• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.130-130
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• 2000

타이타늄(CP Ti)과 타？늄합금은 인체의 골격을 구성하고 있는 물질과 가장 흡사한 물리적 성질과 우수한 생체적합성으로 인해 임플란트용 재료로 많이 사용되고 있으며, 최근에 인공관절이나 치근으로의 사용이 증가하고 있다. 그러나 교합면에서의 취약한 마모특성으로 인해 wear debris에 의한 골 흡수 및 이완 등을 야기하는 문제점으로, 이의 개선에 관한 연구가 활발히 진행되어 왔다. 다이아몬드상 카본 (Diamond-Like-Carbon) 박막은, 다이아몬드와 유사한 높은 경도, 내마모성 그리고 화학적 안정성 등의 매우 우수한 물리화학적 특성을 가지고 있는 박막재료로 고체 윤활박막으로서 hard disk나 VCR head drum의 보호막, 우주항공기의 bearing 재료코팅 등으로의 적용이 최근에 급격히 증가하고 있다. 본 연구에서는 이와 같은 특성을 지닌 다이아몬드상 카본 박막의 생체재료로의 적용을 위해, CP Ti과 Ti-6Al-4V에 13.56MHz를 사용하는 r.f PACVD법으로 DLC를 증착하여 생체적합적 특성을 조사하였다. C6H6 가스를 사용하여 1$\mu\textrm{m}$의 두께로 DLC 박막을 증착하였으며, 기판과의 밀찰력 향상을 위해 Si을 증간층으로 합성하였다. 마모특성은 pin-on-disk type wear tester을 사용하였으며 직경 5mm의 ruby ball로 실험을 수행하였다.

• Transactions of Materials Processing
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• v.16 no.4 s.94
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• pp.223-228
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• 2007

The profile ring rolling process of Ti-6Al-4V alloy was investigated by finite element(FE) simulation and experimental analysis. The process design of the profile ring rolling includes geometry design and optimization of process variables. The geometry design such as initial billet and blank sizes, and final rolled ring shape was carried out with the calculation method based on the uniform deformation concept between the wall thickness and ring height. FEM simulation was used to calculate the state variables such as strain, strain rate and temperature and to predict the formation of forming defects during ring rolling process. Finally, the mechanical properties of profiled Ti-6Al-4V alloy ring product were analyzed with the evolution of microstructures during the ring rolling process.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.05a
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• pp.148-151
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• 2009

This paper presents an experimental study of deep-drawing and rubber-pad forming process using titanium alloy sheet. The process and results of the work carried out to investigate the capability of the process and to optimize th process parameters to ensure a sound forming. Room and high temperature tensile tests were carried out at various process conditions and microstructural evaluation was investigated. The experimental investigation was done using 150 ton hydraulic press to produce a deep-drawn part. Both graphite lubricant and polyethylene sheet were essential for defect-free product. Regarding the rubber-pad forming, reasonable formability was obtained only for pure-Ti not for Ti-6Al-4V.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.6
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• pp.256-262
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• 2019

The microstructural features and texture development by both hot rolling and hot forging in ${\gamma}-TiAl$ alloy were investigated. In addition, additional heat treatment after hot forging was conducted to recognize change of the microstructure and texture evolution. The obtained microstructural features through dynamic recrystallization after hot deformed ${\gamma}-TiAl$ were quite different because two kinds of formation process were occurred depending on deformation condition. However, analyzed texture tends to be random orientation due to intermediate annealing up to ${\alpha}+{\beta}$ region during the hot deformation process. After additional heat treatment, microstructure transformed into fully lamellar microstructure and randomly oriented texture was also observed due to the same reason as before. Tensile test at room temperature demonstrated that anisotropy of mechanical properties were not appeared and transgranular fracture was occurred between interface of ${\alpha}_2/{\gamma}$. As a result, it could be suggested that microstructural features influenced much more than texture development on mechanical properties at room temperature.

