• 한국결정성장학회지
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• 제9권1호
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• pp.84-88
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• 1999

결정성장 조건을 달리하여 공공관련 결함들의 발생영역의 크기가 다르게 형성되도록 성장한 실리콘 결정에서 반경 방향의 산소석출 거동을 고찰하였다. 반경 방향의 산소석출 거동은 결정성장 조건에 따른 공공 영역의 크기에 의존적이다. 반경 방향의 산소석출 거동은 공공우세 영역이 격자간원자 우세영역보다 산소석출이 증가한다. 또한 공공우세 영역과 격자간원자 우세영역 가장자리에서는 비정상적으로 산소석출이 크게 증가한다. 이 두 영역 경계에서는 산소석출이 거의 일어나지 않는다.

• 동력기계공학회지
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• 제5권1호
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• pp.97-103
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• 2001

The present study was investigated changes of precipitation behaviour of laves phase in ferrite single phase and ferrite-martensite dual phase and the mechanical properties of 10%Cr ferritic alloys. In the ferrite phase, laves phase was mainly precipitated, whereas in the martensite phase, carbide was preferentially formed during the initial stage of aging and with increasing aging time. Laves phase and carbide were simultaneously precipitated by precipitation of laves phase at around carbide. Strength and toughness were lowered by the disk-type precipitator in the initial stage of aging and toughness was recovered with increasing of aging time and then, decreasing by precipitation of laves phase.

• 한국주조공학회지
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• 제15권2호
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• pp.194-200
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• 1995

Rapidly Solidified (RS) Al-Zr base splats with various alloy contents were prepared by atomization-splat quenching method to understand the continuous and discontinuous precipitation in the aged alloys. And the RS alloys were consolidated by hot extrusion and swaging to analyze the effect of plastic deformation on the precipitation behavior. Discontinuous precipitation dominated at relatively low temperature in the Al-Zr alloy, whereas both V additions to Al-Zr alloys and hot metal working appeared to suppress the discontinuous precipitation. As continuous precipitation is favored in the grain interiors, the driving force for discontinuous precipitation become to disappear with a further process.

• 한국농공학회논문집
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• 제54권5호
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• pp.141-153
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• 2012

In this study, we estimated probable precipitation amounts at the target year (2020, 2030, 2040) of 55 weather stations in Korea using the 24 hour annual maximum precipitation data from 1973 through 2009 which should be useful for management of agricultural reservoirs. Not only trend tests but also non-stationary tests were performed and non-stationary frequency analysis were conducted to all of 55 sites. Gumbel distribution was chosen and probability weighted moment method was used to estimate model parameters. The behavior of the mean of extreme precipitation data, scale parameter, and location parameter were analyzed. The probable precipitation amount at the target year was estimated by a non-stationary frequency analysis using the linear regression analysis for the mean of extreme precipitation data, scale parameter, and location parameter. Overall results demonstrated that the probable precipitation amounts using the non-stationary frequency analysis were overestimated. There were large increase of the probable precipitation amounts of middle part of Korea and decrease at several sites in Southern part. The non-stationary frequency analysis using a linear model should be applicable to relatively short projection periods.

• 대기
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• 제22권1호
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• pp.57-71
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• 2012

Influences of orographic and ocean effect, which depend on the detailed geographic characteristics, upon winter time (December-February) precipitation in the Yeongdong region are investigated. Most of precipitation events in the Yeongdong region during the wintertime are associated with moist northeasterly (coming from the northeast direction) winds and also the spatial distribution of precipitation shows a great difference between Mountain area (Daegwallyeong) and Coastal area (Gangneung). The linear correlation coefficient between the meteorological variables obtained from NCEP/NCAR Reanalysis Data and precipitation amount for each precipitation type is calculated. Mountain type precipitation is dominated by northeasterly wind speed of the low level (1000 hPa and 925 hPa) and characterized with more precipitation in mountain area than coastal area. However, Coastal type precipitation is affected by temperature difference between ocean and atmosphere, and characterized with more precipitation in coastal area than mountain area. The results are summarized as follows; In the case of mountain type precipitation, the correlation coefficient between wind speed at 1000 hPa (925 hPa) and precipitation amount at Daegwallyeong is 0.60 (0.61). The correlation is statistical significant at 1% level. In the case of coastal type precipitation, the correlation coefficient of temperature difference between ocean and 925 hPa (850 hPa) over the East sea area and precipitation amount at Gangneung is 0.33 (0.34). As for the mountain type precipitation, a detailed analysis was conducted in order to verify the relationship between precipitation amount at Daegwallyeong and low level wind speed data from wind profiler in Gangneung and Buoy in the East Sea. The results also show the similar behavior. This result indicates that mountain type precipitation in the Yeongdong region is closely related with easterly wind speed. Thus, the statistical analysis of the few selected meteorological variables can be a good indicator to estimate the precipitation totals in the Yeongdong region in winter time.

