Dynamics of a dislocation bypassing an impenetrable precipitate: The Hirsch mechanism revisited

The dynamical process where an edge dislocation in fcc copper bypasses an impenetrable precipitate is investigated by means of molecular dynamics simulation. A mechanism that is quite different from the Orowan mechanism is observed, where a dislocation leaves two prismatic loops near a precipitate, i.e., the Hirsch mechanism. It is found that the critical stress for the Hirsch mechanism is almost the same as the Orowan stress, while spatial inhomogeneity of the shear stress is essential to the Hirsch mechanism. We also find that repetition of the Hirsch mechanism does not increase the critical stress.