• 한국군사과학기술학회지
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• 제5권3호
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• pp.89-97
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• 2002

In this study, the effect of $\alpha$-phase morphology on the dynamic deformation behavior at ultra high strain rate was investigated by EBW(Explosive Bridge Wire) test. All of tests and analyses were conducted on three typical microstructures of Ti-6Al-4V alloy, i.e. equiaxed, widmanstatten and bimodal microstructures. The spall strength and HEL(Hugoniot Elastic Limit) of the specimens that have the thickness of 2mm and 4mm were highest with the bimodal microstructure. These results were similar with previous study which was performed by dynamic torsion test(Kolsky torsion test).

• 한국재료학회지
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• 제22권4호
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• pp.211-214
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• 2012

Optimal conditions for HA plasma spray-coating on Ti6Al4V alloy were investigated in order to obtain enhanced bone-bonding ability with Ti6Al4V alloy. The properties of plasma spray coated film were analyzed by SEM, XRD, surface roughness measurement, and adhesion strength test because the film's transformed phase and crystallinity were known to be influential to bone-bonding ability withTi6Al4V alloy. The films were formed by a plasma spray coating technique with various combinations of plasma power, spray distance, and auxiliary He gas pressure. The film properties were analyzed in order to determine the optimal spray coating parameters with which we will able to achieve enhanced bone-bonding ability with Ti6Al4V alloy. The most influential coating parameter was found to be the plasma spray distance to the specimen from the spray gun nozzle. Additionally, it was observed that a relatively higher film crystallinity can be obtained with lower auxiliary gas pressure. Moderate adhesion strength can be achievable at minimal plasma power. That is, adhesion strength is minimally dependent on the plasma power. The combination of shorter spray distance, lower auxiliary gas pressure, and moderate spray power can be recommended as the optimal spray conditions. In this study, optimal plasma spray coated films were formed with spray distance of 70 mm, plasma current of 800 A, and auxiliary gas pressure of 60 psi.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1997년도 춘계학술대회논문집
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• pp.175-178
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• 1997

A modified Mukerjee's model considering the microstructural evolution was developed to study the superplastic bulge forming process of Ti-6Al-4V alloy. Through the microstructual observation after deformation, it was found that the grain growth rate of uniaxially tested specimens was different from that of biaxially deformed specimens. From this result, bulge forming experiments with and without back pressure were performed to examine the grain growth behavior and to compare the results of biaxial test with those of triaxial test. Good agreement between the prediction by a modified Mukerjee's model and the experimental measurements was obtained for bulge profile and thickness distribution.

• 한국분말재료학회지
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• 제14권1호
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• pp.32-37
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• 2007

Using spark plasma sintering process (SPS), Ti-6Al-4V alloy powders were successfully consolidated without any contamination happened due to reaction between the alloy powders and graphite mold. Variation of microstructure and mechanical properties were investigated as a function of SPS temperature and time. Compared with hot isostatic pressing (HIP), the sintering time and temperature could be lowered to be 10 min. and $900^{\circ}C$, respectively. At the SPS condition, UTS and elongation were about 890 MPa and 24%, respectively. Considering the density of 98.5% and elongation of 24%, further improving the tensile strength would obtain by increasing the SPS pressure.

• 한국재료학회지
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• 제16권4호
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• pp.218-224
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• 2006

RF sputtering process was applied to produce thin hydroxyapatite(HAp) films on Ti-6Al-4V alloy substrates. The effects of different heat treatment conditions on the hardness between HAp thin films and Ti-6Al-4V alloy substrates were studied. Before deposition, the Ti-6Al-4V alloy substrates were heat treated for 1h at $850^{\circ}C\;under\;3.0{\times}10^{-3}torr$, and after deposition, the HAp thin films were heat treated for 1h at $400^{\circ}C,\;600^{\circ}C\;and\;800^{\circ}C$ under the atmosphere, and analyzed FESEM-EDX, FTIR, XRD, nano-indentor, micro-vickers hardness, respectively. Experimental results represented that the surface defects of thin films decreased by relaxation of internal stress and control of substrate structure followed by heat treatment of substrates before the deposition, and the HAp thin films on the heat-treated substrates had higher hardness than none heattreated substrates before the deposition, and the hardness properties of HAp thin films and Ti-6Al-4V alloy substrates appeared independent behavior, and the hardness of HAp thin films decreased by formation of $VTiO_3(OH),\;{\theta}-Al_{0.32}V_2O_5,\;Al_{0.33}V_2O_5$.

