Dislocation Interactions in the Immediate Vicinity of a Free Surface

The glide interaction stress between two dislocations in the vicinity of a free surface on neighboring parallel glide planes has been calculated for the special case where the one dislocation lies parallel to the line of interaction between the glide plane and the free surface. Consideration has been given to both the edge and screw component and each case has been calculated for different angles alpha of glide plane - free surface interactions. The presence of the free surface causes the passing stress to become dependent on alpha near the surface. It is also found that if under a given applied stress two dislocations of opposite sign can just pass each other in the bulk of the crystal, they cannot do so near the surface under the same applied stress. Whether similar dislocations can pass easier or block each other near the surface depends on their positions. (Author)