• 한국분말재료학회지
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• 제21권4호
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• pp.277-285
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• 2014

The effects of processing parameters on the flow behavior and microstructures were investigated in hot compression of powder metallurgy (P/M) Ti-6Al-4V alloy. The alloy was fabricated by a blended elemental (B/E) approach and it exhibited lamellar ${\alpha}+{\beta}$ microstructure. The hot compression tests were performed in the range of temperature $800-1000^{\circ}C$ with $50^{\circ}C$ intervals, strain rate $10^{-4}-10s^{-1}$, and strain up to 0.5. At $800-950^{\circ}C$, continuous flow softening after a peak stress was observed with strain rates lower than $0.1s^{-1}$. At strain rates higher than $1s^{-1}$, rapid drop in flow stress with strain hardening or broad oscillations was recorded. The processing map of P/M Ti-6Al-4V was designed based on the compression test and revealed the peak efficiency at $850^{\circ}C$ and $0.001s^{-1}$. As the processing temperature increased, the volume fraction of ${\beta}$ phase was increased. In addition, below $950^{\circ}C$, the globularization of phase at the slower strain rate and kinking microstructures were found. Based on these data, the preferred working condition of the alloy may be in the range of $850-950^{\circ}C$ and strain rate of $0.001-0.01s^{-1}$.

• 한국세라믹학회지
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• 제33권4호
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• pp.455-463
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• 1996

Aluminium nitride (AlN) powder was prepared by using aluminium (III) complexes with dibasic carboxylate ligands(adipato)(hydroxo) aluminium(III) and (hydroxo)(succinato)aluminium (III) as a precursor. The AlN pow-der was obtained by calcining the complexes without mixing any carbon source under a flow of ammonia at 120$0^{\circ}C$ Contary to the conventional carbothermal reduction and nitridiation the process of decarboniza-tion of the residual carbon was not required because of the reaction of ammonia with carbon at temperature >100$0^{\circ}C$. Fine AlN powder was also prepared by calcining a mixture of an (adipato)(hydroxo)aluminium(III) complex and carbon under a flow of nitrogen at 140$0^{\circ}C$ The AlN powders prepared were ultrafine and their morphology was almost the same as that of powders of two precursors.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2004년도 추계학술대회 논문집
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• pp.327-330
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• 2004

Laser aided direct metal deposition (LADMD) process offers the ability to make a metal component directly from 3-D CAD dimensions. A 3-D object can be formed by repeating laser cladding layer by layer. The key of the build-up mechanism is the effective control of powder delivery and laser power to be irradiated into the melt-pool. A feedback control system using optical sensors is introduced to control laser power and powder mass flow rate. Using H13 tool steel and $CO_2$ laser system, comprehensive analysis are executed to test the efficiency of the system. In addition, the dimensional characteristics of directed deposited material are investigated with the parameters of deposition thickness, laser power, traverse speed and powder mass flow rate.

• Journal of Welding and Joining
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• 제20권5호
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• pp.120-126
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• 2002

Ni-5%Al alloy powder is widely used as the bond coating powder to improve the adhesive strength between the substrate and coating. The important properties in the bond coating are the deposition efficiency and surface roughness. In this study, it was tried to optimize the plasma spray parameters to maximize the deposition efficiency and surface roughness. In the first step, spray current and hydrogen gas flow rate were optimized in order to increase the deposition efficiency. In the next step, the seven plasma spray variables were selected and optimized to improve both the deposition efficiency and surface roughness using the Taguchi experimental method. By these optimization, the deposition efficiency was improved from about 10 % at the frist time to 51.2 % by the optimization of spray current and hydrogen gas flow rate and finally to 65.2 % by the Taguchi experimental method. The average surface roughness was increased from about $12.9\mu\textrm{m}$ to $15.4\mu\textrm{m}$.

• 한국세라믹학회지
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• 제26권2호
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• pp.235-241
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• 1989

A study on the APCVD(atmospheric pressure chemical vapor deposition) Al2O3 was done by using the aluminum-tri-isopropoxide/N2 reaction system at 40$0^{\circ}C$. When the flow rate of the carrier gas(N2) was over 2SLPM, heterogeneous reaction was observed. However, when the flow rate of the carrier gas was below 2SLPM, a porously deposited film or powder formation was observed. The film formed by a heterogeneous reaction was optically dense. The dense film is thought to be a kind of a hydrated alumina. After a thermal treatment of the film in the range of temperature from $600^{\circ}C$ to 1, 20$0^{\circ}C$, properties of the film seems to be changed due to dehydration and densification process. In the case of the powder on heat treatment(600~1, 20$0^{\circ}C$), both a phase transformation and the change of OH peak was observed.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2011년도 춘계 학술논문 발표대회 1부
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• pp.93-95
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• 2011

This study is to investigate experimentally the engineering characteristics of cement mortar incorporating both recycled aggregate powder (RP) below 0.08 mm and cement kiln dust(CKD). RP is substituted for fine aggregate ranged from 5~15% and CKD is also substituted for RP from 10~30%. The use of RP resulted in a decrease in flow value at fresh mortar, while an increase in CKD did not affect the flow value significantly. The combination of RP and CKD provided slight increase in compressive strength at early and 28 days and in the high curing temperature at early age showed an increasing Strength value.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.477-478
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• 2006

Close-coupled atomizers are of great interest and controlling their performance parameters is critical for metal powder producing and spray forming industries. In this study, designed close-coupled nozzle systems were used to investigate the effect of the nozzle types and protrusion length of the melt delivery tube on the pressure formation at the melt delivery tube tip. The observed metal flow rate was not behaving as what was earlier assumed, namely that, deeper aspiration enhanced metal flow rate. Higher aspiration pressure at the tip of the melt delivery tube increases the stability of atomization process.

• 한국분말재료학회지
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• 제25권6호
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• pp.482-486
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• 2018

Despite numerous advances in the preparation and use of GaN, and many leading-edge applications in lighting technologies, the preparation of high-quality GaN powder remains a challenge. Ammonolytic preparations of polycrystalline GaN have been studied using various precursors, but all were time-consuming and required high temperatures. In this study, an efficient and low-temperature method to synthesize high-purity hexagonal GaN powder is developed using sub-micron $Ga_2O_3$ powder as a starting material. The sub-micron $Ga_2O_3$ powder was prepared by an ultrasonic spray pyrolysis process. The GaN powder is synthesized from the sub-micron $Ga_2O_3$ powder through a nitridation treatment in an $NH_3$ flow at $800^{\circ}C$. The characteristics of the synthesized powder are systematically examined by X-ray diffraction, scanning and transmission electron microscopy, and UV-vis spectrophotometer.

• 한국건설순환자원학회논문집
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• 제4권2호
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• pp.118-124
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• 2016

본 연구는 단열성능 향상 재료의 타입별 단열콘크리트의 레올로지 특성을 분석하여 최적 유동설계 및 펌핑해석을 위한 기초자료로 활용하고자 하였다. 그 결과 경량골재 혼입시 항복응력이 큰 폭으로 감소한 것으로 나타났으며, 2 type의 경우 마이크로기포제 (MFA) + 규조토 미분말(DM)의 조합이 가장 이상적인 유동특성을 나타내었다. 또한 3 type의 경우 마이크로기포제(MFA) + 규조토 미분말(DM) + 경량골재(L)의 조합이 가장 우수한 유동특성을 나타내었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.287-288
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• 2012