Highly collective atomic transport mechanism in high-entropy glass-forming metallic liquids

doi:10.1016/j.jmst.2018.09.008

Abstract

Abstract:

Quasielastic neutron scattering (QENS) has been used to study the atomic relaxation process and microscopic transport mechanism in high-entropy glass-forming metallic (HE-GFM) liquids. Self-intermediate scattering functions obtained from the QENS data show unusually large stretching, which indicates highly heterogeneous atomic dynamics in HE-GFM liquids. In these liquids, a group of atoms over a length scale of about 21?? diffuses collectively even well above the melting temperature. However, the temperature dependence of diffusion process in one of the HE-GFM liquid is Arrhenius, but in the other HE-GFM liquid it is non-Arrhenius. Although the glass-forming ability of these HE-GFM liquids is very poor, the diffusion coefficients obtained from the QENS data indicate the long range atomic transport process is much slower than that of the best metallic glass-forming liquids at their melting temperatures.

Key words: High-entropy alloy, Neutron scattering, Atomic relaxation, Diffusion

Changjiu Chen, Kaikin Wong, Rithin P. Krishnan, Lei Zhifeng, Dehong Yu, Zhaoping Lu, Suresh M. Chathoth. Highly collective atomic transport mechanism in high-entropy glass-forming metallic liquids[J]. J. Mater. Sci. Technol., 2019, 35(1): 44-47.

Figures/Tables 4

Fig. 2 shows the Φ(Q,t) of Ti20Zr20Hf20Cu20Co20 and Ti20Zr20Hf20Cu20Fe20 measured at different temperatures and at the Q value of 1.2??-1. The Φ(Q, t) exhibits non-exponential decay with time and can be well fitted with a Kohlrausch-Williams-Watts (KWW) function:

Fig. 2. The self-intermediate scattering functions, Φ(Q, t) of (a) Ti20Zr20Hf20Cu20Co20 and (b) Ti20Zr20Hf20Cu20Fe20 high-entropy alloy liquids measured at different temperatures. The solid lines are the fits with Kohlrausch-Williams-Watts (KWW) function (Eq. (1)).

Fig. 3. Q2 dependence of the inverse of the mean relaxation time obtained for (a) Ti20Zr20Hf20Cu20Co20 and (b) Ti20Zr20Hf20Cu20Fe20 high-entropy alloy liquids. The straight solid lines are fits with DQ2 law.

Fig. 4. The atomic diffusion coefficients in Ti20Zr20Hf20Cu20Co20, Ti20Zr20Hf20Cu20Fe20 and Ti20Zr20Cu20Ni20Nb20 high-entropy alloy liquids as a function of the inverse of temperature. The straight dotted line is the Arrhenius fit and the solid line is the Vogel-Fulcher-Tammann law fit. Inset: Q2 dependence of the inverse of the mean relaxation time obtained for Ti20Zr20Cu20Ni20Nb20 liquids. The straight solid lines are fits using DQ2 law.

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