Interface-dislocation interaction on sub-micron scales

Interfaces are given considerable attention in the field of nanotechnology, as many of the preferred material properties that are observed at the nanoscale are attributed to the high surface to volume ratio that is present at sub-micron scales. The optoelectronic properties of semiconductors, for example, depend on the number of dislocations that are present at the interface between the nano-sized doping elements and the matrix. In the present paper a first step is taken towards understanding the interface-dislocation interactions. The theoretical framework used is that of gradient plasticity framework, enhanced with a separate interface energy term. This interface energy depends on the plastic strain at the interface and defines an interface yield-like criterion which indicates the stress at which the interface begins to deform plastically. Experimentally this interfacial yielding is captured through nanoindentation experiments near the grain boundary of crystalline materials, namely Fe-2.2wt%Si. Fitting the theoretical analytical expression to the experimental data allows the determination of the key material parameters; for Nb it gives the internal length to be approximately 1.4μm, and in fact for pure (single phase) materials the dislocation source distance is approximated as 1.5μm. In order to further render the interface-dislocation interactions, discrete dislocation dynamics simulations are presented for a micronscale tri-crystal with rigid/non-deforming grain boundaries. The resulting strain distribution profile from the simulation coincides with the predicted plastic strain of the gradient plasticity framework, while the best fit results when the internal length in the analytical expression is chosen to be the same as the value of the dislocation source distance used in the simulation. Hence, the gradient plasticity model that considers an interface energy term has been validated using experimental and numerical investigations.