Seminar Prof. Blazej Grabowski (U Stuttgart, Germany) / Mechanics of Materials research unit, ENTEG

Unveiling the Origin of the Yield Stress Anomaly in L1₂ Intermetallics with physically informed Machine-Learning Interatomic Potentials

Xiang Xu, Xi Zhang, Blazej Grabowski

Institute for Materials Science, University of Stuttgart

Add this event to your Google agenda

Ni-based superalloys are essential for high-temperature applications, e.g., energy plants and aircraft engines, due to their exceptional thermal resistance. Their strength largely originates from L1₂-ordered precipitates, e.g., Ni₃Al, which exhibit an unusual phenomenon known as the yield stress anomaly (YSA)—a more than eightfold increase in yield stress from room temperature to 1200 K. While the YSA is believed to be linked to the formation of Kear-Wilsdorf locks (KWLs), the driving atomistic mechanisms have remained elusive.

Here, we tackle this long-standing challenge using machine-learning interatomic potentials derived via a physically informed active learning scheme. We upscale the accuracy of electronic-structure simulations to large-scale molecular dynamics simulations with 1,5 million atoms. Importantly, the ab initio database contains temperature-dependent Gibbs energies for the relevant planar defects in L1₂ Ni₃Al, covering the full temperature range of the YSA.

We successfully capture the key dislocation behavior at the atomistic level, including dislocation cross-slip, formation of KWLs, and their unlocking process, which has been difficult to observe with traditional empirical potentials. We find that the unlocking stress of KWLs strongly depends on temperature, contradicting existing analytical models. These insights allow us to extract a phenomenological model that better explains the YSA, contributing to the broader understanding of Ni- and Co-based superalloys and L1₂-strengthened high-entropy alloys.

References:

[1] X. Xu, X. Zhang, A. Ruban, S. Schmauder, B. Grabowski, Acta Materialia, 255, 118986 (2023).

[2] X. Xu, X. Zhang, A. Ruban, S. Schmauder, B. Grabowski, Scripta Materialia, 242, 115934

(2024).

[3] X. Xu, X. Zhang, E. Bitzek, S. Schmauder, B. Grabowski, Acta Materialia, 281, 120423 (2024).

Organized by: Mechanics of Materials, ENTEG, PI is Prof. Francesco Maresca