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The Acoefficient of Friction Between Boron Carbide (B4 C)Surfaces in Air and Ultrahigh Vacuum (UHV)

Published online by Cambridge University Press:  28 February 2011

Benjamin M. DeKoven
Affiliation:
The Dow Chemical Company, Central Research Catalysis Laboratory, 1776 Building, Midland, Michigan 48674
Patrick L. Hagans
Affiliation:
The Dow Chemical Company, Central Research Catalysis Laboratory, 1776 Building, Midland, Michigan 48674
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Abstract

Friction measurements between two contacting B4C surfaces in airand UHV at room temperature using 0.10-0.13N loads are reported. A novel pin (radius=0.005m) on flat device allowing for interchange in UHV is used. The tribological surfaces can be examined using scanning Auger and XPS in the same UHV system. The coefficient of friction for air exposed surfaces is found to vary between air (0.20-0.25) and UHV (1.2-1.8). Stick-slip behavior, indicating strong adhesion, is observed in UHV while only a smooth friction value is measured in air. Air pressures ≥ 100Pa are necessary toreduce the friction from the high value in UHV. The friction between the clean surfaces in UHV initially is 0.8-1.3, but following mechanical conditioning at a higher velocity the friction drops to 0.17-0.25. In situmechanical conditioning is necessary to obtain reproducible friction values for the clean surface. Exposing the clean surfaces to oxygen (103Pa) while conditioning results in an increase in friction (1.0-1.2). Auger line scans through the scar made using the clean surfaces show enhanced B and reduced C. Similar Auger scans for oxygen exposed surfaces indicate that tearing of the oxide layer may be the reason for the high friction. The friction for a clean pin and an in situ nitrogen-implanted flat (10keV, saturation dose) is 0.70-0.80. Film transfer to the pin is observed.

Type
Research Article
Copyright
Copyright © Materials Research Society 1989

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