A screw dislocation nucleated from a triple junction

Dislocation mechanism is still considered to be an effective way in plastic deformation of nanocrystalline materials. The possible nucleation of a screw dislocation from the triple junction is explored. The nucleation of a screw dislocation is found to be rather difficult from the triple junction with well-bonded grain boundaries due to the small singularity (0 to −1/3) introduced by the elasticity anisotropy. For the triple junction with a free sliding grain boundary, the stress singularity is higher than −0.5 and dislocations can be spontaneously nucleated for grain sizes less than 100 nm.