Behavior of Dislocations in a Surface-Layer/Substrate Elastic System

Abstract

Within the framework of the dislocation theory, we analyzed the behavior of discrete screw dislocations in an elastic system, subjected to transverse shearing, composed of a semi-infinite substrate and a completely bonded surface-layer. The fundamental equations for the image stress due to the discontinuity of the shear modulus at the interface and the surface were derived using the concept of image dislocations. The results of the analysis and dislocation dynamics simulation showed that if the shear modulus of the surface-layer is lower than that of the substrate, the movement of dislocations escaping from the surface is suppressed by the reduction in the applied stress and attractive image stress. In the case of the surface-layer with a shear modulus higher than that of the substrate, the dislocations in the substrate are arrested in the vicinity of the interface by the repulsive image stress. However, such arrested dislocations generate a high stress filed in the surface-layer, so that fracture can occur from the layer even under a relatively low remote applied stress.