Ti-6Al-4Fe-0.5Si 합금에서 Ti-Si 석출과 베타상의 방위관계

최병학,김진우,정희원,현용택,김승언,이용태 대한금속재료학회 2004 대한금속·재료학회지 Vol.42 No.1

This study examined the effect of Si addition in (α+β) Ti alloy on the phase stability about the Ti silicide precipitation from b matrix. The changes in the volume fraction and shape of precipitates with different Si contents were correlated with the tensile properties of the present alloys based on the detailed TEM micrographic observation. In Ti-6Al-4Fe-0.5Si alloy, the precipitates with rectangular or round shape were found at inter-grain of α/β interface and intra-grain of β phase. The precipitates were generally known as Ti5Si₃ with enough stabilizing thermo-mechanically. However, in this study, a new type silicide of Ti_(5)Si₄was mostly observed in the as-cast specimens, representing the metastable or unstable state phase thermo-mechanically compared to Ti_(5)Si₃. It was consistent with the phase transformation processes of TiSi₂TiSiTi_(5)Si₄Ti5Si₃ in the ternary alloy system of Ti-Al-Si. The improvement of mechanical properties including high temperature ones was to be induced by the fine precipitation of Ti silicides such as Ti5Si₄ and Ti5Si₃ in the ductile matrix of b phase. The precipitates of Ti_(5)Si₄ (P1) and Ti_(5)Si₃ (P2) have a coherent relationship with bcc β matrix of (200)_(β) //(220)_(P1) //(2111)_(P2) and (011)_(β) //(001)_(P1)//(0110)_(P2).

마이크로 드로플릿 셀 기법과 임계공식온도 측정 기법을 이용한 적층가공 Ti-6Al-4V 합금의 내식성 평가

서동일 ( Dong-il Seo ),이재봉 ( Jae-bong Lee ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.3

The resistance to corrosion of additive manufactured (3D printing) Ti-6Al-4V alloys was investigated using micro-electrochemical tests. In terms of corrosion resistance, the acicular martensitic α' phase in such additive manufactured Ti-6Al-4V was the focus of attention, and its behavior was distinct from that of conventional subtractive manufactured Ti-6Al-4V. To order to identify α' phase, XRD tests were performed and micro Vickers hardness was measured for different grains (bright and dark grains) in the additive manufactured Ti-6Al-4V alloy. Micro-electrochemical tests were performed to measure corrosion resistance of bright and dark grains in the additive manufactured Ti-6Al-4V alloy with specially designed electrochemical micro-droplet cell. Critical pitting temperature (CPT) measurement was performed to evaluate the resistance to pitting corrosion of additive manufactured Ti-6Al-4V alloys with different volumes of α' phase and subtractive manufactured Ti-6Al-4V alloy. The dark grains of the laminated Ti-6Al-4V alloy distributed broader than the bright grains measured with low microhardness. The dark grains of the Ti-6Al-4V alloy, which was rich in martensite α ', had lower general corrosion and pitting resistance than bright grains. As the fraction of martensite α 'phase increased, the resistance to the pitting corrosion decreased.

CP-Ti 및 Ti-6Al-4V 합금의 전기화학적 특성에 미치는 제조공정의 영향

김기태 ( K. T. Kim ),조현우 ( H. W. Cho ),장현영 ( H. Y. Chang ),김영식 ( Y. S. Kim ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.1

Ti and its alloys show the excellent corrosion resistance to chloride environments, but they show less corrosion resistance in HCl, H₂SO₄, NaOH, H₃PO₄, and especially HF environments at high temperature and concentration. In this study, we used the commercially pure titanium and Ti-6Al-4V alloy, and evaluated the effect of the manufacturing process on the electrochemical properties. We used commercial products of rolled and forged materials, and made additive manufactured materials by DMT (Directed Metal Tooling) method. We annealed each specimen at 760℃ for one hour and then air cooled. We performed anodic polarization test, AC impedance measurement, and Mott-Schottky plot to evaluate the electrochemical properties. Despite of the difference of its microstructure of CP-Ti and Ti-6Al-4V alloys by the manufacturing process, the anodic polarization behavior was similar in 20% sulfuric acid. However, the addition of 0.1% hydrofluoric acid degraded the electrochemical properties. Among three kinds of the manufacturing process, the electrochemical properties of additive manufactured CP-Ti, and Ti-6Al-4V alloys were the lowest. It is noted that the test materials showed a Warburg impedance in HF acid environments.

