• Transactions of Materials Processing
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• v.6 no.2
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• pp.145-151
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• 1997

In order to obtain high quality products in powder metallurgy, it is important to control and understand the densification behavior of metal powders. The effect of the characters of powders on the compaction behavior was studied in this study by using three types of powders produced by the gas atomization, the centrifugal atomization and the twin roll-pulverization. The shape of the powders was a major factor in the apparent or tap density, and the deformation resistance of the matrix of the powders was a major factor in compactibility. Han's yield function (eq.2) for metal powders was simplified from the relationship based on the experimental results of copper powders. In spite of some assumptions, the calculated compaction curves using a new yield functionw was in accordance with the experimental results.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.567-574
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• 2005

Densification of SiC powder with additives of total amount of2, 4, 8 $wt\%$ Al-B-C was carried out by Spark Plasma Sintering (SPS). The unique features of the process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. The heating rate and applied pressure were kept at $100^{\circ}C/min$ and 40 MPa, while the sintering temperature and holding time varied from 1700 - $1800^{\circ}C$ for 10 - 40 min, respectively. The SPS-sintered specimens with different amount of Al-B-C at $1800^{\circ}C$ reached near-theoretical density. The $3C{\rightarrow}6H,\;15R{\rightarrow}4H$ phase transformation of SiC was enhanced by increasing the additive amount. The microstructure of SiC sintered up to $1750^{\circ}C$ consisted of fine equiaxed grains. In contrast, the growth of large elongated grains in small matrix grains was shown in sintered bodies at $1800^{\circ}C$, and the plate-like grains interlocking microstructure had been developed by increasing the holding time at $1800^{\circ}C$. The grain growth rate decreases with increasing amount of Al-B-C in SiC starting powder, however, the both of volume fraction and aspect ratio of large grains in sintered body increased.

• Journal of the Korean Ceramic Society
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• v.46 no.2
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• pp.175-180
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• 2009

Multilayer ceramic capacitors (MLCCs) have continually been made smaller in size and larger in capacity in resent years. However, the end termination electrode is still thick in many MLCCs. In this study, we used small grain glass frit to embody thin film and highly densification in the end termination by improve sintering driving force with well-dispersion and rising surface energy. Pastes were fabricated using size changed glass frit, such as 0.1 ${\mu}m$, 0.5 ${\mu}m$, 1.0 ${\mu}m$, 4.0 ${\mu}m$. Fabricated pastes were applied 05A475KQ5 chip and fired various sintering temperatures to analyze sintering behavior of pastes. Consequently, small glass frit used pastes have many merits than larger, such as well-dispersion, improve cornercoverage and surface roughness, possibility of low temperature sintering. However, we confirmed that small glass frit used pastes have narrow sintering window by rapid completion of sintering densification.

• Journal of the Korean Ceramic Society
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• v.49 no.6
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• pp.485-492
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• 2012

Dense and single phase $BiFeO_3$ (BFO) ceramics were prepared using attrition milled calcined (coarse) powders of an average particle size of ${\approx}3{\mu}m$ by conventional sintering process. A relative density of ${\approx}96%$ with average grain size $7.3{\mu}m$ was obtained when the powder compacts were sintered at $850^{\circ}C$ even for a shorter duration of 10 min. In contrast, densification barely occurred at $800^{\circ}C$ for up to 12 h rather the microstruce showed the growth of abnormal grains. The grain growth behavior at different temperatures is discussed in terms of nonlinear growth rates with respect to the driving force. The sample sintered at $850^{\circ}C$ for 12 h showed enhanced electrical properties with leakage current density of $4{\times}10^{-7}A/cm^2$ at 1 kV/cm, remnant polarization $2P_r$ of $8{\mu}C/cm^2$ at 20 kV/cm, and minimal dissipation factor (tan ${\delta}$) of ~0.025 at $10^6$ Hz. These values are comparable to the previously reported values obtained using unconventional sintering techniques such as spark plasma sintering and rapid liquid phase sintering.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.13 no.4
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• pp.176-181
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• 2003

Rapid densification of a SiC powder with additive 0.5 wt% $B_4$C was conducted by spark plasma sintering (SPS). The unique features of the process are the possibilities of using very fast heating rate and short holding time to obtain fully dense materials. The heating rate and applied pressure were kept to be $100^{\circ}C$/min and 40 MPa, while sintering temperature and soaking time varied to 1800, 1850, 1900 and $1950^{\circ}C$ and 10, 20 and 30 min, respectively. All of the SPS-sintered specimens at $1950^{\circ}C$ reached near-theoretical density. The XRD found that 3C-to-6H transformation at $1850^{\circ}C$. The microstructures of the rapidly densified SiC ceramics consisted of duplex microstructure with ultrafine equiaxed grains under 2 $\mu\textrm{m}$ and elongated grains of 0.5∼2 $\mu\textrm{m}$ wide, length 3∼10 $\mu\textrm{m}$. The biaxial strength increased with the increase of sintering time. Strength of 392.7 MPa was obtained with the fully densified specimen sintered at $1950^{\circ}C$ for 30 min, in agreement with the general tendency that strength increases with decreases pore. On the other hand, the fracture toughness shows the value of 2.17∼2.34 MPa$.$$m^{1/2}$ which might be due to the transgranular fracture mode.

