ABSTRACT
The subject of thermodynamic stability in materials systems is of fundamental importance, underpinning considerations of phase equilibria and phase transformations. When two or more crystallographically distinct phases are considered, two or more Gibbs energy curves are required to construct the two-phase equilibrium and the Gibbs energy at the ‘end-points’ of the mixing curve must be considered. The chapter considers the theme of phase transformations in some detail, particularly those involving solidification and melting processes, with special reference to illustrating changes in compositions and relative proportions of the phases as a function of temperature. The intersection of the respective curves corresponds to the equilibrium temperature for the occurrence of an allotropic transformation. The solid state allotropic transformations in iron and titanium are utilised to their fullest extent in the control of microstructure of important industrial alloys based on the elements.
