Thermal shock resistance of YSZ, YSZ-Al2O3 and YSZ-Al2O3/YSZ coatings

Yttria-stabilized zirconia (YSZ), YSZ-Al2O3, and YSZ-Al2O3/YSZ coatings were fabricated by plasma spraying. Their microstructures were investigated using scanning electron microscope equipped with electron backscatter diffraction attachments. Their thermal shock resistances were measured by water quenching method. YSZ-Al2O3/YSZ coatings exhibited the highest thermal shock resistance. Furthermore, the factors influencing thermal shock resistance of these coatings were analyzed in detail. YSZ-Al2O3 coatings exhibited the lowest thermal shock resistance because of the significant coefficient of thermal expansion (CTE) mismatch between the ceramic layer and the metal substrate. In contrast, the YSZ layer deposited between the YSZ-Al2O3 layer and the metal substrate could relieve the CTE mismatch between the YSZ-Al2O3 layer and the metal substrate because the CTE of the YSZ coating is between those of the YSZ-Al2O3 coating and metal substrate. Moreover, it was found that layered peeling and bulk peeling were major failure forms of YSZ coatings and YSZ-Al2O3 coatings, respectively. The YSZ-Al2O3/YSZ coating exhibited better thermal shock resistance than the YSZ coating due to some small vertical cracks and dense structure.