• Journal of Dental Rehabilitation and Applied Science
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• v.32 no.3
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• pp.194-201
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• 2016

Purpose: The purpose of this study was to evaluate of Zirconium Nitride (ZrN) coating on shear bond strength with denture base resin in Co-Cr and Ti-6Al-4V alloy. Materials and Methods: Co-Cr and Ti-6Al-4V alloy disks (10 mm in diameter, 2.5 mm in thickness; each other: n = 14) were prepared and divided with 2 groups each other by ZrN coating. After primer was applied to disks surface, denture base resin with diameter 6 mm, height 5 mm was bonded on metal disk surface. After surface roughness was measured by Profiler, shear bond strength was determined with Universal testing machine and analyzed with two-way ANOVA. The specimen surfaces and failure mode were examined using a scanning electron microscope. Results: ZrN coated groups showed significantly higher rough surface than non-coated groups (P < 0.05). Irrespective of alloy materials, shear bond strength of ZrN coated groups were lower than non-coated groups (P < 0.001). The scanning electron microscope (SEM) of ZrN coated groups showed mixed and adhesive fractures. Conclusion: ZrN coating weakened bonding strength between denture base resin and Co-Cr, Ti-6Al-4V alloy.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.23-23
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• 2010

마찰교반접합(Friction Stir Welding)은 1991년 영국 TWI에서 개발된 접합 법으로서 일정한 속도로 회전하는 툴이 재료내부에 삽입 되면서 툴과 재료사이에서 마찰열이 발생하여 연화된 재료와 접합 툴 사이에서의 기계적 교반에 의해 소성변형이 일어남과 동시에 접합이 이루어진다. 마찰교반접합은 동적 재결정에 의한 접합부의 미세한 결정립 형성으로 인하여 기계적 특성이 향상되며 보호 가스가 필요 없어 친환경적임과 동시에 용융 용접 법에 비해 접합 시 에너지 소모가 적다는 장점이 있다. 마찰교반접합은 기존의 저융점 재료에 관한 접합을 넘어서 최근에는 철계 합금, 타이타늄 합금, 니켈계 합금 등 고융점 재료에서의 적용에 관한 연구가 이루어지고 있다. 하지만 마찰교반접합을 이용하여 위와 같은 강한 재료를 접합하기 위해서는 내구성이 갖추어진 툴이 반드시 수반된다. 슈퍼 오스테나이트계 스테인리스강은 염화물의 농도가 높은 부식 환경에 적용되는 소재로서, 공식(pitting corrosion) 및 틈부식 (crevice corrosion)에 대한 내식성을 높이기 위하여 Mo의 함량을 6%로 낮추고 20~25% Cr과 Ni을 첨가하여 사용된다. 이러한 고합금의 슈퍼 오스테나이트계 스테인리스강은 여타 내식성 합금에 비하여 내식성이 매우 우수한 것으로 알려져 있다. 최근 SO2 배출에 대하여 규제가 강화되면서 화력 발전소용 탈황 설비 중 일부 장비에서 6% Mo가 첨가된 슈퍼 오스테나이트계 스테인리스강의 사용이 늘어나고 있다. 본 연구에서는 $Si_3N_4$ 툴을 사용하여 Mo이 6% 첨가된 슈퍼 오스테나이트계 스테인리스강인 1925hMo강을 마찰교반접합하였다. 툴 회전속도 (200rpm, 300rpm, 460rpm, 700rpm)를 변수로 하여 접합을 실시하였다. 접합 후 외관상태를 점검하였으며 광학현미경 (optical microscope)과 주사전자현미경 (scanning electron microscope)을 사용하여 미세조직 관찰을 하였으며 경도 및 인장강도 측정 등의 실험을 통하여 접합부의 기계적 특성을 평가하였다. 그 후 이러한 결과를 통하여 미세조직과 기계적 특성과의 관련성을 조사하였다.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.4 s.19
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• pp.70-78
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• 2004

