• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.102-105
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• 2005

The mechanical properties of $SiC_f/SiC$ composites reinforced with continuous SiC fiber have been investigated in conjunction with the detailed analysis of their microstructures. Especially, the effect of test temperature on the characterization of $SiC_f/SiC$ composites was examined. In this composite system, a braiding Hi-Nicalon SiC fibric was selected as a reinforcement. $SiC_f/SiC$ composites have been fabricated by the reaction sintering process, using the complex matrix slurry with a constant composition ratio of SiC and C particles. The characterization of $RS-SiC_f/SiC$ composites was investigated by means of SEM, EDS and three point bending test. Based on the mechanical property-microstructure correlation, the high temperature applicability of $RS-SiC_f/SiC$ composites was discussed.

• Journal of Welding and Joining
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• 제14권4호
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• pp.89-98
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• 1996

This study was performed to establish the characteristics of the heat affected zones from view point of the repair weldability for a damaged CrMoV steam turbine rotor steel. Characterization of the heat affected zones of the weldment was conducted with respect to various of postweld heat treatment temperatures, $566^{\circ}C$, $621^{\circ}C$ and $677^{\circ}C$. The evaluations of the heat affected zones were carried out in terms of microstructural characterization, microhardness measurements, Charpy v-notch impact, tensile and stress-rupture tests. The results indicated that the effect of the postweld heat treatment at $677^{\circ}C$ exhibited the favorable microstructure and mechanical properties for the stability of the heat affected zones. While the heat affected zone of the weldment, produced without postweld heat treatment, displayed the inferior toughness and microstructure indicating localized carbide precipitations on the grain boundary. It was also indicated that the stability of the heat affected zones were deteriorated by the formation of the cavitation on the grain boundaries.

• 한국재료학회지
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• 제9권6호
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• pp.615-621
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• 1999

The new process in order to fabricate of Ni catalyst with high activity by the mechanochemical(MC) method which was combined the mechanical alloying(MA) and the chemical treatment process. The microstructure and characterization of mechanically alloyed Ni-5-wt% Al powder and Ni catalyst gained by alkali leaching were investigated byt he various analysis such as XRD, SEM-EDS, HRTEM and laser particle analyzer. The steady state powder with 1~2$\mu\textrm{m}$ mean particle size was obtained after 30hr milling with the PCA of 2 wt% stearic acid under the condition of grinding stainless steel ball to powder ratio of 60:1 and rotating speed fo 300rpm. According to result of HRTEM diffraction pattern, MA powder of the steady state was nanocrystalline $Al_3$$Ni_2$ intermetallic compound. Ni catalyst was obtained after KOH leaching of the steady state powder was about 20nm nanocrystalline which contained about 8 wt % Al.

• Corrosion Science and Technology
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• 제23권2호
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• pp.104-112
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• 2024

Al-Zn-Mg-Si alloy coatings have been developed to inhibit corrosion of cold rolled steel sheets, and an understanding of the alloy system helps prevent coating defects. We used a Bridgman furnace to characterise the nature and formation mechanisms of the phases present in the quaternary system with 0.4 wt% Fe. In the directional solidification experiments we imposed steep temperature gradients and varied the pull rate. After the samples were quenched in the furnace, detailed characterization of the samples was carried out by electron microscopy (SEM/EDS). From the dT/dt vs T plots of the cooling curves of the alloys, the solidification path was determined to be $Liquid{\longrightarrow[80]^{544-558}}{\alpha}-Al{\longrightarrow[80]^{453-459}}Al/Mg_2Si{\longrightarrow[80]^{371-374}}Al/Zn{\longrightarrow[80]^{331-333}}Zn/mgZn_2$. The formation mechanisms of the Mg and Zn containing phases and their morphology was discussed together with the effects of the cooling rate. Key findings include the lengthening of the mushy zone in directionally solidified samples remelted against a positive temperature gradient, as well as an enrichening of the α-Al phase by Zn through remelting. Mg₂Si and other Si based phases were observed to adopt a much finer faceted microstructure in favour of a script-like microstructure when exposed to the higher cooling rate of coolant quenching.

• Metals and materials international
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• 제24권6호
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• pp.1359-1368
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• 2018

The mechanical properties and microstructure evolution of Mg-8Li-3Al-1Y alloy undergoing different rolling processes were systematically investigated. X-ray diffraction, optical microscope, scanning electron microscopy, transmission electron microscopy as well as electron backscattered diffraction were used for tracking the microstructure evolution. Tensile testing was employed to characterize the mechanical properties. After hot rolling, the $MgLi_2Al$ precipitated in ${\beta}-Li$ matrix due to the transformation reaction: ${\beta}-Li{\rightarrow}{\beta}-Li+MgLi_2Al+{\alpha}-Mg$. As for the alloy subjected to annealed hot rolling, ${\beta}-Li$ phase was clearly recrystallized while recrystallization rarely occurred in ${\alpha}-Mg$ phase. With regard to the microstructure undergoing cold rolling, plenty of dislocations and dislocation walls were easily observed. In addition, the microstructure of alloys subjected to annealed cold rolling revealed the formation of new fresh ${\alpha}-Mg$ grains in ${\beta}-Li$ phase due to the precipitation reaction. The mechanical properties and fracture modes of Mg-8Li-3Al-1Y alloys can be effectively tuned by different rolling processes.

