MODELING MELTING IN BINARY-SYSTEMS

A coarsened model for a binary system with limited miscibility of comp onents is proposed; the system is described in terms of structural sta tes in small parts of the material. The material is assumed to have tw o alternative types of crystalline local arrangements associated with two components of the alloy. Fluctuating characteristics of a cluster are the type and the space orientation of its crystalline arrangement. There are two different phase transitions in the model system, an ori entation order-disorder transition representing melting, and a phase t ransition between phases differing in concentration of components. Dep ending on the parameters characterizing the interaction in the system, this last transition may take place both in the crystalline and in th e amorphous (molten) phase. A special approximation is used to study t he thermodynamics of the system. The calculated phase diagram describe s, at least qualitatively, the most important features of a binary sys tem.