A study has been made to investigate the high temperature deformation behavior of Ti-6Al-4V alloyand to predict the final microstructure under given forming conditions. Equiaxed and $Widmanst\ddot{a}tten$ microstructures of Ti-6Al-4V alloys were prepared as initial microstructures. By performing the compression tests at high temperatures$(700\~1100^{\circ}C)$ and at a wide range of strain rates$(10^{-4}\~10^2/s)$, various parameters such as strain rate sensitivity(m) and activation energy(Q) were calculated and used to establish constitutive equations. When the specimens were deformed up to strain 0.6, equiaxed microstructure did not show any significant changes in microstructure, while $Widmanst\ddot{a}tten$ microstructure revealed considerable flow softening, which was attributed to the globularization of a platelet at the temperature range of $800\~970^{\circ}C$ and at the strain rate range of $10^{-4}\~10^{-2}/s$. To predict the final microstructure after forming, finite element analysis was performed considering the microstructural evolution during the deformation. The grain size and the volume fraction of second phase of deformed body were predicted and compared with the experimental results.

• Korean Journal of Metals and Materials
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• v.49 no.9
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• pp.678-685
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• 2011

The aim of this study was to determine the effect of applied pressure and sintering temperature on the microstructure and mechanical properties for spark plasma sintering (SPS) from commercial pure titanium (CP-Ti) powders. Spark plasma sintering is a relatively new sintering technique in powder metallurgy which is capable of sintering metal and ceramic powers quickly to full density at a fairly low temperature due to its unique features. SPS of -200 mesh or -400 mesh CP-Ti powders was carried out in an $Ar+H_2$ mixed gas flowing atmosphere between $650^{\circ}C$ and $750^{\circ}C$ under 10 to 80 MPa pressure. When SPS was carried out at relatively low temperatures ($650^{\circ}C$ to $750^{\circ}C$), the high (>60 MPa) pressure had a marked effect on densification and grain growth suppression. The full density of titanium was achieved at temperatures and pressures above $700^{\circ}C$ and 60 MPa by spark plasma sintering. The crystalline phase and microstructure of titanium sintered up to $700^{\circ}C$ consisted of ${\alpha}$-Ti and equiaxed grains. Vickers hardness ranging from 293 to 362 Hv and strength ranging from 304 to 410 MPa were achieved for spark plasma sintered titanium.

• Korean Journal of Metals and Materials
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• v.49 no.9
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• pp.692-698
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• 2011

The thermo-chemical treatment (TCT) process was applied to achieve surface hardening of CP titanium. The following three different surface modification conditions were tested so that the best surface hardening process could be selected:(a) PVD, (b) TCT+PVD, and (c) TCT+Aging+PVD. These specimens were tested and analyzed in terms of surface roughness, wear, friction coefficient, and the gradient of hardening from the surface of the matrix. The three test conditions were all beneficial to improve the surface hardness of CP titanium. Moreover, the TCT treated specimens, that is, (b) and (c), showed significantly improved surface hardness and low friction coefficients through the thickness up to $100{\mu}m$. This is due to the functionally gradient hardened surface improvement by the diffused interstitial elements. The hardened surface also showed improvement in bonding between the PVD and TCT surface, and this leads to improvement in wear resistance. However, TCT after aging treatment did not show much improvement in surface properties compared to TCT only. For the best surface hardening on CP titanium, TCT+PVD has advantages in surface durability and economics.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.33 no.6
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• pp.276-281
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• 2023

With the high design freedom of the additive manufacturing process, there is a growing interest in multi-dimensional lattice structures among researchers, who are studying intricate structural modeling that is challenging to produce using conventional manufacturing processes. In the case of titanium alloy implants for human insertion, a multi-dimensional lattice structure is employed to ensure compatibility with bones, adjusting strength and elastic modulus to levels similar to those of bones. Therefore, securing a database on the mechanical properties based on lattice structure design variables and the development of related simulation techniques are believed to efficiently facilitate the customization of implants. In this study, lattice structures were additively manufactured using Ti-6Al-4V alloy, and the elastic modulus was measured based on design parameters. The results were compared with simulations, and an approach to finite element analysis for accurate prediction of the elastic modulus was proposed.