• 한국분말재료학회지
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• 제5권1호
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• pp.42-49
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• 1998

A study on the improvement of the impact energy in 93W heavy alloy with a Ni/Fe ratio of 9/1 has been carried out as a function of heat treatment temperature. The obtained results were compared to that of the traditional alloy system in which the Ni/Fe ratio is 7/3 or 8/2. With increasing heat treatment temperature from 1150 to 125$0^{\circ}C$, the impact energy of the alloy with the Ni/Fe ratio of 9/1 is remarkably increased from 42 to 72 J, which is higher than that of traditional alloy, up to 118$0^{\circ}C$ and then saturated. Fracture mode was also changed from brittle W/W boundary failure to W cleavage. The temperature showing the dramatic shrinkage by dilatometric anaysis of the heavy alloy with Ni/Fe ratio of 9/1 was found to be 1483 $^{\circ}C$, which is higher than that (146$0^{\circ}C$) of the heavy alloy with Ni/Fe ratio of 7/3. Auger Electron Spectroscopy showed that the segregation of impurities, such as S, P, and C in W/W grain boundary was considerably decreased with increasing heat treatment temperature from 1150 to l18$0^{\circ}C$. From the above results, it was found that the impurity segregation in W/W grain boundary played an important role on the decrease of impact properties, and the heat treatment temperature should be appropriately chosen, as considering the Ni/Fe ratio of the alloy, in order to get good impact properties.

• 한국전기전자재료학회논문지
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• 제33권2호
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• pp.141-146
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• 2020

Thermoelectric Bi₂Te₃ thin films were synthesized by a co-sputtering method at 300℃. A Fe dopant was considered to enhance the thermoelectric properties of the system. The Seebeck coefficient of the Fe-doped films increased whereas the electrical conductivity decreased. As a result, the power factor of the system increased owing to the enhanced Seebeck coefficient. Grain growth inhibition was detected in the Fe-doped system, which produced more grain boundaries in the Fe-doped films than in the undoped system. The increased grain boundary scattering was deemed to be effective for a reduced thermal conductivity. This is advantageous for the preparation of high-performance thermoelectric films.

• 소성∙가공
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• 제18권7호
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• pp.544-549
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• 2009

This study aimed to elucidate the deformation mechanism during low-temperature superplasticity of fine-grained Ti-6Al-2Sn-4Zr-2Mo-0.1Si alloy in the context of constitutive equation. For this purpose, initial coarse equiaxed microstructure was refined to $2.2{\mu}m$ via dynamic globularization. Globularized microstructure exhibited large superplastic elongations(434-826%) at temperatures of $650-750^{\circ}C$ and strain rate of $10^{-4}s^{-1}$. It was found that the main deformation mechanism of fine-grained material was grain boundary sliding accommodated by dislocation motion with both stress exponent (n) and grain size exponent (p) values of 2. When the alpha grain size, not sub-grain size, was considered to be an effective grain size, the apparent activation energy for low-temperature superplasticity of the present alloy(169kJ/mol) was closed to that of Ti-6Al-4V alloy(160kJ/mol).

• 방사성폐기물학회지
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• 제5권1호
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• pp.79-84
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• 2007

처분장에서 지하수로 쉽게 유출될 수 있는 방사성 핵종들의 양을 예측하기 위하여 국내 PWR 사용후핵연료 팰렛들의 갭(gap) 및 입계에 있는 용해성 원소들의 재고량을 측정하였다. 연소도가 $45{\sim}66$ GWD/MTU를 갖는 연료봉에서 얻은 펠렛들에서 세슘의 갭 재고량이 $0.85{\sim}1.7%$M로 나타났으며, 이는 핵분열 생성기체 유출률의 $1/6{\sim}1/3$에 해당하였다. 그러나 핵분열 생성기체 유출 률이 1%이하인 연료봉에서 취한 40 GWD/MTU이하의 연소도를 갖는 펠렛들의 경우, 세슘의 갭 재고량들을 핵분열 생성기체 유출률과 연관시키기는 곤란하였다. 갭 및 입계내 스트론튬의 재고량은 동일 연료봉내 펠렛에서는 크게 다르지 않았으며, 요오드의 갭 재고량은 핵분열 생성기체 유출률보다 작거나 유사한 값을 갖는 것으로 평가되었다.

• Corrosion Science and Technology
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• 제7권3호
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• pp.187-191
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• 2008

Transgranular stress corrosion cracking of nickel base alloys was reported by Copson and Dean in 1965. Study to establish this cracking mechanism needs to be carried out. Laboratory stress corrosion tests were performed for mill annealed(MA) or thermally treated(TT) steam generator tubing materials in a high temperature water containing lead. An electrochemical interaction of lead with the alloying elements of SG tubings was also investigated. Alloy 690 TT showed a transgranular stress corrosion cracking in a 40% NaOH solution with 5000 ppm of lead, while intergranular stress corrosion racking was observed in a 10% NaOH solution with 100 ppm lead. Lead seems to enhance the disruption of passive film and anodic dissolution of alloy 600 and alloy 690. Crack tip blunting at grain boundary carbides plays a role for the transgranular stress corrosion cracking.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.95.1-95.1
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• 2010

