• 한국분말재료학회지
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• 제3권1호
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• pp.25-32
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• 1996

Flying and solidification behaviors of the particles manufactured by centrifugal atomization were investigated. Both models were solved by the explicit FDM. Flying calculation supported the experimental results that the finer particles flied shorter than coarser particles and that particles flied shorter for lower rotation velocity than for higher velocity. Cooling curve and dendrite arm spacing were predicted by use of heat transfer analysis.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권6호
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• pp.235-240
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• 2003

In this paper, we present the fabrication and the characteristic analysis of sequential lateral solidification(SLS) poly-Si thin film transistors(TFT's) with molybdenum gate for active matrix liquid displays (AMLCD's) pixel controlling devices. The molybdenum gate is applied for the purpose of low temperature processing. The maximum processing temperature is 55$0^{\circ}C$ at the dopant thermal annealing step. The SLS processed poly-Si film which is reduced grain and grain boundary effect, is applied for the purpose of electrical characteristics improvements of poly-Si TFT's. The fabricated low temperature SLS poly-Si TFT's had a varying the channel length and width from 10${\mu}{\textrm}{m}$ to 2${\mu}{\textrm}{m}$. And to analyze these devices, extract electrical characteristic parameters (field effect mobility, threshold voltage, subthreshold slope, on off current etc) from current-voltage transfer characteristics curve. The extract electrical characteristic of fabricated low temperature SLS poly-Si TFT's showed the mobility of 100~400cm$^2$/Vs, the off current of about 100pA, and the on/off current ratio of about $10^7$. Also, we observed that the change of grain boundary according to varying channel length is dominant for the change of electrical characteristics more than the change of grain boundary according to varying channel width. Hereby, we comprehend well the characteristics of SLS processed poly-Si TFT's witch is recrystallized to channel length direction.

• 한국재료학회지
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• 제26권11호
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• pp.644-648
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• 2016

In order to examine how the solid-liquid interface responds to temperature variation depending on the materials characteristics, i.e. faceted phase or nonfaceted phase, the moving solid-liquid interface of transparent organic material, as a model substance for metallic materials (pivalic acid, camphene, salol, and camphor-50wt% naphthalene) was observed in-situ. Plots of the interface movement distance against time were obtained. The solid-liquid interface of the nonfaceted phase is atomically rough; it migrates in continuous mode, giving smooth curves of the distance-time plot. This is the case for pivalic acid and camphene. It was expected that the faceted phases would show different types of curves of the distance-time plot because of the atomically smooth solid-liquid interface. However, salol (faceted phase) shows a curve of the distance-time plot as smooth as that of the nonfaceted phases. This indicates that the solid-liquid interface of salol migrates as continuously as that of the nonfaceted phases. This is in contrast with the case of naphthalene, one of the faceted phases, for which the solid-liquid interface migrates in "stop and go" mode, giving a stepwise curve of the distance-time plot.

• 대한기계학회논문집B
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• 제29권12호
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• pp.1307-1312
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• 2005

Turbulent in-situ mixing process is a new material process technology to get dispersed phase in nanometer size by controlling reaction of liquid/liquid, liquid/solid and liquid/gas, flow and solidification speed simultaneously. In this study mixing, the key technology to this synthesis method will be studied by computational fluid dynamics. For the simulation of mixing of liquid metal, static mixers will be investigated. Two inlets for different liquid metal meet and merge like 'Y' shape tube. The tube has various shapes such as straight and curved. Also, the radius of curve will be varied. The performance of mixer will be evaluated with quantitative analysis with coefficient of variance of mass fraction. Also, detailed plots of intersection will be presented to understand effect of mixer shape on mixing.

• 대한금속재료학회지
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• 제47권12호
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• pp.797-810
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• 2009

A study was made of the effects of a Sn addition on the microstructure and microfracture mechanism of squeeze cast AZ51-xSn magnesium alloys. Microstructural observation, in situ fracture testing, and fractographic observations were conducted on these alloys to clarify the microfracture process. The microstructural analyses indicated that $Mg_2Sn$ particles as well as $Mg_{17}Al_{12}$ particles precipitated mainly along the solidification cell boundaries; the volume fraction of these hard particles increased as the amount of added Sn increased, with increased the strength. From in situ fracture observations of the AZ51-7Sn alloy, coarse precipitates located on the cell boundaries worked as easy crack propagation sites and caused abrupt intercellular fracturing. On the other hand, the overall fracture properties of the AZ51-3Sn alloy improved because crack propagation proceeded into the Mg matrix rather than into the cell boundaries as twins developed actively, as confirmed by an R-curve analysis. These findings suggest that the addition of 3~5 wt.% Sn is effective in improving both the tensile and fracture properties on the basis of well-developed twins, the blocking of crack propagation, and crack blunting.

• 열처리공학회지
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• 제12권4호
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• pp.320-326
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• 1999

In rapidly solidified $Al_{92-x}Nd_8$(Cu,Ag)x ($0{\leq}X{\leq}10at%$) alloys, amorphous single phases were obtained in the ranges of $Oat%{\leq}X{\leq}4at%$ for Al-Nd-Cu system and $Oat%{\leq}X{\leq}6at%$ for Al-Nd-Ag system, respectively. Mesoscopic structures consisted of amorphous and crystalline phases were formed above solute ranges. It was founded that the mesoscopic structures were also formed near 1st exothermic peak on DSC curve by aging in amorphous single phase alloys. For example, amorphous $Al_{92-x}Nd_8$(Cu,Ag)x (X=2.4at%) alloys containing nanoscale Al particles and compounds, i.e., mesoscopic structure, exhibited higher tensile fracture strength(${\sigma}_f$) than those of amorphous single phase alloys with the same composition. The ${\sigma}_f$ showed a maximum value in the $V_f$ ranges of 10~15%. The reason is presumed that the nanoscale precipitates which have higher mechanical strength compared with the amorphous phase with the same composition act as an effective resistance to shear deformation of the amorphous matrix.

