THE SCHOOL OF MATERIALS SCIENCE AND ENGINEERING

GEORGIA INSTITUTE OF TECHNOLOGY

Under the provisions of the regulations for the degree

DOCTOR OF PHILOSOPHY

on Tuesday, March 3, 2020

11:00 AM
in Skyles 270

will be held the

DISSERTATION PROPOSAL DEFENSE

for

Hongfang Lu

"A Real Space Random Potential: Search for Theoretical Strength of Amorphous Materials"

Committee Members:

Prof. Mo Li, Advisor, MSE

Prof. Hamid Garmestani, MSE

Prof. Martha Grover, ChBE

Prof. David Sherrill, CHEM

Prof. Naresh Thadhani, MSE

Prof. Angus Wilkinson, CHEM

Abstract:

Metallic glasses, first discovered in early 1960s, possess superior properties, such as high yield strength, large yield strain, low coefficient of friction, high hardness, high resistance to corrosion, oxidation and wear. Due to the disordered nature of the atomic structure, the property-structure relations in this class of materials are still remain open. One is the basic questions is the theoretical strength and the related structural defects. While the strength of crystalline metals is controlled by dislocations, the possible defects remain unknown. In this work, we shall embark on the journey to search for the theoretical strength of the metallic glasses and the possible structure defects through a theoretical framework of potential energy landscape (PEL). PEL offers a great tool to explore the properties of materials via energy distribution and barrier crossing and it has been popular in the study of phase transition and protein folding. Thus combining the theory of PEL and deformation in metallic glasses is expected to provide the needed insights into the strength and possible structure defects.

In this proposal, a theoretical random potential model based on Frenkel model will be proposed and constructed. Starting from the random potential, a model material will be built and analyzed using statistical tool. Furthermore, this random material will be put under deformation and diffusion to explore the deformation mechanism and diffusion coefficient in the sense of PEL. Our preliminary work has been carried out with a one-dimensional random potential model built from utilizing multiple sinusoidal functions. We are able to acquire the theoretical strength in the disordered material. In addition, we analyzed the characteristics of the random potential, such as distribution of energy, potential barrier height and atomic shear modulus. Additionally, our results show apparent two or more regimes of diffusion. In the future work, we propose to extend this work to two and possibly three dimensions.