ABSTRACT
Thermodynamic descriptions in databases for applications in computational thermodynamics require representation of the Gibbs energy of stable as well as metastable phases of the pure elements as a basis to model multi-component systems. In the Calphad methodology these representations are usually based on physical models. Reasonable behavior of the thermodynamic properties of phases extrapolated far outside their stable ranges is necessary in order to avoid that they become stable just because these properties extrapolate badly. This paper proposes a method to prevent crystalline solid phases in multi-component systems to become stable again when extrapolated to temperatures far above their melting temperature.
ABSTRACT
Most models currently used for complex phases in the calculation of phase diagrams (Calphad) method are based on the compound energy formalism. The way this formalism is presently used, however, is prone to poor extrapolation behavior in higher-order systems, especially when treating phases with complex crystal structures. In this paper, a partition of the Gibbs energy into effective bond energies, without changing its configurational entropy expression, is proposed, thereby remarkably improving the extrapolation behavior. The proposed model allows the use of as many sublattices as there are occupied Wyckoff sites and has great potential for reducing the number of necessary parameters, thus allowing shorter computational time. Examples for face centered cubic (fcc) ordering and the σ phase are given.
ABSTRACT
Thermodynamic data are needed for all kinds of simulations of materials processes. Thermodynamics determines the set of stable phases and also provides chemical potentials, compositions and driving forces for nucleation of new phases and phase transformations. Software to simulate materials properties needs accurate and consistent thermodynamic data to predict metastable states that occur during phase transformations. Due to long calculation times thermodynamic data are frequently pre-calculated into "lookup tables" to speed up calculations. This creates additional uncertainties as data must be interpolated or extrapolated and conditions may differ from those assumed for creating the lookup table. Speed and accuracy requires that thermodynamic software is fully parallelized and the Open-Calphad (OC) software is the first thermodynamic software supporting this feature. This paper gives a brief introduction to computational thermodynamics and introduces the basic features of the OC software and presents four different application examples to demonstrate its versatility.
ABSTRACT
For better understanding of corrosion schemes and corrosion mechanisms of a wide range of steels/Fe-alloys, Ni-/NiFe-/Co-superalloys, Al-/Mg-/Ti-/Zr-/Sn-/Cu-/Zn-alloys, electronic-packing alloys, medical-instrument alloys and other materials, under various corrosive environments (such as aqueous solutions, non-aqueous solutions, molten salts, high-temperature gases, etc.) during production/application processes and experimental observations, the Thermo-Calc software/database/programming-interface package can be used. This article is aimed at presenting some application examples of thermodynamic calculations/simulations in some specific areas: aqueous corrosions of stainless steels and other alloys, and of high-performance corrosion-resistant materials (HPCRM); molten salt corrosions of stainless steels and high-temperature alloys; high-temperature gaseous corrosions of steels/alloys; formations of oxide-coated protective layers on steel/alloy surfaces; and emergence conditions during oxidation of steels/alloys.
