Graduation Year

2008

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Physics

Major Professor

David Rabson, Ph.D.

Keywords

Atomistic simulation, Quasicrystals, Nano-tribology, Contact mechanics, Aperiodicity

Abstract

In 2005, Park et al. demonstrated that the 2-fold surface of a d-AlNiCo quasicrystal exhibits an 8-fold frictional anisotropy, as measured by atomic-force microscopy, between the periodic and aperiodic directions [37, 38]. It has been well known that quasicrystals exhibit lower friction than their crystalline counterparts [35, 17, 47, 28, 12, 50]; however, the discovery of the frictional anisotropy allows for a unique opportunity to study the effect of periodicity on friction when chemical composition, oxidation, and wear are no longer variables. The work presented herein is focused on obtaining an understanding of the mechanisms of friction and the dependence of friction on the periodicity of a structure at the atomic level, focusing on the d-AlNiCo quasicrystal studied by Park et al. Using the LAMMPS [41] package to simulate the compression and sliding of an 'adamant' tip, see section 3.3, on a d-AlNiCo quasicrystalline approximant substrate, we have demonstrated, in preliminary results, an 8-fold frictional anisotropy, but in more careful studies the anisotropy is found to be much smaller. The simulations were accomplished using Widom-Moriarty pair potentials to define the interactions between the atoms [33, 52, 51, 9]. The studies presented in this work have shown a clear velocity dependence on the measured frictional response of the quasicrystalline approximant's surface. The final results show between a 1.026-fold and 1.127-fold anisotropy between sliding in the periodic and 'aperiodic' directions, depending on the sliding velocity.

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