• 한국세라믹학회지
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• 제39권1호
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• pp.45-50
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• 2002

평균입경 25$\mu m$의 Si조대분말에 소결조제의 조성과 양을 변화시켜 질화반응 질화규소 (RBSN)세라믹스를 제조할 때 나타나는 치밀화 거동, 미세구조의 발달 및 기계적 특성에 대하여 고찰하였다. 6wt% $Y_2O_3$ + 1wt% $Al_2O_3$(6YlA)의 소결조제를 첨가한 경우에는 치밀화를 이루지 못하였으나, 6wt% $Y_2O_3+3\;wt%\;Al_2O_3+2\;wt%\;SiO_2(6Y3A2S)$와 9wt% $Y_2O_3$+1.5wt% $A1_2O_3$+ 3w% $SiO_2$(9Yl.5A3S)의 소결조제를 첨가하여 이론밀도에 가까운 치밀화를 이루었다. $1900^{\circ}C$에서 소결한 6Y3A2S시편의 경우, 960MPa의 높은 파괴강도값과 $6.5MPa.m^{1/2}$의 파괴인성값을 얻었다.

• 센서학회지
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• 제4권1호
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• pp.35-42
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• 1995

NASICON 분말을 합성하기 위하여 볼밀링법을 사용하였다. 사용된 원료 분말은 3종류 였으며, 이것은 $ZrO_{2}\;+\;Na_{3}PO_{4}\;+\;SiO_{2}$의 미세 및 조립 분말, 그리고 $ZrSiO_{4}\;+\;Na_{3}PO_{4}$의 미세 분말이다. 미세 분말은 $1100^{\circ}C$ 혹은 그 이상의 온도에서 쉽게 반응하여 원하는 생성물로 바뀌었지만, 조립 분말을 사용하면 $1170^{\circ}C$에서도 불완전한 반응이 일어났다. NASICON 전해질을 제조할 때, 원료 분말의 입도가 작을수록 소결 후의 밀도는 높아졌다. 이론적인 밀도($3.27g/cm^{3}$)의 95% 이상의 단일상 NASICON 전해질은 $1150{\sim}1170^{\circ}C$에서 $40{\sim}60$시간 소결할 때에 얻어질 수 있었다.

• 한국분말재료학회지
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• 제1권1호
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• pp.42-51
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• 1994

6061Al-SiCP metal matrix composite materials(MMCs) were fabricated by injecting SiCP particles directly into the atomized spray. The main attraction of this technique is the rapid fabrication of semi-finished, composite products in a combined atomization, particulate injection(10 $\mu\textrm{m}$, 40 $\mu\textrm{m}$, SiCP) and deposition operation. Conclusions obtained are as follows; The microstructure of the unreinforced spray formed 6061Al alloy consisted of relatively fine(50 $\mu\textrm{m}$) equiaxed grains. By comparision, the microstructure of the I/M materials was segregated and consisted of relatively coarse(150 $\mu\textrm{m}$) grains. The probability of clustering of SiCP particles in co-sprayed metal matrix composites increased it ceramic particle size(SiCP) was reduced and the volume fraction was held constant. Analysis of overspray powders collected from the spray atomization and deposition experiments indicated that morphology of powders were nearly spherical and degree of powders sphercity was deviated due to composite with SiCp particles. Interfacial bonding between matrix and ceramics was improved by heat treatment and addition of alloying elements(Mg). Maximum hardness values [Hv: 165 kg/mm2 for Al-10 $\mu\textrm{m}$ SiCp Hv--159 kg/mm2 for Al-40 $\mu\textrm{m}$SiCp] were obtained through the solution heat treatment at $530^{\circ}C$ for 2 hrs and aging at $178^{\circ}C$, and there by the resistance were improved.

