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Neutron Radiography를 이용한 고탄소흑연강에서 붕소 분석
우기도,양창호,박희찬,이창희,심철무,장진성,김현경,U, Gi-Do,Yang, Chang-Ho,Park, Hui-Chan,Lee, Chang-Hui,Sim, Cheol-Mu,Jang, Jin-Seong,Kim, Hyeon-Gyeong 한국재료학회 2001 한국재료학회지 Vol.11 No.12
To study the distribution of boron and the boron effect for nucleation of graphite in high carbon steel, neutron induced autoradiography method is used. High carbon steel is easy to make the graphitization by addition of boron. It is easy to analysis of boron distribution using neutron radiography with neutron fluence of $1.9$\times${\times}10^{13}/cm^2$in the boron added high carbon steel. By the neutron induced autoradiography technique, it was found that the distribution of boron depended on boron content, graphitiging temperature and time. And by the analysis of secondary ion mass spectroscopy (SIMS) and electron probe micro analysis (EPMA), boron or boride were acted at nucleation site of graphite in high carbon steel.
우기도,김동건,이현범,문민석,기웅,권의표,Woo, Kee-Do,Kim, Dong-Keon,Lee, Hyun-Bom,Moon, Min-Seok,Ki, Woong,Kwon, Eui-Pyo 한국재료학회 2008 한국재료학회지 Vol.18 No.6
Single-crystal $ZnIn_2S_4$ layers were grown on a thoroughly etched semi-insulating GaAs (100) substrate at $450^{\circ}C$ with a hot wall epitaxy (HWE) system by evaporating a $ZnIn_2S_4$ source at $610^{\circ}C$. The crystalline structures of the single-crystal thin films were investigated via the photoluminescence (PL) and Double-crystal X-ray rocking curve (DCRC). The temperature dependence of the energy band gap of the $ZnIn_2S_4$ obtained from the absorption spectra was well described by Varshni's relationship, $E_g(T)=2.9514\;eV-(7.24{\times}10^{-4}\;eV/K)T2/(T+489K)$. After the as-grown $ZnIn_2S_4$ single-crystal thin films was annealed in Zn-, S-, and In-atmospheres, the origin-of-point defects of the $ZnIn_2S_4$ single-crystal thin films were investigated via the photoluminescence (PL) at 10 K. The native defects of $V_{Zn}$, $V_S$, $Zn_{int}$, and $S_{int}$ obtained from the PL measurements were classified as donor or acceptor types. Additionally, it was concluded that a heat treatment in an S-atmosphere converted $ZnIn_2S_4$ single crystal thin films into optical p-type films. Moreover, it was confirmed that In in $ZnIn_2S_4$/GaAs did not form a native defects, as In in $ZnIn_2S_4$ single-crystal thin films existed in the form of stable bonds.
자동차 차체재료용 Al-Mg-Si-(Cr,Be) 합금의 기계적 성질에 관한 연구
우기도(Kee Do Woo),이종수(Jong Soo Lee),이민상(Min Sang Lee),김석원(Sug Won Kim) 한국주조공학회 1999 한국주조공학회지 Vol.19 No.2
N/A Al-Mg-Si alloys have good strength, formability, corrosion resistance, and bake hardenability. But there is a weak point to use for the auto body materials. This is because the strength of this alloy was decreased by the precipitation of G.P.I zone formed at room temperature for a long holding time. In practical usage, it is inevitable to hold at room temperature prior to paint baking. The present work is aimed to improve bake hardenability using special heat treatments such as two step aging, and retrogressing and reaging(RRA) in Al-Mg-Si-(Cr, Be) alloys. A differencial scanning calorimeter and tensile test were employed to investigate the precipitation behaviors and the mechanical properties in Al-Mg-Si alloys. The tensile strength of Al-Mg-Si-Be and Al-Mg-Si-Cr-Be alloys were improved by special heat treatments such as two step aging and RRA treatment after pre-aged at 120 and 150˚C for 4 hrs. The combination between strength and ductility of the Cr, Be containing Al-Mg-Si alloy is better than those of no addition of Cr,Be in Al-Mg-Si alloy. (Received February 2,1999)
생체의학 임플란트재료로서 Ti-Nb계 합금의 조직과 기계적 성질에 미치는 HEMM의 영향
우기도,최갑송,이현범,김인용,Woo, Kee-Do,Choi, Gab-Song,Lee, Hyun-Bum,Kim, In-Yong,Zhang, Deliang 한국재료학회 2007 한국재료학회지 Vol.17 No.11
Al-42wt%Nb powder was prepared by high-energy mechanical milling(HEMM). The particle size, phase transformation and microstructure of the as-milled powder were investigated by particle size distribution (PSD) analyzer, scanning electron microscopy (SEM), X-ray diffractometery (XRD), transmission electron microscopy (TEM)and differential thermal analysis (DTA). The milled powders were heated to a sintering temperature at 1000C with under vaccum with vaccum tube furnace. Microstructural examination of sintered Ti-42wt%Nb alloy using 4h-milled powder showed Ti-rich phases (${\alpha}$-Ti) which are fine and homogeneously distributed in the matrix (Nb-rich phase: ${\beta}$-Ti). The sintered Ti-42wt%Nb alloy with milled powder showed higher hardness. The microstructure of the as quenched specimens fabricated by sintering using mixed and milled powder almost are same, but the hardness of as quenched specimen fabricated by using mixed powder increased due to solution hardening of Nb in Ti matrix. The aging effect of these specimens on microstructural change and hardening is not prominent.
