• Title, Summary, Keyword: Pressureless sintering

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Microstructures and Mechanical Properties of Pressureless and Spark Plasma Sintered ZrO2(3 mol%Y2O3) Bodies

  • Shin, Na-Young;Han, Jae-Kil;Lee, Hae-Hyoung;Lee, Byong-Taek
    • Journal of the Korean Ceramic Society
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    • v.42 no.2
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    • pp.140-144
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    • 2005
  • The microstructures and mechanical properties of Tetragonal Zirconia Polycrystals (TZP) sintered bodies, which made by pressureless and spark plasma sintering techniques, were investigated using XRD, SEM, and TEM techniques. In the spark plasma sintered samples, the TZP grains were equiaxed type including many sub-grain boundaries regardless of sintering conditions. The biaxial strength of TZP having an average of 80 nm grains in diameter was high in value with 1025 MPa, but fracture toughness showed a low value due to the absence of a fracture toughening mechanism such as transformation toughening. In the Pressureless Sintered (PLSed) samples, the grain size of TZP was strongly dependent on the sintering temperature; i.e., it gradually increased as the sintering temperature increased. The value of fracture toughness increased as the grain size increased by the stress-induced phase transformation and Borne crack deflection.

Analysis for Densification Behavior and Grain Growth of Nanocrystalline Ceramic Powder under High Temperature (나노 세라믹 분말의 고온 치밀화와 결정립 성장의 해석)

  • 김홍기;김기태
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.11
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    • pp.2749-2761
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    • 2000
  • Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing. Finite element results by using the proposed model also well predicted experimental data in the literature for densification behavior of nanocrystalline zirconia powder during pressureless sintering and sinter forging.

Pressureless Sintering and Spark-Plasma Sintering of Fe-TiC Composite Powders (Fe-TiC 복합재료 분말의 상압소결과 방전플라즈마소결)

  • Lee, B.H.;Bae, S.W.;Bae, S.W.;Khoa, H.X.;Kim, Ji Soon
    • Journal of Korean Powder Metallurgy Institute
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    • v.22 no.4
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    • pp.283-288
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    • 2015
  • Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-TiC composite powders which are fabricated by high-energy ball-milling. A powder mixture of Fe and TiC is prepared in a planetary ball mill at a rotation speed of 500 rpm for 1h. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts show incomplete densification with a relative denstiy of 86.1% after sintering at $1300^{\circ}C$ for 3h. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly complete densification of 98.6% relative density under the sintering pressure of 50 MPa.

Phase and Microstructure of SiC-AlN Ceramics Prepared by Pressureless Sintering (상압소결에 의하여 제조된 SiC-AlN 세라믹스의 상 및 미세구조)

  • Choi, Woong;Lee, Jong-Kook;Cho, Duk-Ho;Kim, Hwan
    • Journal of the Korean Ceramic Society
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    • v.32 no.11
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    • pp.1308-1314
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    • 1995
  • Changes in phase and microstructure were investigated in the SiC-AlN ceramics prepared by pressureless sintering using yttrium aluminum garnet (YAG) as a sintering aid at 200$0^{\circ}C$ and 210$0^{\circ}C$. The SiC/AlN ratio made a remarkable difference in densification, phase relations and the morphology of grains. In the AlN-rich composition, major phase was 2H and microstructure was composed of the densified equiaxed grains irrespective of the sintering temperatures. While those sintered at 200$0^{\circ}C$ were porous with major phase being 3C, the rod-like and the equiaxed grains were coexisted when sintered at 210$0^{\circ}C$ in the SiC-rich composition.

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Microstructure and Mechanical Properties of Self-Reinforced Si3N4 Ceramic Prepared by Pressureless-Sintering (상압소결에 의해 제조한 자체 강인화 질화규소 세리믹의 미세조직과 기계적 성질)

  • 김완중;이영규;조원승;최상욱
    • Journal of the Korean Ceramic Society
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    • v.36 no.5
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    • pp.547-554
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    • 1999
  • The self-reinforced Si3N4 ceramics were prepared by pressureless-sintering using ${\beta}$-Si3N4 whiskers as a seed. Effects of ${\beta}$-Si3N4 whiskers on microstructure and mechanical properties and the ${\alpha}$ to ${\beta}$ phase transition of Si3N4 were investigated. The self-reinforced Si3N4 ceramics were densified(relative density$\geq$98%) by pressureless-sintering (1800$^{\circ}C$ 2h) using 8mol% Y2O3 and 6mol% Al2O3 as sintering aids and 5 vol% ${\beta}$-Si3N4 whiskers within self-reinforced Si3N4 ceramic seemed to hinder the densification owing to their acicular shapes but accelerated the ${\alpha}$ to ${\beta}$ phase transition because they acted as pre-existing nuclei. It was found that the more ${\beta}$-Si3N4 nucei the faster ${\alpha}$ to ${\beta}$ phase transition.

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Near-Net-Shape Forming and Finite Element Analysis for Ceramic Powder Under Cold Combination Pressing and Pressureless Sintering (냉간 조합압축과 상압소결에 의한 세라믹 분말의 정밀정형과 유한요소해석)

  • Kim, Hong-Gi;Lee, Hyeong-Man;Kim, Gi-Tae
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.24 no.2
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    • pp.526-534
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    • 2000
  • Near-net-shape forming of zirconia powder was investigated under the combination of cold die and isostatic pressing and pressureless sintering. A novel combination pressing technique, i.e., die com paction under cold isostatic pressing, allowed to produce a complex shaped ceramic powder compact with the controlled dimensions and relatively uniform density distributions. The constitutive models proposed by Kim and co-workers for densification of ceramic powder under cold compaction and high temperature were implemented into a finite element program (ABAQUS). Experimental data for relative density distributions and deformations of zirconia powder compacts produced by cold combination pressing and pressureless sintering were compared with finite element results. Finite element results agreed well with experimental data.

