Doctor of Philosophy
Materials Science and Engineering
Rickman, Jeffrey M.
Other advisers/committee members
Harmer, Marin P.; Chan, Helen M.; Webb III, Edmund B.
In the first part of this study, we investigate the impact of grain-boundary variability on mass transport behavior in a polycrystal. More specifically, we perform both numerical and analytical studies of steady-state diffusion in prototypical microstructures in which there is either a discrete spectrum of grain-boundary activation energies or else a complex distribution of grain-boundary character, and hence a continuous spectrum of boundary activation energies. An effective diffusivity is calculated for these structures using simplified multi-state models and, in some cases, employing experimentally obtained grain-boundary energy data in conjunction with the Borisov assumption. For some condition, we find marked deviations from Arrhenius behavior, and we are able to quantify these deviations analytically.The second part of this work is devoted to fluid imbibition via diffusion in deformable solid which results in solid stresses that may, in turn, alter subsequent fluid uptake. To examine this interplay between diffusional and elastic fields, we employ a hybrid Monte Carlo-molecular dynamics scheme to model the coupling of a fluid reservoir to a deformable solid, and then simulate the resulting fluid permeation into the solid. By monitoring the instantaneous structure factor and solid dimensions, we are able to determine the compositional strain associated with imbibition, and the diffusion coefficient in the Fickian regime is obtained from the time dependence of the fluid uptake. Finally, for large, mobile fluid atoms, a non-Fickian regime is highlighted and possible mechanisms for this behavior are identified.
Mohebi-Moghadam, Mahyar, "Special Topics in Solid State Diffusion: I. Grain Boundary Variability II. Fluid in Deformable Solid" (2015). Theses and Dissertations. 1561.