SPS로 제조된 HA/β-TCP 복합재의 기공의 크기와 분포에 미치는 지지체 량의 영향
이택,우기도,강동수,이해철,장준호,Lee, Tack,Woo, Kee-Do,Kang, Dong-Soo,Lee, Hae-Cheol,Jang, Jun-Ho 한국재료학회 2015 한국재료학회지 Vol.25 No.4
Ceramics biomaterials are useful as implant materials in orthopedic surgery. In this study, porous HA(hydroxyapatite)/${\beta}$-TCP(tricalcium phosphate) composite biomaterials were successfully fabricated using HA/${\beta}$-TCP powders with 10-30 wt% $NH_4HCO_3$ as a space holder(SH) and $TiH_2$ as a foaming agent, and MgO powder as a binder. The HA/${\beta}$-TCP powders were consolidated by spark plasma sintering(SPS) process at $1000^{\circ}C$ under 20 MPa conditions. The effect of SH content on the pore size and distribution of the HA/${\beta}$-TCP composite was observed by scanning electron microscopy(SEM) and a microfocus X-ray computer tomography system(SMX-225CT). These microstructure observations revealed that the volume fraction of the pores increased with increasing SH content. The pore size of the HA/${\beta}$-TCP composites is about $400-500{\mu}m$. The relative density of the porous HA/${\beta}$-TCP composite increased with decreasing SH content. The porous HA/${\beta}$-TCP composite fabricated with 30%SH exhibited an elastic modulus similar to that of cortical bone; however, the compression strength of this composite is higher than that of cortical bone.
AOD공정으로 재활용된 니켈합금의 산소주입량에 따른 조직과 기계적 성질 변화
이덕희,우기도,강황진,윤진호,Lee, Duk-Hee,Woo, Kee-Do,Kang, Whang-Jin,Yoon, Jin-Ho 한국자원리싸이클링학회 2016 資源 리싸이클링 Vol.25 No.2
본 연구에서는 Inconel 713C 스크랩을 원료로 아르곤-산소 탈탄 공정을 이용하여 니켈계 초내열합금을 재활용 하였다. 아르곤-산소 탈탄 공정에서 아르곤은 1,000 sccm으로 지속적으로 주입되었고 산소는 100, 250, 500 sccm의 유량으로 10, 20, 30 분씩 주입되었다. 산소 주입 초기 단계에서는 산소 양이 증가하면서 Al, Cr, 및 Mo 함량은 증가하였고 탄소 함량은 감소하였다. 그리고 Al 함유량은 탄소의 반응이 끝난 후 Al, Cr 등의 원소와 산화가 일어났기 때문에 첨가원소와 탄소의 반응에 의해 감소하였다. 결과적으로, Al 함유량이 감소하였기 때문에 ${\gamma}^{\prime}$상이 줄어들었으며 이는 Al이 ${\gamma}^{\prime}$을 형성하는 주요 원소이기 때문이다. 또한, 탄소의 양이 줄어들면서 탄화물도 줄어들었으며 산소가 과잉 공급된 시료의 기계적인 물성(강도, 경도 등)은 감소하게 된다. In this study, the Ni base superalloy was recycled by Argon oxygen decarburization(AOD) process using an inconel 713C scrap. During AOD process, argon gas was continuously injected 1,000 sccm and oxygen gas was injected into 10, 20 and 30 minutes of 100, 250 and 500 sccm.. In early stage of oxygen injection, the oxygen dose increased with increasing Al, Cr, and Mo content and decreasing C content. And Al content was decreased by carburization with added elements in late stage Because of oxidation was occurred with Al, Cr etc. after the reaction of carbon has been finished. From the results, the ratio of ${\gamma}^{\prime}$ phase reduced due to decreasing of Al content for that reason Al is the main element to form the ${\gamma}^{\prime}$ phase. Also carbide reduced owing to decreasing of C content so the mechanical properties of the specimens excessively injected by excess $O_2$ gas were decreased.
