Origin of the Yield Stress Anomaly in L1 2 Intermetallics - Unveiled with Physically-Informed Machine-Learning Potentials

Aug 5, 2026

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Yield stress anomaly in L1 2 intermetallics such as Ni3Al and Ni3Ga is governed by the Kear-Wilsdorf lock (KWL), whose formation and unlocking depend on dislocation cross-slip. Molecular dynamics simulations use a physically-informed, active-learning machine-learning interatomic potential to model dislocation behavior in Ni3Al with near–ab initio fidelity. Simulations capture KWL formation and unlocking and reveal a strong temperature dependence of unlocking stress that contradicts existing analytical assumptions. A phenomenological model is proposed to fit atomistic unlocking stresses and extrapolate to macroscopic behavior, applicable to other L1 2 intermetallics.

LanguageEnglish

CategoryResearch & Report

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Pages22

Reading Time55 min

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Introduction

Yield stress anomaly in L1 2 intermetallics

Kear-Wilsdorf lock and dislocation cross-slip

Limitations of existing analytical and atomistic models

Physically-informed machine-learning interatomic potentials

Study approach and dataset construction (DFT/MlIP)

arXiv :2406 .04948v1 [ cond-mat .mtrl-sci ] 7 Jun 2024 Origin of the yield stress anomaly in L1 2 intermetallics unveiled with physically-informed machine-learning potentials Xiang Xu 1,2,* , Xi Zhang 1,* , Erik Bitzek3 , Siegfried Schmauder2 , and Blazej Grabowski 1 1 Institute for Materials Science, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany 2 Institute for Materials Testing, Materials Science and Strength of Materials, University of Stuttgart, Pfaffenwaldring 32, 70569 Stuttgart, Germany 3 Computational Materials Design, Max Planck Institute for Sustainable Materials, Max-Planck-Straße 1, 40237 Düsseldorf, Germany. * Emails: [xiang.xu@imw.uni-stuttgart.de](xiang.xu@imw.uni-stuttgart.de); [xi.zhang@imw.uni-stuttgart.de](xi.zhang@imw.uni-stuttgart.de) Abstract The yield stress anomaly of L1 2 intermetallics such as Ni3 Al or Ni3 Ga is controlled by the so-called KearWilsdorf lock (KWL), of which the formation and unlocking are governed by dislocation cross-slip. Despite the importance of L1 2 intermetallics for strengthening Ni-based superalloys, microscopic understanding of the KWL is limited. Here, molecular dynamics simulations are conducted by employing a dedicated machine-learning interatomic potential derived via physically-informed active-learning. The potential facilitates modelling of the dislocation behavior in Ni3 Al with near ab initio accuracy. KWL formation and unlocking are observed and analyzed. The unlocking stress demonstrates a pronounced temperature dependence, contradicting the assumptions of existing analytical models. A phenomenological model is proposed to effectively describe the atomistic unlocking stresses and extrapolate them to the macroscopic scale. The model is general and applicable to other L1 2 intermetallics. The acquired knowledge of KWLs provides a deeper understanding on the origin of the yield stress anomaly. Keywords: Yield stress anomaly; Dislocation cross-slip; L1 2 intermetallics; Molecular dynamics simulations; Machine-learning potentials. 1 Introduction Ni-based superalloys are used for turbine blades because they withstand thermal mechanical loadingsunder high turbine-entry temperatures [1 , 2] . Over several generations of these superalloys and corresponding thermal barrier coatings, the turbine-entry temperatures have increased by 700 K [3], significantly improving the thermodynamic efficiency of aircraft engines. The outstanding thermal resistance mainly originates from a high volume fraction of L1 2-ordered precipitates. In contrast to common structural materials, the yield stress of certain L1 2 intermetallics, e.g., Ni3 Al [4] or Ni3 Ga [5], increases with temperature, typically accompanied with an anomalously increasing work-hardening rate. As this so-called yield stress anomaly (YSA) is pivotal for strengthening advanced alloys, the steady increase of understanding YSA has been a key ingredient not only to the evolution of Ni-based superalloys [1 , 2 , 6] and Co-based superalloys [7–9], and also for the development of L1 2 strengthened high-entropy alloys [10 , 11] . However, the origin of YSA is still not satisfactorily clarified [6] . What is known from transmission electron microscopy (TEM) on samples deformed in the temperature region of the YSA [12, 13] is that the dislocations in Ni3 Al exhibit a unique non-planar dislocation core structure—nowadays referred to asthe Kear-Wilsdorf lock (KWL) . The dislocation core was shown to evolve through cross-slip [14 , 15] in which three planar defects are involved: two antiphase boundaries (APBs) on the (100) and (111) planes plus a complex stacking fault (CSF) . Several analytical models [16–22] have been proposed to comprehend KWLs and their relation to YSA, considering factors like the difference between the formation energies of the (111)APB and (100)APB [16], and torque interactions between the superpartials [17] . The “APB-jump” phenomenon observed in in situ TEM e

FAQs

What controls the yield stress anomaly in L1 2 intermetallics like Ni3Al and Ni3Ga?

It is controlled by the Kear-Wilsdorf lock (KWL), whose formation and unlocking are governed by dislocation cross-slip.

How are the dislocation processes studied in this work?

The study performs molecular dynamics simulations using a dedicated machine-learning interatomic potential derived via physically-informed active learning, enabling near–ab initio accuracy.

What key finding challenges existing analytical models?

The unlocking stress shows a pronounced temperature dependence, contradicting the assumptions of existing analytical models.

Aug 5, 2026

Upload by Oliver