Dislocation Nucleation and Interaction under Nanoindentation in Single Crystalline Al and Cu: Molecular Dynamics Simulations

Recent advances in miniaturization and highly-accurate measurement techniques have allowed mechanical properties to be measured at the nanometer scale. Nanoindentation has been widely used because of its applicability in ambient conditions. Unstable displacement burst or the abrupt growth of indent displacement after homogeneous elastic deformation observed in crystalline materials is a unique plastic deformation characteristic (nanoplasticity). In the present paper, a series of atomistic simulations of nanoindentation in single crystalline aluminum and copper are performed in analyzing the critical state for dislocation nucleation and interaction between dislocations beneath the indenter. With reference to the Hertzian solution based on isotropic linear elastic theory, both the anisotropic effect and nonlinear behavior of nanoindentation are discussed in detail. The discovery was made that the incipient yield process is strongly related to the triaxial stress state created beneath the indenter, and that energetically unfavorable interactions accompanied with cross slip induce the formation of prismatic dislocations.