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김정,이갑호,홍순익,Kim, Joung,Lee, Kap-Ho,Hong, Sun-Ig 한국재료학회 2005 한국재료학회지 Vol.15 No.11
The ultrastructure ore of a nanostructured apatite film nucleated from solution was studied to gain insights into that of bone minerals which is the most important constituent to sustain the strength of bones. Needle-shaped apatite crystal plates with a bimodal size distribution $(\~100\;to\;\~1000 nm)$ were randomly distributed and they were found to grow parallel to the c-axis ([002]), driven by the reduction of surface energy. Between these randomly distributed needle-shaped apatite crystals which are parallel to the film, apatite crystals (20-40nm) with the normal of the grains quasi-perpendicular to the c-axis were observed. These observations suggest that the apatite film is the interwoven structure of apatite crystals with the c-axis parallel and quasi-perpendicular to the fan. In some regions, amorphous calcium phosphate, which is a precursor of apatite, was also observed. In the amorphous phase, small crystalline particle with the size of 2-3 nm were observed. These particles were quite similar, in size and shape, to those observed in the femoral trabecular bone, suggesting the nucleation of apatites by a biomimetic process in vitro is similar to that in vivo.
ASTM Gr.92강의 미세조직 및 기계적 성질에 미치는 템퍼링 온도 및 열처리경로의 영향
김연근 ( Yeon Keun Kim ),한창희 ( Chang Hee Han ),백종혁 ( Jong Hyuk Baek ),김성호 ( Sung Ho Kim ),이찬복 ( Chan Bock Lee ),홍순익 ( Sun Ig Hong ) 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.1
In order to investigate the effects of tempering temperature and heat-treatment path on the microstructural and mechanical properties of ASTM Gr.92 steels, foul samples with different tempering temperatures and heat-treatment paths were prepared. Three experimental steels showed tempered martensitic microstructures. but the sample tempered at 8l0℃ was presumed to retain partially untempered martensitic microstructures due to a lower α+γ phase regime. M23C6. V(C,N), and Nb(C.N) precipitates were observed in all samples. In addition, Cr2N was observed to be precipitated finely and uniformly by isothermal heat-treatment. The lath width and precipitate size increased with an increase of the tempering temperature. In particular, the lath width and precipitate size in the isothermal heat-treated samples were much smaller than those of the tempered-only specimens. Because of a fine and uniform precipitate, a reduction of lath width would enhance precipitation hardening, and it was shown that mechanical propertiesincluding the hardness and tensile properties of the steels were improved by isothermal heat-treatment.
면저항 45 ohms/sq.의 ITO/PET Sheets의 변형률 속도에 따른 균열 형성 거동
김진열,홍순익,Kim, Jin-Yeol,Hong, Sun-Ig 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.1
The stress-strain behavior and its effects on the crack initiation and growth of ITO film on PET substrate with a sheet resistance of 45 ohms/sq were investigated. Electrical resistance increased gradually at the strain of 0.7% in the elastic to plastic transition region of the stress strain curves. Numerous cracks were observed after 1% strain and the increase of the resistance can be linked to the cracking of ITO thin films. The onset strain for the increase of resistance increased with increasing strain rate, suggesting the crack initiation is dependent on the strain rate. Upon loading, the initial cracks perpendicular to the tensile axis were observed and propagated the whole sample width with increasing strain. The spacing between horizontal cracks is thought to be determined by the fracture strength and the interfacial strength between ITO and PET. The crack density increased with increasing strain. The spacing between horizontal cracks (perpendicular to the stress axis) increased with decreasing strain rate, The increase of crack density with decreasing strain rate can be attributed to the higher fraction of the plastic strain to the total strain at a given total strain. As the strain increased over 5% strain, cracks parallel to the stress axis were developed and increased in number with strain, accompanied by drastic increases of resistance.
20 nm 두께의 ITO층이 코팅된 ITO/PET Sheet의 저항 및 균열형성 특성 연구
김진열,홍순익 한국세라믹학회 2009 한국세라믹학회지 Vol.46 No.1
The crack formation and the resistance of ITO film on PET substrate with a thickness of 20 ㎚ were investigated as a function of strain. The onset strain for the increase of resistance increased with increasing strain rate, suggesting the crack initiation is dependent on the strain rate. Electrical resistance increased at the strain of 1.6% at the strain rates below 10−4 /sec while it increased at ~2% at the strain rates above 10−3 /sec. The critical strain at which the cracks were formed is close to the proportional limit. Upon loading, the initial cracks perpendicular to the tensile axis were observed and propagated the whole sample width with increasing strain. The spacing between horizontal cracks is thought to be determined by the fracture strength and the interfacial strength between ITO and PET. The crack density increased with increasing strain. However, the effect of the strain rate on the crack density was less pronounced in ITO/PET with 20 nm ITO thickness than ITO/PET with 125 nm ITO thickness, the strength of ITO film is thought to increase as the thickness of ITO film decreases. The absence of cracks on ITO film at a strain as close as 1.5% can be attributed to the compressive residual stress of ITO film which was developed during cooling after the coating process. The higher critical strain for the onset of the resistance increase and the crack initiation of ITO/PET with a thinner ITO film (20 nm) can be linked with the higher strength of the thinner ITO film. The crack formation and the resistance of ITO film on PET substrate with a thickness of 20 ㎚ were investigated as a function of strain. The onset strain for the increase of resistance increased with increasing strain rate, suggesting the crack initiation is dependent on the strain rate. Electrical resistance increased at the strain of 1.6% at the strain rates below 10−4 /sec while it increased at ~2% at the strain rates above 10−3 /sec. The critical strain at which the cracks were formed is close to the proportional limit. Upon loading, the initial cracks perpendicular to the tensile axis were observed and propagated the whole sample width with increasing strain. The spacing between horizontal cracks is thought to be determined by the fracture strength and the interfacial strength between ITO and PET. The crack density increased with increasing strain. However, the effect of the strain rate on the crack density was less pronounced in ITO/PET with 20 nm ITO thickness than ITO/PET with 125 nm ITO thickness, the strength of ITO film is thought to increase as the thickness of ITO film decreases. The absence of cracks on ITO film at a strain as close as 1.5% can be attributed to the compressive residual stress of ITO film which was developed during cooling after the coating process. The higher critical strain for the onset of the resistance increase and the crack initiation of ITO/PET with a thinner ITO film (20 nm) can be linked with the higher strength of the thinner ITO film.