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Korean Society of Electron Microscopy
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Volume 45, Issue 2 - Jun 2015
Volume 45, Issue 1 - Mar 2015
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Phase Transformation and Work-hardening Behavior of Ti-based Bulk Metallic Glass Composite
Hong, Sung Hwan ; Kim, Jeong Tae ; Park, Hae Jin ; Kim, Young Seok ; Park, Jin Man ; Suh, Jin Yoo ; Na, Young Sang ; Lim, Ka Ram ; Kim, Ki Buem ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 37~43
DOI : 10.9729/AM.2015.45.2.37
In present work, work-hardening behavior of TiCu-based bulk metallic glass composite with B2 particles has been studied by systemic structural and mechanical investigations. After yield, pronounced work-hardening of the alloy was clearly exhibited, which was mainly related to the martensitic transformation as well as the deformation twinning in B2 particles during deformation. At the early plastic deformation stage (work-hardening stage), the stress-induced martensitic transformation from B2 phase to B19' phase and deformation-induced twinning of B19' phase was preferentially occurred in the around interface areas between B2 phase and amorphous matrix by stress concentration. The higher hardness value was observed in vicinity of interface within the B2 particles which are probably connected with martensitic transformation and deformation twinning. This reveals that the work-hardening phenomenon of this bulk metallic glass composite is a result of the hardening of B2 particles embedded in amorphous matrix.
Influence of Stress-strain on the Microstructural Change in the Metallic Glass and Metallic Glass Matrix Composite
Kim, Song-Yi ; Lee, A-Young ; Oh, Hye-Ryung ; Lee, Min-Ha ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 44~51
DOI : 10.9729/AM.2015.45.2.44
At room temperature, metallic glasses deform inhomogeneously by strain localization into narrow bands as a result of yielding due to an external force. When shear bands are generated during deformation, often nanocrystals form at the shear bands. Experimental results on the deformation of bulk metallic glass in the current study suggest that the occurrence of nanocrystallization at a shear band implies the loading condition that induces deformation is more triaxial in nature than uniaxial. Under a compressive stress state, the geometrical constraint strain imposed by the stress triaxiality plays a crucial role in the deformation-induced nanocrystallization at the shear bands.
Researches on the Enhancement of Plasticity of Bulk Metallic Glass Alloys
Kim, Byoung Jin ; Kim, Won Tae ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 52~57
DOI : 10.9729/AM.2015.45.2.52
Bulk metallic glass (BMG) shows higth strength, high elastic limit, corrosion resistance and good wear resistance and soft magnetic properties and has been considering as a candidate for new structural materials. But they show limited macroscopic plasticity and lack of tensile ductility due to highly localized shear deformation, which should be solved for real structural application. In this paper researches on the enhancement of plasticity of BMG were reviewed briefly. Introducing heterogeneous structure in glass is effective to induce more shear transformation zones (STZs) active for multiple shear band initiation and also to block the propagating shear band. Several methods such as BMG alloy design for high Poisson's ratio, addition of alloying element having positive heat of mixing, pre-straining BMG and variety of BMG composites have been developed for homogenous distribution of locally weak region, where local strain can be initiated. Therefore enhancement of plasticity of BMG is normally accompanied with some penalty of strength loss.
Formation of Icosahedral Phase in Bulk Glass Forming Ti-Zr-Be-Cu-Ni Alloy
Park, Jin Man ; Lee, Jun Hyeok ; Jo, Mi Seon ; Lee, Jin Kyu ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 58~62
DOI : 10.9729/AM.2015.45.2.58
Formation of an icosahedral phase in the bulk glass forming
alloy during crystallization from amorphous phase and solidification from melt is investigated. The icosahedral phase with a size of 10 to 15 nm forms as a thermodynamically stable phase at intermediate temperature during the transformation from amorphous to crystalline phases such as Laves and
-(Ti-Zr) phases, indicating that the existence of the icosahedral cluster in the undercooled liquid. On the other hand, the icosahedral phase forms as a primary solidification phase even though the Laves phase is stable at high temperature, which is can be explained based on the high nucleation rate of icosahedral phase relative to that of competing crystalline Laves phase due to lower interfacial energy between icosahedral and liquid phases.
Understanding of the Shear Bands in Amorphous Metals
Park, Eun Soo ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 63~73
DOI : 10.9729/AM.2015.45.2.63
Shear banding is an evidence of plastic instability that localizes large shear strains in a relatively thin band when a material is plastically deformed. Shear bands have attracted much attention in amorphous metals, because shear bands are the key feature that controls the plastic deformation process. In this article, we review recent advances in understanding of the shear bands in amorphous metals regarding: dislocations versus shear bands, the formation of shear bands, hot versus cold shear bands, and property manipulation by shear band engineering. Although there are many key issues that remain puzzling, the understanding built-up from these approaches will provide a new insight for tailoring shear bands in amorphous metals, which potentially leads to unique property changes as well as improved mechanical properties. Indeed, this effort might open a new era to the future use of amorphous metals as a new menu of engineering materials.
