Electrical Properties of Nanostructured Al_2O_3-3wt% TiO_2 Coating Deposited by Plasma Spraying Deposited by Plasma Spraying

Conventional and nanostructured Al_2O_3-3wt%TiO_2 coatings were deposited by plasma spraying with conventional and nanostructured powders, respectively. The phase compositions and microstructure of the as-spraying coatings were characterized by XRD, SEM and TEM. The electrical resistivity, dielectric constant and dielectric loss of coatings were measured. In both conventional and nanostructured Al_2O_3-3wt%TiO_2 coatings, alumina mainly existed in the form of γ-Al_2O_3 with some α-Al_2O_3. Non-stoichiometric Ti_2O_3 was found in the conventional coating; while in the nanostructured coating, titania reacted with alumina to form solid solution. The conventional Al_2O_3-3wt%TiO_2 coating exhibited a typical splat microstructure. For the nanos- tructured Al_2O_3-3wt%TiO_2 coating, many equiaxed α-Al_2O_3 grains besides splat lamellae were also observed. The size of equiaxed α-Al_2O_3 grains was about 150～800nm. Compared to the con- ventional Al_2O_3-3wt%TiO_2 coating, electrical resistivity of the nanostructured Al_2O_3-3wt%TiO_2 coating increased. But the nanostructured coating exliibited lower dielectric constant and dielectric loss.