[SY-E1] Symposium E-1

[SY-E1] Interaction of screw dislocations with interfaces during multiaxial loading: large scale 3D simulations

Invited

^○maxime Dupraz¹, S.I. Rao², Helena Van Swygenhoven^1,3 (1.PEM-LSC-PSD, Paul Scherrer Institute, Villigen, Switzerland, 2.Materials Directorate, Air Force Research Laboratory, WPAFB,, United States of America, 3.NXMM-IMX-STI, École Polytechnique Fédérale de Lausanne, Switzerland)

In spite of extensive numerical and experimental studies, there are still many open questions related to the interaction of dislocations with interfaces. Large scale 3D Molecular Dynamics simulations of a screw dislocation interacting with Coherent Twin Boundaries (CTB) are presented for Al, Cu and Ni bi-crystals modeled with 6 different embedded atom (EAM) potentials. The simulation cell containing approximately 7.2 million atoms mimics a bi-pillar geometry subjected to compression. Two scenarii were investigated for the interaction between the screw dislocation and the CTB. In the first one, we consider the case of a single arm source: the dislocation is pinned at one end of the sample while interacting with the CTB. In the second one, the dislocation is free to propagate into the incoming grain and to interact with the twin boundary over its entire length. It is shown that both the reaction mechanism and reaction stress depend on the material, the sign of the dislocation, the stacking fault energy, the potential chosen and can differ significantly from the results reported for quasi-2D simulations. In Cu and Ni, screw dislocations can overcome the CTB at a much lower resolved shear stress than in the quasi-2D case by cross-slip using the Friedel-Escaig (FE) mechanism. In Al, the transmission of the screw dislocation into the twinned grain occurs at a much larger stress and is achieved by a sequential mechanism using both Fleischer (FL) and FE mechanism. For all materials, the critical stress for transmission is affected by the dislocation line length and curvature. Our results highlight the importance of directly modeling the slip transfer reactions using full 3D-models.

Following these first results, we extended this study on two fronts. First, we evaluated the impact of the boundary structure on the interaction mechanism and on the critical stress for transmission, by considering the case of Incoherent Twin Boundaries containing ledges. Second, we investigated the influence of complex loading conditions on the GB-dislocation interactions. In particular we simulated intergranular interaction by applying shear stress on the bi-crystal, and performing multiaxial loading tests with different load ratios.