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熱分析에 의한 7075 알루미늄 합금의 二段時效에 關한 硏究
禹基道,尹正模 全北大學校 1984 論文集 Vol.26 No.-
Differential scanning calorimetry (DSC) was used to establish the microstructural effects of various aging treatment on aluminum alloy 7075. DSC was used to characterize the matrix microstructure while hardness tester was used to characterize the mechanical properties. The aging treatments were in three categories: isochronal pre-aging, isothermal pre-aging and isochronal final aging treatments. The results obtained in this study are as follows: 1. The variation in pre-aging treatment did not have much of effect on the final microstructures but that changing the final aging temperature had significant effects on the final microstructures. 2. When the pre-aging treatment was carried out for 6hr, 24hr and 96hr at 90℃ or 120℃ before final aging for 8hr at 150℃, the dissolution of G.P. zones decreased regulary as the time and temperature of pre-aging increased. 3. For two-step treatments where the first aging treatment is 4hr at 95℃, increasing the final aging temperature from 150℃ to 155℃ or 160℃ results in a significant increase in the amount of η' in the microstructure.
Cu-Al-Ni 合金에 있어서 마르텐사이트 變態에 따른 內部摩擦
趙顯麒,禹基道,金圭鎭 慶北大學校 1984 論文集 Vol.37 No.-
The internal friction measurement was carried out by the torsion pendulum method with automatic recording of the virbration patterns. The critical range of the martensitic transformation was checked by measuring the electrical resistance and by morphological observation. The extent of internal friction in the region of the peak depends on the previous rate of temperature change and decreases sharply during a few minutes of isothermal holding. The high level of internal friction found in Cu~Al-Ni alloy is likely to due to the reversible movement of interfacial and twin boundaries on exposure to alternating stresses.
이준우,이도한,백운기 충남대학교 환경문제연구소 2000 環境硏究 Vol.18 No.-
This study was conducted to investigate the distribution of wildbird at campus in Chungnam National University. The survey was carried over 5 districts by line transect method from May, 1999 to April 2000, The observed birds were 7 orders 21 families 46 species and 3,057 individuals, these consist of 25 species for residents, 12 species for summer visitors, 5 species for winter visitors, and 4 species for passage migrant. The average density of birds was 12 ea/ha, and main dominant species was Pica pica, Paradoxornis webbianus, Parus major, Aegithalos caudatus, Ixos amaurotis in order. Species richness of bird community showed a maximum value in spring, but density showed a maximum value in winter. Breeding bird community in study area were mainly predominated by hole-nesting guild, canopy-nesting guild and canopy-foraging guild. For the protection of wildbirds at campus, it needs to plant bushes around trails and to control users. Artificial food, water station and artificial nest are needed for the habituation of wildbirds.
Woo, Kee-Do,Kwak, Seung-Mi,Lee, Tack,Oh, Seong-Tak,Woo, Jeong-Nam Materials Research Society of Korea 2016 한국재료학회지 Vol.26 No.8
$HA(hydroxyapatite)/{\beta}-TCP$ (tricalcium phosphate) biomaterial (BCP; biphasic calcium phosphate) is widely used as bone cement or scaffolds material due to its superior biocompatibility. Furthermore, $NH_4HCO_3$ as a space holder (SH) has been used to evaluate feasibility assessment of porous structured BCP as bone scaffolds. In this study, using a spark plasma sintering (SPS) process at 393K and 1373K under 20MPa load, porous $HA/{\beta}-TCP$ biomaterials were successfully fabricated using $HA/{\beta}-TCP$ powders with 10~30 wt% SH, TiH2 as a foaming agent, and MgO powder as a binder. The effect of SH content on the pore size and distribution of the BCP biomaterial was observed by scanning electron microscopy (SEM) and a microfocus X-ray computer tomography system (SMX-225CT). The microstructure observations revealed that the volume fraction of the pores increased with increasing SH content and that rough pores were successfully fabricated by adding SH. Accordingly, the cell viabilities of BCP biomaterials were improved with increasing SH content. And, good biological properties were shown after assessment using Hanks balanced salt solution (HBSS).
