Date of Award
Doctor of Philosophy (PhD)
Metallurgy and Materials Science
The influence of the elastic interaction energy of plate-shaped precipitates causing tetragonal distortion on nucleation, growth and coarsening is considered.
The analysis shows that the elastic interaction energy may be minimized by the formation of regular three-dimensional arrays, which emphasize the "edge-face" configuration. Algebraic conditions of stability against coarsening are developed, and the results of the detailed numerical test of stability against coarsening for a particularly simple and symmetric array are reported. Experimental observations on θ" (Al-3%Cu alloy) microstructures show strong evidence of short-range ordering, with two characteristic configurations (edge-face and "parallel-step"), both energetically favourable.
It is shown that the elastic interaction energy may have a decisive role in the nucleation stage of θ' preoipitates. The θ' microstructure, in a relatively early stage of development, is often inhomogeneous and consists mainly of linear (parallel inclined and cross-like) stacks.
Numerical calculations of the elastic interaction energy show that the experimentally observed stacks are energetically favourable, and can be generated in an auto-catalytic way. Numerical and preliminary experimental results on the stability against growth and coarsening of elastically-locked linear arrays are reported.
Finally, the chemical driving force and elastic retarding force acting on moving ledges on a planar interphase boundary are considered. It is shown that elastic interaction may cause a departure from the local equilibrium at a moving growth ledge, and may dictate the location of "homogeneous" nucleation of growth ledges. Some experimental results concerning ledge nucleation and ledge interaction are reported.
Perovic, Vuko, "On the elastic interaction of plate-shaped precipitates" (1980). Open Access Dissertations and Theses. Paper 3260.