High temperature tribological behavior of W-DLC against aluminum

Diamond-like carbon (DLC) coatings are well suited for applications that require minimum adhesion and low coefficient of friction (COF) against aluminum alloys. These properties however deteriorate rapidly at elevated temperatures, and coating wear occurs. In this study, tribological behavior of W c...

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Bibliographic Details
Published in:Surface & coatings technology 2011-12, Vol.206 (7), p.1905-1912
Main Authors: Gharam, A. Abou, Lukitsch, M.J., Balogh, M.P., Irish, N., Alpas, A.T.
Format: Article
Language:English
Subjects:
Aluminum base alloys
Applied sciences
Carbon
Coatings
Coefficient of friction
Contact of materials. Friction. Wear
Cross-disciplinary physics: materials science
rheology
Diamond like carbon
Diamond-like carbon films
Exact sciences and technology
Material transfer
Materials science
Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology
Metals. Metallurgy
Physics
Surface treatments
Tribology
Tungsten
Tungsten oxide
Tungsten oxides
W-DLC
Wear mechanisms
X-ray photoelectron spectroscopy
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Summary:Diamond-like carbon (DLC) coatings are well suited for applications that require minimum adhesion and low coefficient of friction (COF) against aluminum alloys. These properties however deteriorate rapidly at elevated temperatures, and coating wear occurs. In this study, tribological behavior of W containing DLC (W-DLC) were studied as a function of testing temperatures up to 500°C, and the sliding-induced surface and subsurface damage at these temperatures was investigated. Pin-on-disk tests performed on W-DLC run against 319 Al showed a low COF of 0.2 at 25°C, whereas between 100°C and 300°C, a high average steady-state COF of 0.60 was recorded. At 400°C the COF decreased to 0.18, and this reduction in COF continued with increasing the temperature to 500°C (0.12). It was observed that the formation of transferred material layers on 319Al was the governing mechanism for the low COF. The Raman analysis revealed that at room temperature these layers were rich in carbon, whereas at 400°C the transfer layers consisted of tungsten oxide. According to transmission electron microscopy (TEM), and X-Ray photoelectron spectroscopy (XPS), of the coatings tested at 400°C and 500°C a thin (20nm) tungsten oxide layer was formed on their top surface. This in turn led to the formation of tungsten oxide rich transfer layers that is believed to reduce the COF at temperatures above 400°C. ► The coefficient of friction, COF, of W-DLC was measured against aluminum at elevated temperatures. ► A low COF of 0.12 was observed at 500ºC. ► Raman, XPS and TEM revealed formation of a tungsten oxide layer at the sliding interface. ► This layer inhibited aluminum adhesion and reduced the friction.
ISSN:0257-8972
1879-3347
DOI:10.1016/j.surfcoat.2011.08.002