Influence of Al-modification on CMAS Corrosion Resistance of PS-PVD 7YSZ Thermal Barrier Coatings

Abstract

7YSZ thermal barrier coatings with feather-like columnar structure were prepared by plasma spray-physical vapor deposition (PS-PVD), and were carried out with Al-modification. After that, the as-sprayed and Al-modified 7YSZ TBCs were conducted with thermal cycling, heated at 1050 ℃ for 5 min and air-cooling for 5 min, respectively. And the CMAS corrosion tests were carried out at 1200 ℃. Microstructure, element and phase composition of the coating were analyzed by SEM, EDS and XRD. Corrosion mechanism of CMAS and the corrosion resistance mechanism of Al-modified coating were investigated. The results showed that the Al-modified coatings kept good thermal stability. And the coating had no apparent spallation, after 5200 thermal cycles. The as-sprayed coating was destroyed by CMAS, and "wave" deformation was observed. The 7YSZ coating was completely permeated by CMAS. Dense corrosion-resistant layer of α-Al2O3 was formed on the surface of the coating by Al-modification, and the corrosion of the coating was significantly improved. It was found that α-Al2O3 layer not only protected the coating by separating CMAS, but also had positive effect on the thermochemical reaction in CMAS corrosion. Due to formation of α-Al2O3 layer, the oxides of CaO, Al2O3 and SiO2 were hard to penetrate the coating. However, the penetration of MgO was not significantly affected by Al-modification. In addition, a mathematical model based on Fick's second law was established to evaluate the effect of Al-modification on the CMAS corrosion resistance of 7YSZ coatings.