Tongue Movement and Role of Frenulum Linguae Effecting Tongue Movement during Prey Capture in Rana nigromaculata
Im, So-Yeon ; Je, Soo-Hyoun ; Lee, Jung-Hun ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 74~79
DOI : 10.9729/AM.2015.45.2.74
This study investigated the tongue movement during prey capture by Rana nigromaculata and the location of the frenulum linguae, which effects tongue movement. The tongue of R. nigromaculata are elliptical at the anterior and concave U-shaped at the posterior. The location of the frenulum linguae of R. nigromaculata is located at the front of the submentalis. This is due to the location of the frenulum linguae, which has significantly effects the movement and the expandability of the tongue. In terms of mobility, the tongue of R. nigromaculata and the expandability of the frenulum linguae allow the tongue to increase in length two or more times compared to immobile tongue in the other species. The time required until the swallowing movement after looking at and capturing the prey was 0.692000 seconds. Filming prey capture with a high speed camera showed that the rear part of the U-shaped tongue captures the prey with an appearance of stretching out longer to the front of tongue and turning in a reverse direction to bring the prey to the mouth.
Cell Death and Proliferation after Treatment and Reinfection of Clonorchis sinensis in the Sprague-Dawley Rat Bile Duct
Min, Byoung-Hoon ; Ahn, Ka-Young ; Lee, Haeng-Sook ; Kim, Soo-Jin ; Joo, Kyoung-Hwan ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 80~88
DOI : 10.9729/AM.2015.45.2.80
The structural change and distribution of mitochondrial enzyme (ATPase, cytochrome-c-oxidase), cell proliferation (proliferating cell nuclear antigen, PCNA), cell death (caspase-3) and cell growth factor (fibroblast growth factor 8, FGF-8) in the Sprague-Dawley rat bile duct during Clonorchis sinensis infection was investigated. Experimental groups were divided into C. sinensis infection, superinfection and reinfection of C. sinensis after 'praziquantel' treatment group. As a result, C. sinensis infected rat bile ducts showed the features of chronic clonorchiasis, i.e., connective tissue thickening, ductal fibrosis and epithelial tissue dilatation. PCNA for cell proliferation increased in the infection group, and decreased after praziquantel treatment. Caspase-3 was distributed in reinfection group only. FGF-8 was distributed in the rat bile duct after praziquantel treatment but not distributed in infection and reinfection group. Overall, C. sinensis infection causes physical and chemical irritations and then brings on the abnormalities of intracellular energy metabolism and cellular growth factors, which hinders bile duct tissue from functioning properly, and resultingly, fibrosis occurs and epithelial cells dilated abnormally. More intense infection makes tissue fibrosis chronical and activates apoptosis factors.
Development of High-Temperature Solders: Contribution of Transmission Electron Microscopy
Bae, Jee-Hwan ; Shin, Keesam ; Lee, Joon-Hwan ; Kim, Mi-Yang ; Yang, Cheol-Woong ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 89~94
DOI : 10.9729/AM.2015.45.2.89
This article briefly reviews the results of recently reported research on high-temperature Pb-free solder alloys and the research trend for characterization of the interfacial reaction layer. To improve the product reliability of high-temperature Pb-free solder alloys, thorough research is necessary not only to enhance the alloy properties but also to characterize and understand the interfacial reaction occurring during and after the bonding process. Transmission electron microscopy analysis is expected to play an important role in the development of high-temperature solders by providing accurate and reliable data with a high spatial resolution and facilitating understanding of the interfacial reaction at the solder joint.
Temperature Calibration of a Specimen-heating Holder for Transmission Electron Microscopy
Kim, Tae-Hoon ; Bae, Jee-Hwan ; Lee, Jae-Wook ; Shin, Keesam ; Lee, Joon-Hwan ; Kim, Mi-Yang ; Yang, Cheol-Woong ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 95~100
DOI : 10.9729/AM.2015.45.2.95
The in-situ heating transmission electron microscopy experiment allows us to observe the time- and temperature-dependent dynamic processes in nanoscale materials by examining the same specimen. The temperature, which is a major experimental parameter, must be measured accurately during in-situ heating experiments. Therefore, calibrating the thermocouple readout of the heating holder prior to the experiment is essential. The calibration can be performed using reference materials whose phase-transformation (melting, oxidation, reduction, etc.) temperatures are well-established. In this study, the calibration experiment was performed with four reference materials, i.e., pure Sn, Al-95 wt%Zn eutectic alloy, NiO/carbon nanotube composite, and pure Al, and the calibration curve and formula were obtained. The thermocouple readout of the holder used in this study provided a reliable temperature value with a relative error of <4%.
DigitalMicrograph Script Source Listing for a Geometric Phase Analysis
Kim, Kyou-Hyun ;
Applied Microscopy, volume 45, issue 2, 2015, Pages 101~105
DOI : 10.9729/AM.2015.45.2.101
Numerous digital image analysis techniques have been developed with regard to transmission electron microscopy (TEM) with the help of programming. DigitalMicrograph (DM, Gatan Inc., USA), which is installed on most TEMs as operational software, includes a script language to develop customized software for image analysis. Based on the DM script language, this work provides a script source listing for quantitative strain measurements based on a geometric phase analysis.