, residual stress was decreased less than 30 MPa without grain growth and phase transformation which causes dimensional distortion and deterioration of mechanical properties. In addition, hardness was increased with increasing heat treatment temperature and duration time. It was deduced that the refinement of acicular martensitic α' phase due to the increasing duration time of isothermal heat treatment at 773~873 K, which was not detected by XRD and phase map analysis using SEM-EBSD, probably increases the hardness.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2584-2594
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• 2024

A novel approach to incorporating oxide formers into ferritic ODS production has been developed using the co-precipitation technique. This method enables the tailored design of complex nano-oxides, integrated during Mechanical Alloying (MA) and precipitated during Spark Plasma Sintering (SPS) consolidation. Findings illustrate that co-precipitation effectively produces nano-powders with customised compositions, enriching Y, Ti, and Zr in the ferritic grade to condition subsequent oxide precipitation. While the addition of Y-Ti-Zr-O nano-oxides did not prevent the formation of Y-Al-O and Al-containing nano-oxides, these were refined thanks to the presence of well-dispersed Zr. Additionally, the Spark Plasma Sintering (SPS) parameters were optimised to tailor the bimodal grain size distribution of the ODS steels, aiming for favourable strength-to-ductility ratios. Comprehensive microstructural analyses were performed using SEM, EDS, EBSD, and TEM techniques, alongside mechanical assessments involving microtensile tests conducted at room temperature and small punch tests carried out at room temperature, 300 ℃, and 500 ℃. The outcomes yielded promising findings, showcasing similar or better performance with conventionally manufactured ODS steels. This reinforces the effectiveness and success of this innovative approach.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.259-272
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• 2020

The seismic properties in the crust are affected by the lattice preferred orientation(LPO) of major minerals in the crust. Therefore, in order to understand the internal structure of the crust using seismic data, information on the LPO of the major constituent minerals and the seismic properties of major rocks in a specific region are needed. However, there is little research on the LPOs of minerals in the crust in Korea. In this study, we collected amphibolites from two outcrops in Wigokri, Gapyeong, located in the nothern portion of Gyeonggi Massif, and we measured the LPOs of major minerals of amphibolite, especially amphibole and plagioclase through EBSD analysis, and calculated seismic properties of amphibolite. Two types of LPOs of amphibole, which are defined as type I and type IV, were observed in the two outcrops of Gapyeong amphibolites, respectively. In the case of amphibolites with the type I LPO of amphibole, large seismic anisotropy of both P- and S-wave was observed, while in the amphibolites with the type IV LPO of amphibole, small seismic anisotropy was observed. This is consistent with previous experimental results. The polarization direction of the fast S-wave was aligned subparallel to the lineation regardless of the LPO types of amphibole. The seismic anisotropy observed in Gapyeong is expected to be helpful to interpret the structure and seismic data within the crust in Gyeonggi Massif.

• Journal of the Microelectronics and Packaging Society
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• v.25 no.3
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• pp.61-66
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• 2018

This research scrutinizes the self-annealing characteristics of copper used to metal interconnection for application of DRAM fabrication process. As the time goes after the copper deposited, the grain of copper is growing. It is called self-annealing. We use the electroplating method for copper deposition and estimate two kinds of electroplating chemicals having different organic additives. As the time of self-annealing is elapsed, sheet resistance decreases with logarithmic dependence of time and is finally saturated. The improvement of sheet resistance is approximately 20%. The saturation time of experimental sample is shorter than that of reference sample. We can find that self-annealing is highly efficient in grain growth of copper through the measurement of TEM analysis. The structure of copper grain is similar to the bamboo type useful for current flow. The results of thermal excursion characteristics show that the reliability of self-annealed sample is better than that of sample annealed at higher temperature. The self-annealed sample is not contained in hillock. The self-annealed samples grow until $2{\mu}m$ and develop in [100] direction more favorable for reliability.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.109-110
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• 2014

