Abstract
The influence of in-plane residual stress on Hertzian nanoindentation for single-crystal copper thin film is investigated using molecular dynamics simulations (MD). It is found that: (i) the yield strength of incipient plasticity increases with compressive residual stress, but decreases with tensile residual stress; (ii) the hardness decreases with tensile residual stress, and increases with compressive residual stress, but abruptly drops down at a higher compressive residual stress level, because of the deterioration of the surface; (iii) the indentation modulus reduces linearly with decreasing compressive residual stress (and with increasing tensile residual stress). It can be concluded from the MD simulations that the residual stress not only strongly influences the dislocation evolution of the plastic deformation process, but also significantly affects the size of the plastic zone.
Highlights
Nowadays, thin film materials at micro- and nano-scale play a significant role in a wide range of engineering applications, such as medical instruments, micro-/nano-electromechanical systems (MEMS/NEMS), and optical devices [1,2,3,4]
We found that the residual stress has an effect on the local surface hardness and incipient plasticity
The effects of in-plane residual stress on Hertzian nanoindentation behaviors for single-crystal copper thin film have been investigated through molecular dynamics simulations (MD) simulations
Summary
Thin film materials at micro- and nano-scale play a significant role in a wide range of engineering applications, such as medical instruments, micro-/nano-electromechanical systems (MEMS/NEMS), and optical devices [1,2,3,4]. Residual stress is a particular non-ignorable factor, which can influence the thin film material’s hardness and its plastic deformation behavior. The controversy about residual stress function on the plastic deformation of nanoindentation in the literature suggests that more efforts need to be made, and new research approaches need to be employed, to reveal the deformation mechanism at micro-scale. The nanoindentation behavior of a metal film under a spherical indenter was first simulated using MD by Kelchner et al [20]. We [24] simulated the nanoindentation of a virtual sphere indenter for single-crystal copper thin film. We perform MD simulations of nanoindentation for single-crystal copper thin film with pre-existing equiaxial stress, to study the effect of residual stress on plasticity deformation. The mechanism of the elastic–plastic transition will be explored, and the dynamics of dislocation evolution and the indentation stress field will be investigated
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