Date of Graduation

5-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Hameed A. Naseem

Committee Member

Rick J. Couvillion

Second Committee Member

Uchechukwe C. Wejinya

Third Committee Member

Darin W. Nutter

Fourth Committee Member

Po-Hao Huang

Keywords

Applied sciences, Nano-porous topographies, Si-cu composites, Tribology of sliding surfaces

Abstract

As the expectations for modern machinery's tribological and thermal performances continue to rise, the retention of lubricant on the contact surfaces of their sliding components becomes an increasingly important issue. Friction and wear cause heat-related failures which lead to catastrophic damage to machinery. Evaporation of a lubricant's volatile constituents as well as lubricant migration leads not only to a reduction in lubricant quantity but also in its quality, thus facilitating component failures. In order to enhance component reliability, the surface should incorporate features that actively retain lubricants. The unique properties of nano-porous topographies such as their high surface area-to-volume ratio indicate they hold great potential to address these lubrication issues.

Thermodynamics-based numerical models of smooth and nano-porous Si-Cu composite topographies were developed to predict the trends of lubricant retention. Photolithographic processes as well as physical etching and thin film deposition tools were utilized to fabricate smooth and patterned Si-Cu composite sample types. The nano-porous topographies incorporated various nano-pore geometries for determination of the optimum conditions for lubricant retention. Amorphous Si film was deposited on the samples using chemical vapor deposition which served as a surface chemistry modification to examine the film's potential to enhance lubricant retention. Lubricant retention tests were performed using a custom-fabricated apparatus for evaporating lubricant from the sample types. Finally, the model's predictions of lubricant retention trends were compared to actual testing results to examine the validity of those predictions.

The predictions of the models were supported by the evaporation testing data obtained from the samples. It was found that surface nano-pores having the proper geometry, in combination with the dehydrogenated amorphous Si surface chemistry, could significantly enhance retention above the one micrometer fluid film thickness typically formed between interacting surfaces of machine components undergoing relative motion. The surface features show potential to prevent many types of mechanical failures, reduce maintenance costs, and achieve higher energy efficiency.

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