Structure and tribological behavior of nanocomposite C-Ti-WSe x coatings

Abstract

Transition metal chalcogenides with lamellar structure are known for their use in tribological applications although limited to vacuum due to their easy degradation in presence of oxygen and/or moisture. Here we present a tailored WSe x coating with low friction (0.07) and low wear rates (3×10-7 mm 3 Nm-1) even in ambient air. To understand the low friction behaviour and lower chemical reactivity a tribological study is carried out in a high vacuum tribometer under variable pressures (atmospheric pressure to 10-8 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 2 embedded in an amorphous matrix richer in W, a-W(Se). After the friction test, an increased crystalline order and orientation of WSe 2 lamellas along the sliding direction 2 have been observed in the interfacial region. Based on 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 2 phase from oxidation. The increase of the WSe 2 crystalline order and the buffer effect of W capturing oxygen atoms would explain the enhanced chemical and tribological response of this designed nanocomposite material.

Self-Healing of PVD-Coatings

“…High-tech methods of applying vacuum ion-plasma coatings show their presence in an increasing variety of industrial applications [1][2][3][4][5][6][7]. A wide range of experimental data obtained in the field of studying the structure and properties of nanocomposite ion-plasma coatings made it possible to generalize and systematize the characteristic features of coatings of various cermet systems [8][9][10][11][12]. Coatings of this type are highly sensitive to the quality of the substrate surface and to the presence of a droplet phase in a vacuum chamber.…”