• Title, Summary, Keyword: Liquid phase sintering

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Influence of Liquid-Phase Amount on the Microstructure and Phase Transformation of Liquid-phase Sintered Silicon Carbide (액상량이 탄화규소 소결체의 미세구조 및 상변태에 미치는 영향)

  • 이종국;강현희;박종곤;이은구
    • Journal of the Korean Ceramic Society
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    • v.35 no.4
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    • pp.413-419
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    • 1998
  • ${\beta}$-silicon carbides with yttrium aluminum garnet of 2,5,10 mol% were prepared by a liquid--phase sint-ering and the microstructural evolution and phase transformation were investigated during sintering as functions of liquid-phase amount and sintering time. The rate of grain growth decreases with the addition of the amount of yttrium aluminum garnet (YAG) in the SiC starting powder however the apparent density and the aspect ratio of grains in sintered body increase. The phase transformation from ${\beta}$-SiC to ${\alpha}$-SiC were dependent on the liquid-phase amount and sintering time.

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Monte Carlo Simulation of Densification during Liquid-Phase Sintering

  • Lee, Jae Wook
    • Journal of the Korean Ceramic Society
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    • v.53 no.3
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    • pp.288-294
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    • 2016
  • The densification process during liquid-phase sintering was simulated by Monte Carlo simulation. The Potts model, which had been applied to coarsening during liquid-phase sintering, was modified to include vapor particles. The results of two- and threedimensional simulations showed a temporal decrease in porosity, in other words, densification, and an increase in the average size of pores. The results also showed growth of solid grains and the effect of wetting angle on microstructure.

A study on Sintering Characteristics of Commercial 7xxx Series Al Alloy Powders (상용 7xxx Series Al 합금계 혼합분말의 소결 특성)

  • ;;;Panyu
    • Journal of Korean Powder Metallurgy Institute
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    • v.11 no.1
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    • pp.69-73
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    • 2004
  • The sintering characteristics of commercial 7xxx series Al-Zn-Mg-Cu alloy have been investigated. Sintering system of this blended elemental powder has aspects of both transient and supersolidus liquid phase sintering. Transient liquids occur when the constitution point during sintering lies in a solid phase region but where the sintering temperature is greater than either the melting point of one of the constituent or a eutectic temperature. Supersolidus liquid phase sintering occurs when a preblended powder is heated to a temperature between the solidus and liquids. However, these reaction were restrained their inter diffusion due to the appearance of the oxide film. Thus, 7xxx series Al alloy is extremely sensitive to process variables, including particle size, holding time and sintering temperature. Therefore, above phenomenons were observed formation and behaviour of the liquid by using SEM and DSC.

High Resolution Transmission Electron Microscopy Observations on Sintering Processes in KNbO3 Ceramics

  • Lee, Hwack Joo;Kim, Young Heon;Ryu, Hyun;Cho, Yang-Koo;Nahm, Sahn
    • Applied Microscopy
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    • v.47 no.3
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    • pp.203-207
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    • 2017
  • A homogeneous $KNbO_3$ (KN) phase was formed by sintering at $1,040^{\circ}C$ for 1 hour, without formation of the $K_2O$-deficient secondary phase even though suffering the minor loss of $K_2O$. KN liquid phase was formed during sintering and abnormal grain growth occurred in this specimen. The detailed microstructural observations on KN during sintering were carried out using high resolution transmission electron microscopy. The ledged structures were found at the KN grain boundary and the abnormal grain growth was performed by the lateral migration of these ledges in the presence of the liquid phase. The liquid pockets were found in the KN grains. They have various external shapes mainly due to the kinetic factors. They have atomically flat interfaces with some ledges with one atomic height. The slight deficient $K_2O$ by evaporation might somewhat reduce the melting point of KN from the reported at $1,058^{\circ}C$. The liquid pockets play an important role in supplying the liquid phase during the abnormal grain growth in the sintering process of KN ceramics.

