[SY-C1] Symposium C-1

[SY-C1] Generalized yield criterion in BCC metals from first principles

^○Antoine Kraych¹, Lucile Dezerald², Emmanuel Clouet³, Lisa Ventelon³, François Willaime³, David Rodney¹ (1.Institut Lumière Matière, Université Lyon 1, France, 2.Institut Jean Lamour, Université de Lorraine, France, 3.DEN-Département des Matériaux pour le Nucléaire, CEA, Université Paris-Saclay, France)

At low-temperature, the plastic deformation of tungsten and other body-centered cubic (BCC) metals is anisotropic, and does not follow the Schmid law applicable to most other metals. This feature arises from the behavior of 1/2<111> screw dislocations, which control the plasticity of BCC materials. Under the application of a simple shear stress, the dislocation trajectory undergoes microscopic deviations that are directly linked to the so-called twinning/antitwinning asymmetry (Dezerald et al. 2016). However, other components of the applied stress tensor, the non-glide stresses, are also known to influence the dislocation mobility (Duesbery & Vitek 1998). In this work we use first principles calculations to explore the influence of non-glide stresses on the mobility of screw dislocations in BCC tungsten and determine a generalized yield criterion.

DFT calculations and nudged elastic band method are used in order to determine the Peierls potential of screw dislocations under stress. Different stress tensors are applied to the simulation cells, allowing to calculate the sensibility of the Peierls potential to non-glide stresses, and obtain the dependence of the dislocation Peierls stress on these stresses. These calculations are used to adjust a yield criterion, predicting the response of a single crystal to a tensile test, and the corresponding activated glide systems. Implications regarding non-Schmid slip on weakly stressed systems will be discussed.