Transparent conducting ZnO films were deposited to apply DSSC Substrate on glass substrates at $500^{\circ}C$ by ionbeam-assisted deposition. Crystallinity, microstructure, surface roughness, chemical composition, electrical and optical properties of the films were investigated as a function of deposition parameters such as ion energy, and substrate temperature. The microstructure of the polycrystalline ZnO films on the glass substrate were closely related to the oxygen ion energy, arrival ratio of oxygen to Zinc Ion bombarded on the growing surface. The main effect of energetic ion bombardment on the growing surface of the film may be divided into two categories; 1) the enhancement of adatom mobility at low energetic ion bombardment and 2) the surface damage by radiation damage at high energetic ion bombardment. The domain structure was obtained in the films deposited at 300 eV. With increasing the ion energy to 600 eV, the domain structure was changed into the grain structure. In case of the low energy ion bombardment of 300 eV, the microstructure of the film was changed from the grain structure to the domain structure with increasing arrival ratio. At the high energy ion bombardment of 600 eV, however, the only grain structure was observed. The electrical properties of the deposited films were significantly related to the change of microstructure. The films with the domain structure had larger carrier concentration and mobility than those with the grain structure, because the grain boundary scattering was reduced in the large size domains compared with the small size grains. The optical transmittance of ZnO films was dependent on a surface roughness. The ZnO films with small surface roughness, represented high transmittance in the visible range because of a decreased light surface scattering. By varying the ion energy and arrival ratio, the resistivity and optical transmittance of the films were varied from $1.1{\times}10^{-4}$ to $2.3{\times}10^{-2}{\Omega}cm$ and from 80 to 87%, respectively. The ZnO film deposited at 300 eV, and substrate temperature of $500^{\circ}C$ had the resistivity of $1.1{\times}10^{-4}{\Omega}cm$ and optical transmittance of 85% in visible range. As a result of experiments, we provides a suggestition that ZnO thin Films can be effectively used as the DSSC substrate Materials.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.305-307
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• 1997

Gd-doped $CeO_2$, ultrafine powders were synthesized by the glycine-nitrate process and then their sintering and electrical characteristics were analysed using the dilatometric and AC impedance measurements. In the dilatometric measurements green bodies from the synthesized powders after milling shrinked to about $1470^{\circ}C$ in appearance and then expanded thermally with the increase of the heating temperature, whereas those from the synthesized powders before milling continuously shrinked to the temperatures of $1600^{\circ}C$. It may be due to the change of the packing density of the synthesized powders by milling. In the AC impedance measurements, the electrical resistivity of the Gd-doped $CeO_2$ bodies from the as-milled powders, sintered at $1500^{\circ}C$ with the increase of the sintering time, showed the minimum value at the sintering time of 10h. The minimum total resistivity of the Gd-doped $CeO_2$ bodies sintered at $1500^{\circ}C$ for 10h seems to result from the lowest activation energy by the combination between the activation energies for the resistivities at the grain interior and grain boundary.

• 한국수소및신에너지학회논문집
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• 제17권2호
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• pp.141-148
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• 2006

This study was carried out to analyze the microstructure characteristics of electrolyte membrane through XRD, SEM and AC impedance measurement for using in high temperature steam electrolysis(HTE). It was investigated that thermal stability and electric characteristics by sintering condition using dry and wet process, and confirmed growth of particle and density change by sintering temperature. The sintering temperature and behavior had an effect on the relative density of the ceramic and the average grain size. The more amount of dispersant in organic compound increase, the more the density increased. But the binder was shown opposite phenomenon. It was analyzed that electrolyte resistance and electrical characteristics using AC impedance. The electrical properties of YSZ grain boundary changed with the sintering temperature.

• 대한기계학회논문집A
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• 제22권2호
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• pp.311-320
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• 1998

The cryogenic fracture behaviors of austenitic stainless steel HN2 developed for nuclear fusion reactor were evaluated quantitatively by using the small punch(SP) test. The electrochemical polarization test was applied to study thermal aging degradation of HN2 steel. The X-ray diffraction(XRD) analysis was conducted to detect carbides and nitrides precipitated on the grain boundary of the heat treated HN2 steel. The mechanical properties of the HN2 steel significantly decreased with increasing time and temperature of heat treatment or with decreasing testing temperature. The integrated charge(Q) obtained from electrochemical polarization test showed a good correlation with the SP energy(ESP) obtained by means of SP tests. From the results observed in the x-ray diffraction and anodic polarization curve, it was known that the material the grain boundary. Combining SP test and electrochemical polarization test, it could be useful tools to non-destructively evaluate the cryogenic fracture behaviors and the aging degradation for cryogenic structural material.

• Journal of Welding and Joining
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• 제28권2호
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• pp.79-83
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• 2010

In this study, newly developed welding consumables for EGW were welded in EH 36 TM steel plates and their welded joints were evaluated in point of mechanical properties and microstructures compared with imported consumables. Newly developed welding consumables were evaluated as good arc stability and slag fluidity, substantially the same with imported products. The tensile strength of all welded joints were sufficient to meet the requirements specified in a ship’s classification(490~640MPa) and all areas of fracture were heat affected zone(HAZ). Charpy absorbed energy values of all EG welded metals were sufficient to meet the requirements of classification(min. 34J) and those of newly developed wires were evaluated to be better than those of imported wires. As a result observing microstructures of single and tandem EG welded metals through optical and scanning electron microscope (OM&SEM), no grain boundary ferrite(PF(G)) were created in a prior austenite grain boundary and a volume fraction of a fine acicular ferrite were observed very high.