Improvement of oxidation resistance of spatial-network Al2O3/YSZ composite coatings by chemical densification

• Oxidation resistance of Al2O3/YSZ Coatings was improved by chemical densification.
• Oxidation resistance of the coatings was analyzed by a novel theoretical model.
• The model is analogous to the calculating electric resistance of composite material.
• The improvement of oxidation resistance by CD was also analyzed by the model.

In our previous study, spatial-network Al2O3/YSZ composite coatings have been prepared by modified sol–gel techniques. It demonstrated that the structure of YSZ particles covered with a spatial-network Al2O3 blanket was beneficial to oxidation and spallation resistance of the ceramic coatings. To further improve oxidation resistance of the ceramic coatings, filling and sealing processes of chemical densification (FSPCD) were applied for as-prepared coatings in the present study. Cyclic oxidation test at 1050 °C demonstrates that their oxidation resistance is greatly enhanced due to the FSPCD. To understand the mechanisms underlying the improvement of oxidation resistance of the coatings by the filling and sealing processes, a concept analogous to calculation of electrical resistance of a composite material has been utilized to analyze diffusion resistance of the coatings against oxygen. The relationship between reduced oxygen diffusion rate and the micro-structure changed by the chemical densification is discussed by means of the novel theoretical model.