• Transactions of Materials Processing
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• v.19 no.4
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• pp.230-235
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• 2010

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 for aerospace parts but also for bio prothesis and motorcycle. However, the database is insufficient in the titanium alloy for press forming process. In this study, the effect of temperature on the forming limit diagram was investigated for Ti-6Al-4V titanium alloy sheet through the Hecker‘s punch stretching test at elevated temperature. Experimental results obtained in this study can provide a database for the development of press forming process at elevated temperature of Ti-6Al-4V titanium alloy sheet. From the experimental studies it can be concluded that the formability of Ti-6Al-4V titanium alloy sheet is governed by the ductile failure for the testing temperature. The formability of Ti-6Al-4V titanium alloy sheet at $700^{\circ}C$ increases about 7 times compared with that at room temperature.

• Metals and materials international
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• v.24 no.6
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• pp.1213-1220
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• 2018

The effects of Cr and Fe addition on the mechanical properties of Ti-6Al-4V alloys prepared by direct energy deposition were investigated. As the Cr and Fe concentrations were increased from 0 to 2 mass%, the tensile strength increased because of the fine-grained equiaxed prior ${\beta}$ phase and martensite. An excellent combination of strength and ductility was obtained in these alloys. When the Cr and Fe concentrations were increased to 4 mass%, extremely fine-grained martensitic structures with poor ductility were obtained. In addition, Fe-added Ti-6Al-4V resulted in a partially melted Ti-6Al-4V powder because of the large difference between the melting temperatures of the Fe eutectic phase (Ti-33Fe) and the Ti-6Al-4V powder, which induced the formation of a thick liquid layer surrounding Ti-6Al-4V. The ductility of Fe-added Ti-6Al-4V was thus poorer than that of Cr-added Ti-6Al-4V.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.87-90
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• 2008

Since fastener bolt for airplane require high specific strength and corrosion resistance, Ti-6Al-4V alloy is widely used. However, the Ti-6Al-4V bolt is generally manufactured by cutting and rolling because of their poor workability. The aim of present work is to develop hot forming technology for high strength Ti-6Al-4V. Various heat-treatments were applied to specimen in order to increase hot-workability and prevent galling with die Multiple forging were simulated with FE code to determine optimum process parameters including specimen temperature, strain rate, local strain, and thermal shrinkage. Forged samples were heat-treated again to increase their mechanical properties.

• Transactions of Materials Processing
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• v.18 no.3
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• pp.251-255
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• 2009

Since fastener bolt for airplane require high specific strength and corrosion resistance, Ti-6Al-4V alloy is widely used. However, the Ti-6Al-4V bolt is generally manufactured by cutting and rolling because of their poor workability. The aim of present work is to develop hot forming technology for high strength Ti-6Al-4V. Various heat-treatments were applied to specimen in order to increase hot-workability and prevent galling with die. Multiple forging were simulated with FE code to determine optimum process parameters including specimen temperature, strain rate, local strain, and thermal shrinkage. Forged samples were heat-treated again to increase their mechanical properties.

• Tribology and Lubricants
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• v.36 no.1
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• pp.47-54
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• 2020

In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment at room and high temperatures (RT and HT of 400℃) on friction and wear behavior of Ti-6Al-4V alloy prepared by selective laser melting (SLM) were investigated. The objective of this study is to improve the mechanical properties and frictional behavior of Ti-6Al-4V alloy by UNSM treatment. Dry friction and wear tests were conducted using a ball-on-disk method at RT with a bearing steel as the counter ball. Due to the high HT and UNSM treatment, the surface hardness tended to increase and surface roughness tended to reduce. X-ray diffraction (XRD) analysis showed that nanocrystallization structure and compressive residual stress were formed at the surface layer after UNSM treatment at both RT and HT. After UNSM treatment, it was observed that the wear rate was reduced by about 6% for the specimen treated at RT and a 28% reduction for the specimen treated at HT in comparison with the untreated one. Based on scanning electron microscope (SEM) images showed that the damage caused by fatigue wear occurred in the wear track of the heat-treated specimen, and it is believed to be the cause of the highest wear rate. Mechanical properties and wear resistance of Ti-6Al-4V alloy were improved and prospect of industrial application was confirmed. Further research is still required to improve the characteristics of SLM Ti-6Al-4V alloy to the level of wrought Ti-6Al-4V alloy.

