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Research Papers: Contact Mechanics

Yield Maps for Single and Bilayer Thin Films Under Scratch

[+] Author and Article Information
Abhish Chatterjee, Pascal Bellon

Department of Materials Science
and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801

Ali Beheshti

Department of Mechanical Engineering,
Lamar University,
Beaumont, TX 77710;
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843

Andreas A. Polycarpou

Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843;
Department of Mechanical Science
and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801
e-mail: apolycarpou@tamu.edu

1Present address: Intel Corporation, Hillsboro, OR 97124.

2Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 13, 2015; final manuscript received December 9, 2015; published online April 21, 2016. Assoc. Editor: Robert L. Jackson.

J. Tribol 138(3), 031402 (Apr 21, 2016) (12 pages) Paper No: TRIB-15-1194; doi: 10.1115/1.4032519 History: Received June 13, 2015; Revised December 09, 2015

Finite element (FE) simulations were performed to study yielding in single and bilayer (BL) film systems using a “yield zone map” approach. Onset of yielding was observed at the interface, substrate, surface, and film in HfB2/silicon and HfB2/stainless steel systems. The interface yield zone in HfB2/stainless steel system was found to be larger due to the dominant effect of interfacial stress gradients. Based on the FE simulations, empirical equations were derived for the maximum contact pressure required to initiate yield at the interface. For BL/substrate systems, onset of yield at the lower film/substrate interface occurred when film thickness ratio was in the range 0.5–5. The maximum contact pressure associated with the initial yielding at this interface is minimum compared to other locations. From the design point of view, for a BL system the preferable film thickness ratio was found to be 20, whereas the optimum hardness ratio ranges from 2 to 4. For these values, maximum contact pressure is very high (∼30 GPa), and thus, yield onset can be avoided at lower film/substrate interfaces. In addition, based on the obtained results, the advantages and disadvantages of using a BL film as compared to a single film and their relevance to practical applications are discussed.

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References

Figures

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Fig. 1

FE model for (a) SL and (b) BL films

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Fig. 6

Variation of contact pressure at the onset of yield with film thickness at different friction coefficient values for HfB2/Si

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Fig. 5

Variation of contact pressure at the onset of yield overlaid as contours on a yield zone map for HfB2/Si system

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Fig. 4

Variation of von Mises stresses at the instant of first yield at (a) interface and (b) surface for HfB2/Si

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Fig. 3

Plastic strains, εpl, distribution at the instant of yield onset in (a) substrate, (b) interface, (c) film, and (d) surface. (Regions where εpl exceeds the maximum limit are depicted in gray color).

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Fig. 2

(a) Normalized maximum pressure as a function of normalized interference based on Hertzian approach and FE analysis and (b) nanoscratch residual surface deformation for Fn = 100 μN, based on FE simulation and experimental measurements

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Fig. 7

Contact pressure variations at the onset of yield overlaid as contours on the yield zone map for HfB2/SS440C system

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Fig. 8

Variation of contact pressure (PCont) at the onset of yielding with film thickness at different friction coefficient values for HfB2/SS440C

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Fig. 12

Surface traction distribution at the onset of yield overlaid as contours on the yield zone map for a BL film at (a) μ = 0.1and (b) μ = 0.5

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Fig. 10

Contact pressure variations at the onset of yield overlaid as contours on the yield zone map for a BL film at (a) μ = 0.1 and (b) μ = 0.5

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Fig. 9

Representative plastic strain distributions when onset of yield occurs at (a) interface 1, (b) interface 2, (c) interfaces 1 and 2 simultaneously, (d) film 1, and (e) surface

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Fig. 11

PCont variation versus H1/H2 at different values of t1/t2 for (a) μ = 0.1 and (b) μ = 0.5

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