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Hui‑Jun Yi,Jin‑Woo Kim,Young‑Lak Kim,Sangyong Shin 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.8
Wire-arc additive manufacturing has emerged as a technology that could replace the conventional manufacturing processof titanium alloys. However, it produces a coarse β grain, which can accumulate via several deposited materials, resulting isstrong texture and anisotropy. To investigate potential solutions, the effects of the cooling rate on the resulting microstructureand tensile properties were studied. The cooling rate of the deposited materials was adjusted by interpass temperaturecontrol. Under rapid cooling, fine α + α′ grain with a low aspect ratio were observed and tensile and hardness propertieswere also improved.
Hui-Jun Yi,Jin-Woo Kim,Young-Lak Kim,Sangyong Shin 한국재료학회 2021 한국재료학회지 Vol.31 No.5
Wire arc additive manufacturing (WAAM) is being considered as a technology to replace the conventional manufacturing process of titanium alloys. However, coarse β grains, which can extend through several deposited materials, result in strong textures and anisotropy. As a solution, we study the plastic deformation effects of ultrasonic needle peening (UNP) on the microstructure. UNP treated materials deform plastically and the dislocation density increases. Fine α+α' grains with low aspect ratio are observed in the UNP treated specimens. UNP treated WAAM Ti-6Al-4V alloys have higher strength and lower elongation than those characteristics of WAAM Ti-6Al-4V alloys. Due to UNP treatment, the z-axis directional specimens exhibit a greater effect of reducing elongation than do the x-axis directional specimens. The UNP treatment produces fine grains in proportion to the number of times UNP is performed, thereby increasing strength. UNP processes produce a large number of dislocations in the WAAM Ti-6Al-4V alloys, with the most dislocations being formed at the surface.
Yi, Hui-Jun,Lee, Yong-Jun,Kim, Jong-Yun,Kang, Sung-Su 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.9
The effects of the microstructural constituents, chemical composition, and retained austenite on high-strength weld metal were studied using preheat-free steels and GMAW solid wires with a low hydrogen content. The cold cracking susceptibility of these GMAW wires was evaluated using the y-groove Tekken test. The results showed that acicular ferrite produced the greatest resistance to cold cracking and that the microstructure of the deposit was more important than the hardness and diffusible hydrogen content in low-hydrogen weld metal. Crack blunting and branching occurred when a crack propagated through fine acicular ferrite because of the fine interlocking nature of the microstructure, Alloying elements for nucleating acieular ferrite, such as Ti, Al, and V, are required for proper austenite grain size, and sequence of inclusion formation was identified in the present paper. Furthermore, the retained austenite was not found to play the role of a hydrogen trapping site and so had no effect on the cold cracking susceptibility at a low preheating temperature (${\leq}100^{\circ}C$) and low heat input (${\leq}1.5$ KJ/mm) to the weld metal.
Hui-Jun Yi,Jong-Yun Kim,Jin-Ho Yoon,Sung-Soo Kang 대한기계학회 2011 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.25 No.12
In the present work, both experimental and numerical simulation methods are used to investigate the characteristics of welding distortion and residual stress distribution. A 3D thermo-mechanical Finite Element Analysis (FEA) method is used to predict the welding distortion and residual stress of cylinder-shaped multi-pass layer weldments. Each weld pass is performed using a quarter-circle balanced welding procedure. To investigate the influence of deposition sequence and welding heat input on the welding distortion and residual stress, a continuous welding procedure is also calculated. The corresponding FEA models considered a moving heat source, the deposition sequence, and temperature-dependent thermal and mechanical properties. The results predicted by 3D FEA model are generally in good agreement with the measurements. Finally, the numerical and experimental results suggest that both deposition sequence and heat input affect welding distortion and residual stress distribution. Furthermore, the 3D thermal-mechanical FEA method can predict cylinder-type welding distortion.
