Degree Type

Dissertation

Date of Award

1987

Degree Name

Doctor of Philosophy

Department

Materials Science and Engineering

Abstract

Quantitative directional solidification experiments have been carried out in transparent metal analog systems to examine linear and nonlinear theories of planar interface instability, to track the pattern formation process, to examine steady-state and dynamical processes in the cellular growth region, and to examine the effects of anisotropy of interface properties on growth morphologies. Studies of planar interface instability show that the linear theory of stability accurately describes the critical conditions for the planar interface instability, but it does not accurately describe the wavelengths observed. The nonlinear theory of planar interface instability predicts the possibility of subcritical bifurcation, which was experimentally observed here;Studies of pattern formation show that the pattern formation process is not entirely caotic, but rather, a discrete set of transition wavenumbers exist during the pattern formation process;Studies in the cellular growth region show that the steady-state cellular spacing decreases, increases sharply, and again decreases as the velocity is increased from the point of planar interface instability to the maximum cell growth velocity. Dynamic experiments in the cellular growth region show that adjustment of the cell spacing requires drastic growth morphology changes when the growth conditions are changed slowly in systems where anisotropy of interface properties are present;Studies of the effects of anisotropy on solidification morphologies show that anisotropic interface properties cause cell translation parallel to an advancing solid-liquid interface when the 001 crystallographic direction is not in line with the heat flow direction.

DOI

https://doi.org/10.31274/rtd-180813-13098

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Mark Alan Eshelman

Language

en

Proquest ID

AAI8716763

File Format

application/pdf

File Size

281 pages

Included in

Metallurgy Commons

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