Stress induced grain boundary processes in metals and minerals : new insights from in-situ TEM nanomechanical testing

The first part of this talk will focus on quantitative in-situ transmission electron microscopy (TEM) observations of the mechanisms of interaction between a coherent twin boundary (CTB) and single arm dislocation sources (SASs) under tensile loading in submicron Ni bi-crystal. The results show that the absorption of curved screw dislocations at the CTB leads to the formation of constriction nodes in agreement with large scale 3D atomistic simulations. The coordinated motion of the twinning dislocation pairs due to the presence of the nodes leads to a unique CTB sliding mechanism, which plays an important role in initiating the fracture process at a CTB ledge. TEM observations of the interactions between non-screw dislocations and the CTB highlight the importance of the synergy between the repulsive force of the CTB and the back stress from SASs when the interactions occur in small volumes. In the second part, I will present resent recent results on a new fundamental mechanisms controlling GB siding in Olivine revealed by TEM. The mechanical properties of olivine-rich rocks are central to decipher the partial mechanical coupling between the lithosphere and asthenosphere.