The role of surface steps in the nucleation of dislocations from a free surface was studied by means of static atomistic simulations, using a many-body potential for Al. A face-centered cubic crystal with a {100} free surface that contained a monatomic step lying along a <110> dense direction was submitted to an increasing uniaxial stress along a direction in the {100} plane. At a sufficiently high applied stress, which was nevertheless well below the theoretical strength, dislocations were nucleated at the step and glided in the {111} planes which emerged at the step. The type of dislocation which formed (Shockley partial of 90º or 30º type, perfect dislocations) was predicted by considering the resolved shear stress in the {111} planes. The plane where glide would occur was favoured well before nucleation, and shear of increasing amplitude and extent was progressively localized on this plane.

Dislocation Nucleation from Surface Steps - Atomistic Simulation in Aluminium. S.Brochard, P.Beauchamp, J.Grilhé: Philosophical Magazine A, 2000, 80[3], 503-24