Sintering Mixtures in the Stage of Establishing Chemical Equilibrium

  • Savitskii, A.P.
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • pp.5-5
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    • 1999
  • The Principal deficiency of the existing notion about the sintering-mixtures consists in the fact that almost no attention is focused on the Phenomenon of alloy formation during sintering, its connection with dimensional changes of powder bodies, and no correct ideas on the driving force for the sintering process in the stage of establishing chemical equilibrium in a system are available as well. Another disadvantage of the classical sintering theory is an erroneous conception on the dissolution mechanism of solid in liquid. The two-particle model widely used in the literature to describe the sintering phenomenon in solid state disregards the nature of the neighbouring surrounding particles, the presence of pores between them, and the rise of so called arch effect. In this presentation, new basic scientific principles of the driving forces for the sintering process of a two-component powder body, of a diffusion mechanism of the interaction between solid and liquid phases, of stresses and deformation arising in the diffusion zone have been developed. The major driving force for sintering the mixture from components capable of forming solid solutions and intermetallic compounds is attributed to the alloy formation rather than the reduction of the free surface area until the chemical equilibrium is achieved in a system. The lecture considers a multiparticle model of the mixed powder-body and the nature of its volume changes during solid-state and liquid-phase sintering. It explains the discovered S-and V-type concentration dependencies of the change in the compact volume during solid-state sintering. It is supposed in the literature that the dissolution of solid in liquid is realised due to the removal of atoms from the surface of the solid phase into the melt and then their diffusicn transfer from the solid-liquid interface into the bulk of liquid. It has been shown in our experimental studies that the mechanism of the interaction between two components, one of them being liquid, consist in diffusion of the solvent atoms from the liquid into the solid phase until the concentration of solid solutions or an intermetallic compound in the surface layer enables them to pass into the liquid by means of melting. The lecture discusses peculimities of liquid phase formation in systems with intermediate compounds and the role of the liquid phase in bringing about the exothermic effect. At the frist stage of liquid phase sintering the diffusion of atoms from the melt into the solid causes the powder body to grow. At the second stage the diminution of particles in size as a result of their dissolution in the liquid draws their centres closer to each other and makes the compact to shrink Analytical equations were derived to describe quantitatively the porosity and volume changes of compacts as a result of alloy formation during liquid phase sinteIing. Selection criteria for an additive, its concentration and the temperature regime of sintering to control the density the structure of sintered alloys are given.

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Sintering Behavior of 7xxx Series Al Blended Powder with Variation of Heating Rate (7xxx계 Al 혼합분말의 승온속도에 따른 소결거동)

  • Kang Shin Pil;Min Kyung Ho;Park Hyun Woo;Chang Si-Young;Kim Young Do
    • Journal of Korean Powder Metallurgy Institute
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    • v.12 no.2
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    • pp.131-135
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    • 2005
  • 7xxx series Al alloy has the most attractive properties including its excellent high specific strength, stress corrosion cracking and corrosion-resistance. However, in case of the Al-Zn system, the liquid phase has a transient aspect because of the high solid solubility of Zn in Al. Therefore, transient liquid phase sintering behavior was observed during the sintering process. And the amount of liquid and its duration were influenced by the process variables including heating rate and final sintering temperature. At high heating rates($100^{\circ}C/min$), the liquid fraction increased during sintering because diffusion was minimized and therefore local saturation could easily occur. The sintered density increased with increasing heating rate.

