• 열처리공학회지
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• 제10권4호
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• pp.246-254
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• 1997

The 6.5wt %Si-Fe alloy sheets were made by the twin roll process. The magnetic properties and microstructures of sheets annealed in the sulfur atmosphere were studied. In the as-prepared sheet, non-oriented columnar grains about $10{\mu}m$ in diameter were observed, which grew from the surface to the inner part of the sheet. When the annealing temperature was around $700^{\circ}C$, the primary recrystallization was formed around the middle part of the sheet thickness, and the grain size increased with increasing annealing temperature. At the annealing temperature of $900^{\circ}C$, the grain size became $30{\sim}40{\mu}m$. Around the annealing temperature, the motive force of the grain growth is the grain boundary energy. However, above $1000^{\circ}C$ the surface energy played an important role in the observed grain growth. When the sheet were annealed at $1200^{\circ}C$, the grains whose (100) planes were paralled to the thin plate surface grew, and all sheet surfaces were covered with these grains after 1 hour annealing. This phenomenon is called tertiary recrystallization. A difference in surface energy between (100) and (110) surfaces provides a driving force for growth of tertiary grains. The coercive force was 0.27 mOe and the AC core loss $W_{12/50}$ was 0.38w/kg for the 6.5wt%Si-Fe alloy.

• Journal of Welding and Joining
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• 제18권2호
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• pp.232-232
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• 2000

The hydrogen attack characteristics of 3Cr-1Mo-V steel as simulated weld heat affected state were studied in this paper. The hydrogen attack susceptibility was evaluated by the ratios of Charpy impact absorbed energy at 0℃($vE_{0HA}$/$vE_{0}$) and reduction of area by tensile test ($RA_{HA}$/RA) before and after exposure to hydrogen at 600℃ under 450kgf/㎠ for 300hr. The values of $vE_{0HA}$/$vE_{0}$ and $RA_{HA}$/RA were aggravated as the peak temperature of the simulated heat affected zone(HAZ) raised. These results were due to the increase of the possession of bubbles along the grain boundaries, which were resulted in the reduction of grain boundary area to be precipitated carbides due to grain coarsening and the carbon dissolved in the martensite-austenite constituent near by the prior austenite grain boundary. The possession ratio of methane bubbles formed along prior austenite grain boundaries were increased with raising the peak temperature. (Received February 22, 2000)

• Journal of Welding and Joining
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• 제18권2호
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• pp.105-111
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• 2000

The hydrogen attack characteristics of 3Cr-1Mo-V steel as simulated weld heat affected state were studied in this paper. The hydrogen attack susceptibility was evaluated by the ratios of Charpy impact absorbed energy at 0℃({TEX}$vE_{0} {HA}_/vE_{0}${/TEX}) and reduction of area by tensile test({TEX}$RA_{HA}/RA${/TEX}) before and after exposure to hydrogen at 600℃ under 450kgf/㎠ for 300hr. The values of {TEX}$vE_{0} {HA}_/vE_{0}${/TEX} and {TEX}$RA_{HA}/RA${/TEX} were aggravated as the peak temperature of the simulated heat affected zone(HAZ) raised. These results were due to the increase of the possession of bubbles along the grain boundaries, which were resulted in the reduction of grain boundary area to be precipitated carbides due to grain coarsening and the carbon dissolved in the martensite-austenite constituent near by the prior austenite grain boundary. The possession ratio of methane bubbles formed along prior austenite grain boundaries were increased with raising the peak temperature.

• Nuclear Engineering and Technology
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• 제45권6호
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• pp.821-826
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• 2013

In the present study, the effects of various heat treatments on the microstructure and mechanical properties of dual phase ODS steels were investigated to enhance the high strength at elevated temperature. Dual phase ODS steels have been designed by the control of ferrite and austenite formers, i.e., Cr, W and Ni, C in Fe-based alloys. The ODS steels were fabricated by mechanical alloying and a hot isostatic pressing process. Heat treatments, including hot rolling-tempering and normalizing-tempering with air- and furnace-cooling, were carefully carried out. It was revealed that the grain size and oxide distributions of the ODS steels can be changed by heat treatment, which significantly affected the strengths at elevated temperature. Therefore, the high temperature strength of dual phase ODS steel can be enhanced by a proper heat treatment process with a good combination of ferrite grains, nano-oxide particles, and grain boundary sliding.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.518-524
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• 2016

The thermal aging effects on mechanical properties and microstructures in China low-activation martensitic steel have been tested by aging at $550^{\circ}C$ for 2,000 hours, 4,000 hours, and 10,000 hours. The microstructure was analyzed by scanning and transmission electron microscopy. The results showed that the grain size and martensitic lath increased by about $4{\mu}m$ and $0.3{\mu}m$, respectively, after thermal exposure at $550^{\circ}C$ for 10,000 hours. MX type particles such as TaC precipitated on the matrix and Laves-phase was found on the martensitic lath boundary and grain boundary on aged specimens. The mechanical properties were investigated with tensile and Charpy impact tests. Tensile properties were not seriously affected by aging. Neither yield strength nor ultimate tensile strength changed significantly. However, the ductile-brittle transition temperature of China low-activation martensitic steel increased by $46^{\circ}C$ after aging for 10,000 hours due to precipitation and grain coarsening.

