• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.62-63
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• 2006

Both densification and grain growth are driven by the reduction of the interfacial area, kinetics of which depends strongly on the interface structure. Abnormal grain coarsening in the system of singular solid/liquid interface such as WC-Co alloys was explained by the growth mechanism of 2-dimensional nucleation. Based on this concept, the marked inhibition of coarsening of WC grains by VC addition can be approached by the increase in the step free energy, which increases the barrier of 2-dimensional nucleation. The activated sintering in tungsten powders can be approached by the interface structure change induced by the addition of a small amount of nickel.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.66-67
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• 2006

The master sintering curve (MSC) is derived from densification data over a range of heating rates and temperatures. To improve the accuracy, several modifications were proposed: multi-phase MSC for solid state sintering with phase changes, MSC for liquid phase sintering, and MSC with consideration of grain growth. The developed MSC models were applied to several material systems such as molybdenum, stainless steels, and tungsten heavy alloys (WHA), in order to evaluate the effect of compaction pressure, phase change, grain growth, and composition on densification, to classify regions having different sintering mechanism, and to help engineer design, optimize, and monitor sintering cycles.

• 한국분말재료학회지
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• 제25권2호
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• pp.109-119
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• 2018

The objective of this study is to reveal the sintering mechanism of mixed Ti-6Al-4V powders considering the densification and the homogenization between Ti and Al/V particles. It is found that the addition of master alloy particles into Ti enhances densification by the migration of Al into the Ti matrix prior to the self-diffusion of Ti. However, as Ti particles become coarser, sintering of the powders appears to be retarded due to slower inter-diffusion of the particles due to the reduced surface energies of Ti. Such phenomena are confirmed by a series of dilatometry tests and microstructural analyses in respect to the sintering temperature. Furthermore, the results are also consistent with the predicted activation energies for sintering. The energies are found to have decreased from 299.35 to $135.48kJ{\cdot}mol^{-1}$ by adding the Al/V particles because the activation energy for the diffusion of Al in ${\alpha}-Ti$ ($77kJ{\cdot}mol^{-1}$) is much lower than that of the self-diffusion of ${\alpha}-Ti$. The coarser Ti powders increase the energies from 135.48 to $181.16kJ{\cdot}mol^{-1}$ because the specific surface areas of Ti decrease.

• 한국분말재료학회지
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• 제29권5호
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• pp.357-362
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• 2022

The low-temperature sinterability of TiO₂-CuO systems was investigated using a solid solution of SnO₂. Sample powders were prepared through conventional ball milling of mixed raw powders. With the SnO₂ content, the compositions of the samples were Ti_1-xSn_xO₂-CuO(2 wt.%) in the range of x ≤ 0.08. Compared with the samples without SnO₂ addition, the densification was enhanced when the samples were sintered at 900℃. The dominant mass transport mechanism seemed to be grain-boundary diffusion during heat treatment at 900℃, where active grain-boundary diffusion was responsible for the improved densification. The rapid grain growth featured by activated sintering was also obstructed with the addition of SnO₂. This suggested that both CuO as an activator and SnO₂ dopant synergistically reduced the sintering temperature of TiO₂.

• 한국결정학회지
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• 제3권1호
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• pp.44-52
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• 1992

Ti(C, N)-Cr3C2계 ceramics 의 소결에 있어 서, 소결 분위기가 소결체의 물성에 미치는 영 향과 Cr3c2월 상변화 현상을 검토하였다. Ti(C, N)-Crsc2 혼합분말을 진공 및 질소 분위기에서 소결할 경우 치밀한 소결체를 얻을 수 있었으나, 아르곤 분위기에서는 치밀한 소결체를 얻을 수 없었다. 이들 소결체의 X-선 회절 분석결과, 진공 분위기에서는 Cr3c2가 CrIC3로 변화하 였으며 질소 및 아르곤 분위기에서는 상변화가 거의 없었다 이는 진공소결시 Ti(C, N)에서 탈질 현상이 일어나고 이에 따라 Cr3c2중의 C의 이동에 의해 CrTCE 상으로 변하며, 따라서 활발 한 Ti 및 Cr의 이동으로 인해 치밀한 소결이 이루어지는 것으로 해석되며 반면 질소분위기에서는,가질 현상이 일어나고 이에 따라 유리탄 소의 생성, 이 유리탄소에 의한 입계 내의 산소 의 제거 및 입계 사이의 유리탄소의 잔존 등의 소결기구에 의해 치밀화가 이루어 지는 것으로 해석된다.

