• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.45-50
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• 2002

Effect of sintering additives on the densification behavior of reaction-bonded silicon nitride prepared by using coarse Si powders is discussed. Sintering additives such as 6 wt% $Y_2O_3$+1wt% $A1_2O_3$ (6YlA) did not give rise to full densification, while full densification was obtained by using the sintering additives such as 6wt% $Y_2O_3$+3 wt% $A1_2O_3$+ 2wt% $SiO_2$ (6Y3A2S) and 9wt% $Y_2O_3$+ 1.5wt% $A1_2O_3$+ 3wt% $SiO_2$ (9Yl.5A3S). In the case of 6Y3A2S addition, high fracture strength of 960 MPa and the fracture toughness of $6.5 MPa.m^{1/2}$ were obtained.

• Journal of Sensor Science and Technology
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• v.4 no.1
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• pp.35-42
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• 1995

Conventional ball-milling technique was used to synthesize NASICON powders. The NASICON powders were made from three kinds of component powders : coarse($ZrO_{2}$, $Na_{3}PO_{4}$, $SiO_{2}$), fine ($ZrO_{2}$, $Na_{3}PO_{4}$, $SiO_{2}$) and fine ($ZrSiO_{4}$, $Na_{3}PO_{4}$) powders. The fine component powders were easily reacted to form the desired product at $1100^{\circ}C$ or higher, whereas incomplete reaction due to the coarse component powders occurred even at $1170^{\circ}C$. The finer the grain size of the starting powders was, the higher the bulk density of NASICON electrolyte after sintering was observed. Almost single phase NASICON electrolytes with more than 95% of the theoretical density, $3.27g/cm^{3}$, could be fabricated by sintering for $40{\sim}60$ hours at temperatures between 1150 and $1170^{\circ}C$.

• Journal of Powder Materials
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• v.1 no.1
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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.

• Journal of Powder Materials
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• v.27 no.2
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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.

• Journal of Powder Materials
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• v.2 no.3
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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.

• Journal of Korea Foundry Society
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• v.12 no.3
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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.

• Korean Journal of Materials Research
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• v.9 no.6
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• pp.577-582
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• 1999

In order to make the electroconductive $Si_3N_4$-TiN composities, the Si-Ti(N) compacts were nitrided at $1450^{\circ}C$ for 20hours, and then they were post-sintered by a gas-pressure-sintering technique at 1TEX>$1950^{\circ}C$ for 3.5 hours. As starting powders, commercial si powder of about $10\mu\textrm{m}$, two types of Ti powders of 100 and 325 mesh, and fine-sized TiN of $2.5\mu\textrm{m}$ powders were used. In the $Si_3N_4$-TiN sintered bodies used Ti powders, the relative density and fracture strength and electrical conductivity are low due to the existence of large amounts of coarse pores. However, in the $Si_3N_4$-TiN composite used TiN powder, the fracture toughness, fracture strength and electrical resistivity were $5.0MPa{\cdot}m^{1/2}$, 624MPa and $1400{\omega}cm$, respectively. The dispersion of TiN particles in the composite inhibited the growth of $Si_3N_4$ in the shape of rod and made strong strain field contrasts at the $Si_3N_4$-TiNinterfaces. It was recognized that microstructural control is required to improve the electrical conductivity and mechanical properties of $Si_3N_4$-TiN composites by dispersing TiN particles homogeneously.

• Journal of Powder Materials
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• v.10 no.5
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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.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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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.

• Journal of Powder Materials
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• v.5 no.1
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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.