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기계적합금화로 제조된 Ni-20Cr-20Fe-5Nb 합금에서 PCA로서 H<sub>2</sub>O의 역할과 시효석출거동
김일호,권숙인,이원식,채수원,황선근,김명호,Kim Il-Ho,Kwun S.I.,Lee Won-Sik,Chae S.W.,Hwang S.K.,Kim M.H. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.3
The effect of use of $H_2O$ as PCA(process control agent) to prevent the carbon contamination during mechanical alloying process and the precipitation behavior in Ni-20Cr-20Fe-5Nb bulk alloy after aging were investigated. NbC and $Cr_2O_3$ were formed during mechanical alloying and consolidation processes in the Ni-20Cr-20Fe-5Nb alloy in which methanol($CH_3OH$) was added as PCA. Formation of NbC in this alloy decreased the amount of Nb dissolved in the Ni matrix. The use of $H_2O$ as PCA in Ni-20Cr-20Fe-5Nb alloy prevented the formation of NbC and increased the hardness. The increase of hardness in this alloy was attributed to the increased amount of Nb dissolved in the Ni matrix. After aging treatment for 20 hours at $600^{\circ}C\;and\;720^{\circ}C$ of Ni-20Cr-20Fe-5Nb bulk alloy in which $H_2O$ added as PCA, ${\gamma}"$$(Ni_3Nb,\;tetragonal)\;and\;{\delta}\;(Ni_3Nb,\;orthorhombic)$ precipitates were formed, respectively. The precipitation temperatures of ${\gamma}"$ and ${\delta}$ in this bulk alloy were lower than those in commercial IN 718 alloy. It seemed that the lower precipitation temperatures for ${\gamma}"$ and ${\delta}$ in this bulk alloy than in commercial IN 718 alloy were due to severe plastic deformation during mechanical alloying.
Skutterudite CoSb<sub>3</sub>의 합성 및 열전특성
김일호,유신욱,박종범,이정일,어순철,장경욱,최국선,김준수,김현주,Kim I. H.,You S. W.,Park J. B.,Lee J. I.,Ur S. C.,Jang K. W.,Choi G. S.,Kim J. S.,Kim H. J. 한국재료학회 2005 한국재료학회지 Vol.15 No.10
Binary skutterudite $CoSb_3$ compounds were prepared by the arc melting and hot pressing processes and their thermoelectric properties were investigated in the range from 300 to 600 K. Annealing effect was correlated to phase transformation and homogenization. Thermoelectric properties of the arc-melted and hot-pressed $CoSb_3$ were discussed and compared. Undoped intrinsic $CoSb_3$ prepared by the arc melting showed p-type conduction, while it showed metallic behavior with increasing measuring temperature. However, hot pressed specimens showed n-type conduction, possibly due to Sb evaporation. Thermoelectric properties were remarkably improved by annealing In vacuum and they were closely related to phase transformation.
아크용해법으로 제조된 Skutterudite CoSb<sub>3</sub>의 열전특성
유신욱,박종범,조경원,장경욱,어순철,이정일,김일호,Yu S.W.,Park J.B.,Cho K.W.,Jang K.W.,Ur S.C.,Lee J.I.,Kim I.H. 한국재료학회 2005 한국재료학회지 Vol.15 No.2
The arc melting was employed to prepare undoped $CoSb_3$ compounds and their thermoelectric properties were investigated. Specimen annealed at $400^{\circ}C$ for 24 hrs showed sound microstructure. However, considerable voids and cracks were found after annealing at above $500^{\circ}C$. It seems to be attributed to the phase dissociation and thermal expansion due to phase transitions during annealing and cooling. Single phase $\delta-CoSb_3$ was successfully obtained by annealing at $400^{\circ}C$ for 24 hrs. In the case of increasing annealing temperature, phase decompositions occurred. Undoped $CoSb_3$ showed p-type conduction and intrinsic semiconducting behavior at all temperatures examined. Thermoelectric properties were remarkably improved by annealing and they were closely related to phase transitions.
