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MM: Fachverband Metall- und Materialphysik

MM 11: Structurally and Chemically Complex Alloys

MM 11.4: Vortrag

Dienstag, 10. März 2026, 11:00–11:15, SCH/A215

Effect of partial occupancy on the properties of FeCr σ-phase — •Mariano Forti¹, Guillaume Laplanche¹, Wenhao Zhang², Ralf Drautz¹, and Thomas Hammerschmidt¹ — ¹Ruhr Universität Bochum, Germany — ²LINK, CNRS-Saint-Gobain- NIMS

The σ-phase forms in Fe-Cr alloys over 870K at about 50 at.% Cr, strongly affecting their performance. Atomistic studies usually assume a sublattice model, but experiments show fractional occupancy of the Whyckoff sites, creating many possible local atomic configurations. This complexity limits direct sampling with DFT and opens questions about the effect of partial occupancy on properties of the σ-phase.

We address the problem using a combination of DFT and MLIPs for a Fe16Cr14 σ-phase with experimentally observed site occupancy. We use a GRACE potential to screen all possible configurations of the intermetallic and validate the predictions with DFT calculations of a representative selection of configurations.

This approach enables a direct comparison between the traditional sublattice models and explicit disorder. Our results show that partial occupancy stabilizes the σ-phase, while mechanical properties differ roughly 10% from those predicted by sublattice models.

These findings provide a clearer picture of the local chemical disorder effects on the mechanical response of the σ-phase.

Keywords: sigma phase; elastic constant; DFT; FeCr; machine learning interatomic potential