Local Dynamics and Atomic-level Structures in Metallic Liquids and Glasses

Author

Zengquan Wang, University of Tennessee, KnoxvilleFollow

Date of Award

5-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Takeshi Egami

Committee Members

Wojciech Dmowski, Yanfei Gao, Cristian D. Batista

Abstract

Structure and dynamics at the atomic level in metallic glasses and liquids are poorly understood when compared to the crystalline solids. For instance, even though viscosity is the basic property of liquids, its atomistic origin is not well elucidated. Also, the physics of the fragility of liquids and the crossover phenomenon is far from full understanding. Earlier, through molecular dynamics (MD) simulations a direct connection was found between the timescale describing the macroscopic viscous behavior, the Maxwell relaxation time (t_M = h/G_∞, h is the shear viscosity and G_∞ is the high-frequency shear modulus) and the timescale of microscopic atomic behavior, t_LC, which is the time for an atom to lose or gain one nearest neighbor by cutting or creating a bond.

To verify this relationship experimentally and further the study of dynamics of liquid metals, we carried out the inelastic neutron scattering (INS) experiments at ARCS beamline at the Spallation Neutron Source (SNS) on metallic liquid droplets of Zr₅₀Cu₅₀ and Zr₈₀Pt₂₀, using an electro-static levitator (NESL), which provided a high vacuum containerless environment. This was the first experiment of this kind allowing us to determine the dynamic structure function S(Q,E) over a large Q-E space with high statistics and low backgrounds. Time dependent Van Hove correlation function G(r, t), including the self and the distinct part, was obtained with high reliability through a double Fourier transformation using the developed data analysis procedure and codes. Atomic-level relaxation times and diffusivity were determined by analyzing the time dependence of the G(r, t) peak features, and were compared with the results of viscosity measurements and MD simulations. This research experimentally verifies conclusion of the previous MD simulation that viscosity is controlled by the local atomic connectivity change in metallic liquids above the crossover temperature T_A. Using the experimental and data processing procedures developed by us, significant progress is made in the elucidation of local atomic dynamics in metallic liquids.

In addition, the thermal structural evolution of two Zr-based metallic glasses were studied by in-situ high energy X-ray diffraction experiment and MD simulations with the pair distribution function (PDF) analysis. The different phase transition behavior and thermal atomic structural evolution for Zr₆₅Cu₁₇Ni₈Al₁₀ and Zr₈₀Pt₂₀ are observed and attributed to the different topological and chemical effects of different atomic pairs.

Recommended Citation

Wang, Zengquan, "Local Dynamics and Atomic-level Structures in Metallic Liquids and Glasses. " PhD diss., University of Tennessee, 2021.
https://trace.tennessee.edu/utk_graddiss/6706