주사전자현미경(Scanning Electron Microscopy: SEM)은 고체상태에서 미세조직과 형상을 관찰하는 데에 가장 다양하게 쓰이는 분석기기로서 최근에 판매되고 있는 고분해능 SEM은 수 나노미터의 분해능을 가지고 있다. 그리고 SEM의 초점심도가 크기 때문에 3차원적인 영상의 관찰이 용이해서 곡면 혹은 울퉁불퉁한 표면의 영상을 육안으로 관찰하는 것처럼 보여준다. 활용도도 매우 다양해서 금속파면, 광물과 화석, 반도체 소자와 회로망의 품질검사, 고분자 및 유기물, 생체시료 nnnnnnnnn와 유가공 제품 등 모든 산업영역에 걸쳐 있다(Fig. 1). 입사된 전자빔이 시료의 원자와 탄성, 비탄성 충돌을 할 때 2차 전자(secondary electron)외에 후방산란전자(back scattered electron), X선, 음극형광 등이 발생하게 되는 이것을 통하여 topography (시료의 표면 형상), morphology(시료의 구성입자의 형상), composition(시료의 구성원소), crystallography (시료의 원자배열상태)등의 정보를 얻을 수 있다. SEM은 2차 전자를 이용하여 시료의 표면형상을 측정하고 그 외에는 SEM을 플랫폼으로 하여 EDS (Energy Dispersive X-ray Spectroscopy), WDS (Wave Dispersive X-ray Spectroscope), EPMA (Electron Probe X-ray Micro Analyzer), FIB (Focus Ion Beam), EBIC (Electron Beam Induced Current), EBSD (Electron Backscatter Diffraction), PBMS (Particle Beam Mass Spectrometer) 등의 많은 분석장치들이 SEM에 부가적으로 장착되어 다양한 시료의 측정이 이루어진다. 이 중 결정구조, 조성분석을 쉽고 효과적으로 할 수 있게 하는 X선 분석장치인 EDS를 SEM에 일체화시킨 장비와 EDS 및 PBMS를 SEM에 장착하여 반도체 공정 중 발생하는 나노입자의 형상, 성분, 크기분포를 측정하는 PCDS(Particle Characteristic Diagnosis System)에 대해 소개하고자 한다. - EDS와 통합된 SEM 시스템 기본적으로 SEM과 EDS는 상호보완적인 기능을 통하여 매우 밀접하게 사용되고 있으나 제조사와 기술적 근간의 차이로 인해 전혀 다른 방식으로 운영되고 있다. 일반적으로 SEM과 EDS는 별개의 시스템으로 스캔회로와 이미지 프로세싱 회로가 개별적으로 구현되어 있지만 로렌츠힘에 의해 발생하는 전자빔의 왜곡을 보정을 위해 EDS 시스템은 SEM 시스템과 연동되어 운영될 수 밖에 없다. 따라서, 각각의 시스템에서는 필요하지만 전체 시스템에서 보면 중복된 기능을 가지는 전자회로들이 존재하게 되고 이로 인해 SEM과 EDS에서 보는 시료의 이미지의 차이로 인한 측정오차가 발생한다(Fig. 2). EDS와 통합된 SEM 시스템은 중복된 기능인 스캔을 담당하는 scanning generation circuit과 이미지 프로세싱을 담당하는 FPGA circuit 및 응용프로그램을 SEM의 회로와 프로그램을 사용하게 함으로 SEM과 EDS가 보는 시료의 이미지가 정확히 일치함으로 이미지 캘리브레이션이 필요없고 측정오차가 제거된 EDS 측정이 가능하다. - PCDS 공정 중 발생하는 입자는 반도체 생산 수율에 가장 큰 영향을 끼치는 원인으로 파악되고 있으며, 생산수율을 저하시키는 원인 중 70% 가량이 이와 관련된 것으로 알려져 있다. 현재 반도체 공정 중이나 반도체 공정 장비에서 발생하는 입자는 제어가 되고 있지 않은 실정이며 대부분의 반도체 공정은 저압환경에서 이루어지기에 이 때 발생하는 입자를 제어하기 위해서는 저압환경에서 측정할 수 있는 측정시스템이 필요하다. 최근 국내에서는 CVD (Chemical Vapor Deposition) 시스템 내 파이프내벽에서의 오염입자 침착은 심각한 문제점으로 인식되고 있다(Fig. 3). PCDS (Particle Characteristic Diagnosis System)는 오염입자의 형상을 측정할 수 있는 SEM, 오염입자의 성분을 측정할 수 있는 EDS, 저압환경에서 기체에 포함된 입자를 빔 형태로 집속, 가속, 포화상태에 이르게 대전시켜 오염입자의 크기분포를 측정할 수 있는 PBMS가 일체화 되어 반도체 공정 중 발생하는 나노입자 대해 실시간으로 대처와 조치가 가능하게 한다.

• Journal of the Korean institute of surface engineering
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• v.52 no.6
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• pp.283-288
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• 2019

MCrAlY overaly coatings are used as oxidation barrier coatings to prevent degradation of the underlying substrate in high temperature and oxidizing environment of the hot section of gas turbines. Therefore, oxidation resistance in high temperature is important property of MCrAlY coatings. Also, coefficients of thermal expansion (CTE) of MCrAlY have middle value of that of Ni-based superalloys and oxides, which have the effect of preventing the delamination of the surface oxides. Cyclic oxidation test is one of the most useful methods for evaluating the high temperature durability of coatings used in gas turbines. In this study, NiCoCrAlY overlay coatings were formed on Inconel 792(IN 792) substrates by vacuum plasma spraying process. Vacuum plasma sprayed NiCoCrAlY coatings and IN 792 susbstrates were exposed to 1000℃ one-hour cyclic oxidation environment. NiCoCrAlY coatings showed lower weight gain in short-term oxidation. In long-term oxidation, IN 792 substrates showed higher weight loss due to delamination of surface oxide but NiCoCrAlY coatings showed lower weight loss. X-ray diffraction (XRD) analysis showed α-Al2O3 and NiCr₂O₄ was formed during the cyclic oxidation test. Through cross-section observation using scanning electron microscopy (SEM) and electron back scatter diffraction (EBSD) analysis, thermally grown oxide (TGO) layer composed of α-Al₂O₃ and NiCr₂O₄ was formed and the thickness of TGO increased during 1000℃ cyclic oxidation test. β phase in upper side of NiCoCrAlY coating was depleted due to oxidation of Al and outer beta depletion zone thickness also increased as the cyclic oxidation time increased.