PHASE REACTIONS UNDER HIGHLY NONEQUILIBRIUM CONDITIONS

A common feature of novel technologies for the production of materials for advanced structural and functional applications is that phase for mation frequently occurs under extremely non-equilibrium conditions. D ue to the high driving forces of phase reactions, new phase selection phenomena are observed, which are less determined by the thermodynamic s of the system than by the atomic mobilities in the competing phases. Striking examples are the formation of metastable and even unstable p hases, the (inverse) melting of supersaturated solid solutions upon co oling and the occurrence of a kinetically controlled phase selection d uring interface reactions. This new area of materials science will be highlighted by selected examples. First approaches to obtain a quantit ative description of phase reactions under highly non-equilibrium cond itions will be outlined, which unify thermodynamic and kinetic descrip tions. 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 Elsevi er Science S.A.