고에너지 밀링분말과 급속소결을 이용한 Ti-Nb-Zr-HA 생체복합재의 기계적 성질 및 생체적합성
박상훈,우기도,김상혁,이승민,김지영,고혜림,김상미,Park, Sang-Hoon,Woo, Kee-Do,Kim, Sang-Hyuk,Lee, Seung-Min,Kim, Ji-Young,Ko, Hye-Rim,Kim, Sang-Mi 한국재료학회 2011 한국재료학회지 Vol.21 No.7
Ti-6Al-4V ELI (Extra Low Interstitial) alloy has been widely used as an alternative to bone due to its excellent biocompatibility. However, it still has many problems, including a high elastic modulus and toxicity. Therefore, nontoxic biomaterials with a low elastic modulus should be developed. However, the fabrication of a uniform coating is challenging. Moreover, the coating layer on Ti and Ti alloy substrates can be peeled off after implantation. To overcome these problems, it is necessary to produce bulk Ti and Ti alloy with hydroxyapatite (HA) composites. In this study, Ti, Nb, and Zr powders, which are biocompatible elements, were milled in a mixing machine (24h) and by planetary mechanical ball milling (1h, 4h, and 6h), respectively. Ti-35%Nb-7%Zr and Ti-35%Nb-7%Zr-10%HA composites were fabricated by spark plasma sintering (SPS) at $1000^{\circ}C$ under 70MPa using mixed and milled powders. The effects of HA addition and milling time on the biocompatibility and physical and mechanical properties of the Ti-35%Nb-7%Zr-(10%HA) alloys have been investigated. $Ti_2O$, CaO, $CaTiO_3$, and $Ti_xP_y$ phases were formed by chemical reaction during sintering. Vickers hardness of the sintered composites increases with increased milling time and by the addition of HA. The biocompatibilty of the HA added Ti-Nb-Zr alloys was improved, but the sintering ability was decreased.
Al-Li계 합금의 가공열처리에 따른 조직과 기계적성질의 변화
김기원,우기도,이광로,이민상,이민호,황호을 ( Ki Won Kim,Kee Do Woo,Kwang Ro Lee,Min Sang Lee,Min Ho Lee,Ho Eul Hwang ) 한국열처리공학회 1991 熱處理工學會誌 Vol.4 No.3
The present work was aimed to examine the variation of precipitations and mechanical properties by thermomechanical treatments(TMT) in Al-2.19wt%Li and Al-2.0wt%Li-0.11wt%Zr alloys. This study was perfomed by TEM, SEM observation, DSC, electrical resistance measurement, hardness and tensile strength measurment. First peak of resistivity aged at 90℃ was caused by precipitation of δ` -precursor phase, and second peak was caused by precipitation of δ` phase. According to this result, the precipitation process of Al-2.19wt%Li alloy was as follow : SSSS→δ` -precursor phase→δ`(Coherent→Semi-coherent)→δ In a Al-2.0wt%Li-0.11wt%Zr ternary alloy, the first peak of resistivity was appeared at initial aging heat-treatment. It is result from exsistant of δ` -precursor phase. The effect acceleration in a binary alloy was not appeared and the over-aging ternary alloy was accelerated with increase of the reduction rate. 1t is caused by combination effect of δ` and composite phase.
마찰교반공정을 통한 강재의 개질 영역에서의 미세조직에 미치는 합금원소의 영향
김상혁,이광진,우기도,Kim, Sang Hyuk,Lee, Kwang Jin,Woo, Kee Do 한국재료학회 2015 한국재료학회지 Vol.25 No.8
In this study, to confirm the effect of alloying elements on the phase transformation and conditions of the friction stir process, we processed two materials, SS400 and SM45C steels, by a friction stir process (FSP) under various conditions. We analyzed the mechanical properties and microstructure of the friction stir processed zone of SS400 and SM45C steels processed under 400RPM - 100mm/min conditions. We detected no macro (tunnel defect) or micro (void, micro crack) defects in the specimens. The grain refinement in the specimens occurred by dynamic recrystallization and stirring. The microstructure at the friction stir processed zone of the SS400 specimen consisted of an ${\alpha}$-phase. On the other hand, the microstructure at the friction stir processed zone of the SM45 specimen consisted of an ${\alpha}$-phase, $Fe_3C$ and martensite due to a high cooling rate and high carbon content. Furthermore, the hardness and impact absorption energy of the friction stir processed zone were higher than those of base metals. The hardness and impact absorption energy of FSPed SM45C were higher than that of FSPed SS400. Our results confirmed the effect of alloying elements on the phase transformation and mechanical properties of the friction stir processed zone.