• 제목/요약/키워드: Abnormal Grain Growth

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Effect of Crystal Shape on the Grain Growth during Liquid Phase Sintering of Ceramics

  • Jo, Wook;Hwang, Nong-Moon;Kim, Doh-Yeon
    • 한국세라믹학회지
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    • 제43권11호
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    • pp.728-733
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    • 2006
  • The equilibrium or growth shape of ceramic materials is classified largely into two categories according to the thermodynamic conditions imposed. One is a polyhedral shape where the surface free energy is anisotropic, and the other a spherical shape where the surface free energy is isotropic. In the case of grains with a polyhedral shape of anisotropic surface free energy, socalled abnormal grain growth usually takes place due to a significant energy barrier for a growth unit to be attached to the crystal surface. In the case of grains with a spherical shape of isotropic surface free energy, however, normal grain growth with a uniform size distribution takes place. In this contribution, the state-of-the-art of our current understanding of the relationship between the crystal shape and the microstructure evolution during the sintering of ceramic materials in the presence of a liquid phase was discussed.

CuO 첨가에 따른 $Y_3$Fe$_5$O$_{12}$ 소결체의 미세구조 변화 (Dependence of Microstructure of Sintered $Y_3$Fe$_5$O$_{12}$ in Addition of CuO)

  • 이재동;김광석;김성재;김태옥
    • 한국세라믹학회지
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    • 제35권10호
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    • pp.1014-1019
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    • 1998
  • As results of the study on the sinterbility of YIG at the low temperature using CuO as additive CuO com-pound which contain {{{{ { {Fe }_{2 }O }_{3 } }} was shown liquid in sintering process. YIG crystal dissolved into CuO compound liquid phase and then Y element which is considered no solubility in solid CuO compound moved to the grain during cooling. The abnormal grain growth up to 150${\mu}{\textrm}{m}$ at CuO 8.6mole% was shown due to shape accomdation reaction and local liquid distribution. The apparent density of YIG shows minimum at CuO 8.6 mole% due to abnormal grain growth and the saturation magnetization decrease dramatically at 32.5mole% due to orthoferrite formation.

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Model Calculation of Grain Growth in a Liquid Matrix

  • Jung, Yang-Il;Yoon, Duk-Yong;L.Kang, Suk-Joong
    • 한국분말야금학회:학술대회논문집
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    • 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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    • pp.70-71
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    • 2006
  • Growth behavior and kinetics of grains in a liquid matrix has been studied by computer simulation for various physical and processing conditions. The kinetics of growing and dissolving grains were considered to follow those of single crystals in a matrix. Depending on the shape of crystals, rounded or faceted, different kinetic equations were adopted for growing grains and an identical equation for dissolving grains. Effects of such critical parameters as step free energy, temperature, and liquid volume fraction were evaluated.

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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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    • 제47권3호
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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.

구리 기판에 전착시킨 니켈과 니켈합금의 집합조직 형성 (Texture Formation of Eletroplated Nickel and Nickel Alloy on Cu Substrate)

  • 김재근;이선왕;김호진;홍계원;이희균
    • Progress in Superconductivity
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    • 제7권2호
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    • pp.145-151
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    • 2006
  • Nickel and nickel-tungsten alloy were electroplated on a cold rolled and heat treated copper(Cu) substrate. 4 mm-thick high purity commercial grade Cu was rolled to various thicknesses of 50, 70, 100 and 150 micron. High reduction ratio of 30% was applied down to 150 micron. Rolled texture was converted into cube texture via high temperature heat treatment at $400-800^{\circ}C$. Grain size of Cu was about 50 micron which is much smaller compared to >300 micron for the Cu prepared using smaller reduction pass of 5%. 1.5 km-long 150 micron Cu was fabricated with a rolling speed of 33 m/min and texture of Cu was uniform along length. Abnormal grain growth and non-cube texture appeared for the specimen anneal above $900^{\circ}C$. 1-10 micron thick Ni and Ni-W film was electroplated onto an annealed cube-textured Cu or directly on a cold rolled Cu. Both specimens were annealed and the degree of texture was measured. For electroplating of Ni on annealed Cu, Ni layer duplicated the cube-texture of Cu substrate and the FWHM of in plane XRD measurement for annealed Cu layer and electroplated layer was $9.9^{\circ}\;and\;13.4^{\irc}$, respectively. But the FWHM of in plane XRD measurement of the specimen which electroplated Ni directly on cold rolled Cu was $8.6^{\circ}$, which is better texture than that of nickel electroplated on annealed Cu and it might be caused by the suppression of secondary recrystallization and abnormal grain growth of Cu at high temperature above $900^{\circ}C$ by electroplated nickel.

