{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

JOT_NFC2004 - P L Dickrell W G Sawyer University of Florida...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
P. L. Dickrell W. G. Sawyer University of Florida, Mechanical Engineering Department, Gainesville, FL 32611, USA A. Erdemir Argonne National Laboratory, Energy Technology Division, Argonne, IL 60439, USA Fractional Coverage Model for the Adsorption and Removal of Gas Species and Application to Superlow Friction Diamond-Like Carbon The frictional behavior of diamond-like carbon (DLC) films varies with environmental condition. One theory asserts that the cause of variations in the frictional performance is environmental contaminants adsorbing onto the DLC film surface. Testing of the frictional performance of DLC films in a pin-on-disk contact has mapped the transient behavior of the friction coefficient. A model for fractional coverage, based on the adsorption of envi- ronmental contaminants and their removal through the pin contact, is developed. The rate of adsorption is taken from Langmuir’s model [17], which is combined with the removal ratio from Blanchet and Sawyer [18]. The coefficient of friction is based on the average fractional coverage under the pin contact. The model also gives a closed-form expression for the steady-state fractional coverage. Model calculations compared favorably to the time progression of the friction coefficient for a series of earlier experiments on a super- low friction DLC coating [7], when the fractional removal term was allowed to increase with increasing sliding speed. @ DOI: 10.1115/1.1739408 # Introduction The unique properties of diamond-like carbon ~ DLC ! films are characterized by excellent wear resistance, biocompatibility, and chemical inertness. These films can potentially be used in a wide range of applications, such as bearings, cutting tools, submersible parts, and biomedical applications @ 1–4 # . Testing of DLC films as solid lubricant coatings has shown them to possess low coeffi- cients of friction, spanning the range m 5 0.001 to 0.6 @ 3–6 # , al- though the testing conditions and type of DLC film ~ i.e., hydro- genated versus hydrogen-free ! have a strong influence on its frictional behavior. The frictional behavior of the superlow fric- tion DLC film, recently investigated at Argonne National Labora- tory @ 4,7 # , has been theorized to be dependent on the amount of contaminants adsorbed on the rubbing surface @ 7 # . Some attempts have been made to model the frictional behavior of DLC and other carbon films in various environments @ 3,8,9 # . A hypothesis is that the variations in friction coefficient with sliding speed in a pin-on-disk contact are the result of competitive rate processes that involve an interaction of a contaminant gas species with the surface of the diamond-like carbon, such as the adsorp- tion of water, and the removal of these species under the contact of the pin. Much like vapor-phase lubrication @ 10–16 # , such pro- cesses have a strong dependence on the gas pressures of the con- taminants, available areas for adsorption, time exposed to the en- vironment, and temperature. This paper outlines the development of a closed-form, time-dependent model for such competitive pro- cesses using, principally, the works
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern