Author

Vuko Perovic

Date of Award

6-1980

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Metallurgy and Materials Science

Supervisor

G.R. Purdy

Abstract

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.


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