Microstructure characteristics of EB-PVD YSZ thermal barrier coatings corroded by molten volcanic ash

Y2O3-stabilized ZrO2 (YSZ) thermal barrier coatings (TBCs) grown on a polycrystalline alumina (Al2O3) substrate are corroded by a natural volcanic ash (VA) at 1150 degrees C. The VA corrosion-induced microstructure development and composition evolution across the YSZ coating layer and at the VA/YSZ and YSZ/Al2O3 interfaces are investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM). It is found that the VA-corroded YSZ coating undergoes grain growth and becomes well-connected along the deposition direction. It is shown that VA-molten depositions penetrate through the entire YSZ layer and fully fill the intercolumnar gaps in the YSZ layer, which results in crystalline ZrSiO4 precipitates between the intercolumnar gaps near the VA/YSZ interface and anorthite (CaAl2Si2O8) precipitates at the YSZ/Al2O3 interface with the micro-crack formation. The growth stresses associated with the anorthite precipitation is suggested as the driving force to initiate the degradation of TBCs at the YSZ/Al2O3 interface region. (C) 2015 Elsevier B.V. All rights reserved.