It is easy to imagine applications in vibration damping materials, catalysis etc. The purpose of this article is to illustrate the methodology of modelling as an aid to the design and optimisation of alloys, using experience on iron an steel. In fact, the role of ferromagnetism in stabilising b.c.c. iron has been known for some fifty years, long before electron theory became prominent in metallurgy. Zener factorised the free energy of iron into the magnetic and non-magnetic components in order to explain the peculiar stability of b.c.c. iron at high and low temperatures, interrupted by the occurrence of austenite. This eventually explained why austenite has a larger thermal expansion coefficient than ferrite, even though the two phases have the same Debye temperature and electronic specific heat coefficients.
Elements lose their identity - they simply contribute to an overall free energy.
The friendly output of the such calculations consists of phase fractions and compositions as a function of the overall alloy composition and variables such as temperature and pressure. Scientists have become so used to appreciating the quantitative data for alloys with large numbers of components and phases that it is no longer necessary to teach the tortuous geometries of ternary and quarternary phase diagrams. A system is in thermodynamic equilibrium when there is no perceptible change no matter how long one waits. Most useful microstructures cannot be estimated from phase diagrams because they are not at equilibrium, but the thermodynamic parameters are essential inputs to kinetic theory which describes the approach to equilibrium. The flux could represent an interface velocity, an electrical current or a heat flux, with the driving force, the electromotive force and temperature gradient representing the corresponding forces.