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Mechanism of thermally-activated prismatic slip in Mg

Xin Liu1*, William Curtin1

1 Laboratory for Multiscale Mechanics Modeling, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Vaud, Switzerland

* Corresponding authors emails: xin.liu@epfl.ch
DOI10.24435/materialscloud:bf-5x [version v1]

Publication date: Nov 30, 2023

How to cite this record

Xin Liu, William Curtin, Mechanism of thermally-activated prismatic slip in Mg, Materials Cloud Archive 2023.185 (2023), https://doi.org/10.24435/materialscloud:bf-5x


Prismatic slip of the screw <a> dislocation in magnesium at temperatures ≳ 150 K is understood to be governed by double-cross-slip of the stable basal screw through the unstable prism screw and back to the basal screw, with the activation energy controlled by the formation energy of two basal-basal kinks. However, atomistic studies of the double-kink process predict activation energies roughly twice those derived experimentally. Here, a new mechanism of prism glide is proposed, analyzed theoretically, and demonstrated qualitatively and quantitatively via direct molecular dynamics (MD) simulations. The new mechanism is intrinsically 3d, and involves the nucleation of a single kink at the junction where a 3d prismatic dislocation loop transitions from the basal screw segment to non-screw prismatic character. The relevant kink energies are calculated using recently-developed Neural-Network Potentials (NNPs) for Mg that show good agreement versus DFT for basal and prism <a> dislocations, enabling a parameter-free analytic model for the activation barrier. Direct MD simulations show both operation of the precise proposed mechanism and a stress-dependent activation barrier that agrees reasonably with the analytic model. Predictions of dislocation velocity compare very well with in-situ TEM data, and macroscopic strength versus temperature can also be understood. Overall, the new intrinsically 3d mechanism for dislocation glide due to single kink nucleation rather than double-kink nucleation explains key features of the prismatic slip in Mg and may have broader applicability in other metals where kink nucleation processes control thermally-activated flow.

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External references

Journal reference
X. Liu, W. Curtin, Acta Materialia 262, 119402 (2024) doi:10.1016/j.actamat.2023.119402


Magnesium Prismatic slip Neural network potential MARVEL

Version history:

2023.185 (version v1) [This version] Nov 30, 2023 DOI10.24435/materialscloud:bf-5x