Construction of Pt-Au EAM potential and molecular dynamics simulation of friction and nanoindentation

Jianguo Wu, Purdue University

Abstract

This thesis describes the construction of a Pt-Au binary embedded atom model (EAM) potential and molecular dynamics simulations (MD) of Atomic Force Microscopy (AFM) atomic friction and nanoindentation with the new potential. The Pt-Au binary EAM potential is constructed using the existing Pt and Au pure potentials and fitting the Pt-Au cross pair potential. The pure potentials are tested and the cross pair potential is fitted by using Density Functional Theory (DFT) calculated formation energies of several intermetallic alloys. MD simulations are applied to simulate the sliding of an AFM tip on a substrate. Ultra-low friction, also called superlubricity is observed for the incommensurate contact between tip and substrate. The virial atomic shear stress of the contact surfaces is calculated to explain the anisotropy of the friction. Along different scanlines the maximum friction is almost unchanged, while the periodicity of friction varies with that of the potential energy surfaces along the scanlines. The friction force is proportional to the normal load with a fixed contact area and proportional to the contact area with a constant normal load. MD simulations of nanoindentation of a single hemispherical asperity on a surface are quantified using the force-displacement curves. The (1 1 1) surface has the largest maximum repulsive/attractive forces and energy dissipation among three contact surfaces. The Pt-Pt system has the largest maximum force and energy dissipation of all material combinations studied. And, the adhesion effect mainly influences the separating process and has little influence on the approach process.

Degree

M.S.M.E.

Advisors

Martini, Purdue University.

Subject Area

Mechanical engineering|Nanotechnology

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