• 한국주조공학회지
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• 제32권2호
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• pp.86-90
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• 2012

Aluminium-silicon based casting alloys have received an attention for high electrical and thermal conductivity applications, however relatively low conductivity of Al-Si alloys often limits the application. Efforts have been made to develop new high conductivity aluminium casting alloys containing no or less silicon. In this study Al-Zn-Fe based alloys were selected as the new alloys, and the effect of Mg additions on their properties and casting characteristics were investigated. As the magnesium content was increased, the tensile strength of Al-2Zn-0.2Fe based alloy was remarkably increased, while the electrical conductivity was deteriorated. It was observed that the fluidity of the alloys was generally inversely proportional to the Mg content but the hot cracking resistance was rather proportional to it. Cooling curve analyses were carried out to measure the actual solidification range and dendrite coherency temperature.

• 한국주조공학회지
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• 제28권1호
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• pp.31-36
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• 2008

Ti-Ni-Cu alloys are very attractive shape memory alloys for applications as actuators because of a large transformation elongation and a small transformation hysteresis. Rapidly solidified Ti-Ni alloy ribbons have been known to have the shape memory effect and superelasticity superior to the alloy ingots fabricated by conventional casting. In this study, solidification structures and shape memory characteristics of $Ti-Ni_{30}-Cu_{20}$ alloy ribbons prepared by melt spinning were investigated by means of DSC and XRD. Operating parameters to fabricate the amorphous ribbons were the wheel velocity of 55 m/s and the melt spinning temperature of $1500^{\circ}C$. The crystallization temperature was measured to be $440^{\circ}C$. The crystallized ribbons exhibited very fine microstructure after annealing at $440^{\circ}C$ for 10 minutes and $460^{\circ}C$ for 5 minutes and was deformed up to about 6.8% and 6.23% in ductile manner, respectively. Stress-strain curve of the ribbon exhibited a flat stress-plateau at 64 MPa and this is associated with the stress-induced a B2-B19 martensitic transformation. During cycle deformation with the applied stress of 220 MPa, transformation hysteresis and elongation associated with the B2-B19 transformation were observed to be $4.3^{\circ}C$ and 3.6%.

• 한국주조공학회지
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• 제33권2호
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• pp.55-62
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• 2013

Effect of Fe and Mn contents on the castability of Al-4wt%Mg-0.9wt%Si system alloy has been studied. According to the analysis of cooling curve for Al-4wt%Mg-0.9wt%Si-0.3wt%Fe-0.3/0.5wt%Mn alloy, ${\alpha}-Al_{15}(Fe,Mn)_3Si_2$ and ${\beta}-Al_5FeSi$ phases crystallized above eutectic temperature of $Mg_2Si$. Therefore, these phases affected both the fluidity and shrinkage behaviors of the alloy during solidification. As Fe and Mn contents of Al-4wt%Mg-0.9wt%Si system alloy increased from 0.1 wt% to 0.4 wt% and from 0.3 wt% to 0.5 wt% respectively, the fluidity of the alloy decreased by 26% and 33%. When Fe content of the alloy increased from 0.1 wt% to 0.4 wt%, 23% decrease of macro shrinkage and 19% increase of micro shrinkage appeared. Similarly, Mn content of the alloy increased from 0.3 wt% to 0.5 wt%, 11% decrease of macro shrinkage and 14% increase of micro shrinkage appeared. Judging from the castability of the alloy, Al-4wt%Mg-0.9wt%Si alloy with low content of Fe and Mn, 0.1 wt% Fe and 0.3 wt% Mn, is recommendable.

• 한국지반공학회논문집
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• 제19권6호
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• pp.363-369
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• 2003

액상화후 과잉간극수압 소산양상을 파악하고 액상화를 겪는 지반의 침하량을 예측하는데 필요한 진동하중이 작용하는 동안의 포화된 모래지반의 투수계수 변화를 추정하기 위하여, 액상화 가능성이 큰 5종류의 모래에 대해 1-g 진동대시험을 수행하였다. 시험과정중에 깊이별 과잉간극수압과 지표면 침하량을 계측하였다. 액상화후 계측된 과잉간극수압 소산곡선을 침강이론으로 선형모사하였고 선형모사된 소산곡선의 기울기를 분석함으로써 소산속도와 입도특성치와의 상관관계를 얻었다. 이러한 상관관계와 계측된 침하량을 침강이론에서 제안한 소산속도식에 대입하여 소산과정중 투수계수를 역산하였고 산정된 소산과정중 투수계수를 이용하여 진동하중이 작용하는 동안의 투수계수 변화를 추정하였다. 액상화후 과잉간극수압의 소산속도는 유효입경을 균등계수로 나눈 값에 선형적 상관관계를 갖는 것으로 나타났으며, 이러한 상관관계를 이용하여 구한 소산과정과 액상화동안의 투수계수는 원지반의 초기투수계수에 비해 각각 1.1∼2.8배, 1.4∼5배 증가하였다 그리고 이러한 증가 정도는 시험모래의 유효입경이 클수록 균등계수가 작을수록 더 커짐을 알 수 있었다.