Thermal Shock and Hot Corrosion Resistance of Si3N4 Fabricated by Nitrided Pressureless Sintering (질화상압(NPS)법으로 제조한 질화규소의 열충격 저항성 및 내부식성 특성평가)

  • Kwak, Kil-Ho;Kim, Chul;Han, In-Sub;Lee, Kee-Sung
    • Journal of the Korean Ceramic Society
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    • v.46 no.5
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    • pp.478-483
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    • 2009
  • Thermal shock and hot corrosion resistance of silicon nitride ceramics are investigated in this study. Silicon nitrides are fabricated by nitride pressureless sintering (NPS) process, which process is the continuous process of nitridation reaction of Si metal combined with subsequent pressureless sintering. The results of thermal shock test show it sustains 400MPa of initial strength during test in the designated condition of ${\Delta}T=700{\sim}25^{\circ}C$ up to maximum 4,800 cycles. Hot corrosion tests also reveal that the strength degradation of NPS silicon nitride did not occur at $700^{\circ}C$ with an exposure in Ar, $H_2$, Na and K for 1,275 h.

Sinterability of Low-Cost 3Y-ZrO2 Powder and Mechanical Properties of the Sintered Body

  • Kim, Min-Sung;Go, Shin-Il;Kim, Jin-Myung;Park, Young-Jo;Kim, Ha-Neul;Ko, Jae-Woong;Jung, Seung-Hwa;Kim, Jae-Yuk;Yun, Jon-Do
    • Journal of the Korean Ceramic Society
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    • v.54 no.4
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    • pp.285-291
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    • 2017
  • This study investigated the effects of grain size and phase constitution on the mechanical properties of $3Y-ZrO_2$ by varying the sintering conditions. The raw powder prepared by a low-cost wet milling using the coarse solid oxide powders was sintered by both pressureless sintering and hot-pressing, respectively. As increasing holding time at $1450^{\circ}C$ for pressureless sintering, it promoted the microstructural coarsening of matrix grains and the phase transformation to tetragonal phase, whereas the bimodal microstructure embedded with abnormal $cubic-ZrO_2$ grains was observed regardless of sintering time. On the other hand, the specimens hot-pressed at $1300^{\circ}C$ for 2 h reached ~ 97% of relative density with homogeneous fine microstructure and mixed phase constitution. It was found that the proportion of untransformed monoclinic zirconia had the most adverse effect on the biaxial strength compared to the impacts of grain size and density. The pressureless sintering of the low-cost powder for prolonged sintering time to 8 h led to a decent combination of mechanical properties ($H_V=13.2GPa$, $K_{IC}=8.16MPa{\cdot}m^{1/2}$, ${\sigma}=981MPa$).

Influence of Sintering Condition on Characteristics of $\alpha$-SiC Ceramics ($\alpha$-SiC 소결체의 특성에 미치는 소성조건의 영향)

  • 정두화;김인술;김효준
    • Journal of the Korean Ceramic Society
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    • v.28 no.10
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    • pp.824-830
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    • 1991
  • $\alpha$-SiC(B; 0.4 wt, C; 3 wt%) was sintered in Ar atmosphere from 205$0^{\circ}C$ to 220$0^{\circ}C$ by means of pressureless sintering and gas pressure sintering in order to find optimum sintering condition of $\alpha$-SiC. Mechanical properties and microstructures of sintered bodies were investigated according to sintering method. The effect of sintering condition on sinterability of $\alpha$-SiC was also examined by using the dilatometer. 97.5% and 98.8% of theoretical density were obtained from pressureless sintering and gas pressure sintering of $\alpha$-SiC powder, respectively. And modulus of rupture was measured as 270~350 MPa and 420 MPa respectively.

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Sintering of Fe-30 wt% TiC Composite Powders Fabricated from (Fe, TiH2, C) Powder Mixture ((Fe, TiH2, C) 혼합 분말로부터 제조된 Fe-30 wt% TiC 복합재료 분말의 소결)

  • Lee, Byunghoon;Kim, Ji Soon
    • Journal of Korean Powder Metallurgy Institute
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    • v.22 no.5
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    • pp.356-361
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    • 2015
  • Fe-30 wt% TiC composite powders are fabricated by in situ reaction synthesis after planetary ball milling of (Fe, $TiH_2$, Carbon) powder mixture. Two sintering methods of a pressureless sintering and a spark-plasma sintering are tested to densify the Fe-30 wt% TiC composite powder compacts. Pressureless sintering is performed at 1100, 1200 and $1300^{\circ}C$ for 1-3 hours in a tube furnace under flowing argon gas atmosphere. Spark-plasma sintering is carried out under the following condition: sintering temperature of $1050^{\circ}C$, soaking time of 10 min, sintering pressure of 50 MPa, heating rate of $50^{\circ}C/min$, and in a vacuum of 0.1 Pa. The curves of shrinkage and its derivative (shrinkage rate) are obtained from the data stored automatically during sintering process. The densification behaviors are investigated from the observation of fracture surface and cross-section of the sintered compacts. The pressureless-sintered powder compacts are not densified even after sintering at $1300^{\circ}C$ for 3 h, which shows a relative denstiy of 66.9%. Spark-plasma sintering at $1050^{\circ}C$ for 10 min exhibits nearly full densification of 99.6% relative density under the sintering pressure of 50 MPa.