2005 Fiscal Year Final Research Report Summary
Experimental and theoretical approach for mobile defect clusters introduced under heavy ion irradiations
| Project/Area Number |
16560732
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Nuclear engineering
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| Research Institution | The University of Tokyo |
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Principal Investigator |
ABE Hiroaki The University of Tokyo, School of Engineering, Associate Professor, 大学院・工学系研究科, 助教授 (40343925)
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| Co-Investigator(Kenkyū-buntansha) |
SEKIMURA Naoto The University of Tokyo, School of Engineering, Professor, 大学院・工学系研究科, 教授 (10183055)
IWAI Takeo The University of Tokyo, School of Engineering, Research Associate, 大学院・工学系研究科, 助手 (30272529)
LI Zhengcao The University of Tokyo, School of Engineering, Research Associate, 大学院・工学系研究科, 助手 (30376496)
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| Project Period (FY) |
2004 – 2005
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| Keywords | electron microscopy / ion accelerator / displacement cascade / molecular dynamics / coherent precipitate / crowdion / copper / copper-cobalt alloy |
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| Research Abstract |
It is well known that ion beams interact with materials introducing microstructural change of material properties due to accumulation of point defects and displacement cascades. This has been attracting attentions from both points of view of its basic understandings and applications, however, the process of the interaction and the behaviors of defects induced by ion irradiation have not yet been fully understood. Recent molecular dynamic calculations successfully detected mobile defect clusters in metals. The motion suggests that dislocation loops transform into mobile clusters enabling diffusion with relatively low activation energy. However, its mechanism has not been clarified yet experimentally. In this work, TEM observations and molecular dynamic calculations were performed so as to accumulate experimental evidences of the mobile clusters for its identifications as follows.
(1) in-situ TEM observations of the mobile defect clusters with a TEM interfaced with an ion accelerator : In
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-situ TEM observations in copper and gold under irradiations with 100-keV C^+, 240-keV Cu^+, 600-keV Kr^<2+> and 900-keV Xe^<3+> ions at temperatures from 573K to 823K were performed to get direct experimental insights into the defect accumulation processes. Defect clusters corresponding to displacement cascades were observed to be unstable depending on temperature, ion species and fluence. High mobility of instable defect clusters were also detected. The directions both of cascade-driven and instability-driven diffusion were strongly related to crowdion directions, suggesting that the mechanism is based on motion of crowdion-related glissile defects.
(2) Detection of point defects in Cu-1%Co under ion irradiation by means of precipitate coherency : Transmission electron microscopy has been widely used to investigate the radiation-damage microstructures, but has limitations when observing point defects due to its resolution limit. In the present study, a dilute Cu-Co alloy, which is a typical precipitation-hardened alloy, has been selected to investigate the formation and the mobility of point defects upon ion irradiation, during which the coherent precipitates lose their coherency and exhibit incoherent strain contrast, and the coherency loss can be used to detect the point defects.
(3) Molecular dynamic simulations on the stability of crowdion bundles in copper : The cluster was first input in a pure copper and the thermal stability has achieved at OK. The cluster transformed into sessile clusters. By annealing at temperatures up to 100K, the crowdions were generated so as to change its habit plane from {111} to another. Less
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