Phase reactions under highly non-equilibrium conditions

A common feature of novel technologies for the production of materials for advanced structural and functional applications is that phase formation frequently occurs under extremely non-equilibrium conditions. Due to the high driving forces of phase reactions, new phase selection phenomena are observed, which are less determined by the thermodynamics of the system than by the atomic mobilities in the competing phases. Striking examples are the formation of metastable and even unstable phases, the (inverse) melting of supersaturated solid solutions upon cooling and the occurrence of a kinetically controlled phase selection during interface reactions. This new area of materials science will be highlighted by selected examples. First approaches to obtain a quantitative description of phase reactions under highly non-equilibrium conditions will be outlined, which unify thermodynamic and kinetic descriptions. In addition, examples of technical applications are given where highly non-equilibrium processing is utilised, or high-energy states of the material are required for advanced performance. (C) 1997 Elsevier Science S.A.