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Research Papers: Elastohydrodynamic Lubrication

Effect of Stiff Coatings on EHL Film Thickness in Point Contacts

[+] Author and Article Information
Yuchuan Liu1

Center for Surface Engineering and Tribology, Northwestern University, 2145 Sheridan Road, No. B224, Evanston, IL 60208ycliu@northwestern.edu

Q. Jane Wang

Center for Surface Engineering and Tribology, Northwestern University, 2145 Sheridan Road, No. B224, Evanston, IL 60208

Dong Zhu

Innovation Center, Eaton Corporation, 26201 Northwestern Highway, Southfield, MI 48037

1

Corresponding author.

J. Tribol 130(3), 031501 (Jun 20, 2008) (6 pages) doi:10.1115/1.2908908 History: Received January 29, 2007; Revised January 31, 2008; Published June 20, 2008

Coatings are widely used for interface performance enhancement and component life improvement, as well as for corrosion prevention and surface decoration. More and more mechanical components, especially those working under severe conditions, are coated with stiff (hard) thin coatings. However, the effects of coatings on lubrication characteristics, such as film thickness and friction, have not been well understood, and designing coating for optimal tribological performance is a grand challenge. In this paper, the influences of coating material properties and coating thickness on lubricant film thickness are investigated based on a point-contact isothermal elastohydrodynamic lubrication (EHL) model developed recently by the authors. The results present the trend of minimum film thickness variation as a function of coating thickness and elastic modulus under a wide range of working conditions. Curve fitting of numerical results indicates that the maximum increase in minimum film thickness, Imax, and the corresponding optimal dimensionless coating thickness, H2max, can be expressed in the following forms: Imax=0.769M0.0238R20.0297L0.1376exp(0.0243ln2L) and H2max=0.049M0.4557R20.1722L0.7611exp(0.0504ln2M0.0921ln2L). These formulas can be used to estimate the effect of coatings on film thickness for EHL applications.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Description of the EHL with coated surfaces in a point contact

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Figure 2

Variation of minimum film thickness with increasing coating thickness for four extreme working conditions

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Figure 3

Film thickness and pressure profiles in X along Y=0 and film thickness profile in Y along X=0 for two extreme cases (a) Results for Case 7 and (b) results for Case 8

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Figure 4

Effect of dimensionless load M while L=6.965 and R2=4

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Figure 5

Effect of dimensionless material parameter L while M=71.36 and R2=4

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Figure 6

Effect of coating/substrate material parameter ratio R2 while M=71.36 and L=6.965

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