Atomistic simulation of surface cyclic slip irreversibility in FCC metals

International audienceThe mechanical behaviour of surface steps created by the emergence at the free surface of gliding dislocations, subjected to cyclic loading is examined using molecular dynamics simulations. Different face centred cubic metals, Al, Cu, Ag and Ni are analysed. An atomistic reconstruction phenomenon is observed at these surface steps which can induce strong irreversibility. The irreversibility cumulates and a micronotch is produced whose depth increases cyclically. A rough estimation of surface irreversibility for pure edge dislocations gives an irreversibility fraction between 0.5 and 0.75 in copper. An analysis coupling surface mechanisms with the classical EGM bulk slip irreversibility model gives an irreversibility fraction of 0.62 in copper for pure screw dislocations, contrary to many sketches proposed in the past. It seems that oxygen molecules cannot lead to higher irreversibility as they have no major influence on different mechanisms linked to surface relief evolution

Relationship between structure, segregation and electrical activity in grain boundaries

Using the contactless microwave phase-shift technique (μ W-PS) and High Resolution Transmission Electron Microscopy (HRTEM), we show that the twist and mixed parts of a Σ = 51(θ = 16.10∘) grain boundary in germanium (Ge) are electrically active. We also show that we can passivate the electrically active grain boundaries by sulfur segregation which has been studied by energy filtering HRTEM. Atomistic simulations show that the most favorable places for this segregation are the high energy sites of grain boundar