wearActivatedTL2008 - Tribol Lett DOI...

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ORIGINAL PAPER A Possible Link Between Macroscopic Wear and Temperature Dependent Friction Behaviors of MoS 2 Coatings Matthew A. Hamilton Æ Luis A. Alvarez Æ Nathan A. Mauntler Æ Nicolas Argibay Æ Rachel Colbert Æ David L. Burris Æ Chris Muratore Æ Andrey A. Voevodin Æ Scott S. Perry Æ W. Gregory Sawyer Received: 1 February 2008 / Accepted: 18 September 2008 Ó Springer Science+Business Media, LLC 2008 Abstract Studies to explore the nature of friction, and in particular thermally activated friction in macroscopic tri- bology, have lead to a series of experiments on thin coatings of molybdenum disul±de. Coatings of predomi- nately molybdenum disul±de were selected for these experiments; ±ve different coatings were used: MoS 2 /Ni, MoS 2 /Ti, MoS 2 /Sb 2 O 3 , MoS 2 /C/Sb 2 O 3 , and MoS 2 /Au/ Sb 2 O 3 . The temperatures were varied over a range from - 80 ° C to 180 ° C. The friction coef±cients tended to increase with decreasing temperature. Activation energies were estimated to be between 2 and 10 kJ/mol from data ±tting with an Arrhenius function. Subsequent room tem- perature wear rate measurements of these ±lms under dry nitrogen conditions at ambient temperature demon- strated that the steady-state wear behavior of these coatings varied dramatically over a range of K = 7 9 10 - 6 to 2 9 10 - 8 mm 3 /(Nm). It was further shown that an inverse relationship between wear rate and the sensitivity of fric- tion coef±cient with temperature exists. The highest wear- rate coatings showed nearly athermal friction behavior, while the most wear resistant coatings showed thermally activated behavior. Finally, it is hypothesized that ther- mally activated behavior in macroscopic tribology is reserved for systems with stable interfaces and ultra-low wear, and athermal behavior is characteristic to systems experiencing gross wear. Keywords Solid lubrication ± Molybdenum disul±de ± Wear ± Cryotribology 1 Introduction There have been increasing efforts to measure and under- stand tribological behavior at cryogenic temperatures; to date, results of these efforts show either no trend or con- ²icting trends and often require cryogenic speci±c hypotheses. These measurements are dif±cult to make and often require sacri±cing one or more experimental controls (e.g. dry sliding conditions, friction sensitivity, and back- ground environment). Michael et al. [ 1 ], Theiler et al. [ 2 ], and Hubner et al. [ 3 ] compared results of ambient lab air testing with those of test submerged in cryogenic liquids and have shown either no trend or trends of reduced friction at cryogenic temperatures. Recent constant environment macroscale studies of various solid lubricants [ 4 7 ], and atomic-scale studies with terraces of graphite [ 8 ] show consistent trends of increased friction with decreased tem- perature, and the notion of thermally activated friction has been proposed [ 4 , 8 , 9 ]. Variable temperature experiments conducted on beds of aligned carbon nanotubes [ 10 ] and various high temperature polymer studies [ 11 16 ] have also
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This note was uploaded on 08/22/2011 for the course EGM 4313 taught by Professor Mei during the Spring '08 term at University of Florida.

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wearActivatedTL2008 - Tribol Lett DOI...

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