• Korean Journal of Materials Research
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• v.24 no.9
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• pp.495-501
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• 2014

Despite having many attractive properties, $ZrO_2$ ceramic has a low fracture toughness which limits its wide application. One of the most obvious tactics to improve its mechanical properties has been to add a reinforcing agent to formulate a nanostructured composite material. Nanopowders of $ZrO_2$ and Cr were synthesized from $CrO_3$ and Zr powder by high energy ball milling for 10 h. Dense nanocrystalline $2/3Cr-ZrO_2$ composite was consolidated by a high-frequency induction heated sintering method within 5 min at $600^{\circ}C$ from mechanically synthesized powder. The method was found to enable not only rapid densification but also the inhibition of grain growth, preserving the nano-scale microstructure. Highly dense $2/3Cr-ZrO_2$ composite with relative density of up to 99.5% was produced under simultaneous application of a 1 GPa pressure and the induced current. The hardness and fracture toughness of the composite were 534 kg/mm2 and $7MPa{\cdot}m1/2$, respectively. The composite was determined to have good biocompatibility.

• Korean Journal of Metals and Materials
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• v.50 no.12
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• pp.891-896
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• 2012

Nanopowders of MgO and $TiO_2$ were made by high energy ball milling. The rapid synthesis and sintering of the nanostructured $MgTiO_3$ compound was investigated by the high-frequency induction heated sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition grain growth. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. A highly dense nanostructured $MgTiO_3$ compound was produced with simultaneous application of 80 MPa pressure and induced current within 2 min. The sintering behavior, gain size and mechanical properties of $MgTiO_3$ compound were investigated.

• Korean Journal of Metals and Materials
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• v.46 no.4
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• pp.223-226
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• 2008

The comparison of sintering behavior and mechanical properties of ultra-fine WC-10wt.%Co and WC-10wt.%Fe hard materials produced by high-frequency induction heated sintering (HFIHS) was accomplished using ultra fine powder of WC and binders(Co, Fe). The advantage of this process allows very quick densification to near theoretical density and prohibition of grain growth in nano-structured materials. Highly dense WC-10Co and WC-10Fe with a relative density of up to 99% could be obtained with simultaneous application of 60 MPa pressure and induced current within 1 minute without significant change in grain size. The hardness and fracture toughness of the dense WC-10Co and WC-10Fe composites produced by HFIHS were investigated.

• Korean Journal of Materials Research
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• v.6 no.5
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• pp.489-493
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• 1996

다공질 실리콘층(Porous Silicon LayerLPSL)을 사용하여 저온 열산화 (50$0^{\circ}C$, 1시간)와 급속 열산화공정(rapid thermal oxidationLRTO)(115$0^{\circ}C$, 1분)을 통하여 저온 산화막을 제조하였다. 제조된 산화막의 특성을 IR흡수 스펙트럼, C-V 곡선, 절연파괴전압, 누설전류, 그리고 굴절률을 조사함으로써 알아보았다. 절연파괴전압은 2.7MV/cm, 누설전류는 0-50V 범위에서 100-500pA의 값을 보였다. 산화막의 굴절률은 1.49의 값으로서 열산화막의 굴절률에 근접한 값을 나타냈다. 이 결과로부터 다공질 실리콘층을 저온산화막으로 제조할 때, RTO공정이 산화막의 치밀화(densification)에 크게 기여함을 알 수 있었다.

• Korean Journal of Materials Research
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• v.4 no.4
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• pp.393-400
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• 1994

A new process for uniform coating of copper to submicron tungsten powder has been developed. W-Cu alloy where copper can be uniformly distibuted has been made by the liquid phase sintering of thus prepared tungsten powder. It has been found that copper content can be lowered less than IOwt. % in our new process, maintaining the uniform distribution of copper in W-Cu alloy. Relative density above 96% was obtained after the liquid phase sintering when small amount of cobalt was added. It was revealed that the rapid increase of densification rate was due to the enhancement of wettability between tungsten particle and liquid copper.