Thermodynamic quantities in nucleation

This paper reviews the present knowledge on experiments and modelling of th ermodynamic quantities which determine the nucleation rate of crystals from undercooled melts and glasses: the free energy difference between liquid a nd crystal phases and the crystal/melt interfacial free energy. The main em phasis is on primary transformations in which the nucleating phase differs in composition from the matrix. The most significant cases, widely studied in the last decade, are those leading to two-phase materials made of a nano crystalline phase, e.g. Fe or Al, embedded in a glass. Such a microstructur e must imply high nucleation rates of compact phases but also low nucleatio n rate of other phases which may result From thermodynamic contributions. At first a method is presented for calculation of the interfacial energy in pure metals at the melting point and on undercooling. It allows to establi sh a reference state for this quantity. Then, extension to alloy systems is achieved by means of conventional thermodynamic relationships. Subsequentl y, the free energy difference between matrix and crystals in primary transf ormations is discussed. (C) 2001 Elsevier Science B.V. All rights reserved.