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비납계 (Na,K)NbO3-M(Cu,Nb)O3, (M = Ca, Sr, Ba) 압전 세라믹의 비정상 결정 성장 거동 비교 (Comparison of Abnormal Grain Growth Behavior of Lead-Free (Na,K)NbO3-M(Cu,Nb)O3, (M = Ca, Sr, Ba) Piezoelectric Ceramics)

  • 정승운;임지호;정한보;지성엽;최승곤;정대용
    • 한국재료학회지
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    • 제30권7호
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    • pp.343-349
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    • 2020
  • NKN [(Na,K)NbO3] is a candidate lead-free piezoelectric material to replace PZT [Pb(Zr,Ti)O3]. A single crystal has excellent piezoelectric-properties and its properties are dependent of the crystal orientation direction. However, it is hard to fabricate a single crystal with stoichiometrically stable composition due to volatilization of sodium during the growth process. To solve this problem, a solid solution composition is designed (Na,K)NbO3-Ba(Cu,Nb)O3 and solid state grain growth is studied for a sizable single crystal. Ceramic powders of (Na,K)NbO3-M(Cu,Nb)O3 (M = Ca, Sr, Ba) are synthesized and grain growth behavior is investigated for different temperatures and times. Average normal grain sizes of individual specimens, which are heat-treated at 1,125 ℃ for 10 h, are 6.9, 2.8, and 1.6 ㎛ for M = Ca, Sr, and Ba, respectively. Depending on M, the distortion of NKN structure can be altered. XRD results show that (NKN-CaCuN: shrunken orthorhombic; NKN-SrCuN: orthorhombic; NKN-BaCuN: cubic). For the sample heat-treated at 1,125 ℃ for 10 h, the maximum grain sizes of individual specimens are measured as 40, 5, and 4,000 ㎛ for M = Ca, Sr, and Ba, respectively. This abnormal grain size is related to the partial melting temperature (NKN-CaCuN: 960 ℃; NKN-SrCuN: 971 ℃; NKN-BaCuN: 945 ℃).

지르코니아 분말의 치밀화와 소결거동 : II. 소결거동 (Compaction and Sintering Behavior of Zirconia Powders : II. Sintering Behaviour)

  • 박홍채;김겸;김영우;이윤복;오기동
    • 한국세라믹학회지
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    • 제30권6호
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    • pp.449-456
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    • 1993
  • Sintering behaviour of zirconia powders prepared by different processing treatment was discussed. About >99% densities of theoretical were obtaiend on sintering at 140$0^{\circ}C$ for 2h in case of 300MPa uniaxially cold-pressed compact. But the lower densities were obtained on sintering above this temperature due to abnormal grain growth enabling the tetragonal to monoclinic phase transformation during cooling resulted in microcracks. All kinds of different dried powders exhibited nearly the same shrinkage behaviour with end-point shrinkage between 19 and 20%, and had maximum shrinkage rate (0.99~1.27%/min) around 120$0^{\circ}C$. During whole sintering process densification was mainly governed by grain growth and rearrangement of agglomerates. Heterogeneous abnormal grain growth and abrupt decrease in shrinkage were observed when continuous interagglomerate pore collapsed into isolated pores.

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트윈롤 주조 후 열간압연된 Mg-0.6wt.%Zn-0.6wt.%Ca 합금 판재의 열처리에 따른 결정립 성장 거동 (Grain Growth Behavior of Heat Treated Mg-0.6wt.%Zn-0.6wt.%Ca Alloy Sheet Manufactured via Twin Roll Casting and Hot Rolling)

  • 이희재;박노진
    • 열처리공학회지
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    • 제35권2호
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    • pp.74-81
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    • 2022
  • This study aims to mitigate the microstructural heterogeneity arising from the manufacture of magnesium alloy plates using the twin roll casting (TRC) process. Homogenization was introduced through hot rolling and heat treatment, followed by confirmation of observed changes in the microstructure. Following the TRC process, the hot rolled 2mm plate exhibited a dendritic cast structure tilted in the roll rotation direction, while central segregation were developed. This nonuniform structure and central segregation disappeared upon heat treatment, followed by recrystallization to form uniform and fine grains. Abnormal grain growth (AGG) was observed over the course of heat treatment; grains exhibiting AGG occupied up to 75% of the total area after having held the sample at 400℃ for 64 h. The formation of coarse grains was also observed during heat treatment at 340℃ over a relatively long duration, though the maximum grain size was significantly smaller than that corresponding to the heat treatment at 400℃. AGG in the 400℃ heat treatment occurred because of movement of the grain boundary, which had been fixed prior as a result of the grain boundary fixing effect of the precipitation phase. The re-dissolution of the Ca2Mg5Zn5 precipitated phase over the long duration of the high-temperature annealing process caused the surrounding grains to disappear and regrow.

방전플라즈마 소결 공정을 이용한 WC-Co-B4C 소재의 기계적 특성평가 (Mechanical Property Evaluation of WC-Co-B4C Hard Materials by a Spark Plasma Sintering Process)

  • 이정한;박현국
    • 한국재료학회지
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    • 제31권7호
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    • pp.397-402
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    • 2021
  • In this study, binderless-WC, WC-6 wt%Co, WC-6wt% 1 and 2.5 B4C materials are fabricated by spark plasma sintering process (SPS process). Each fabricated WC material is almost completely dense, with a relative density up to 99.5 % after the simultaneous application of pressure of 60 MPa. The WC added Co and Co-B4C materials resulted in crystalline growth. The WC with HCP crystal structure has respective interfacial energy (basal facet direction: 1.07 ~ 1.34 J·m-2, prismatic direction: 1.43 ~ 3.02 J·m-2) that depends on the grain growth direction. It is confirmed that the continuous grain growth, biased by the basal facet, which has relatively low energy, is promoted at the WC/Co interface. As abnormal grain growth takes place, the grain size increases more than twice from 0.37 to 0.8 um. It is found through analysis that the hardness property also greatly decreases from about 2661.4 to 1721.4 kg/mm2, along with the grain growth.