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Influence of bias voltage and oxygen flow rate on morphology and crystallographic properties of gas flow sputtered zirconia coatings

: Rösemann, N.; Ortner, K.; Petersen, J.; Schadow, T.; Bäker, M.; Bräuer, G.; Rösler, J.


Surface and coatings technology 276 (2015), pp.668-676
ISSN: 0257-8972
Journal Article
Fraunhofer IST ()
a-C; gas flow sputtering; reactive sputtering; yttria stabilized zirconia; thermal barrier coatings; substrate bias; oxygen flow rate; morphology; microstructure; grain orientation; thermal cycling

The aim of this work is to gain a fundamental understanding of the influence of bias voltage and oxygen flow rate on the resulting microstructure and crystallographic properties of gas flow sputtered (GFS) yttria stabilized zirconia coatings. At given substrate temperature of 500 °C fully yttria stabilized zirconia (FYSZ) coatings (10-30 μm) were deposited on a FeCrAl-alloy. The oxygen flow rate and the substrate bias voltage were varied over a wide range. The resulting microstructures were columnar, but varied widely in porosity and column diameter. While increased oxygen flow rate generally results in coarser microstructures with higher porosity, bias voltage seems to increase the effective surface temperature due to ion bombardment at low voltage, but has a destructive effect at higher voltages leading to randomized grain orientations and small grain sizes. Thermal cycling experiments were conducted between 100 °C and 1050 °C. Although no large scale spallation was observed, the former columnar coating degraded due to sintering, resulting in sinter necks between former single columns and diminished intra-columnar porosity. However, high oxygen flow rate and moderate bias increase the resistance to sintering due to coarser morphologies.