Study on the Sintering, Repressing and Mechanical Properties of Al2O3 and Al-Cu-SiC Composites (Al2O3와 SiC 강화재가 첨가된 Al-Cu 기지 복합재료의 소결, 재압축 및 기계적 특성에 관한 연구)

  • 박정수;이성규;안재환;정형식
    • Journal of Korean Powder Metallurgy Institute
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    • v.11 no.2
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    • pp.171-178
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    • 2004
  • Effects of liquid phase and reinforcing particle morphology on the sintering of Al-6 wt%Cu-10 vol% $Al_2O_3$ or SiC particles were studied in regards to densification, structure and transverse rupture properties. The Al-Cu liquid phase penetrated the boundaries between the aluminum matrix powders and the interfaces with reinforcing particles as well, indicating a good wettability to the powders. This enhanced the densification during sintering and the resulting strength and ductility. Since most of the copper added, however, was dissolved in the liquid phase and formed a brittle $CuAl_2$ phase upon cooling rather than alloyed with the aluminum matrix, the strengthening effect by the copper was not fully realized. Reinforcing particles of agglomerate type were found less suitable for the liquid phase sintering than solid type particles. $Al_2O_3$ and SiC particles protluced little difference on the sintering behavior but their size had a large effect. Repressing of the sintered composites increased density and bending properties but caused debonding at the matrix-particle interfaces and also fracturing of the particles.

Redistribution of an Intergranular-Liquid Phase During Sintering of 1 mol%-Al2O3-doped Calcia-Stabilized Zirconia: Estimation by Impedance Spectroscopy

  • Choi, Jung-Hae;Lee, Jong-Heun;Kim, Doh-Yeon
    • Journal of the Korean Ceramic Society
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    • v.39 no.9
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    • pp.818-821
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    • 2002
  • The grain boundary resistivity of a 1-mol%-$Al_2O_3$-dopedd CaO-Stabilized Zirconia(CSZ) specimen was determined by impedance spectroscopy using sub-millimeter-scale electrodes. At the initial stage of sintering, the grain-boundary resistivity of the specimen interior was observed to be higher than that of the surface. However, upon further sintering the boundary resistivity of the specimen interior became lower than that of the surface. The results were explained in terms of a redistribution of the intergranular liquid phase. The liquid phase was predicted to initially coagulate at the interior of the specimen then spread outward during sintering.

Sintering of Zriconium Diboride through Fe-based Liquid Phase (철계 액상을 통한 붕화지르코늄의 소결)

  • 우상국;한인섭;김흥수;양준환;강을손;김종희
    • Journal of the Korean Ceramic Society
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    • v.33 no.3
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    • pp.259-268
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    • 1996
  • In the present study the effect of the addition of Fe on the pressureless and hot press sintering behavior was studied under Ar atmosphere. Pressureless sintering was performed 1900~220$0^{\circ}C$ under. Ar atmosphere. The addition of 1 wt% Fe was increased effectively of the sintered density. However it was impossible to obtain high density higher than 90%,. Zr-Fe-B compound in liquid phase was observed from the EDS and WDS analysis. It was considered that sinterability was enhanced due to the mass transfer through Fe based liquid phase formed at the sintering temperature. Hot pressing was performed at 1600~1$700^{\circ}C$ under Ar atmos-phere for 1 hr. It was possible obtain 95% relative density of ZrB2 specimen which is higher density at pressure-less sintering. It could be thought that ZrB2 particles was rearranged through liquid phase by applied pressure during initial stage of sintering.

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Effects of Particle Size of Alumina on Densification Behaviors of Alumina-Talc System During Liquid-Phase Sintering (알루미나-활석계의 액상소결에서 알루미나 입자크기가 치밀화 거동에 미치는 영향)

  • 김호양;이정아;김정주
    • Journal of the Korean Ceramic Society
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    • v.35 no.12
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    • pp.1308-1315
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    • 1998
  • Effects of particle size of alumina on densification behavior during liquid-phase sintering of alumina-talc system were investigated with emphasis on particle rearrangement process. In the case of using coarse alu-mina powder densiication of specimens was rapidly accelerated after formation of liquid phase due to easy particle rearrangement process with addition of talc and increase of sintering temperature. On the contrary when fine alumina powder was used premature densification of alumina matrix region formed before for-mation of liquid phase rigid skeleton structure and then it seemed to inhibit rearrangement process during crease of sintering temperature. As results the densification of specimens using coarse alumina powder was higher than that of the case of using fine one.

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