치과용 Ti-xCr 합금의 물리적 성질에 미치는 Cr 함량의 영향

송진원(Jin-Won Song),이민호(Min-He Lee),윤동주(Dong-Joo Yoon),서재민(Jae -Min Seo),안승근(Seung-Geun Ahn),송광엽(Kwang-Yeob Song),박주미(Ju-Mi Park) 대한치과재료학회 2010 대한치과재료학회지 Vol.37 No.1

Titanium and titanium alloys have become very attractive biomaterials due to their good corrosion resistance, excellent biocompatibility and specific strength. However, the properties of pure titanium are not suitable for all purposes. Many titanium alloys have been developed to improve the strength, workability and castibility of pure titanium. In addition, the casting of pure titanium is difficult because it has a high melting temperature and high reactivity with oxygen and impurities at elevated temperatures. The purpose of this study was to investigate the structure, corrosion resistance, workability and, microhardness of a series of binary Ti-xCr alloys with Cr content ranging from 5 to 35 wt%. This study evaluated the precipitated phase and structure of Ti-xCr alloys using X-ray diffraction and optical microscope and scanning electron microscope for microstructure of the etched alloys. Workability was evaluated by measuring the surface condition after rolling. With 5 wt% Cr, β phase starts to be retained. The ω phase was found in the Ti-5Cr and Ti-10Cr alloys. The microhardness values and corrosion resistance of all the Ti-xCr alloys were significantly higher than that of pure Ti and the Ti-10Cr alloy had the highest microhardness and the best corrosion resistance due to ω phase. Ti-xCr alloys with addition of Cr up to 15wt% showed good workability.

Evaluating Corrosion Resistance of Additive-Manufactured Ti–6Al–4V Using Electrochemical Critical Localized Corrosion Temperature

Jae‑Bong Lee,Dong‑il Seo,Hyun Young Chang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.1

A new concept to evaluate the localized corrosion resistance of stacked Ti alloys such as additive-manufactured (AM)Ti–6Al–4V alloy is proposed. Crevice corrosion of subtractive-manufactured (SM) Ti–6Al–4V occurred on the surfacebeneath the crevice former, whereas localized corrosion of the AM alloy occurred in any vulnerable site irrespective of thecrevice assembly. The electrochemical critical localized corrosion temperature (E-CLCT) was measured to evaluate theresistance of AM Ti–6Al–4V alloys to localized corrosion. The results showed that the localized corrosion of AM Ti–6Al–4V was attributable to the anisotropy and microstructure that resulted from rapid cooling, which were completely differentfrom the anisotropy and microstructure of SM Ti–6Al–4V. The optimum applied potential of AM Ti–6Al–4V in 25 wt%NaCl aqueous solution was deduced. The E-CLCT provides a useful criterion for determining the resistance of AM Ti alloysto localized corrosion and for comparing their resistances.

Selective Laser Melting 방식으로 적층가공된 Ti-6Al-4V 합금의 내마모성 특성에 미치는 고온 UNSM 처리 영향에 대한 연구

산성충호(Choongho Sanseong),노준석(Jun-Suek Ro),편영식(Young-Sik Pyoun),아마노프 아웨즈한(Auezhan Amanov) 한국트라이볼로지학회 2020 한국윤활학회지(윤활학회지) Vol.36 No.1

In this study, the effects of ultrasonic nanocrystal surface modification (UNSM) treatment at room and high temperatures (RT and HT of 400oC) 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 heattreated 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.

고온자전합성과 확산 열처리를 이용한 V 이 첨가된 TiAl계 금속간화합물 복합판재의 제조

김연욱,Kim, Yeon-Wook 한국재료학회 2002 한국재료학회지 Vol.12 No.9

The Ti-aluminide intermetallic compound was formed from high purity elemental Ti and Al foils by self-propagating, high-temperature synthesis(SHS) in hot press. formation of $TiAl_3$ at the interface between Ti and Al foils was controlled by temperature, pressure, heating rate, and so on. According to the thermal analysis, it is known in this study that the heating rate is the most important factor to form the intermetallic compound by this SHS reaction. The V layer addition between Al and Ti foils increased SHS reaction temperatures. The fully dense, well-boned inter-metallic composite($TiA1/Ti_3$Al) sheets of 700 m thickness were formed by heat treatment at $1000^{\circ}C$ for 10 hours after the SHS reaction of alternatively layered 10 Ti and 9 Al foils with the V coating layer. The phases and microstructures of intermetallic composite sheets were confirmed by EPMA and XRD.

