Influence of CrO3 sealing treatment on properties of Plasma sprayed Al2O3 coating

Abstract

Plasma sprayed ceramic coatings inherently contain pores and usually also cracks. Post-treatment of the plasma sprayed coatings is a way to close the connected pores and cracks. In this study, post-sealing treatment in plasma sprayed Al2O3 coatings was employed to overcome the reduction of coating properties. Al2O3 plasma thermal spray coating was made on aluminum alloys plate, CrO3 post coating and heat treatment at 550°C was carried out in order for final Cr 2O3 to be saturated through phase transformation. Chromia sealing began at the fine defect in coated microstructure, while larger pores were permeated later. The increase in concentration and treatment frequency of sealing solution resulted in the decrease of porosity of coating layer, while cracks occurred partially after the third treatment. After twice treatment of 10M CrO3 solution, microhardness and breakdown voltage of Al 2O3 coatings were found to increase by ≓50% and ≓390% respectively than without post-treatment.