Influence of Cr content and initial Cr particle size on the dielectric properties of plasma-sprayed Cr/Al2O3 coatings

Cr/Al2O3 coatings were deposited by low-power plasma spray process with dry-crushed powders. The coatings exhibited a microstructure formed by fully molten splat-like metallic lamellae and partially molten or un-molten submicron Al2O3 particles, surround by a fully molten alumina matrix. The content and size of metallic Cr in the coatings played a dominant role in the formation of metallic clusters. Complex permittivity measurement showed that the coatings with higher Cr content and larger Cr particle size exhibited higher ε′ and ε″ values due to the enhanced interfacial polarization and conductance loss. Furthermore, strong frequency dependency was observed for the coatings with 15 wt% Cr addition and 50-74 μm Cr particle size.