• 한국주조공학회지
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• 제16권2호
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• pp.149-157
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• 1996

Several aluminum based alloys were fabricated by a twin roll strip casting mill. As-cast microstructures and microsegregations of these aluminum alloys were investigated by means of optical microscope, scanning electron microscope and electron probe micro analysis. Clear distinction on microsegregation among the alloy systems was observed, that is, A1235 and A8011 alloys showed diffused segregation in the middle of the strip, while A3003 and A5086 alloys revealed a centerline segregation consisted of lamellar structure. Above center line segregation was resulted from enrichment of the alloying elements such as Mn, Fe, Cu, Si and eutictic reaction in central region of the alloy strip.

• 폴리머
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• 제28권6호
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• pp.509-518
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• 2004

비대칭 블록 공중합체와 단일고분자로 구성된 블렌드의 미세 도메인 구조와 결정화 거동을 소각 X-선 산란, 광학 현미경 및 DSC를 사용하여 조사하였다. 본 연구에서는 폴리(메틸 메타크릴레이트) 블록의 무게 분률이 0.53인 폴리(메틸 메타크릴레이트)-폴리스티렌 이종 블록 공중합체 (PMMA-b-PS)를 저분자량 폴리(비닐리덴 플루오라이드) (PVDF)와 혼합하였다. PVDF 함량 증가에 따라 블렌드 미세구조가 라멜라에서 실린더 구조로 전이하였으며, PVDF의 결정화는 결정화 이전에 형성된 미세구조의 배열을 교란시켜 질서도가 낮은 형태를 야기시켰다. 또한, PVDF 결정화 거동은 PMMA 블록과의 혼화성 및 미세 도메인에 의해 부가되는 공간적 제한에 큰 영향을 받았다.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• 제50권1호
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• pp.13-26
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• 2024

Objectives: The aim of this study was to perform a comparative analysis of the ultrastructural and chemical composition of sialoliths, tonsilloliths, and antroliths and to describe their growth pattern. Materials and Methods: We obtained 19 specimens from 18 patients and classified the specimens into three groups: sialolith (A), tonsillolith (B), and antrolith (C). The peripheral, middle, and core regions of the specimens were examined in detail by histology, micro-computed tomography (micro-CT), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy, and transmission electron microscopy (TEM). Results: In the micro-CT, group A showed alternating radiodense and radiolucent layers, while group B had a homogeneous structure. Group C specimens revealed a compact homogeneous structure. Histopathologically, group A showed a laminated, teardrop-shaped, globular structure. Group B demonstrated degrees of immature calcification of organic and inorganic materials. In group C, the lesion was not encapsulated and showed a homogeneous lamellar bone structure. SEM revealed that group A showed distinct three layers: a peripheral multilayer zone, intermediate compact zone, and the central nidus area; groups B and C did not show these layers. The main elemental components of sialoliths were O, C, Ca, N, Cu, P, Zn, Si, Zr, F, Na, and Mg. In group B, a small amount of Fe was found in the peripheral region. Group C had a shorter component list: Ca, C, O, P, F, N, Si, Na, and Mg. TEM analysis of group A showed globular structures undergoing intra-vesicular calcification. In group B, bacteria were present in the middle layer. In the outer layer of the group C antrolith, an osteoblastic rimming was observed. Conclusion: Sialoliths had distinct three layers: a peripheral multilayer zone, an intermediate compact zone and the central nidus area, while the tonsillolith and antrolith specimens lacked distinct layers and a core.

• 한국표면공학회지
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• 제41권2호
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• pp.69-75
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• 2008

Electrochemical behaviors of surface modified and MC3T3-E1 cell cultured Ti-30Ta alloys have been investigated using various electrochemical methods. The Ti alloys containing Ta were melted by using a vacuum furnace and then homogenized for 6 hrs at $1000^{\circ}C$. MC3T3-E1 cell culture was performed with MC3T3-E1 mouse osteoblasts for 2 days. The microstructures and corrosion resistance were measured using FE-SEM, XRD, EIS and potentiodynamic test in artificial saliva solution at $36.5{\pm}1^{\circ}C$. Ti-Ta alloy showed the martensite structure of ${\alpha}+{\beta}$ phase and micro-structure was changed from lamellar structure to needle-like structure as Ta content increased. Corrosion resistance increased as Ta content increased. Corrosion resistance of cell cultured Ti-Ta alloy increased predominantly in compared with non cell cultured Ti- Ta alloy due to inhibition of the dissolution of metal ion by covered cell. $R_p$ value of MC3T3-E1 cell cultured Ti-40 Ta alloy showed $1.60{\times}10^6{\Omega}cm^2$ which was higher than those of other Ti alloy. Polarization resistance of cell-cultured Ti-Ta alloy increased in compared with non-cell cultured Ti alloy.

• 대한기계학회논문집A
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• 제29권4호
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• pp.584-590
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• 2005

The effect of microstructure on mechanical behavior for Ti-6Al-4V alloy was studied. Two different kinds of specimens are prepared using heat treatments (rolled plate, $1050^{\circ}C)$ in order to Produce different microstructures. Various kinds of mechanical tests such as hardness, tensile, fatigue and fretting fatigue tests are performed for evaluation of mechanical properties with the changes of microstructures. Through these tests, the following conclusions are observed: 1) Microstructures are observed as equiaxed and $widmanst{\ddot{a}}ten$ microstructures respectively. 2) Impact absorbed energy is superior for the equiaxed microstructure, and the hardness and tensile strength are superior for the $widmanst{\ddot{a}}ten$ microstructure. 3) The fatigue endurance of $widmanst{\ddot{a}}ten$ microstritcture shows higher value than that of the equiaxed microstructure. 4) The fatigue endurance in fretting condition was reduced about $50{\%}$ from that of the non-fretting condition.

• 한국군사과학기술학회지
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• 제20권2호
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• pp.206-216
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• 2017

This paper studies on the dynamic properties of Ti-6Al-4V alloy. After forming the four different micro structures(equiaxed, lamellar, and 2 bimodals) through heat treatments, static and dynamic properties of each structure were investigated quantitatively. Dynamic behaviors of the alloy are observed by the compressive split Hopkinson pressure bar(SHPB) tests. In additon, parameters of Johnson-Cook equation were determined from the SHPB test results. In order to verify the suitability of the parameters, high velocity impact tests were performed and the results were compared with the numerical analysis results. Although the flow stress and the fracture strain of the bimodal structures were higher than those of the equiaxed structure at the static tests, the superior dynamic properties were observed at the equiaxed structure due to the effects of higher maximum flow stress and fracture strain. From the numerical analysis, J-C parameters which are determined on this study describe well the dynamic behavior of Ti-6Al-4V alloy. Experimental and analysis results are consistent with ${\pm}5%$ of an average error.