• Title/Summary/Keyword: Si3N4-Al2O3 joining

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Reduction of functionally graded material (FGM) layers for joining dissimilar ceramics in Si3N4-Al2O3 system using polytypoid functional gradients (폴리타이포이드 기능경사를 이용한 Si3N4-Al2O3 계 이종 세라믹 간 접합을 위한 기능경사재료(FGM) 적층의 저감)

  • Ryu, Sae-Hui;Park, Jong-Ha;Lee, Seon-Yeong;Lee, Jae-Cheol;An, Seong-Hun;Hong, Hyeon-Jeong;Ryu, Do-Hyeong
    • Proceedings of the Materials Research Society of Korea Conference
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    • 2007.11a
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    • pp.117.1-117.1
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    • 2007
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A Study for Joining of Silicon Nitride with Crystallized Glass Solder of $SiO_2-Al_2O_3-MgO$ System ($SiO_2-Al_2O_3-MgO$계 결정화 유리 솔더에 의한 질화규소의 접합에 관한 연구)

  • 안병국
    • Journal of Welding and Joining
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    • v.21 no.1
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    • pp.107-113
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    • 2003
  • Joining of $Si_3N_4$ to $Si_3N_4$ with crystallized glass solder was studied. $SiO_2-Al_2O_3-MgO$ glass with $P_2O_5$ as a crystallizing reagent was used as a solder. To improve the hish temperature toughness of joined specimen, two stage heat treatment was applied to Joined sample for the crystallization of joined layer, Two factors, i.e. thickness of soldered layer and crystallization were taken and thier effects on joining strength were investigated by a SEM-EDX observation of joined interface and bending strength both at room and elevated temperatures. Obtained results are summarized as follows: (1) Nitrogen diffused from $Si_3N_4$ to solder during the Joining process. Average amount of nitrogen in soldered layer depended on the thickness of the soldered layer and increased with decrease of the thickness. (2) Joining strength of the specimen having a thinner soldered layer was stronger than that of thicker layer. This can be mainly attributed to the difference of the nitrogen content in the soldered layer. (3) Higher content of nitrogen in solder brought forth higher viscosity of the solder. Hence the crystallization of the solder become more difficult in thinner layer of the solder than thicker one. (4) Thus, the effect of crystallization was evaluated mostly by the thicker layer specimen. Crystallization of soldered layer improved markedly the fracure strength of joining at higher temperatures than the softening temperature of glass solder.

Optimization of Crack-Free Polytypoidally Joined Dissimilar Ceramics of Functionally Graded Material (FGM) Using 3-Dimensional Modeling (폴리타이포이드 경사 방식으로 접합 된 이종 세라믹간의 적층 수의 최적화 및 잔류응력 해석에 대한 연구)

  • Ryu, Sae-Hee;Park, Jong-Ha;Lee, Sun-Yong;Lee, Jae-Sung;Lee, Jae-Chul;Ahn, Sung-Hoon;Kim, Dae-Keun;Chae, Jae-Hong;Riu, Do-Hyung
    • Korean Journal of Materials Research
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    • v.18 no.10
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    • pp.547-551
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    • 2008
  • Crack-free joining of $Si_3N_4\;and\;Al_2O_3$ using 15 layers has been achieved by a unique approach introducing Sialon polytypoids as a functionally graded materials (FGMs) bonding layer. In the past, hot press sintering of multilayered FGMs with 20 layers of thickness $500{\mu}m$ each has been fabricated successfully. In this study, the number of layers for FGM was reduced to 15 layers from 20 layers for optimization. For fabrication, model was hot pressed at 38 MPa while heating up to $1700^{\circ}$, and it was cooled at $2^{\circ}$/min to minimize residual stress during sintering. Initially, FGM with 15 layers had cracks near 90 wt.% 12H / 10 wt.% $Al_2O_3$ and 90 wt.% 12H/10 wt.% $Si_3N_4$ layers. To solve this problem, FEM (finite element method) program based on the maximum tensile stress theory was applied to design optimized FGM layers of crack free joint. The sample is 3-dimensional cylindrical shape where this has been transformed to 2-dimensional axisymmetric mode. Based on the simulation, crack-free FGM sample was obtained by designing axial, hoop and radial stresses less than tensile strength values across all the layers of FGM. Therefore, we were able to predict and prevent the damage by calculating its thermal stress using its elastic modulus and coefficient of thermal expansion. Such analyses are especially useful for FGM samples where the residual stresses are very difficult to measure experimentally.