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문석재(S. J. MOON),박승원(S. W PARK),안석환(S. W. AHN),김종순(J. S. KIM),남기우(K. W. NAM) 한국동력기계공학회 2008 한국동력기계공학회 학술대회 논문집 Vol.2008 No.11
Sialon was produced by hot-pressing the mixtures of Si<sub>3</sub>N<sub>4</sub>, AIN and Y<sub>2</sub>O<sub>3</sub> powders. Fracture toughness and Vickers hardness of smooth specimen were average 7.05 MPa·m<sup>0.5</sup> and Hν = 1580, respectively. Density of three kinds of specimens, smooth specimen, smooth and healed specimen, smooth with SiO<sub>2</sub> colloidal coating and healed specimen, had beyond 99 % of theoretical density. Bending strength of smooth healed specimens had high strength more than 1 GPa. Crack healed specimens recovered as strength as smooth specimen, That is, cracked specimen with SiO<sub>2</sub> colloidal coating on cracked part recovered strength by heat treatment' completely. Crack healing of Si3N4 composite ceramics had contributed SiO<sub>2</sub> glassy phase and Y<sub>2</sub>Al<sub>2</sub>O- crystal phase to strength recovery.
Y₂O₃의 첨가에 의한 Al₂O₃ 복합 세라믹스의 균열 치유 거동과 강도특성
김해숙(H. S. Kim),박승원(S. W. Park),손창석(C. S. Son),안석환(S. H. Ahn),남기우(K. W. Nam) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
Al₂O₃/SiC composite ceramics were sintered to evaluate the bending strength and behavior of crack healing. The three-point bending test was carried out under room temperature. The crack healing behavior was investigated from 1373 K to 1723 K. The bending strength of Al₂O₃/SiC composite by nanocomposite is higher than that of Al₂O₃ monolithic. Crack-healing behavior was depended on an amount of additive powder Y₂O₃. In Al₂O₃/SiC composite ceramics with 3 wt. % Y₂O₃ for additive powder, the bending strength at 1573 K is about 100% increase than that of the smooth specimens. The strength of Al₂O₃/SiC composite ceramics was a little higher than those of Al₂O₃ monolithic.
〈논문〉 SiO₂ 콜로이달 첨가량에 의한 Si₃N₄ 복합 세라믹스의 균열 치유와 굽힘 강도 특성
남기우(K. W. Nam),박승원(S. W. Park),박상현(S. H. Park),김종순(J. S. Kim),안석환(S. H. Ahn) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Crack-healing behavior of Si₃N₄ composite ceramics has been studied as functions of heat-treatment temperature and amount of additive SiO₂ colloidal. Results showed that optimum amount of additive SiO₂ colloidal and coating of SiO₂ colloidal on crack could significantly increase the bending strength. The heat-treatment temperature has a profound influence on the extent of crack healing and the degree of strength recovery. The optimum heat-treatment temperature depends on the amount of additive SiO₂ colloidal. Crack healing strength was far the better cracked specimen with SiO₂ colloidal coating on crack surface. After heat treatment at the temperature 1,273 K in air, the crack morphology almost entirely disappeared by scanning prob microscope. At optimum healing temperature 1,273 K, the bending strength with additive SiO₂ colloidal 0.0 wt.% without SiO₂ colloidal coating recovered to the value of the smooth specimens at room temperature for the investigated crack sizes 100 ㎛. But that with SiO₂ colloidal coating increase up to 140 %. The amount of optimum additive SiO₂ colloidal was 1.3 wt.% and crack healed bending strength with SiO₂ colloidal coating increase up to 160 % to smooth specimen of additive SiO₂ colloidal 0.0 wt.%. Crack closure and rebonding of the crack due to oxidation of cracked surfaces were suggested as a dominant healing mechanism operating in Si₃N₄ composite ceramics.
TiO₂첨가에 의한 Si₃N₄/SiC 복합 세라믹스의 굽힘강도와 균열치유 특성
김미경(M. K. Kim),박승원(S. W. Park),손창석(C. S. Son),안석환(S. H. Ahn),남기우(K. W. Nam) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.11
Si₃N₄/SiC composite ceramics was sintered in order to investigate their bending strength behavior after crack healing, Y₂O₃ and TiO₂ power was added as sintering additives to enhance it's sintering property. A three-point bending specimen was cut out from sintered plates. About 100 ㎛ semi-circular surface cracks were made on the center of the tension surface of the three-point bending specimen using Vickers indenter. After the crack-healing processing from 700 ℃ to 1300 ℃, for 1 h, in air, the bending strength behavior of these crack-healed specimen coated with SiO2₂ gel solution were determined systematically at room temperature. Si₃N₄/SiC ceramics using added powder (Y₂O₃+TiO₂) was superior to that of added powder Y₂O₃. The added powder TiO₂ exerted influence at growth of Si₃N₄. The optimum crack healing conditions coated with SiO2₂ colloidal were 1000 ℃ at Si₃N₄ using added powder (Y₂O₃+TiO₂), and 1300 ℃ at Si₃N₄ using added powder Y₂O₃.
소결보조재 Al₂O₃ 및 Y₂O₃ 첨가에 따른 Sialon 특성
남기우(K. W. Nam),문석재(S. J. Moon),박승원(S. W. Park),안석환(S.H. Ahn),김종순(J. S. Kim) 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-
Various Sialon ceramics were fabricated by hot-pressing mixtures of Si₃N₄, Y₂O₃ and Al₂O₃ powder. The polished specimen of SiAION Ⅰ~Ⅲ showed increased strength by heat treatment, heat treated non-polished specimen were similar or up in strength to polished specimen. The polished specimen of SiAIONN Ⅳ and Ⅴ showed a very high strength, but couldn't obtain increased strength by heat treatment, all specimens were fractured surfaces and inner flaws. Surfaces fractures were initiated from polished surface flaw and comer flaw. inner fractures were initiated from an internal defect.
〈논문〉SiO₂ 콜로이달 첨가에 의한 Si₃N₄ 복합 세라믹스의 Morphology
남기우(K. W. Nam),박승원(S. W. Park),김종순(J. S. Kim),안석환(S. H. Ahn) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Surface morphology of Si₃N₄ composite ceramics has been studied as functions of heat-treatment temperature and additive SiO₂. Additive SiO₂ colloidal and SiO₂ colloidal coating on crack could significantly increase the bending strength. Crack healing temperature decreased 300 K by additive TiO₂. Bending strength of specimen with additive SiO₂ is higher than that of non-additive SiO₂. Moreover, bending strength of specimen with SiO₂ colloidal coating is much higher that of non-coating specimen. In in-situ observation, crack-healed specimen at 1,573 K shows phenomenon like a fog on the surface. By SPM, both crack-healed specimen, non-coating and coating with SiO₂ colloidal, at 1,273 K were healed completely but both of 1,573 K exist crack. This was made by evaporation of SiO₂ at high temperature. Crack-healing materials of Si₃N₄ composite ceramics is crystallized Y₂Si₂O?, Y₂Ti₂O? and SiO₂. A large amount of Si and O, and little C were detected by EPMA. Si and a increase but C decreases according to heat treatment temperature. Specimens with additive SiO₂ were more detected Si and a than that of non-additive SiO₂. Specimen with SiO₂ colloidal coatings were much more detected O.