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Abstract The image forces on a screw dislocation due to a grain boundary, or a free surface on which is a surface film, are evaluated. For the case of an oxide layer on aluminium it is shown that there is an equilibrium position for the dislocation, at a depth in the metal approximately equal to the thickness of the oxide film. The behaviour of an edge dislocation is approximately the same.
A. K. Head (Thu,) studied this question.