Date of Graduation

12-2013

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor

Min Zou

Committee Member

Rick J. Couvillion

Second Committee Member

Douglas E. Spearot

Keywords

Applied sciences; Composite thin films; Graphene oxide; Polytetrafluoroethylene; Thin film polymers; Tribology

Abstract

Polytetrafluoroethylene (PTFE) is a commonly used solid lubricant due to its low coefficient of friction and chemical inertness. As a polymer, PTFE suffers from high wear and low adhesion to substrates limiting its use as a thin film. Thin PTFE films are ideal candidates for solid lubrication in micro-machines and bearing applications. The main goal of this work is to enhance the durability of thin PTFE films through the addition of few layered graphene oxide (GO) as filler. In order to address adhesion issues, the addition of an adhesive layer of polydopamine (PDA) between stainless steel substrates and thin PTFE films was also investigated.

An automatic friction abrasion analyzer was used to perform friction and wear testing with a ball-on-flat configuration. Wear tracks of the thin PTFE films were analyzed using optical microscopy and a surface profilometer. Counterfaces were examined using optical microscopy and atomic force microscopy for the formation of PTFE transfer film.

The lone addition of GO to PTFE thin films increased durability by nearly 6 times. Combining an adhesive layer of PDA and GO as filler to thin PTFE films resulted in a significant increase in durability of approximately 41 times. Single coatings of unfilled PTFE films experienced large amounts of delamination, plowing, and global shearing of PTFE bands within the wear track during friction and wear testing. The addition of GO particles impeded global shearing of the PTFE bands while slowing the wear rate of thin PTFE films through load support. Upon the addition of PDA, changes in the wear mechanism were evident. A mixture of plowing and cutting was observed for samples employing a PDA adhesive layer. Ribbon-like wear debris was generated during testing. Increasing the adherence also minimized delamination of the thin PTFE film from the substrate. Overall, the results showed that significant increases in durability of thin PTFE films can be achieved through the addition of GO as filler, especially when an adhesive layer of PDA is applied between the film and substrate.

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