First-principles-based phase diagram for the Al-Ni system

Theresa Davey1, Nguyen-Dung Tran1, Arkapol Saengdeejing1, Ying Chen1

1. School of Engineering, Tohoku University, Japan

JIM Spring 2019, Tokyo Denki University, Tokyo, Japan

Contributed oral presentation

Phase diagrams calculated entirely from first principles have potential to reduce time and expense in investigations for materials design by providing important thermodynamic information on new material systems at the prediction stage. However, it is still difficult to create a thermodynamic description of most systems using only calculated data and conventional methods.

An approach is proposed that considers several theoretical techniques to inform a CALculation of PHAse Diagrams (CALPHAD)-based thermodynamic description derived only from first principles data. Commonly, thermodynamic descriptions made using the CALPHAD approach use the Bragg-Williams approximation to describe the configurational entropy of a solid, which is a point correlation model ignoring the pair and higher order interactions [1]. Generally, other entropy contributions are indirectly contained within the excess energy terms that have optimized parameters fitted to experimental data. The Bragg-Williams entropy model with pure computational data does not give a proper description of the phase diagram, which is partially attributed to the lack of consideration of short range ordering. Various techniques have been implemented to modify the Gibbs energy of the CALPHAD descriptions of the fcc and bcc phases, such as by using reciprocal interaction parameters in a structure based on the compound energy formalism (CEF) [2,3].

Al-Ni is taken as a prototype system to compare various thermodynamic models and test the proposed new approach for calculating phase diagrams. The modified interaction parameters introduce the effects of short range ordering and consider higher order cluster contributions to the configurational entropy. A satisfactory solid phase diagram that has topological features of the experimental phase diagram is produced, using a CALPHAD platform and only first principles data.

[1] W. Shockley; J. Chem. Phys. 6 (1938) 130
[2] A. Kusoffsky et al.; Calphad 25 (2001) 549
[3] T. Abe et al.; Calphad 45 (2014) 40