• 한국전기전자재료학회논문지
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• 제23권3호
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• pp.240-244
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• 2010

The surface segregation and surface order near the order-disorder phase transition of FeCo alloy was studied through Monte Carlo simulation of an Ising type model Hamiltonian. The results showed that the proper choice of Hamiltonian parameters could reproduce the recent observation of surface order above the transition temperature and that the field term played dominant role.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.731-732
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• 2006

Recently warm compaction techniques are focused on and commercialization of one high-density compaction process in the P/M industry. Another development is a new SEGLESS using a developed lubricant that reduces ejection force at room temperature compaction. It is possible to achieve high-density by reducing lubricant amount. In this paper we confirmed that green density was $7.35g/cm^3$ at 686MPa of compaction pressure when the new SEGLESS was applied to relatively lower temperature warm compaction process, such as $80^{\circ}C$.

• 한국진공학회지
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• 제5권1호
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• pp.39-47
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• 1996

The segregation of S in electrotransport-purified polycrystaline $\alpha$-Ti and Ti-aluminide alloys has been studied by Auger electron spectroscopy(AES), Ion scattering spectroscopy(ISS) and Secondary ion mass spectrometry(SIMS) in the temperature range extending from 20 to $1000^{\circ}C$. The chemisorbed oxygen and carbon on Ti were observed to disappear at T>$400^{\circ}C$ after which the S signal increased to levels approaching 0.5 monolayer. At lower temperatures the presence of the surface oxygen and carbon appeared to inhibit the segregation, presumably because there were no available surfaces sites for the S emerging from the bulk. The activation energy for the S segregation in pure polycrystaline Ti was determined to be 16.7 kcal/mol, which, when compared to S segretation from single-crystal Ti, is quite small and suggests grain boundary or defect diffusion segregation kinetics. In the Ti-aluminide alloys, the presence of Al appeared to enhance the retention of surface oxygen which, in turn, substantially reduced the S segretation. The $\gamma$ alloy, with its high Al content, exhibited the greatest retention of surface oxygen and the smallest quantity of the S segregation(T$\simeq1000^{\circ}C$).

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 추계학술대회논문집
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• pp.60-63
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• 2003

Semi-solid forming is the process of stirring alloy during solidification, making the mixture of liquid and solid, solidifying it, reheating it to the solid-liquid coexistent temperature, and then injecting this semi solid slurry into dies. In the semi-solid die casting process, it is very important to find out the correlation of injection condition, microstructure and mechanical properties. Especially, an improper injection condition is the main cause of liquid segregation and non-homogeneous mechanical properties due to the difference of solid fraction according to the position of the products. To ensure the database requisite to the semi-solid die casting product, it is essential to acquire the mechanical properties considering liquid segregation to the injection condition. In this study, the effect of injection condition on liquid segregation, formability, microstructure and mechanical properties in a thin product was investigated.

• 소성∙가공
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• 제10권3호
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• pp.214-222
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• 2001

The homogeneous distribution of solid region without liquid segregation is important in terms of high quality component during thixoforming process. In closed die semi-solid forging process, liquid segregation is strongly affected by injection velocity than solid fraction because the material has to travel relatively long distance to fill the cavity through a narrow gate. The designed die by computer simulation data was used to thixoforging process. The thixoforming velocity to prediction the liquid segregation had been determined with strain rate associated with multistage velocity control during compression test of semi-solid material. The optimal forging velocity and die temperature were investigated to produce the near-net-shape compressor component. The mechanical properties of thixoformed component were tested with various die and material temperatures before and after heat treatment.

• 한국전기전자재료학회논문지
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• 제20권10호
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• pp.864-868
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• 2007

Effect of high-temperature annealing on morphology of fully coherent self-assembled InAs quantum dots' grown on Si (100) substrates at $450^{\circ}C$ by atmospheric pressure metalorganic chemical vapor deposition(APMOCVD) was investigated by atomic force microscopy(AFM). When the dots were annealed at 500 - 600$^{\circ}C$ for 15 sec - 60 min, there was no appreciable change in the dot density but the heights of the dots increased along with the reduction in the diameters. In segregation from the InAs quantum dots and/or from the 2-dimensional InAs wetting layer which was not transformed into quantum dots looked responsible for this change in the dot size. However the change rates remained almost same regardless of annealing time and temperature, which may indicate that the morphological change due to thermal annealing is done instantly when the dots are exposed to high temperature annealing.

• 한국주조공학회지
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• 제14권6호
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• pp.566-575
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• 1994

The effects of varying the pouring temperature and the die preheating temperature in producing centrifugally cast HP alloy modified with Nb was evaluated on the basis of the resultant macrostructure, microstructure and hardness of these castings. Increased die preheating temperatures and pouring temperatures resulted in an increase in the thickness of the columnar dendritic zone, the primary and secondary dendrite arm spacing and the thickness of the zone of porosity at the casting I.D.(inner diameter). Lower die preheating temperature and pouring temperatures result in increased grain fineness and an increased zone of equiaxed grains. A higher hardness was achieved toward the casting O.D.(outer diameter) compared to the casting I.D., attributable to alloy segregation toward the casting I.D. and segregation differences resulting from reduced solidification cooling rates toward the casting I.D. Also, a higher hardness was realized at the cold end of the casting attributed to a more uniform distribution of carbides.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 추계학술대회 논문집
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• pp.178-184
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• 2000

To obtain high quality component with thixoforming process, it is important that the homegeneous distribution of solid particles without liquid segregation. In closed-die semi-solid forging process, liquid segregation is strongly affected by injection velocity than any other process variables because the material has to travel relatively long distance to fill the cavity through a narrow gate before solidification begins. The optimal injection velocity and die temperature were investigated to fabricate near-net-shape compressor component called Al frame.

• KIEE International Transactions on Electrophysics and Applications
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• 제5C권1호
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• pp.18-22
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• 2005

We developed a new systematic calibration procedure and applied it to the calibration of the diffusivity, segregation and TED model of the indium impurity. The TED of the indium impurity was studied under 4 different experimental conditions. Although the indium proved to be susceptible to the TED, the RTA was effective in suppressing the TED effect and in maintaining a steep retrograde profile. Just as in the case of boron, indium demonstrated significant oxidation-enhanced diffusion in silicon and its segregation coefficients at the Si/SiO₂ interface were significantly below 1. In contrast, the segregation coefficient of indium decreased as the temperature increased. The accuracy of the proposed technique has been validated by SIMS data and 0.13-㎛ device characteristics such as Vth and Idsat with errors less than 5% between simulation and experiment.

• Transactions on Electrical and Electronic Materials
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• 제5권6호
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• pp.211-214
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• 2004

We developed a new systematic calibration procedure which was applied to the calibration of the diffusivity, segregation and TED model of the indium impurity. The TED of the indium impurity has been studied using 4 different groups of experimental conditions. Although the indium is susceptible to the TED, the RTA is effective to suppress the TED effect and maintain a steep retrograde profile. Like the boron, the indium shows significant oxidationenhanced diffusion in silicon and has segregation coefficients at the $Si/SiO_2$ interface much less than 1. In contrast, however, the segregation coefficient of indium decreases as the temperature increases. The accuracy of the proposed technique is validated by SIMS data and $0.13 {\mu}m$ device characteristics such as $V_{th}$ and $Id_{sat}$ with errors less than $5 \%$ between simulation and experiment.