Effect of CMAS attack behaviour on stress distribution in double-ceramic-layer thermal barrier coatings

Stress distribution has a significant effect on crack nucleation and propagation in thermal barrier coatings (TBCs). The stress distribution of different types of double-layer plasma-sprayed coatings, such as YbYSZ/YSZ (YbYSZ: Yb2O3-Y2O3 co-stabilised ZrO2; YSZ: Y2O3 stabilised ZrO2) and YbYSZ/EMAP-YSZ (EMAP-YSZ: embedded micron-agglomerated particle-YSZ) coatings, was numerically studied using the finite element method (FEM) under the condition of thermal shock experiments coupled with calcium-magnesium-alumina-silicate (CMAS) attack. The maximum stress increased with the increasing thickness of CMAS deposition when CMAS was deposited on the coated surface. Among the three coatings of YSZ, YbYSZ/YSZ, and YbYSZ/EMAP-YSZ attacked by CMAS, the stress change of the YbYSZ/EMAP-YSZ coating was lower when CMAS was deposited on the surface of the ceramic layer and penetrated 200 mu m below the original surface but was worse after penetration up to 250 mu m. Furthermore, traditional YSZ in a CMAS environment was also compared to demonstrate the thermal shock life of double-ceramic layer coatings in a better manner. The relationship among CMAS attack, thermal shock, temperature distribution, stress distribution, and cracking initiation of TBC systems has been clarified to provide significant insight in understanding the failure mechanism and important guidance for optimising TBCs to enhance their service life.