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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)
직접가압주조한 Al-5%Ni-5%Mg-(Mm) 합금의 조직 및 기계적 성질에 미치는 가압력의 영향
우기도(Kee Do Woo),정동석(Dong Sug Chung),황인오(In O Hwang),김석원(Sug Won Kim) 한국주조공학회 2001 한국주조공학회지 Vol.21 No.2
Misch metal (rare earth element, Ce, La, Nd, Pr) which has large influence on high-temperature stability and toughness was added to the Al-5%Ni-5%Mg alloy, and squeeze casting was used for Al-5%Ni-5%Mg-(Mm) alloys. The effect of applied pressure and misch metal additions on mechanical properties in Al-5%Ni-5%Mg alloy by direct squeeze casting has been investigated. The applied pressure were 0㎫(gravity casting), 25, 50 and 75㎫. Squeeze-cast Al-5%Ni-5%Mg-(Mm) alloys had better mechanical properties than those of non-pressurized cast alloys because of the increased cooling rate by the application of pressure during solidification. By the addition of misch metal in Al-5%Ni-5%Mg alloy, better combination of strength and elongation was obtained. The addition of 0.3%Mm in Al-5%Ni-5%Mg alloy improved the heat resistant property due to the formation of fine eutectic phases.
급속소결에 의한 HA가 첨가된 Ti-Nb-HA 복합재료의 제조 및 생체재료 특성
우기도 ( Kee Do Woo ),김상혁 ( Sang Hyck Kim ),김지영 ( Ji Young Kim ),박상훈 ( Sang Hoon Park ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.1
Ti-6Al-4V extra low interstitial (ELI) alloy has been widely used as an orthopedic implant material because of its excellent biocompatibility, corrosion resistance and mechanical properties. However, V-free titanium alloys such as Ti-6%Al-7%Nb and Ti-5%Al-2.5%Fe have recently been developed because of the toxicity of V. Hydroxyapatite (HA) is used as a coating material on Ti or Ti biomaterials due to its good biocompatibility. However, HA coated on Ti alloy causes a problem for tissue by peeling off during usage. Therefore, such peeling off during long time usage can be suppressed by adding HA in Ti or Ti alloy composites. The aim of this study was to manufacture an ultra fine grained (UFG) Ti-Nb-HA bulk alloy, which is usually difficult to fabricate using melting and casting technology, by rapid sintering process using high energy mechanical milled (HEMM) powder.
Leaching공정으로제조한표면다기공Ti-HA생체재료의표면조직및기계적성질의평가
우기도 ( Kee Do Woo ),강덕수 ( Duck Soo Kang ),문민석 ( Min Seok Moon ),김상혁 ( Sang Hyuk Kim ),( Zhi Guang Liu ),( Abdel Nasser Omran ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.4
Ti-6Al-4V ELI alloy, which is commonly used as a biomaterial, is associated with a high elastic modulus and poor biocompatibility. This alloy presents a variety of problems on several areas. Therefore, the development of good non-toxic biocompatible biomaterials with a low elastic modulus is necessary. Particularly, hydroxyapatite (HA) is an attractive material for human tissue implantation. This material is widely used as artificial bone due to its good biocompatibility and similar composition to human bone. Many scientists have studied the fabrication of HA as a biomaterial. However, applications of bulk HA compact are hindered by the low strength of HA when it is sintered. Therefore, HA has been coated on Ti or Ti alloy to facilitate good bonding between tissue and the HA surface. However, there are many problems when doing this, such as the low bonding strength between HA and Ti due to the different thermal expansion coefficients and mechanical properties. In this study, a Ti-HA composite with a porous surface was successfully fabricated by pulse current activated sintering (PCAS) and a subsequent leaching process. (Received January 12, 2010)
통전가압활성소결에 의한 생체재료용 Ti-HA복합재료 제조 및 특성
우기도 ( Kee Do Woo ),강덕수 ( Duck Soo Kang ),권의표 ( Eui Pyo Kwon ),문민석 ( Min Seok Moon ),손인진 ( In Jin Shon ),( Zhi Guang Liu ) 대한금속·재료학회 2009 대한금속·재료학회지 Vol.47 No.8
Ti-6Al-4V biomaterial is widely used as a bone alternative. However, Ti-6Al-4V ELI alloy suffers from numerous problems such as a high elastic modulus and high toxicity. Therefore, non-toxic biomaterials with low elastic moduli need to be developed. Ti-HA(hydroxyapatite) composites were fabricated in the present work by pulsed current activated sintering (PCAS) at 1000℃ under 60 MPa using mixed Ti and HA powders. The effects of HA content on the physical and mechanical properties of the sintered Ti-HA composites have been investigated. X-ray diffraction(XRD) analysis of the Ti-HA composites, including Ti-40 wt%HA in particular, revealed new phases, Ti2O, CaO, CaTiO3, and TixPy, formed by chemical reactions between Ti and HA during sintering. The hardness of the Ti-HA composites decreased with an increase in HA content. The corrosion resistance of these composites was observed to be an excellent candidate as a commercial Ti-6Al-4 V ELI alloy. A Ti-5 wt%HA composite fabricated by PCAS is recommended as a new biomaterial, because it offers good corrosion resistance, compressive strength, wear resistance, and biocompatibility, and a low Young`s modulus.
