Influence of Defect Orientation on Electrical Insulating Properties of Plasma-Sprayed Alumina Coatings

The influence of the microstructure (pores and cracks) on electrical properties of plasma-sprayed alumina coatings was investigated using the so-called Scanning Electron Microscope Mirror Effect (SEMME) technique. Coatings were sprayed with different alumina feedstock powders in various atmospheres. Microstructures with various amounts of porosity and crack orientation distributions were analysed. Both outer surfaces and cross-sections of alumina coatings were analysed by SEMME technique using two complementary modes. The SEMME technique was successfully applied to porous coatings. It is proved that crack orientation modifies both motion and trapping of charges and therefore the dielectric properties of plasma-sprayed alumina coatings.