Ion and pulsed electron-beam surface modification of YSZ coatings synthesized in a forevacuum beam-plasma

Surface roughness is an important parameter of yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) that directly determines their heat-resistivity, thermal protection and durability. When TBCs are synthesized at higher working gas pressure the intense ion flux from dense electron beam-produced plasma can affect the properties of the synthesized coatings. We have explored several different approaches to ion and electron beam surface modification: dc or bipolar RF (50 kHz) biasing for ion-plasma in-situ modification during synthesis of YSZ coatings, and post-synthesis surface treatment of the YSZ coatings by a pulsed wide-aperture high-current electron beam. We find that for ion treatment with DC bias, the surface roughness grows slightly, while for RF bias, the roughness fluctuates with bias amplitude. Following numerical simulation of these approaches, we conjecture that the heating of plasma electrons (by external electric field via biasing) increases both the density and the fraction of ions of the evaporating YSZ target in the plasma, which together with ion acceleration by the substrate bias may cause additional effects on the coating properties. Using e-beam treatment, one can achieve a controllable non-monotonic trend of surface roughness with pulse energy. Results are attractive for the synthesis of advanced YSZ coatings with advanced properties.