Grain boundary traction signatures: Quantifying the asymmetrical dislocation emission processes under tension and compression

The disruption in crystallographic arrangement of atoms across a grain boundary interface generates local stress fields in the vicinity. Here, we reconstruct the continuum-equivalent grain boundary tractions from local atomic stresses near symmetrical-tilt (110) Ni grain boundaries. We show that the resolved shear stress contribution from the grain boundary tractions, tau(GB), along active slip-systems either assists or prevents the emission of dislocations, depending on its direction with respect to the resolved shear stress contribution from external loading, tau(ext). When tau(GB) acts in the same direction as tau(ext), Shockley partial dislocations are readily emitted from the boundary once vertical bar tau(GB) + tau(ext)vertical bar exceeds the critical barrier stress for shear-slip. When tau(GB) opposes tau(ext), the higher sustainable stresses in the grain boundary structure instead triggers: (a) emission of dislocations from the bulk, or (b) reconfiguration of the grain boundary atomic structure and subsequent emission of non-Schmid dislocations or formation of extrinsic stacking faults. Our results quantitatively explain the asymmetrical grain boundary dislocation emission processes observed in molecular dynamics (MD) simulations under applied tensile and compressive loads. The relationship between the traction signatures and periodic structural units along the grain boundary is discussed. (C) 2017 Elsevier Ltd. All rights reserved.