• 한국분말재료학회지
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• 제27권2호
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• pp.103-110
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• 2020

Aluminum (Al) - based powders have attracted attention as key materials for 3D printing because of their excellent specific mechanical strength, formability, and durability. Although many studies on the fabrication of 3D-printed Al-based alloys have been reported, the influence of the size of raw powder materials on the bulk samples processed by selective laser melting (SLM) has not been fully investigated. In this study, AlSi10Mg powders of 65 ㎛ in average particle size, prepared by a gas atomizing process, are additively manufactured by using an SLM process. AlSi10Mg powders of 45 ㎛ average size are also fabricated into bulk samples in order to compare their properties. The processing parameters of laser power and scan speed are optimized to achieve densified AlSi10Mg alloys. The Vickers hardness value of the bulk sample prepared from 45 ㎛-sized powders is somewhat higher than that of the 65 ㎛m-sized powder. Such differences in hardness are analyzed because the reduction in melt pool size stems from the rapid melting and solidification of small powders, compared to those of coarse powders, during the SLM process. These results show that the size of the powder should be considered in order to achieve optimization of the SLM process.

• 한국분말재료학회지
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• 제2권3호
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• pp.238-246
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• 1995

The purpose of this study is to establish powder metallurgy (P/M) fabrication processes for high performance 2XXX Al composites reinforced with SiC whiskers. Rapidly solidified 2XXX Al powders produced by commercial atomization technique were mixed with SiC whiskers. The results of mixing processes indicated that fluidized zone mixing technique was considerably effective for the large scale production of the mixture of Al powders and whiskers. In order to consolidate these $Al-SiC_w$ mixtures into $Al-SiC_w$ composite billets, a vacuum hot press was set up, and hot processing variables were investigated. Using the hot pressing temperature of $620^{\circ}C$ under the pressure of 50 MPa, good quality $Al-SiC_w$ composite billets having relatively homogeneous microstructure and sound Al/sic interfacial bonding were obtained. Composite billets were then extruded to bars having relatively homogeneous microstructures at the extrusion temperature of 450~500$^{\circ}C$ under the extrusion pressure of 700~ 1000 MPa. Mechanical properties of the extruded bars were found to be comparable with those of the composite processed by Advanced Composite Materials Corp. To improve mechanical properties of the composites, elimination of coarse intermetallic compounds, uniform distribution of reinforcements, and minimization of whisker breakage are suggested.

• 한국주조공학회지
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• 제12권3호
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• pp.210-219
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• 1992

The measurement of the apparent and tap density for Al-Pb-X(Sn,Sn-Si) powders produced by centrifugal atomizer showed that the larger theoretically calculated densities the larger those densities. And tap densities were not over 50% of the theoretical densities. The nip angle of Al-5wt%Pb alloy powders produced with 38000 r.p.m. of disk rotation was $3^{\circ}$ degree larger than that of Al-8.5wt%Pb-3wt%Sn(-4wt%Si, 8wt%Si) with 50000 r.p.m. The effects of roll gap and rolling speed on thickness and density of the single strips by rolling were that rolling speed increasing the thickness and density of strip decreased and roll gap increasing, the thickness of strip increased but the density decresed. The compactibility of Al-Pb-X with Al by rerolling showed that the coarse powder-strips were better than fine powder-strips. From the SEM study with EDX analysis on the sintered strips, it was found that Pb and Sn were segregated with maximum size $5{\mu}m$, and Si existed surrounding the segregation zone. After sintering the clad strips at $500^{\circ}C$, the pores, which were spherical with $5{\mu}m$ of mean diameter, partly remained around the particles of alloy powders area, while completely disappeared at clad interface. The hardness of strips of alloy powders decreased linearly with increasing sintering temperature.