• 열처리공학회지
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• 제12권1호
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• pp.21-30
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• 1999

The present study were investigated changes of precipitation behaviour of laves phase in ferrite single phase and ferrite-martensite dual phase and precipitation of laves phase under stress. Hardness changes in ferrite phase appeared two hardness peaks by precipitation of initial fine precipitator and laves phase in 3Mo-0.3Si and 3Mo-0.3Si-C specimens, respectively. Hardness changes in martensite phase of 3Mo-0.3Si-C specimen was lower in the initial stage of aging by carbide precipitation and after this, increased by re-hardening due to precipitation of laves phase. In the ferrite phase, laves phase was mainly precipitated, whereas in the martensite phase, carbide was preferentially formed during the initial stage of aging and with increasing aging time, laves phase and carbide were simultaneously precipitated by precipitation of laves phase at around carbide. In the ferrite-martensite interface, laves phase was mainly precipitated and carbide was mainly formed at boundary of lath martensite than grain boundary. Adding the stress in aging, fine precipitator of inital precipitation of laves phase precipitated in (100) of perpendicular to tensile direction and has grown to only followed<010>direction and also, volume fraction of laves phase increased. Consequently, the stress added was accelerated initial precipitation of laves phase.

• Journal of Welding and Joining
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• 제26권1호
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• pp.76-82
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• 2008

The effect of Nb addition on the precipitation and precipitate coarsening behavior was investigated in Ti and Ti + Nb steel weld HAZ. A dilatometer equipped with a He-quenching system was used to simulate the weld thermal cycle. Compared to $TiC_yN_{1-y}$ precipitate in a Ti containing steel, $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle with addition of Nb is precipitated in a Ti + Nb containing steel. Meanwhile, precipitate coarsening occurred more easily in Ti + Nb steel, which may be because the high temperature stability of $Ti_xNb_{1-x}C_yN_{1-y}$ complex particle is deteriorated by the Nb addition.

• 열처리공학회지
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• 제19권5호
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• pp.257-261
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• 2006

Scandium(Sc) in Al-Zn-Mg-Cu based Al alloy on precipitation phenomenon was compared to a 7001(Al-7.2%Zn-3.2%Mg-1.8%Cu) Al alloy. GP zone and ${\eta}^{\prime}$ phases were the main strengthening phases at low aging temperature under $100^{\circ}C$, but ${\eta}^{\prime}$ and $Al_3Sc$ phases were the main strengthening phases at high aging temperature above $1600^{\circ}C$ in Sc added 7000(Al-7.7%Zn-2.0%Mg-1.9%Cu-0.1%Zr) Al alloy. With the addition of 0.1%Sc in 7000 Al alloy, the activation energy for the GP zone, ${\eta}^{\prime}$ and ${\eta}$ phase decreased compared to the 7001 Al alloy. This result indicates that the Sc accelerated the precipitation for the GP zone, ${\eta}^{\prime}$ and ${\eta}$ phases in 7000 Al alloy. Al-7.7%Zn-2.0%Mg-1.9%Cu-0.1%Zr-0.1 Sc alloy has higher strength than 7001 Al alloy, which has high strength.

• 한국방재학회 논문집
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• 제8권5호
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• pp.103-109
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• 2008

사면에서의 강우는 경사와 토양의 물리적 성질에 따라 침투와 유출이 분리되게 되는데, 사면 해석에서는 강우가 모두 침투된다는 가정 하에 분석이 이루어져 지하수위가 과대 산정되는 경향이 있다. 따라서 본 연구에서는 서울지점의 강우분석에 이어 해석적 침투모형 중 적용성이 뛰어난 NRCS 모형과 Horton 모형을 이용하여 토양형에 따른 침투량과 유출량을 분리시킨 후, 토양을 분석하였다. 사면의 경사는 국내 설계기준에 의해 많이 적용되는 경사에 대한 단면을 구성하였으며, 산정된 침투량을 바탕으로 경사보정을 한 후 수치해석을 통해 침투거동 및 지하수위양상에 대해 분석하였다. 분석 결과에서 토양형이 D형에서 A형으로 갈수록 지하수위 변화양상이 크게 나타났다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.69-72
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• 2002

The high temperature deformation behavior of SiCp/2124Al composite and 2124Al alloy was investigated by hot compression test in a temperature ranged $400~475^{\circ}C$ over a strain rate ranged $10^{-3}~1s^{-1}$. The billets of 2124Al alloy and SiCp/2124Al composite were fabricated by vacuum hot pressing process. The stress-strain curve during high temperature deformation exhibited a peak stress, and then the flow stress decreased gradually into a steady state stress with increasing the strain. It was found that the flow-softening behavior was attributed to the dynamic recovery, local dynamic recrystallization and dynamic precipitation during the deformation. The precipitation phases were identified as S' and S by TEM diffraction pattern. Base on the TEM inspection, the relationship between the Z-H parameter and subgrain size was found based on the experiment data. The dependence of flow stress on temperature and strain rate could be formulated well by a hyperbolic-sinusoidal relationship using the Zener-Hollomon parameter.