Sc을 첨가한 Al-7.7wt%Zn-2.0wt%Mg-1.9wt%Cu합금의 고온 변형거동
우기도,유용석,김석원,Woo, Kee-Do,Ryu, Yong-Seok,Kim, Sug-Won,Deliang Zhang 한국재료학회 2003 한국재료학회지 Vol.13 No.12
The Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc alloy exhibited excellent elongation by the new thermomechanical treatment (TMT) process; solution treatment and furnace cooling\longrightarrowhot and cold rolling and then annealing for short time. Tensile test at high temperature from 430 to $500^{\circ}C$ has been performed with various strain rates using for the Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc alloy obtained by the TMT process. The elongation of the Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc was 550% tensile tested at $470^{\circ}C$ temperature and 2.2 $\times$ $10^{-3}$ $s^{-1}$ strain rate. The m value of Al-7.7Zn-2.0Mg-1.9Cu-0.1Zr-0.1Sc alloy deformed 85% increased from 0.33 to 0.46 with increasing total elongation. This new TMT process was very simple and easy to make the sheets in the company.
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.
Al-Li-Cu-Mg합금의 조직과 기계적 성질에 미치는 가공열처리의 영향
우기도,조현기 ( Kee Do Woo,Hyun Kee Cho ) 한국열처리공학회 1990 熱處理工學會誌 Vol.3 No.1
Effects of thermomechanical treatments(TMT) on the microstructures and mechanical properties in Al-2.27%, Li-1.28%, Cu-0.63%, Mg-0.12%, Zr alloy were investigated. The TMT process improved the tensile strength. Growth of δ`, S` and T₁phases was restrained by TMT processes while the density of δ`, S` and T₁phases was increased by TMT processes. The TMT treated specimens tend to fail in inter-subboundary mode. The increases of strength by the T-HA processes were compared to those of the T-AHA processes.
통전가압활성소결을 이용한 나노 결정립 Ti-35%Nb-7%Zr-10%CPP 복합재료의 미세조직 및 기계적 특성
우기도,강덕수,김상혁,박상훈,김지영,고혜림,Woo, Kee-Do,Kang, Duck-Soo,Kim, Sang-Hyuk,Park, Sang-Hoon,Kim, Ji-Young,Ko, Hye-Rim 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.2
The aim of this study was to investigate microstructures and mechanical properties of nano-sized Ti-35 wt.%Nb-7 wt.%Zr-10 wt.%CPP composite fabricated by high energy mechanical milling (HEMM) and pulse current activated sintering (PCAS). Grain growth of the mechanically milled powder was prevented by performing PCAS. The principal advantages of calcium phosphate materials include: similarity in composition to the bone mineral, bioactivity, osteoconductivity and ability to form a uniquely strong interface with bone. The hardness and wear resistance property of nano-sized Ti-35 wt.%Nb-7 wt.%Zr-10 wt.%CPP composites increased with increasing milling time because of decreased grain-size of sintered composites.