Ab initio simulations on the pure Cr lattice stability at 0K: Verification with the Fe-Cr and Ni-Cr binary systems

TL;DR

This study compares ab initio and CALPHAD methods for Cr lattice stability, revealing uncertainties in CALPHAD predictions and proposing an integrated approach using both methods for improved thermodynamic modeling.

Contribution

It systematically evaluates the reliability of Cr lattice stability from both ab initio and CALPHAD approaches and proposes integrating ab initio results into CALPHAD databases.

Findings

CALPHAD approach has large uncertainties in Cr lattice stability.

Ab initio HFCC-Cr is a viable method despite FCC-Cr being unstable at ambient conditions.

Integration of ab initio results into CALPHAD enhances thermodynamic modeling.

Abstract

Significant discrepancies have been observed and discussed on the lattice stability of Cr between the predictions from the ab initio calculations and the CALPHAD approach. In the current work, we carefully examined the possible structures for pure Cr and reviewed the history back from how Kaufman originally determined the Gibbs energy of FCC-Cr in the 1970s. The reliability of Cr lattice stability derived by the CALPHAD and ab initio approaches was systematically discussed. It is concluded that the Cr lattice stability based on the CALPHAD approach has large uncertainty. Meanwhile, we cannot claim that the ab initio HFCC-Cr is error-free as FCC-Cr is an unstable phase under ambient conditions. The present work shows that the ab initio HFCC-Cr can be a viable scientific approach. As both approaches have their limitations, the present work propose to integrate the ab initio results into the CALPHAD platform for the development of the next generation CALPHAD database. The Fe-Cr and Ni-Cr binary systems were chosen as two case studies demonstrating the capability to adopt the ab initio Cr lattice stability directly into the current CALPHAD database framework.