Characteristic curves of voltage and current, phase generation and properties of tungsten- and vanadium-oxides deposited by reactive d.c.-MSIP-PVD-process for self-lubricating applications

Various transition metal oxides, like tungsten and vanadium oxides, are promising to be usable as solid lubricants at elevated temperatures because of their possible formation of Magneli-phases. So far, they have mainly been investigated as powdery material for tribological applications. Metal-oxides are interesting for tribological insets under atmospheric conditions because of their expected oxidation stability and low adhesion. This study reports investigations made to find stable process windows for the deposition of tungsten and vanadium oxides in a reactive d.c. mode by the MSIP-PVD-process. Therefore, the voltage-current characteristics were measured and a correlation between the phase generation of polycrystalline VO2 as well as polycrystalline V2O5 and the electric process parameters were identified. For tungsten oxides, no comparable correlation was found, even if there was a distinct formation of a metallic and a WO3-phase. As a result, a simplified 'phase diagram' of the binary systems V-O and W-O as a function of the deposition temperature (378-650 K) and the oxygen content (0-50%) will be presented. Furthermore, the deposited metal oxide-phases and selected mechanical properties, like the hardness and elastic-modulus (measured by nanoindentation) will be discussed. The coatings were analyzed by various testing methods to characterize their structural and mechanical properties, especially with XRD and nanoindentation. (C) 2001 Elsevier Science B.V. All rights reserved.