Calcium-magnesium-alumino-silicate induced degradation and failure of La-2(Zr0.7Ce0.3)(2)O-7/YSZ double-ceramic-layer thermal barrier coatings prepared by electron beam-physical vapor deposition

Calcium-magnesium-alumino-silicate (CMAS) induced degradation of the La-2(Zr0.7Ce0.3)(2)O-7/YSZ double ceramic-layer thermal barrier coatings (TBCs) prepared by electron beam-physical vapor deposition (EB-PVD) was investigated in this study. CMAS reacted with La-2(Zr0.7Ce0.3)(2)O-7 to form a dense crystalline layer composed of apatite and fluorite phases, while the penetration was not arrested in the double-ceramic-layer coating due to the formation of vertical cracks during heat-treatment. In fact, the vertical cracks in the LZ7C3 layer inevitably provided efficient infiltration paths for molten CMAS to attack the bottom YSZ layer. Since the formation of Ca-2(La1-xCe)(8)(SiO4)(6)O-26 apatite phase during CMAS reactions led to CaO enrichment in the melt, the YSZ buffer layer of the double-ceramic-layer coating even suffered a severer CMAS attack than the single YSZ coating.