• 대한기계학회논문집A
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• 제29권4호
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• pp.584-590
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• 2005

The effect of microstructure on mechanical behavior for Ti-6Al-4V alloy was studied. Two different kinds of specimens are prepared using heat treatments (rolled plate, $1050^{\circ}C)$ in order to Produce different microstructures. Various kinds of mechanical tests such as hardness, tensile, fatigue and fretting fatigue tests are performed for evaluation of mechanical properties with the changes of microstructures. Through these tests, the following conclusions are observed: 1) Microstructures are observed as equiaxed and $widmanst{\ddot{a}}ten$ microstructures respectively. 2) Impact absorbed energy is superior for the equiaxed microstructure, and the hardness and tensile strength are superior for the $widmanst{\ddot{a}}ten$ microstructure. 3) The fatigue endurance of $widmanst{\ddot{a}}ten$ microstritcture shows higher value than that of the equiaxed microstructure. 4) The fatigue endurance in fretting condition was reduced about $50{\%}$ from that of the non-fretting condition.

• 소성∙가공
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• 제11권6호
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• pp.519-528
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• 2002

The microstructural evolution during the equal channel angular pressing of Ti-6Al-4V alloy was investigated using the transmission electron microscopy (TEM). ECA pressing was carried out isothermally with route C at $600^{\circ}C$ for two types of initial microstructure, i.e., equiaxed and Widmanstatten microstructures. At an initial stage of ECA pressing, the equiaxed microstructure showed more uniform flow than the Widmanstatten microstructure. However, both microstructures were significantly refined revealing nearly equiaxed grains of 0.3$mu extrm{m}$ in diameter with high angle grain boundaries after 4 passes of ECA pressing. These ultrafine gains were found to be stable with little grain growth, when annealed up to $600^{\circ}C$ for 1hr.

• 한국재료학회:학술대회논문집
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• 한국재료학회 1993년도 춘계학술발표회
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• pp.94-94
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• 1993

• 대한금속재료학회지
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• 제50권2호
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• pp.164-170
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• 2012

Nanotubular structure formation on the Ti-6Al-4V and Ti-Ta alloy surfaces by electrochemical methods has been studied using the anodizing method. A nanotube layer was formed on Ti alloys in 1.0 M $H_3PO_4$ electrolyte with small additions of $F^-$ ions. The nanotube nucleation and growth of the ${\alpha}$-phase and ${\beta}$-phase appeared differently, and showed different morphology for Cp-Ti, Ti-6Al-4V and Ti-Ta alloys. In the ${\alpha}$-phase of Cp-Ti and martensite ${\alpha}^{\prime}$ and in the ${\alpha}^{{\prime}{\prime}}$ and ${\beta}$-phase of the Ti-Ta alloy, the nanotube showed a clearly highly ordered $TiO_2$ layer. In the case of the Ti-Ta alloy, the pore size of the nanotube was smaller than that of the Cp-Ti due to the ${\beta}$-stabilizing Ta element. In the case of the Ti-6Al-4V alloy, the ${\alpha}$-phase showed a stable porous structure; the ${\beta}$-phase was dissolved entirely. The nanotube with two-size scale and high order showed itself on Ti-Ta alloys with increasing Ta content.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.158-163
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• 2009

Titanium alloy sheets have excellent specific strength and corrosion resistance as well as good performance at high temperature. Recently, titanium alloys are widely employed not only aerospace parts but also bio prothesis and motorcycle. However, due to the low formability and large spring back at room temperature, titanium alloy sheets were usually formed by slow forming or hot forming with heating die and specimen. In the sheet metal forming area, FE simulation technique to optimize forming process is widely used. To achieve high accuracy FE simulation results, Identification of material properties and deformation characteristic such as yield function are very important. In this study, uniaxial tensile and biaxial tensile test of Ti-6Al-4V alloy sheet with thickness of 1.0mm were performed at elevated temperature of 873k. Biaxial tensile tests with cruciform specimen were performed until the specimen was breakdown to characterize the yield locus of Ti-6Al-4V alloy sheet. The experimental results for yield locus are compared with the theoretical predictions based on Von Mises, Hill, Logan-Hosford, and Balat's model. Among these Logan-Hosford's yield criterion well predicts the experimental results.