• Transactions of Materials Processing
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• v.14 no.8 s.80
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• pp.681-688
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• 2005

The high-temperature deformation mechanisms of a ${\alpha}+{\beta}$ titanium alloy (Ti-6Al-4V), near-a titanium alloy (Ti-6.85Al-1.6V) and a single-phase a titanium alloy (Ti-7.0Al-1.5V) were deduced within the framework of inelastic-deformation theory. For this purpose, load relaxation tests were conducted on three alloys at temperatures ranging from 750 to $950^{\circ}C$. The stress-versus-strain rate curves of both alloys were well fitted with inelastic-deformation equations based on grain matrix deformation and grain-boundary sliding. The constitutive analysis revealed that the grain-boundary sliding resistance is higher in the near-${\alpha}$ alloy than in the two-phase ${\alpha}+{\beta}$ alloy due to the difficulties in relaxing stress concentrations at the triple-junction region in the near-${\alpha}$ alloy. In addition, the internal-strength parameter (${\sigma}^*$) of the near-${\alpha}$ alloy was much higher than that of the ${\alpha}+{\beta}$ alloy, thus implying that dislocation emission/ slip transfer at ${\alpha}/{\alpha}$ boundaries is more difficult than at ${\alpha}/{\beta}$ boundaries.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.5
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• pp.217-221
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• 2018

Selective laser melting (SLM) technique is one of the additive manufacturing processes, in which functional, complex parts can be directly manufactured by selective melting layers of powder. SLM technique has received great attention due to offering a facile part-manufacturing route and utilizing a hard-to-manufacturing material (e.g. Ti6Al4V). The SLM process allows the accurate fabrication of near-net shaped parts and the significant reduction in the consumption of raw materials when compared to the traditional manufacturing processes such as casting and/or forging. In this study, we focus the high-speed additive manufacturing of Ti6Al4V parts in the aspect of manufacturing time, controlling various process parameters.

• Korean Journal of Materials Research
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• v.16 no.3
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• pp.178-182
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• 2006

A single electro-discharge-sintering (EDS) pulse (1.0 kJ/0.7 g), from a $300{\mu}F$ capacitor, was applied to atomized spherical Ti-6Al-4V powder in a low vacuum to produce porous-surfaced implant compacts. A solid core surrounded by a porous layer was formed by a discharge in the middle of the compact. XPS (X-ray photoelectron spectroscopy) was used to study the surface characteristics of the implant material. C, O, and Ti were the main constituents, with smaller amounts of Al, V, and N. The implant surface was lightly oxidized and was primarily in the form of $TiO_2$ with a small amount of metallic Ti. A lightly etched EDS implant sample showed the surface form of metallic Ti, indicating that EDS breaks down the oxide film of the as-received Ti-6Al-4V powder during the discharge process. The EDS Ti-6Al-4V implant surface also contained small amounts of aluminum oxide in addition to $TiO_2$. However, V detected in the EDS Ti-6Al-4V implant surface, did not contribute to the formation of the oxide film..

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.144-145
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• 1994

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.6
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• pp.29-35
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• 2001

The cutting characteristics of Ti-6Al-4V alloy and total wear when machining Ti-6Al-4V alloy was studied to understand the machining characteristics. This material is one of the strong candidate materials present and future aerospace or met ical applications. Nowadays their usage has already been broaden to commercial applications such as golf club head, finger rings and many decorative items. Anticipating the general use of this material and development of the titanium alloy in domestic facilities, the review and the study of the machining parameters far those alloys are deemed necessary. This study is concentrated to the machining parameters of the Ti-6Al-4V alloy due to their dominant position in the production of tita mum alloys.