• 한국세라믹학회지
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• 제49권6호
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• pp.586-591
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• 2012

$Zr_2WP_2O_{12}$ powder, which has a negative thermal expansion coefficient, was synthesized by a solid-state reaction with $ZrO_2$, $WO_3$ and $NH_4H_2PO_4$ as the starting materials. The synthesis behavior was dependent on the solvent media used in the wet mixing process. The $Zr_2WP_2O_{12}$ powder prepared with a solvent consisting of D. I. water was fully crystallized at $1200^{\circ}C$, showing a sub-micron particle size. According to the results obtained from a thermal analysis, a $ZrP_2O_7$ was synthesized at a low temperature of $310^{\circ}C$, after which it was reacted with $WO_3$ at $1200^{\circ}C$. A new sintering additive, $Al(OH)_3$, was applied for the densification of the $Zr_2WP_2O_{12}$ powders. The cold isostatically pressed samples were densified with 1 wt% $Al(OH)_3$ additive or more at $1200^{\circ}C$ for 4 h. The main densification mechanism was liquid-phase sintering due to the liquid which resulted from the reaction with amorphous or unstable $Al_2O_3$ and $WO_3$. The densified $Zr_2WP_2O_{12}$ ceramics showed a relative density of 90% and a negative thermal expansion coefficient of $-3.4{\times}10^{-6}/^{\circ}C$. When using ${\alpha}-Al_2O_3$ as the sintering agent, densification was not observed at $1200^{\circ}C$.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.621-626
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• 2022

Tungsten is a high melting point metal unlike other steel materials, and it is difficult to manufacture because of its high melting temperature. In this study, pressure sintering process method was applied to manufacture the tungsten materials at low temperature. Therefore, it is necessary to densify the sintered material by using a sintering additive. Studies have been conducted on how the amount of titanium for sintering tungsten affects the mechanical properties of tungsten in this study. In order to secure the densification mechanism of tungsten powder during the sintering process, the characteristics of the sintered tungsten material according to the change of titanium content were evaluated. It was investigated the relationship between sintering parameters and mechanical properties for densification of microstructures. The sintered tungsten materials according to sintering additive content showed high sintered density (about 16.31g/cm³) and flexural strength (about 584 MPa) when the content of sintering additive was 3 wt%. However, as the content of the sintering additive increases, mechanical property of flexural strength is decreased, and the porosity is increased due to the heterogeneous sintering around titanium.

• 한국분말재료학회지
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• 제31권2호
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• pp.146-151
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• 2024

Pure SnO₂ has proven very difficult to densify. This poor densification can be useful for the fabrication of SnO₂ with a porous microstructure, which is used in electronic devices such as gas sensors. Most electronic devices based on SnO₂ have a porous microstructure, with a porosity of > 40%. In pure SnO₂, a high sintering temperature of approximately 1300℃ is required to obtain > 40% porosity. In an attempt to reduce the required sintering temperature, the present study investigated the low-temperature sinterability of a current system. With the addition of TiO₂, the compositions of the samples were Sn_1-xTi_xO₂-CoO(0.3wt%)-CuO(2wt%) in the range of x ≤ 0.04. Compared to the samples without added TiO₂, densification was shown to be improved when the samples were sintered at 950℃. The dominant mass transport mechanism appears to be grain-boundary diffusion during heat treatment at 950℃.

• 한국분말재료학회지
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• 제29권5호
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• pp.424-431
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• 2022

3Y-TZP ceramics obtained by doping 3 mol.% of Y₂O₃ to ZrO₂ to stabilize the phase transition are widely used in the engineering ceramic industry due to their excellent mechanical properties such as high strength, fracture toughness, and wear resistance. An additional increase in mechanical properties is possible by manufacturing a composite in which a high-hardness material such as oxide or carbide is added to the 3Y-TZP matrix. In this study, composite powder was prepared by dispersing a designated percentage of WC in the 3Y-TZP matrix, and the results were compared after manufacturing the composite using the different processes of spark plasma sintering and HP. The difference between the densification behavior and porosity with the process mechanism was investigated. The correlation between the process conditions and phase formation was examined based on the crystalline phase formation behavior. Changes to the microstructure according to the process conditions were compared using field-emission scanning electron microscopy. The toughness-strengthening mechanism of the composite with densification and phase formation was also investigated.

• 한국세라믹학회지
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• 제30권11호
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• pp.881-890
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• 1993

MAS system has narrow sintering temp. range due to the liquid phae sintering and thereby densify rapidly. And especially, its poor mechanical properties limitedthe industrial application. In this study, the improvement of mechanical properties and densification is suggested by the consideration of the toughening mechanisms and isolated pore generation mechanism which is derived by the liquid phase sintering theory in 3Y-TZP added composites. After Pressureless sintering up to 140$0^{\circ}C$ for 5hr, the dihedral angle and contact angle are analyzed by the observation of microstructure. As a result of microstructure analysis, the sintering stage of the specimen sintered for 5hr is analyzed as solid-skeleton stage. And the isolated pore generation mechanisms are considered as (1) The swelling of the liquid phase is predominent due to the facts that dihedral angle is larger than 60$^{\circ}$, contact angle is large and that liquid volume fraction is smaller than 10%. (2) The porous characteristics of the MAS system is also suggested as: the SiO2-rich liquid film is firstly formed at the srface and therefore this reduces the contiguity of the pore, which induces the isolated pore. The strength and fracture toughness increased with the addition of 3Y-TZP and the main fracture toughness improvement mechanisms are analyzed as the crack deflection.