Hot corrosion behavior of ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 TBCs in CMAS: CaO-MgO-Al2O3-SiO2

Abstract

Improvement of hot corrosion resistance in calcium-magnesium-aluminosilicate (CMAS: CaO-MgO-Al2O3-SiO2) environments is one of the main goals in the development of aero-engines especially in their thermal barrier coatings (TBCs). In this regard, this study aims to improve the quality and efficiency of the yttria-stabilized ZrO2 (8YSZ) TBCs by substitution of new coatings such as ZGYbY: ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3. For this purpose, 8YSZ and ZGYbY topcoats with CoNiCrAlY bond coat were applied on IN738LC substrates using atmospheric plasma spray (APS) technique. Hot corrosion behavior of the coatings was investigated in CMAS environment by a furnace method at 1150 °C in the 4-h cycles. Phase and microstructural investigations of the coatings by XRD and FESEM/EDS methods before and after the hot corrosion test indicated the better performance of ZGYbY coating (relative to 8YSZ) in preventing from the diffusion of the CMAS particles. This could be due to the formation of the impermeable apatite compounds (i.e., Ca4Y(Yb/Gd)6O(SiO4)6). Furthermore, the destruction of the TBCs in CMAS environment can be attributed to the diffusion of molten silicates through the pores and micro-cracks of the ceramic top layer to the TBC and then release of the ZrO2 stabilizer and finally the tetragonal to monoclinic ZrO2 phase transformation.