Size-dependent elastic interaction of screw dislocations with semi-infinite coating materials revealed by atomistic simulation and two dimensional analysis

The aim of this work is to study the size-dependent elastic interaction of a screw dislocation with an elastic isotropic layered semi-infinite matrix using molecular dynamics analysis. The analytic solutions of complex functions of a screw dislocation in the matrix and in the thin layer are solved by means of applying complex potential approach in conjunction with the techniques of the image method. With the aid of the obtained stress fields and the Peach-Koehler formula, the explicit expressions for the image force acting on the screw dislocation are obtained. The results indicate that a large change in distance between dislocation and interface leads to a slight change in potential energy and stress. The material elastic dissimilarity, the thin layer thickness and the dislocation position play a crucial role in the image force acting on the dislocation. When a screw dislocation is in the matrix or in the layer, the image force approaches a constant value with the increasing thickness of thin layer. In addition, when the matrix is softer than the layer and the dislocation is in the matrix, there is a stable equilibrium position for dislocation; while, when the matrix is softer than the layer and the dislocation is in the layer, there exists a non-stable equilibrium position for dislocation.