용접 입열량에 따른 티타늄 합금의 기계적 성질 평가에 대한 연구
이희준(Yi, Hui-Jun),이정수(Lee, Jung-Soo),양해진(Yang, Hae-Jin),오명환(Oh, Myung-Hwan) 한국추진공학회 2011 한국추진공학회 학술대회논문집 Vol.2011 No.5
티타늄 합금은 높은 내부식성, 우수한 피로 수명과 무게비에 비해 높은 강도를 가진다는 우수성으로 인해 항공기 부품과 화학 공업 분야등에 다양하게 사용되고 있다. 이번 연구에서는 Ti-3Al-2.5V 합금 TIG 용접부에 대하여 용접부 인성과 기계적 성질에 영향을 주는 가장 중요한 인자인 용접 입열에 대한 영향을 평가하고자 하였다. 이에 입열조건에 대한 용접부에 대한 강도, 충격 인성과 노치 인성을 평가하였으며 적정 입열 조건에서 강도와 인성이 우수한 용접부를 얻을 수 있다는 것을 확인하였다.
Antimycobacterial Activity of Fusaric Acid from a Mangrove Endophyte and its Metal Complexes
Jia-Hui Pan,Yi Chen,Yu-Hong Huang,Yi-Wen Tao,Jun Wang,Yan Li,Yi Peng,Tao Dong,Xiao-Min Lai,Yong-Cheng Lin 대한약학회 2011 Archives of Pharmacal Research Vol.34 No.7
Due to the increasing prevalence of multidrug-resistant Mycobacterium tuberculosis, there is an urgent need for new antituberculosis drugs that have novel mechanisms of action. As part of our ongoing search for antimycobacterial metabolites from mangrove endophytes, chemical analysis of the active extract of a strain of Fusarium sp. was performed, which led to the isolation of fusaric acid as the predominant constituent. A variety of metal complexes of fusaric acid were prepared. Antimycobacterial assays showed that Cadmium (II) and Copper (II) complexes exhibited potent inhibitory activity against the M. bovis BCG strain [minimum inhibitory concentration (MIC) = 4 μg/mL] and the M. tuberculosis H37Rv strain (MIC = 10 μg/mL), respectively. This is the first report of the antimycobacterial activity of the mangrove Fusarium metabolite and its coordinating metal complexes.
Taxonomic study of the genus Conistra (Lepidoptera, Noctuidae) from Northeast China
Hui-Lin Han,Yi Ding,Jun-Qing Jiang 한국응용곤충학회 2008 Journal of Asia-Pacific Entomology Vol.11 No.1
A total of six species belonging to the genus Conistra from Northeast China are reviewed in this study. Among them, two species–C. fletcheri Sugi and C. filipjevi Kononenko–are reported in China for the first time in this report. The adults and male genitalia of the species are briefly redescribed and illustrated, along with their distributions and host plants. A total of six species belonging to the genus Conistra from Northeast China are reviewed in this study. Among them, two species–C. fletcheri Sugi and C. filipjevi Kononenko–are reported in China for the first time in this report. The adults and male genitalia of the species are briefly redescribed and illustrated, along with their distributions and host plants.
Yi-Kai Zeng,Shenyu Bo,Jun-hui Wang,Bin Cui,Lei Zhu,Won-Chun Oh,Hao Gu 한국재료학회 2020 한국재료학회지 Vol.30 No.11
In this work, Ag3PO4/In2S3 nanocomposites with low loading of In2S3 (5-15 wt %) are fabricated by two step chemical precipitation approach. The microstructure, composition and improved photoelectrochemical properties of the asprepared composites are studied by X-ray diffraction pattern (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photocurrent density, EIS and amperometric i-t curve analysis. It is found that most of In2S3 nanoparticles are deposited on the surfaces of Ag3PO4. The as-prepared Ag3PO4/ In2S3 composite (10 wt%) is selected and investigated by SEM and TEM, which exhibits special morphology consisting of lager size substrate (Ag3PO4), particles and some nanosheets (In2S3). The introduction of In2S3 is effective at improving the charge separation and transfer efficiency of Ag3PO4/In2S3, resulting in an enhancement of photoelectric behavior. The origin of the enhanced photoelectrochemical activity of the In2S3-modified Ag3PO4 may be due to the improved charge separation, photocurrent stability and oriented electrons transport pathways in environment and energy applications.