Abstract
An understanding of grain shape and structure is important in order to develop a means of controlling creep cavitation in industrial materials. The present thesis is a fundamental study aimed at providing a basis for this. Quasi-equilibrium grain morphologies resulting from plastic deformation of model two-dimensional and columnar cellular materials, based on arrays of regular hexagonal grains and hexagonal prisms, strained in an arbitrary way, have been investigated. The shapes are characterised in two separate ways. The effect on the grain morphology of subsequent exposure to elevated temperatures has been examined. It has been found possible to deduce the recent thermal and strain history of a model specimen from shape considerations. Experiments on artificial polycrystals have shown great potential for the evaluation of the influence of a wide variety of phenomena on the process of plastic deformation. An experimental technique is described by means of which the underlying assumptions of the theoretical model have been tested quantitatively, and which may be extended to study the details of shape changes in real polycrystals. The analysis has been extended to three dimensions by means of a model based on a body centred array of tetrakaidecahedra, based in general on a triclinic lattice, which reduces to cubic in the strain-free state. The strain history can be deduced, and a recovery process is analysed for the tetragonal and orthorhombic lattices. Model material composed of body centred cubic tetrakaidecahedra has been sectioned computationally. It is demonstrated that metallographic measurements on any single irrational plane reflect the known structure in three dimensions. Some available stereological procedures have been rigorously tested for the first time. The methods in use forequiaxed structures were proved adequate, but some of those pertaining to elongated grains give serious errors.