Corrosion resistance of modified YSZ coatings subjected to CMAS attacks

The deterioration of thermal barrier coatings in reaction engines due to Ca-Mg-Al-Si (CMAS) attacks has been an important issue in recent years. Al2O3-20 wt-% TiO2 (AT) powder was mechanically doped into yttria-stabilized zirconia (YSZ). The corresponding coatings were fabricated using APS to modify the CMAS corrosion resistance. The corrosion-induced microstructure evolution and the composition development in the YSZ and AT-YSZ coatings were investigated. The AT-YSZ coating contained smaller voids and fewer cracks with a much more obvious laminated structure in contrast with the YSZ coatings. After CMAS attack, the YSZ coating flaked off, while the AT-YSZ coating was strongly bonded to the substrate. Phases from tetragonal (t'-ZrO2) to monoclinic (m-ZrO2) were detected, while the MgAl2O4 spinel and gehlenite Ca2Al2Si2O8 phases were formed after the CMAS corrosion. AT20 exists independently in the AT-YSZ coating, which readily causes Al2O3 to accumulate in the CMAS and effectively arrests its infiltration.