Within the scope of this diploma thesis, the effect of vanadium on reactively magnetron-sputtered zirconia coatings was investigated with respect to its structural and mechanical properties as well as its thermal management abilities for high temperature sliding interfaces. ZrO2 coatings with different V-content (0, 2.2, 5.8 and 17.4 at%) were synthesized using an Ar/O2 discharge. The resulting phases and compositions were investigated by EDX, XRD and Raman spectroscopy. The XRD pattern of the as-deposited coatings show a change in crystal structure from monoclinic (0-2.2 at%) to cubic/tetragonal (5.8 at%) and finally X-ray amorphous structure at even higher V content (17.4 at%). Hardness and Young’s modulus were evaluated by nanoindentation showing a decrease beyond 2.2 at% V from 17.4 to 7.5 GPa and from 230 to 150 GPa, respectively. The tribological investigations were carried out at three different temperature levels (RT, 600 and 800°C). At RT, the coefficient of friction (COF) is around 0.2 for low V contents (≤ 2.2 at%). For higher V contents, the COF increases up to 0.5 and higher. At 600°C, the COF measured was between 0.4 to 0.8. At the even higher temperature of 800°C, the COF decreased to values below 0.2 for high V contents of 17.4 at%, where a self-lubricating film was formed in the sliding contact. DSC measurements of virgin powder samples showed a characteristic exothermic peak at ~600°C which is due to the formation of a stoichiometric ZrV2O7 phase which was found to decompose at ~800°C by an endothermic reaction in ZrO2 and V2O5. The re-runs of the DSC measurements showed a precipitation of liquid V2O5 at 670°C. In summary, alloying of V to ZrO2 coatings has on the one hand been proven to result in self-lubricious properties at temperatures above 700°C. On the other hand, the endothermic reactions needed for formation of the self-lubricious phase have the potential to reduce high local temperatures in the sliding contact.
|Translated title of the contribution
|Untersuchungen an Vanadium-legierten, gesputterten Zirkonoxidschichten bezüglich ihrer tribologischen Eigenschaften bei erhöhten Temperaturen
|8 Apr 2011
|Published - 2011