Effect of Sealing Treatment on the Dielectric Properties of Plasma-Sprayed Al2O3 Coatings

In this paper, alumina (Al2O3) coatings were prepared via atmospheric plasma spraying. To improve the insulation performance of the as-sprayed coatings, infiltration sealing treatment processes were performed using silicone resin and epoxy resin sealants. The mechanical properties and dielectric strength of the coatings were characterized. For the as-sprayed coating, the average microhardness was 914.94 HV0.2, and the bond strength was 38.07 MPa. The phase composition of the coatings was presented by γ-Al2O3, as the primary phase, and α-Al2O3, as the second phase. The dielectric strengths of the as-sprayed, silicone resin-sealed, and epoxy resin-sealed coatings were 10.27, 15.78, and 17.91 kV/mm, respectively. The results indicate that the porosity of the coatings was reduced, and the dielectric strength was enhanced by the sealing treatment. Sealants filled the pores of the coatings and prevented the accumulation of electric charges, thereby increasing the dielectric strength. The dielectric breakdown of the coatings was due to combined mechanisms of intrinsic, corona discharge, and thermal breakdown.