Molecular dynamics simulations of strengthening due to silver precipitates in copper matrix

Molecular dynamics simulations of edge dislocation interactions with coherent and incoherent silver precipitates in the copper matrix are applied to investigate precipitation strengthening. Simulated shear tests with spherical and octahedral precipitates revealed that dislocations can cut a precipitate or circumvent it by the Orowan mechanism. Precipitates with radii below 3nm are cut whereas both processes were observed for radii in the range of 3-9nm. The reason for the occurrence of the Orowan mechanism is that dislocation reactions at the interface can lead to sessile dislocations. Orowan circumvention is more likely for spheres than for octahedra which is due to different dislocation types existing at the matrix/precipitate interfaces. On average, the critical resolved shear stress is found to be slightly higher for Orowan processes. In case of small precipitates, the critical resolved shear stress depends strongly on the coherency, whereas for larger precipitates, it is mainly influenced by dislocation reactions at the interface. In some cases, the formation of a jog was observed which can reduce the critical resolved shear stress whereas it was increased significantly in the cases of pronounced cross-slip without jog formation.