• 한국해양공학회지
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• 제25권3호
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• pp.28-33
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• 2011

The thermal shock properties of SiC materials were investigated for high temperature applications. In particular, the effect of thermal shock temperature on the flexural strength of SiC materials was evaluated, in conjunction with a detailed analysis of their microstructures. The efficiency of a nondestructive technique using ultrasonic waves was also examined for the characterization of SiC materials suffering from a cyclic thermal shock history. SiC materials were fabricated by a liquid phase sintering process (LPS) associated with hot pressing, using a commercial submicron SiC powder. In the materials, a complex mixture of $Al_2O_3$ and $Y_2O_3$ powders was used as a sintering additive for the densification of the microstructure. Both the microstructure and mechanical properties of the sintered SiC materials were investigated using SEM, XRD, and a three point bending test. The SiC materials had a high density of about 3.12 Mg/m3 and an excellent flexural strength of about 700 MPa, accompanying the creation of a secondary phase in the microstructure. The SiC materials exhibited a rapid propagation of cracks with an increase in the thermal shock temperature. The flexural strength of the SiC materials was greatly decreased at thermal shock temperatures higher than $700^{\circ}C$, due to the creation of microcracks and their propagation. In addition, the SiC materials had a clear tendency for a variation in the attenuation coefficient in ultrasonic waves with an increase in thermal shock cycles.

• 한국분말재료학회지
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• 제24권1호
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• pp.53-57
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• 2017

In this study, we report the microstructure and the high-temperature oxidation behavior of Fe-Ni alloys by spark plasma sintering. Structural characterization is performed by scanning electron microscopy and X-ray diffraction. The oxidation behavior of Fe-Ni alloys is studied by means of a high-temperature oxidation test at $1000^{\circ}C$ in air. The effect of Ni content of Fe-Ni alloys on the microstructure and on the oxidation characteristics is investigated in detail. In the case of Fe-2Ni and Fe-5Ni alloys, the microstructure is a ferrite (${\alpha}$) phase with body centered cubic (BCC) structure, and the microstructure of Fe-10Ni and Fe-20Ni alloys is considered to be a massive martensite (${\alpha}^{\prime}$) phase with the same BCC structure as that of the ferrite phase. As the Ni content increases, the micro-Vickers hardness of the alloys also increases. It can also be seen that the oxidation resistance is improved by decreasing the thickness of the oxide film.

• Applied Microscopy
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• 제29권3호
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• pp.265-274
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• 1999

DC마그네트론 스퍼터링방법으로 공정조건을 변화시키며 종착된 구리박막의 미세구조를 분석하였다. 폴리이미드위에 두께 50nm의 Cr박막을 증착한 뒤 두께 500 nm 또는 1000nm의 Cu 박막을 아르곤 압력을 5, 50, 100 mtorr로 변화시키며 증착하였으며 박막의 미세구조는 범용 SEM과 고분해능 SEM, TEM을 사용하여 관찰하였다. 스퍼터링 압력이 증가할수록 열린 계면이 더 많이 관찰되었다. 5 mtorr에서 형성된 박막의 표면은 균일하고 치밀한 구조인 반면에 높은 압력에서 증착된 시편에는 많은 미세 균열이 관찰되었다. 50, 100 mtorr에서 증착된 시편은 박막 두께의 영향도 관찰되어 500nm의 경우에 비해 두께가 $1{\mu}m$인 두꺼운 박막에서 더 법고 큰 균열이 발견되며 균열의 수도 증가하였다. 고분해능 SEM과 TEM으로 관찰한 결과 5 mtorr에서 증착된 시편의 특정 미세 형상은 하나의 결정립이며 주상정이 잘발달된 50, 100 mtorr에서 증착된 시편에서는 1개의 주상정 내부에 여러개의 결정립이 존재하였다. 증착압력이 증가할수록 구리박막의 결정립 크기가 감소하였는데 이는 구리원자의 표면 확산이 방해 받았기 때문이다.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.380-385
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• 2004

The efficiency of complex slurry preparation route for developing the high performance SiC matrix of RS-SiCf/SiC composites has been investigated. The green bodies for RS-SiC materials prior to the infiltration of nw/ten silicon were prepared with various C/SiC complex matrix slurries, which associated with both different sizes of starting SiC particles and blending ratios of starting SiC and carbon particles. The characterization of RS-SiC materials was examined by means of SEM, TEM, EDS and three point bending test. Based on the mechanical property-microstructure correlation, process optimization methodology is also discussed. The flexural strength of RS-SiC materials greatly depended on the content of residual Si. The decrease of starting SiC particle size in the C/SiC complex slurry was effective for improving the flexural strength of RS-SiC materials.

• Nuclear Engineering and Technology
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• 제41권2호
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• pp.149-154
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• 2009

The microstructure, the corrosion behavior and the oxide properties were examined for Zr-1.5Nb-0.4Sn-0.2Fe-0.1Cr (HANA-4) alloys which were subjected to two different final annealing temperatures: $470^{\circ}C$ and $570^{\circ}C$. HANA-4 was shown to have $\ss$-enriched phase with a bcc crystal structure and Zr(Nb,Fe,Cr)$_2$ with a hcp crystal structure with $\ss$-enriched phase being more frequently observed compared with Zr(Nb,Fe,Cr)$_2$. The corrosion rate of HANA-4 was increased with an increase of the final annealing temperature in the PWR-simulating loop, $360^{\circ}C$ pure water and $400^{\circ}C$ steam conditions, which was correlated well with a reduction in the size of the columnar grains in the oxide/metal interface region. The oxide growth rate of HANA-4 was considerably affected by the alloy microstructure determined by the final annealing temperature.