Dresden 2017 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 9: Topical session: Dynamics, relaxation and deformation in deeply supercooled metallic liquids and glasses II - Undercooled Melts

MM 9.4: Vortrag

Montag, 20. März 2017, 12:30–12:45, IFW A

Ni-diffusion in a liquid and undercooled NiSi alloy — •Franz Demmel — ISIS Facility, Rutherford Appleton Laboratory, Didcot, OX11 0QX, UK

Understanding the dynamics of liquid metals and alloys can be relevant for technological applications like solidification and welding. Here the Nickel self-diffusion coefficient was measured in a Ni75Si25 alloy in the liquid and undercooled state covering a temperature range of 1400K to 1900K. Quasielastic neutron scattering on a 2.7 mm diameter spherical sample was used to deduce the Ni self-diffusion coefficient. The experiment was performed by applying aerodynamic levitation with CO2 laser heating. That containerless technique allowed an undercooling of about 100K over 4 hours of measurement time. The temperature dependence of the diffusion coefficients follows an Arrhenius type behavior. The derived activation energy for the diffusion process is about 10% larger than in pure Nickel and is probably the reason for the moderately slower self-diffusion coefficients compared to pure Ni. Surprisingly, molecular dynamics simulations predicted a change in dynamics from an Arrhenius-type behavior to a power-law for temperatures as high as twice the glass transition temperature [1]. Our data are compatible with a power-law behavior for the Ni self-diffusion [2]. [1] Y.J. Lu, H. Cheng and M. Chen, J. Chem Phys 136 214505 (2012) [2] F. Demmel, L. Hennet, S. Brassamin, D.R. Neuville, J. Kozaily and M. Koza, Phys Rev B 94 (2016) 014206