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Ti-2Al-9.2Mo-2Fe 합금의 후공정 특성에 미치는 보론의 영향
김태용,임가람,이용태,조경목,이동근,Kim, Tae-Yong,Lim, Ka-Ram,Lee, Yong-Tai,Cho, Kyung-Mok,Lee, Dong-Geun 한국재료학회 2015 한국재료학회지 Vol.25 No.11
Titanium has many special characteristics such as specific high strength, low elastic modulus, excellent corrosion and oxidation resistance, etc. Beta titanium alloys, because of their good formability and strength, are used for jet engines, and as turbine blades in the automobile and aerospace industries. Low cost beta titanium alloys were developed to take economic advantage of the use of low-cost beta stabilizers such as Mo, Fe, and Cr. Generally, adding a trace of boron leads to grain refinement in casted titanium alloys due to the pinning effect of the TiB phases. This study analyzed and evaluated the microstructural and mechanical properties after plastic deformation and heat treatment in boron-modified Ti-2Al-9.2Mo-2Fe alloy. The results indicate that a trace of boron addition made grains finer; this refinement effect was found to be maintained after subsequent processes such as hot forging and solution treatment. This can effectively reduce the number of required manufacturing process steps and lead to savings in the overall cost as well as low-cost beta elements.
Ti-39Nb-6Zr 합금의 시효처리를 통한 미세조직 및 기계적 특성 제어
권현준 ( Hyun Jun Kwon ),임가람 ( Ka Ram Lim ),이용태 ( Yong Tae Lee ),이동근 ( Dong Geun Lee ),이준희 ( Jun Hee Lee ),김승언 ( Seung Eon Kim ) 대한금속재료학회(구 대한금속학회) 2016 대한금속·재료학회지 Vol.54 No.12
The aim of this study is to optimize the microstructure and mechanical properties of Ti-39Nb-6Zr (TNZ40) for bio-implant applications. TNZ40 was designed to have a low elastic modulus (~40 GPa) and good biocompatibility. However, the alloy shows relatively low strength compared to other titanium alloys for bio-implant. In the present study, we tried to obtain the proper combination of elastic modulus and strength by tailoring the direct aging conditions after severe plastic deformation. The mechanical properties are closely linked to characteristics including the distribution and volume fraction of precipitates. †(Received November 6, 2015; Accepted May 19, 2016)
Ti40Zr10Cu36Pd14 비정질기지 복합재의 미세조직과 기계적 특성에 미치는 냉각속도의 영향
박선용 ( Seon Yong Park ),임가람 ( Ka Ram Lim ),나영상 ( Young Sang Na ),김승언 ( Seong Eon Kim ),최윤석 ( Youn Suk Choi ) 대한금속ㆍ재료학회 2016 대한금속·재료학회지 Vol.54 No.11
In this paper, we demonstrate that the microstructure and mechanical properties in the Ti<sub>40</sub>Zr<sub>10</sub>Cu<sub>36</sub>Pd<sub>14</sub> alloy can be tailored by controlling the cooling rate during solidification. A lower cooling rate increases the volume fraction of crystalline phase such as B2 but decreases the free volume of the glassy matrix. The increase of the B2 volume fraction can dramatically enhance the toughness of the composites, since the B2 phase is relatively ductile compared to the glassy matrix and seems to have good interface stability with the matrix. From the experimental results, it was found that there is a transition point in the plasticity of the composites depending on the cooling rate. Here, we explain how the toughness of the composites varies in accordance with the cooling rate in the Ti<sub>40</sub>Zr<sub>10</sub>Cu<sub>36</sub>Pd<sub>14</sub> alloy system. (Received April 22, 2016; Accepted May 25, 2016)
CoCrFeMnNi 고엔트로피합금 주조재의 미세조직 및 기계적 특성
강민주 ( Minju Kang ),원종우 ( Jong Woo Won ),임가람 ( Ka Ram Lim ),박상협 ( Sang Hyeop Park ),서성문 ( Seong Moon Seo ),나영상 ( Young Sang Na ) 대한금속ㆍ재료학회 2017 대한금속·재료학회지 Vol.55 No.10
In this study, we made large-scale ingots of CoCrFeMnNi high entropy alloy by vacuum induction melting. The as-cast CoCrFeMnNi high entropy alloy contained a high proportion of columnar structures with a few equiaxed grains, and showed single phase fcc solid solutions without macro segregation and low interstitial levels. The tensile properties along the three different loading directions were investigated at low-temperature and room temperature. A decrease in temperature led to an increase in yield and tensile strengths. The increase in anisotropy due to the columnar structure was negligible. Unlike wrought CoCrFeMnNi high entropy alloys, twins were actively formed in the specimen deformed at room temperature. Mechanical twinning was found to be a result of the coarse grain size, over 500 μm, of the as-cast CoCrFeMnNi high entropy alloy, which effectively reduced the critical stress for twinning. Charpy impact tests were also conducted, and the absorbed energy of the CoCrFeMnNi high entropy alloy showed no dependence on the temperature or loading directions. The results of this study provide an understanding of pilot-scale high entropy alloy castings, and are expected to be utilized as basic properties for manufacturing large-scale high entropy alloy castings, which are effective in severe environments. (Received May 23, 2017; Accepted June 4, 2017)
Ti-12.1Mo-1Fe-xB 합금의 기계적 특성에 미치는 보론의 영향
안정진 ( Jung-jin An ),이동근 ( Dong-geun Lee ),임가람 ( Ka-ram Lim ),김태용 ( Tae-yong Kim ),이용태 ( Yong Tai Lee ),윤석영 ( Seog-young Yoon ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.6
Beta-type titanium alloys contain high-cost alloy elements, and thus the manufacturing process using them is too expensive. In order to solve these problems, with making a good balance of mechanical properties in the titanium alloy, we added low-cost elements (Fe and Mo) rather than the high-cost beta-stabilizing elements (Nb and Zr). Furthermore, boron was added to the Ti alloy because that containing boron, exhibited greater stiffness and strength, along with good fracture resistance. In order to study phase transformation about these alloys, solution treatment and aging were conducted. The knowledge on the solution treatment of the Ti alloy is important for controlling the microstructure, being the key to enhancing the mechanical properties and nucleation sites. The result shows that β-solution treatment leads to a stable β-matrix and provides the greatest driving force for precipitation. This contributed to good ductility (about 900 MPa of ultimate strength with 25% elongation), in Ti-12.1Mo-1Fe (0A1F). However, Ti-12.1 Mo-1Fe-xB (0A1F-0.05B, 0A1F-0.1B) had more ductility than 0A1F. In the solution-treatmentplus- aging condition, the nano-size ω phase that precipitated at 350-450 ℃ resulted in great strength (above 1500 MPa with 2% elongation). When aged at 550 ℃, the 0A1F only precipitated α-phase, and had ductility of about 1100 MPa with 13% elongation. The specimens to which boron was added, had α and ω phases; so 0A1F-xB was more brittle than 0A1F when aged at 550 ℃. Consequently, the design-alloy exhibited good mechanical properties (i.e. strength and elongation). More detailed investigation is needed to determine its optimal mechanical properties.