Simulations of the Effect of Surface Coatings on Plasticity at Small Scales

Three-dimensional dislocation dynamics simulations were employed to examine how hard coatings affect plastic deformation in micron- and submicron-sized, single-crystal pillars ( micropillars ) of nickel. Cross-slip of dislocations in the coated samples was found to be necessary for the formation of banded structures and subcells. Our simulations thus offer an explanation for both the significant increases in compressive strength and the higher strain-hardening rate as well as formation of banded structures in coated micropillars

Discrete Dislocation Dynamics Simulations of Plasticity at Small Scales

Discrete dislocation dynamics simulations in three dimensions have been used to examine the role of dislocation multiplication and mobility on the plasticity in small samples under uniaxial compression. To account for the effects of the free surfaces a boundary-element method, with a superposition technique, was employed. Cross-slip motion of the dislocation was also included, and found to be critical to the modeling of the dislocation behavior. To compare directly with recent experiments on micropillars, simulation samples at small volumes were created by cutting them from bulk three-dimensional simulations, leading to a range of initial dislocation structures. Application was made to single-crystal nickel samples. Comparison of the simulation results and the experiments are excellent, finding essentially identical behavior. Examination of details of the dislocation mechanism illuminates many features unique to small samples and points directly to the importance of both the surface forces and cross-slip in understanding small-scale plasticity