ICAMS / Interdisciplinary Centre for Advanced Materials Simulation


Third generation CALPHAD databases: New unary database and its application for re-assessment of binary systems

Date: 30.05.2018
Place: CALPHAD XLVII Conference, Juriquilla, Querétaro, México

Irina Roslyakova
Setareh Zomorodpoosh
Abdulmonem Obaied
Brandon Bocklund, Department of Materials Science and Engineering, Pennsylvania State University, University Park, USA
Richard Otis, Engineering and Science Directorate, California Institute of Technology, Pasadena, CA, USA
L. Zhang
Zu-Li Liu, Huazhong University of Science and Technology, Wuhan, China

One core research task towards the 3rd generation thermodynamic database is to establish the reliable and robust thermodynamic description from 0K up to the melting point and far above it. Currently, several alternative physics-based models and approximation methods have been proposed to replace the standard SGTE polynomial description. Many authors contributed to this direction since 1995 to develop the 3rd generation CALPHAD-type thermodynamic descriptions for some pure elements and limited binary systems. One of the successful attempts in this direction has been performed by Roslyakova et al. [1]. A novel thermodynamic modeling strategy of stable, metastable and liquid phases is proposed based on automated segmented regression (SR) approach and has been applied to 18 pure elements, 5 compounds and several binary systems. A most recent results obtained with SR model is a thermodynamic re-assessment of Cr-Nb binary system from 0K [2]. The low-temperature heat capacities missing in all the previous thermodynamic modeling and the newly reported standard enthalpy of formation for Laves C15 phase has been taken into account. Here, the proposed SR model has been applied to describe the Gibbs energy of pure elements and stoichiometric Cr2Nb phase from 0K. The calculated phase equilibria and thermodynamic properties according to the presently obtained thermodynamic descriptions of binary Cr-Nb system agree well with most of the experimental data, and show better agreement than the previous assessments. Taking into account that each new model as well as new experiments or DFT data require a re-assessment of relevant systems and its subsystems, it is clear that data repositories and effective automation tools together with robust mathematical models are essential components to improve the efficiency of future CALPHAD modeling. Therefore, in addition to the classical application of commercial thermodynamic software for the reassessment of binary systems, an integration of SR model into alternative open-source ESPEI software [4] will be presented in this work. EPSEI provides a modern and efficient framework for automation of CALPHAD-type calculation.

[1] Roslyakova, I., et al. „Modeling of Gibbs energies of pure elements down to 0K using segmented regression”, CALPHAD Journal, 55 (2016).
[2] Jiang, Y., et al., “Thermodynamic reassessment of binary Cr-Nb system down to 0 K”, CALPHAD (2018) in revision.
[3] Lu, H. J., et al., “Thermodynamic modeling of Cr-Nb and Zr-Cr with extension to the ternary Zr-Nb-Cr system”, Calphad 50 (Supplement C) (2015) 134–143.
[4] Bocklund, B., et al., ESPEI for Efficient Database Development, Modification and Uncertainty Quantification: Application to the Cu-Mg System”, CALPHAD 2018 conference (accepted talk).

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