Woo, Kee-Do,Kim, Sang-Hyuk,Kang, Dong-Soo,Kim, Dong-Gun Materials Research Society of Korea 2013 한국재료학회지 Vol.23 No.7
To improve coating ability and the life of the coating, Ti based composite materials with hydroxyapatite(HA) should be developed. The raw materials of Ti-26wt%, Nb-1wt%, and Si with 10wt% HA were mixed for 24 h by a mixing machine and milled for 1 h to 6 h by planetary mechanical ball milling. Ti-26%Nb-1%Si-(10%HA) composites, composed of nontoxic elements, were fabricated successfully by spark plasma sintering(SPS) at $1000^{\circ}C$ under 70MPa. The relative density of the sintered Ti-Nb-Si-HA composites using the 24 h mixed powder, and the 6 h milled powder, was 91% and 97 %, respectively. The effects of HA contents and milling time on microstructure and mechanical properties were investigated by SEM and hardness tester, respectively. The Vickers hardness of the composites increased with increasing milling time and higher HA content. The Young's modulus of the sintered Ti-26%Nb-1%Si-10%HA composite using the 6 h-milled powder was 55.6 GPa, as obtained by compression test. Corrosion resistance of the Ti-26wt%Nb-1wt%Si composite was increased by milling and by the addition of 10wt%HA. Wear resistance was improved with increasing milling time. Biocompatibility of the Ti-Nb-Si alloys was improved by the addition of HA.
Fabrication of Ultra Fine β-phase Ti-Nb-Sn-HA Composite by Pulse Current Activated Sintering
Woo, Kee-Do,Wang, Xiaopeng,Kang, Duck-Soo,Kim, Sang-Hyuk,Woo, Jeong-Nam,Park, Sang-Hoon,Liuc, Zhiguang The Korean Powder Metallurgy Institute 2010 한국분말재료학회지 (KPMI) Vol.17 No.6
The $\beta$ phase Ti-Nb-Sn-HA bio materials were successfully fabricated by high energy mechanical milling and pulse current activated sintering (PCAS). Ti-6Al-4V ELI alloy has been widely used as biomaterial. But the Al has been inducing Alzheimer disease and V is classified as toxic element. In this study, ultra fine sized Ti-Nb-Sn-HA powder was produced by high energy mechanical milling machine. The $\beta$ phase Ti-Nb-Sn-HA powders were obtained after 12hr milling from $\alpha$ phase. And ultra fine grain sized Ti-Nb-Sn-HA composites could be fabricated using PCAS without grain growth. After sintering, the microstructures and phase-transformation of Ti-Nb-Sn-HA biomaterials were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The relative density was obtained by Archimedes principle and the hardness was measured by Vickers hardness tester. The $\beta$-Ti phase was obtained after 12h milling. As result of hardness and relative density, 12h milled Ti-Nb-Sn-HA composite has the highest values.
Kee-Do Woo 한양대학교 세라믹연구소 2014 Journal of Ceramic Processing Research Vol.15 No.4
The ultra fine grained TiC-10 vol.% binders (Nicrobraz 30, 150 and LC) hard materials were fabricated successfully by a highfrequency induction heated sintering (HFIHS) using high-energy mechanical ball milled TiC powder. The average grain size of high energy mechanical ball milled TiC powder was approximately 50 nm. TiC-Nicrobraz (30, 150, LC) hard materials with a relative density of up 99% were obtained by HFIHS. The hardness and fracture toughness of the sintered TiC-10 vol% Nicrobraz 30 hard materials produced by HFIHS were 2018.7 kg/mm2 and 8.2 MPa • m1/2, respectively.
Woo, Kee Do,Lee, Hyun Bom Elsevier 2007 Materials science & engineering. properties, micro Vol.449 No.-
<P><B>Abstract</B></P><P>High-energy mechanical milling (HEMM) and sintering were employed to fabricate an Al alloy matrix composite reinforced with subsive-sized Al<SUB>2</SUB>O<SUB>3</SUB> particles. Al–(Mg, Cu, Si)–SiO<SUB>2</SUB>, composite powders were prepared by HEMM. Nano-sized SiO<SUB>2</SUB> particles embedded in Al–(Mg, Cu, Si) matrix particles were obtained by HEMM. Al-based metal matrix composite reinforced with subsive-sized Al<SUB>2</SUB>O<SUB>3</SUB> particles was fabricated successfully by sintering at 650 and 750°C for 2h using milled powder. Subsive-sized Al<SUB>2</SUB>O<SUB>3</SUB> particles and eutectic Si were formed by <I>in situ</I> displacement reaction between Al and SiO<SUB>2</SUB> during sintering, and homogeneously distributed in the Al–Si–(Mg, Cu) matrix. The flexural strength of the sintered specimen (1.2GPa) using 8h milled powder was about four times as the sintered specimen using as-mixed powder.</P>