• 방사성폐기물학회지
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• 제21권1호
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• pp.1-8
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• 2023

The major concern in the deep geological disposal of spent nuclear fuels include sulfide-induced corrosion and stress corrosion cracking of copper canisters. Sulfur diffusion into copper canisters may induce copper embrittlement by causing Cu₂S particle formation along grain boundaries; these sulfide particles can act as crack initiation sites and eventually cause embrittlement. To prevent the formation of Cu₂S along grain boundaries and sulfur-induced copper embrittlement, copper alloys are designed in this study. Alloying elements that can act as chemical anchors to suppress sulfur diffusion and the formation of Cu₂S along grain boundaries are investigated based on the understanding of the microscopic mechanism of sulfur diffusion and Cu₂S precipitation along grain boundaries. Copper alloy ingots are experimentally manufactured to validate the alloying elements. Microstructural analysis using scanning electron microscopy with energy dispersive spectroscopy demonstrates that Cu₂S particles are not formed at grain boundaries but randomly distributed within grains in all the vacuum arc-melted Cu alloys (Cu-Si, Cu-Ag, and Cu-Zr). Further studies will be conducted to evaluate the mechanical and corrosion properties of the developed Cu alloys.

• Corrosion Science and Technology
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• 제20권3호
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• pp.105-111
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• 2021

In oxidizing nitric acid solutions, stainless steel undergoes intergranular corrosion accompanied by grain dropping and changes in the corrosion rate. For the safe operation of reprocessing plants, this mechanism should be understood. In this study, we constructed a three-dimensional computational model using a cellular automata method to simulate the intergranular corrosion propagation of stainless steel. The computational model was constructed of three types of cells: grain (bulk), grain boundary (GB), and solution cells. Model simulations verified the relationship between surface roughness during corrosion and dispersion of the dissolution rate of the GB. The relationship was investigated by simulation applying a constant dissolution rate and a distributed dissolution rate of the GB cells. The distribution of the dissolution rate of the GB cells was derived from the intergranular corrosion depth obtained by corrosion tests. The constant dissolution rate of the GB was derived from the average dissolution rate. Surface roughness calculated by the distributed dissolution rates of the GBs of the model was greater than the constant dissolution rates of the GBs. The cross-sectional images obtained were comparable to the corrosion test results. These results indicate that the surface roughness during corrosion is associated with the distribution of the corrosion rate.

• 한국세라믹학회지
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• 제53권6호
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• pp.635-640
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• 2016

Electrical behavior of AlN ceramics sintered with $Y_2O_3$ as a sintering aid has been investigated with respect to additional $TiO_2$ dopant. From the impedance spectroscopy, it was found that the grain and grain boundary conductivities have greatly decreased with addition of $TiO_2$ dopant. The $TiO_2$ dopant also increased the activation energy of the grain conductivity by about 0.37 eV; this increase was attributed to the formation of an associate between Al vacancies and Ti ions at the Al sites. Similarly, the electronic conductivity was reduced by $TiO_2$ addition. However, $TiO_2$ solubility in AlN grains was below the detection limit of typical EDX analysis. Grain boundary was clean, without liquid films, but did show yttrium segregation. The transference number of ions was close to 1, showing that AlN is a predominantly ionic conductor. Based on the observed results, the implications of using AlN applications as insulators have been discussed.

• 한국결정성장학회지
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• 제28권6호
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• pp.235-242
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• 2018

$Y_2O_3$를 소결조제로 사용한 질화알루미나(AlN)에 다양한 소결조건과 MgO의 도핑이 고온전기전도도의 특성에 대해 미치는 영향에 대해 연구하였다. MgO를 도핑 하였을 때, 2차상으로 스피넬과 페로브스카이트 상이 생성되었고, 이는 전기적 특성에 영향을 끼쳤다. 고온 임피던스를 분석한 결과 MgO의 도핑은 AlN 입내의 활성화 에너지와 전기전도도의 감소를 보이는 반면에, 입계의 경우에는 활성화 에너지와 전기전도도의 증가를 보였다. 이는 저항이 높은 비정질의 액상이 입계에 형성되거나, Mg의 석출에 의하여 쇼트키 장벽이 높아졌기 때문으로 예상된다. MgO가 도핑된 AlN을 어닐링 한 경우에는 어닐링 하지 않은 경우에 비하여, 활성화 에너지와 전기전도도가 더욱 증가하는 것을 볼 수 있었다. 이러한 결과는 $1500^{\circ}C$에서 어닐링을 통하여 미세구조분석에서 보이는 바와 같이 Mg 이온이 입계에서 입내로 확산된 때문으로 예상된다.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 1998년도 추계종합학술대회 논문집
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• pp.601-604
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• 1998

NOX detecting gas sensors using TiO2 doped tungsten oxide semiconductor were prepared and their electrical and sensing characteristics have been investigated. In normal air condition, the sensors of WO3, TiO2 doped WO3 show grain boundary heights of 0.34 eV, 0.25 eV, respectively. The grain boundary barrier energy variation was increased by doping TiO2 into large variation of resistance to NOX gases. And doping the TiO2 4 wt.%, the particle size of WO3 polycrystal films showed higher sensitivity and better sorption characteristics to NOX gas than the pure WO3 films material in air at operating temperature of $350^{\circ}C.$ The TiO2 doped WO3 semiconductor gas sensor shows nano-sized particle size and good sensitivity to sub-ppm concentration of NOX.