Molecularly thin rheological and contact interfaces

Chowdhury, Shahla

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https://hdl.handle.net/2142/45615 Copy

Description

Title

Molecularly thin rheological and contact interfaces

Author(s)

Chowdhury, Shahla

Issue Date

2013-08-22T16:55:30Z

Director of Research (if dissertation) or Advisor (if thesis)

Polycarpou, Andreas A.

Department of Study

Mechanical Sci & Engineering

Discipline

Theoretical & Applied Mechans

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

M.S.

Degree Level

Thesis

Keyword(s)

• Molecularly thin lubricant
• Hard disk drive
• Coating

Abstract

A molecularly thin lubricant layer (of the order of 1-2 nanometers thick) has been shown to provide bearing forces at the interface between contacting solid surfaces under light loads and high shear rates. This phenomenon is important, for example, in the head-disk contact in magnetic storage hard disk drives to ensure that some of the contact is sustained by the lubricant layer and thus avoiding damage of the solid surfaces. The magnitude of the normal and tangential bearing forces that the lubricant layer can provide depends on temperature, viscosity of the lubricant, sliding velocity and radius of gyration of the lubricant molecules. This study shows that viscosity has the greatest effect on the load bearing capacity of the molecularly thin lubricant. Thus, by controlling the flash temperature and the ratio of molecularly thin lubricant-to-bulk viscosity, the bearing load carrying capacity of the layer can be controlled. This would allow for the contact to be sustained within the mobile lubricant layer, avoiding solid contact so as to protect the diamond-like carbon coating, and thus reduce wear and potential catastrophic failures. Another part of the thesis is the work on nano-tribological behavior of Hafnium-Diboride thin films. Dense, hard nanocrystalline films of HfBN and multilayer ones of HfB2/HfBN compositions having thickness in the range of 100-600 nm were deposited using chemical vapor deposition (CVD) technique. The roughness values of HfBN film is extremely small, with a value of 5.38-7.63 nm so it is compatible for use as a very smooth surface such as in microscale miniature systems. Nano-indentation and nano-scratch experiments were done to investigate friction and wear behavior of the films. HfBN exhibited lower coefficient of friction (COF) compared to the multilayer HfB2/HfBN. The amorphous as-deposited films were subjected to annealing at 700 oC in order to study their mechanical properties in the post-treatment conditions. In comparison to as-deposited films the annealed films possessed lower COF (COF 0.02 lower). The overall response of the annealed HfBN is outstanding making it compatible for wear resistant, very low roughness coating.

Graduation Semester

2013-08

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http://hdl.handle.net/2142/45615

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