A comparative study of calcium–magnesium–aluminum–silicon oxide mitigation in selected self-healing thermal barrier coating ceramics

The mitigation of CMAS (calcium–magnesium–aluminum–silicon oxide) infiltration is a major requirement for the stability of thermal barrier coatings. In this study, yttria-stabilized zirconia (YSZ)–Al 2 O 3 –SiC, YSZ–Al 2 O 3 –Ta 2 O 5 , and YSZ–Al 2 O 3 –Nb 2 O 5 self-healing composites produced by uniaxially pressing powders were investigated as an alternative to YSZ. CMAS infiltration in these materials was tested at 1250 °C for 10 h. Comparing the depth of CMAS infiltration using scanning electron microscope (SEM) in tandem with electron-dispersive X-ray spectroscopy (EDS), all self-healing materials were found to perform better than the reference materials. While standard YSZ shows massive CMAS infiltration, SEM micrographs and EDS maps revealed a 33-fold improvement in CMAS resistance for the YSZ–Al 2 O 3 –Nb 2 O 5 system, which exhibited the best performance among the selected self-repairing materials. X-ray diffraction and high-resolution SEM micrographs taken 10 μm below the surface revealed that CMAS only infiltrated pores in the topmost region of the samples. Both YSZ–Al 2 O 3 –Ta 2 O 5 and YSZ–Al 2 O 3 –Nb 2 O 5 systems showed no signs of chemical reaction with CMAS.