• 한국재료학회지
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• 제9권6호
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• pp.577-582
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• 1999

전도성 $Si_3N_4$-TiN 세라믹 복합재료를 제조하기 위해 성형체를 $1450^{\circ}C$에서 20시간 질화처리한 후 $1950^{\circ}C$에서 3.5시간 가스압소결 기술에 의해 후소결하였다. 초기 분말로 약 $10\mu\textrm{m}$로 된 상용 Si분말, 100mesh와 325mesh로된 Ti분말, 그리고 미세한 $\2.5mu\textrm{m}$ TiN분말을 사용하였다. Ti분말울 사용한 $Si_3N_4$-TiN 소결체에서 상대밀도 및 파괴인성값은 다량의 조대한 기공의 존재로 인하여 낮은 값을 보였다. 그러나 TiN분말을 사용한 $Si_3N_4$-TiN 복합체에서 파괴인성, 파괴강도 및 전기저항은 각각 $5.0MPa{\cdot}m^{1/2}$, 624MPa 그리고 $1400{\omega}cm$였다. 복합체에서 TiN 업자의 분산은 $Si_3N_4$ 업자의 조대한 봉상형태로의 성장올 방해하며 $Si_3N_4$/TiN 계면에 강한 변형장울 만든다. $Si_3N_4$-TiN 복합체의 전기전도도 및 기계적 특성을 향상시키기 위해 TiN 업자가 균일하게 분산 된 미세조직 제어가 요망된다.

• 한국분말재료학회지
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• 제10권5호
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• pp.325-332
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• 2003

The effect of extrusion temperature on the microstructure and mechanical properties was studied in gas atomized TEX>$Al_{81}Si_{19}$ alloy powders and their extruded bars using SEM, tensile testing and wear testing. The Si particle size of He-gas atomized powder was about 200-800 nm. Each microstructure of the extruded bars with extrusion temperature (400, 450 and 50$0^{\circ}C$) showed a homogeneous distribution of primary Si and eutectic Si particles embedded in the Al matrix and the particle size varied from 0.1 to 5.5 ${\mu}m$. With increasing extrusion temperature from 40$0^{\circ}C$ to 50$0^{\circ}C$, the ultimate tensile strength (UTS) decreased from 282 to 236 ㎫ at 300 K and the specific wear increased at all sliding speeds due to the coarse microstructure. The fracture behavior of failure in tension testing and wear testing was also studied. The UTS of extrudate at 40$0^{\circ}C$ higher than that of 50$0^{\circ}C$ because more fine Si particles in Al matrix of extrudate at 40$0^{\circ}C$ prevented crack to propagate.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.514-515
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• 2006

In this study, multi-ply SiC fiber reinforced Ti-6Al-4V composites have been manufactured by plasma spraying and subsequent vacuum hot pressing. Two different sizes of Ti-6Al-4V feedstock powders were used for plasma spraying to form matrix. A considerable amount of oxygen was incorporated into as-sprayed Ti matrix during plasma spraying, and consequently caused matrix embrittlement. The use of coarse-sized feedstock powder reduced oxygen contamination, but tended to increase fiber spacing irregularity and fiber strength degradation. Longitudinal tensile strength and ductility of the composites were mainly affected by the matrix oxygen content.

• 한국분말재료학회지
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• 제5권1호
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• pp.15-21
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• 1998

The effect of $\alpha$/$\beta$ phase on the mechanical properties and contact damage of silicon nitrides $Si_3N_4$) was investigated. Silicon nitride materials were prepared from two starting powders, at selective increasing hot-pressing temperatures to coarsen the microstructures: (i) from relatively coarse $\alpha$-phase powder, essentially equiaxed $\alpha$-$Si_3N_4$ grains, with limited, slow transformation to $\beta$-$Si_3N_4$ grain; (ii) from relatively fine $\alpha$-phase powder, a more rapid transformation to $\beta$-$Si_3N_4$, with attendant grain elongation. The resulting micro-structure thereby provided a spectrum of $\alpha$/$\beta$ phase ratios, grain sizes, and grain shapes. Fracture strength, hardness, and toughness were measured, and contact damage and strength degradation after indentation were investigated by Hertzian indentation using spherical indenter. A brittle to ductile transition in $Si_3N_4$ depended on $\alpha$/$\beta$ phase ratio as well as grain size. Silicon nitride with elongated $\beta$ grains showed a superior, contact damage resistance.