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Title

Self-lubricity of WSe<inf>x</inf> nanocomposite coatings

AuthorsDomínguez-Meister, Santiago ; Conte, M.; Igartua, A.; Rojas, T. Cristina; Sánchez-López, J.C.
KeywordsNano-structure, Friction
Raman
Electron microscopy
Tungsten selenide
Issue Date2015
PublisherAmerican Chemical Society
CitationACS Applied Materials and Interfaces 7: 7979- 7986 (2015)
Abstract© 2015 American Chemical Society. Transition metal chalcogenides with lamellar structure are known for their use in tribological applications although limited to vacuum due to their easy degradation in the presence of oxygen and/or moisture. Here we present a tailored WSe<inf>x</inf> coating with low friction (0.07) and low wear rates (3 × 10<sup>-7</sup> mm<sup>3</sup> Nm<sup>-1</sup>) even in ambient air. To understand the low friction behavior and lower chemical reactivity a tribological study is carried out in a high-vacuum tribometer under variable pressure (atmospheric pressure to 1 × 10<sup>-8</sup> mbar). A detailed investigation of the film nanostructure and composition by advanced transmission electron microscopy techniques with nanoscale resolution determined that the topmost layer is formed by nanocrystals of WSe<inf>2</inf> embedded in an amorphous matrix richer in W, a-W(Se). After the friction test, an increased crystalline order and orientation of WSe<inf>2</inf> lamellas along the sliding direction were observed in the interfacial region. On the basis of high angle annular dark field, scanning transmission electron microscopy, and energy dispersive X-ray analysis, the release of W atoms from the interstitial basal planes of the a-W(Se) phase is proposed. These W atoms reaching the surface, play a sacrificial role preventing the lubricant WSe<inf>2</inf> phase from oxidation. The increase of the WSe<inf>2</inf> crystalline order and the buffer effect of W capturing oxygen atoms would explain the enhanced chemical and tribological response of this designed nanocomposite material.
URIhttp://hdl.handle.net/10261/117124
DOI10.1021/am508939s
Identifiersdoi: 10.1021/am508939s
issn: 1944-8252
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