The phase diagrams are visual representation of the material state as a function of temperature, pressure and concentrations of the constituent components. There are two approaches in phase diagrams investigations and thermodynamic properties of multi-component systems were studied, these approaches were: experimental and theoretical methods.[ Udovsky ,2002]
Phase diagrams are critical research tools for many scientific disciplines, including material science, ceramics ,geology, physics, metallurgy, chemical engineering, and chemistry. So phase diagrams can be regarded as “road maps” for materials processing because they contain important information for the development of new materials, control of structure and composition of critical phases, and improvement properties of technologically important materials. The applications of phase diagrams ranging from the preparation of, single-phase bulk materials, deliberate precipitation of second phases, to the formation of melts.[Wong2001, Liu2004]
Over the past decades, CALPHAD (CALculation of PHAse Diagrams) thermodynamic modeling has been widely recognized as a powerful tool in predicting multi- component phase diagrams and guiding new materials development. CALPHAD modeling begins with the evaluation of descriptions of pure elements and binary systems. By combining the constitutive binary systems and ternary experimental data, ternary interactions and Gibbs energy of ternary phases have been obtained. Thermodynamic databases thus developed cover the whole composition and temperature ranges, including experimentally uninvestigated regions. It is based on the fact that a phase diagram is a manifestation of the equilibrium thermodynamic properties of the system, which are the sum of the properties of the individual phases. [Noirfontaine2012, Liu2004]