| AVS 58th Annual International Symposium and Exhibition | |
| Advanced Surface Engineering Division | Wednesday Sessions |
| Session SE+SS-WeM |
| Session: | Surface Engineering for Thermal Management |
| Presenter: | Christian Mitterer, University of Leoben, Austria |
| Authors: | O. Jantschner, University of Leoben, Austria C. Walter, University of Leoben, Austria C. Mitterer, University of Leoben, Austria C. Muratore, Air Force Research Laboratory A.A. Voevodin, Air Force Research Laboratory |
| Correspondent: | Click to Email |
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 co-sputtered from Zr and V targets using an Ar/O2 discharge. The X-ray diffraction pattern of the as-deposited coatings show a change in crystal structure from monoclinic (0-2.2 at% V) to cubic/tetragonal (5.8 at% V) and finally X-ray amorphous structure at even higher V content (17.4 at% V). 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 by ball-on-disc tests against alumina balls were carried out at three different temperature levels (25, 600 and 800°C). Additional in-situ Raman analyses have been done to study the formation of tribolayers in the sliding contact. At 25°C, the coefficient of friction (COF) is about 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 and 0.8. At the even higher temperature of 800°C, the COF decreased to below 0.2 for V contents of 17.4 at%, where a self-lubricating film was formed in the sliding contact. Differential scanning calorimetry (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. This phase was found to decompose at ~800°C by an endothermic reaction in ZrO2 and V2O5. The re-runs of the DSC measurements indicated melting of 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, enabling thermal management abilities of these coatings.