SLM 기술을 이용한 Ti-6Al-4V 합금의 고속 적층 공정 최적화 연구

이강표,김강민,강석현,한준현,정경환 한국결정성장학회 2018 韓國結晶成長學會誌 Vol.28 No.5

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. Selective laser melting(SLM)은 적층 제조 방법 중 하나로서, 분말을 선택적으로 용융하여 기능적이고, 복잡한형상을 즉각적으로 제작 가능하다는 장점이 있다. Ti-6Al-4V 합금의 경우 높은 융점과 산화문제로 인하여 SLM 공정도입에어려움을 겪고 있다. 본 연구에서는 SLM 장비를 사용하여 Ti-6Al-4V 파트를 성공적으로 적층하였으며 스캔속도, 레이저파워의 변수를 조절하여 적층 가능 조건을 도출하였다. 또한 적층 된 Ti-6Al-4V 파트의 형상 정밀도, 면밀도 및 기계적특성평가를 통하여 일반적으로 사용되는 공정조건(스캔 속도 200~700 mm/s)으로 제작된 제작품 물성치와 비교를 통해 Ti-6Al- 4V 합금의 고속 적층 영역에서의 최적 공정을 확립하였다.

SLM 방식으로 적층 제조된 Ti-6Al-4V 합금의 HIP 처리에 따른 준정적 및 동적 기계적 특성 변화

장지훈 ( Ji-hoon Jang ),최영신 ( Young-sin Choi ),김형균 ( Hyeoung-kyun Kim ),이동근 ( Dong-geun Lee ) 한국열처리공학회 2020 熱處理工學會誌 Vol.33 No.3

Selective laser melting (SLM) is an additive manufacturing process by melting metallic powders and stacking into layers, and can product complex shapes or near-net-shape (NNS) that are difficult to product by conventional processes. Also, SLM process is able to raise the efficiency of production by creating a streamlined manufacturing process. For manufacturing in SLM process using Ti-6Al-4V powder, analysis of microstructural evolution and evaluation of mechanical properties are essential because of rapid melting and solidification process of powders according to high laser power and rapid scan speed. In addition, it requires a post-processing because the soundness and mechanical properties are degraded by defects such as pore, un-melted powder, lack-of-fusion, etc. In this study, hot isostatic press (HIP) was conducted as a post-processing on SLM-printed Ti- 6Al-4V alloy. Microstructure of post-processed Ti-6Al-4V alloy was compared to as-built Ti-6Al-4V, and the evolution of quasi-static (Vickers hardness, room temperature tensile characteristic) and dynamic (high-cycle fatigue characteristic) mechanical properties were analyzed. (Received April 2, 2020; Revised April 23, 2020; Accepted May 4, 2020)

적층가공된 티타늄 합금의 전기화학적 특성에 미치는 불산의 영향

김기태 ( K. T. Kim ),조현우 ( H. W. Cho ),장현영 ( H. Y. Chang ),김영식 ( Y. S. Kim ) 한국부식방식학회 2018 Corrosion Science and Technology Vol.17 No.4

In this study, the electrochemical properties of CP-Ti (commercially pure titanium) and Ti-64 (Ti-6Al-4V) were evaluated and the effect of hydrofluoric acid on corrosion resistance and electrochemical properties was elucidated. Additive manufactured materials were made by DMT (Directed Metal Tooling) method. Samples were heat-treated for 1 hour at 760 °C and then air cooled. Surface morphologies were studied by optical microscope and SEM. Electrochemical properties were evaluated by anodic polarization method and AC-impedance measurement. The oxide film formed on the surface was analyzed using an XPS. The addition of HF led to an increase in the passive current density and critical current density and decreased the polarization resistance regardless of the alloys employed. Based on the composition of the oxide film, the compositional difference observed by the addition of HF was little, regardless of the nature of alloys. The Warburg impedance obtained by AC-impedance measurement indicates the dissolution of the constituents of CP-Ti and Ti-64 through a porous oxide film.