Dislocation Nucleation and Interaction Under Nanoindentation in Single Crystalline Al and Cu (Simulations by Molecular Dynamics)

Abstract

Recent advances in miniaturization and high-accuracy measurement techniques have allowed us to measure the mechanical properties at the nanometer scale. Nanoindentation has been widely used because of its applicability under ambient conditions. Unstable displacement burst, that is abrupt growth of indent depth after homogeneous elastic deformation observed in crystalline materials, is one of the unique plastic deformation (nanoplasticity). In the present paper, we perform a series of atomistic simulations of nanoindentation in single crystalline Al and Cu to analyze the critical state for dislocation nucleation and interaction between dislocations beneath the indenter. Referring Hertzian solution based on the isotropic linear elastic theory, we attentively disscuss the anisotropic effect and the nonlinear behavior under nanoindentation. Consequently, it is found that 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.