Composition and thickness optimization of anti-CMAS layer on air plasma sprayed thermal barrier coatings

The work aims to investigate composition and thickness of impedance layers on thermal barrier coatings (TBCs), so that the layers can effective impede corrosion of CMAS deposit and also easily adhere to thermal barrier coatings. Protection effects of uniformly blended different content of nano-sized Al2O3 and 8YSZ on CMAS deposit were studied with porous pressureless sintered ceramic pellets at high temperature. Microstructure, corrosion depth and reaction product of the CMAS corrosion layers was analyzed and studied with scanning electron microscope, energy dispersive spectrometer and X-ray diffractometer, respectively. Then thermal barrier coatings with 8YSZ/Al2O3 ceramic layers were prepared by performing air plasma spraying (APS) based on optimal composition. Corrosion depth of CMAS was analyzed and measured, and thickness of CMAS impedance layers was proposed. Addition of Al2O3 can effectively prevent CMAS from infiltrating. Moreover, the higher the Al2O3 content was, the better the protection effects were. However, there was a nonlinear correlation between CMAS infiltration depth and Al2O3 addition. Concerning thermal properties and mechanical properties of the TBC ceramic layers, optimal composition of TBC composite ceramic layers was determined to be 70wt%8YSZ+30wt%Al2O3. Based upon the experimental results, bilayer TBC ceramic layer structure consisting of YSZ/Al2O3 composite ceramic layers (50 μm) and YSZ ceramic layers was proposed. According to overall calculations, thermal expansion coefficient of the YSZ/Al2O3 composite ceramic layers was 9.93×10-6 °C-1, and thermal conductivity of the bilayer TBC ceramic layers was 2.4 W/(m·K). Finally, the mechanism of CMAS corrosion being mitigated by Al2O3 was quantitatively analyzed. The optimal composition of YSZ/Al2O3 composite ceramic layers is 70wt%8YSZ+30wt%Al2O3, and thickness is 50 μm, which can effectively prevent CMAS corrosion at high temperature. © 2018 Chongqing Wujiu Periodicals Press. All rights reserved.