Doctoral Dissertations

Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Materials Science and Engineering

Major Professor

Takeshi Egami

Committee Members

Wojciech Dmowski, Yanfei Gao, Cristian D. Batista


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 (tM = h/G, h is the shear viscosity and G is the high-frequency shear modulus) and the timescale of microscopic atomic behavior, tLC, 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 TA. 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.

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