유도용해법으로 제조된 Co<sub>1-x</sub>Nb<sub>x</sub>Sb<sub>3</sub>의 열전특성
박종범,유신욱,조경원,장경욱,이정일,어순철,김일호,Park J.B.,You S.W.,Cho K.W.,Jang K.W.,Lee J.I.,Ur S.C.,Kim I.H. 한국재료학회 2005 한국재료학회지 Vol.15 No.2
The induction melting was employed to prepare Nb-doped $CoSb_3$ skutterudites and their thermoelectric properties were investigated. Single phase $\delta-CoSb_3$ was successfully obtained by induction melting and subsequent annealing at $400^{\circ}C$ for 2 hrs in vacuum. The positive signs of Seebeck coefficients for all the specimens revealed that Nb atoms acted as p-type dopants by substituting Co atoms. Electrical conductivity decreased and then increased with increasing temperature, indicating mixed conduction behavior. Electrical conductivity increased by Nb doping, and it was saturated at high temperature. Maximum value of the thermoelectric power factor was shifted to higher temperature with increasing the amount of Nb doping, mainly originated from the high Seebeck coefficient around mixed conduction temperature and high electrical conductivity.
이원식(W.S. Lee),고세현(S.H. Ko),장진만(J.M. Jang),김일호(I.H. Kim) 한국소성가공학회 2009 한국소성가공학회 학술대회 논문집 Vol.2009 No.5
Manufacturing technology of micro spur gear and micro mold by micro PIM were studied with stainless steel feedstock. For molding of gears, micro mold with gear cavity of 1.2㎜ in diameter was produced by wire EDM. The proper injection pressure was selected to 70bar by observation and measuring of shapes and shrinkage of gears before/after sintering. For fabrication of micro mold, a tiny polymer gear was produced by injection into the mold. Then, 316L feedstock was again injected/compressed on the polymer gear and debinded together with polymer gear followed by sintering. As a result, another metal mold with gear cavity reduced to about 20% was fabricated and through repetition of this process chain, micro gear mold with cavity about below 800 um was finally obtained. In reduction of size by injection/compression molding, height of gear tooth was shrunk more and the effort for decrease of roughness of micro cavity were carried out ultrasonic polishing and as a result, the roughness in cavity decreased from 3-4 um to about 200nm.
PMN-PZT계 세라믹스의 압전특성에 미치는 MnO<sub>2</sub>의 영향
김재창,황동연,이미영,유신욱,김영민,어순철,김일호,Kim J.-C,Hwang D.-Y,Lee M.-Y,You S.-W,Kim Y.-M,Ur S.-C,Kim I.-H 한국재료학회 2004 한국재료학회지 Vol.14 No.5
Perovskite PMN-PZT-based ceramics were prepared and the$ MnO_2$ doping effects on their piezoelectric properties were investigated. Grain size decreased with increasing the $MnO_2$ content, and the pyrochlore phase was not identified in the sintered PMN-PZT ceramics with 0.01~1.0wt% $MnO_2$. Piezoelectric voltage and charge constants were reduced and mechanical quality factor increased with increasing the $MnO_2$ content. However, electromechanical coupling coefficient slightly decreased with increasing the MnO$_2$ content without regard to the grain size.
Pb(Ni<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-PZT 세라믹스 고용체에서 과잉 NiO첨가에 따른 압전특성 변화
최용길,손영진,권준철,조경원,윤만순,김일호,김영민,어순철,Choi Y. G.,Son Y. J.,Kweon J. C.,Cho K. W.,Yoon M. S.,Kim I. H.,Kim Y. M.,Ur S. C. 한국재료학회 2005 한국재료학회지 Vol.15 No.6
Perovskite $Pb(Ni_{1/3}Nb_{2/3})O_3-Pb(Zr,Ti)O_3[PNN-PZT]$ ceramics were synthesized by conventional ceramic processing technique. In order to modify piezoelectric properties for sensor application in this system, NiO addition was considered to provide $Ni^{+2}$ as an acceptor, which was known to occupy with B site in the structure. The effect of NiO addition up to $8\;mol\%$ on the following piezoelectric properties as well as sintering properties was investigated. When NiO added more than $1\;mol\%$, average grain size was decreased and second phase was found to form. Moreover, the second phase caused decrease in relative dielectric constant $(\varepsilon_{33}T/\varepsilon0)$, electro-mechanical coupling factor $(k_p)$, and piezoelectric charge constant $(d_{33})$, while increasing mechanical quality factor $(Q_m)$. When $1\;mol\%$ NiO was added, density, dielectric properties and piezoelectric properties were abruptly increased.