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日時: 8月8日(月)
場所: 東京大学生産技術研究所 As棟 As301-302
アクセス: http://www.iis.u-tokyo.ac.jp/access/access.html
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Date: 2016.8.8 (Mon.) 14:00
Room: As301-302
Speaker:
Prof. Kenneth F. Kelton
Department of Physics & Institute of Materials Science and Engineering,
Washington University, St. Louis, Missouri, USA
Title:
Fragility in Metallic Glass-Forming Liquids
Fragility is a concept that is often correlated with glass formability. It is generally defined in terms of dynamical aspects of the liquid, usually based on the rate of increase of the viscosity as a function of the inverse temperature scaled to the glass transition temperature, T_g (i.e. T_g/T). Our experimental studies of the temperature dependence of the liquid structure factor, S(q), for a range of metallic alloy liquids demonstrate a link between structural and kinetic fragility [1]. A new scaling temperature, T_A, is also identified, which, based on the results of molecular dynamics simulations, corresponds to the onset of cooperative flow in the liquid [2]. Our recent experimental and MD results show that the rate of short-range and medium-range structural ordering in the liquid accelerates below the temperature of this dynamical crossover, further demonstrating the link between structure and dynamics. Further, for all metallic glass-forming liquids studied T_g =~ T_A/2, suggesting a deep connection between the onset of cooperative dynamics and the glass transition [3], which is supported by our recent MD results [4]. Finally, by scaling the inverse temperature by T_A, and the magnitude of the viscosity by the extrapolated viscosity at infinite temperature, \eta_0, a universal curve from T_A down to T_g is obtained for all of the metallic liquids studied [3]. On average, \eta_0 is equal to the product of the number density and Planck's constant [3]. These points will be discussed and suggestions made for further studies. Research was partially supported by the National Science Foundation (DMR-1206707 and 15-06553) and NASA (NNX10AU19G and NNX16AB52G).
[1] N. A. Mauro, M. E. Blodgett, M. L. Johnson, A. J. Vogt and K. F. Kelton, Nature Comm., 5, 4616 (2014).
[2] T. Iwashita, D. M. Nicholson and T. Egami, Phys. Rev. Lett. 110, 205504 (2013).
[3] M. Blodgett, T. Egami, Z. Nussinov and K. F. Kelton, Sci. Reports, 13836 ( 2015).
[4] R. Soklaski, V. Tran, Z. Nussinov, K. F. Kelton, L. Yang, Phil. Mag. 96, 1212 (2016).
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小林美加
東京大学生産技術研究所 田中研究室
〒153-8505 東京都目黒区駒場4-6-1 (Cw-305)
phone: 03-5452-6125
email: mika@iis.u-tokyo.ac.jp