On the relationship between short-range structure and atomic dynamics in melts of glass-forming metallic alloys

Abstract

Despite considerable research effort, the mechanisms of glass-formation are not well understood on the atomic length and time scale. In this work results of studies on the short-range order and on the atomic dynamics in different stable and undercooled glass-forming metallic melts are presented. In order to undercool the melts deeply below the melting temperature and to avoid chemical reactions of the melts with crucible materials, the samples are containerlessly processed using the electromagnetic or the electrostatic levitation technique. For different glass-forming melts of Zr-Ni and Hf-Ni alloys full sets of partial structure factors were determined by neutron diffraction combined with an isotopic substitution technique [1,2], while Ni and Hf self-diffusion coefficients were measured as a function of temperature by quasielastic neutron scattering [2,3]. Similar as recently reported for Zr36Ni64 [4], a decoupling of the diffusion coefficients of the alloy components is observed for Hf35Ni65, showing that Ni diffuses faster than Hf. The relationship between short-range structure and atomic dynamics is discussed within the mode coupling theory. For ternary Hf10Zr25Ni65 melts pronounced deviations of the temperature dependence of the atomic dynamics from an Arrhenius behavior are observed, while the atomic dynamics can be accurately described by the scaling law of mode-coupling theory (MCT) with almost equal parameters for the self-diffusion and the viscosity [5]. Although the measured overall packing fraction remains almost unchanged, the dynamics in Hf10Zr25Ni65 are slower compared to Zr36Ni64. This corresponds also to a higher critical temperature Tc and might be induced by different chemical interactions in the melts. References: [1] B. Nowak, D. Holland-Moritz, F. Yang, Th. Voigtmann, et al., Physical Review Materials 1, 025603 (2017). [2] B. Nowak, D. Holland-Moritz, F. Yang, Th. Voigtmann, et al., Phys. Rev. B 96, 054201 (2017). [3] D. Holland-Moritz, S. Stüber, H. Hartmann, T. Unruh, and A. Meyer, J. Phys. Conf. Ser. 144, 012119 (2009). [4] S. W. Basuki, F. Yang, E. Gill, K. Rätzke, A. Meyer, and F. Faupel, Phys. Rev. B 95, 024301 (2017). [5] B. Nowak, D. Holland-Moritz, F. Yang, Z. Evenson, and A. Meyer, Phys. Rev. B 97, 094202 (2018).