A New Al2O3-Protected EB-PVD TBC with Superior CMAS Resistance

Calcium-magnesium-aluminium-silicate (CMAS) attack is a longstanding challenge for yttria stabilized zirconia (YSZ) thermal barrier coatings (TBCs) particularly at higher engine operating temperature. Here, a novel microstructural design is reported for YSZ TBCs to mitigate CMAS attack. The design is based on a drip coating method that creates a thin layer of nanoporous Al2O3 around YSZ columnar grains produced by electron beam physical vapor deposition (EB-PVD). The nanoporous Al2O3 enables fast crystallization of CMAS melt close to the TBC surface, in the inter-columnar gaps, and on the column walls, thereby suppressing CMAS infiltration and preventing further degradation of the TBCs due to CMAS attack. Indentation and three-point beam bending tests indicate that the highly porous Al2O3 only slightly stiffens the TBC but offers superior resistance against sintering in long-term thermal exposure by reducing the intercolumnar contact. This work offers a new pathway for designing novel TBC architecture with excellent CMAS resistance, strain tolerance, and sintering resistance, which also points out new insight for assembly nanoporous ceramic in traditional ceramic structure for integrated functions.