Tungsten oxide with different oxygen contents: Sliding properties

In this study, tungsten oxide coatings with 13 and 75 at% of oxygen were prepared by DC reactive magnetron sputtering from a pure W target in an Ar+O2 atmosphere. The coating hardness (H) decreased with increasing oxygen content from 25 to 7.7GPa. The values of H/E ratio were 0.08 and 0.07 for W87O13 and W25O75, respectively. The tribological measurements were carried out on a pin-on-disc tribometer at room temperature, with a load of 5N and steel 100Cr6, ceramic Si3N4 and Al2O3 balls as sliding partners. The wear track and wear debris were visualised by scanning electron microscopy and the chemical composition of the later was estimated by energy-dispersive X-ray analysis. The friction coefficient was rather high in case of the W87O13 coating reaching values in the range from 0.7 to 0.75 for both counterpart materials, and slightly lower for W25O75 ( 0.50). The coating wear rate decreased with increasing oxygen content with the Al2O3 ball, while using Si3N4 ball as a counterpart showed an opposite trend. The coating with low oxygen content was more resistant to abrasive wear. r 2007 Elsevier Ltd. All rights reserved.