Microstructure of gas flow sputtered thermal barrier coatings: Influence of bias voltage

The application of a negative bias voltage enhances the surface mobility of the film-forming adatoms and can cause densification due to atom displacements, resputtering or channeling phenomena. Moderate bias voltages up to − 40 V result in more regular columns and a lower porosity. For high bias voltages (− 100 V), the densification effects seem to dominate leading to fully dense coatings with residual stresses up to − 2.5 GPa and no preferential grain orientation, rendering this bias value unsuitable for thermal barrier coatings.