Thermal stability of yttria-stabilized zirconia (YSZ) and YSZ-Al2O3 coatings

Abstract The thermal insulation performance of yttria-stabilized zirconia (YSZ) and YSZ-Al 2 O 3 coatings deposited by atmospheric plasma spraying was evaluated using a thermal shock simulator, revealing the superiority of YSZ-Al 2 O 3 coatings due to their lower thermal conductivity. Furthermore, YSZ-Al 2 O 3 coatings were more thermally stable than YSZ ones, as determined by scanning electron microscopy, electron backscatter diffraction, and energy-dispersive X-ray spectroscopy analyses. Detailed investigations revealed that heating induces partial removal of Y from ZrO 2 , weakening its stabilization and thus leading to a martensitic phase transformation of metastable tetragonal zirconia (t′-ZrO 2 ) into monoclinic zirconia (m-ZrO 2 ). Conversely, in YSZ-Al 2 O 3 coatings, Al diffused into t′-ZrO 2 to further stabilize it by forming an YSZ-Al 2 O 3 solid solution, thus slowing down the above phase transformation.